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Invited talk at the 7th International Conference on Strangeness in Quark Matter, SQM 2003, Atlantic Beach, North Carolina, USA, 12-17 Mar, 2003. 11 pages, 12 figures. Journal-ref: J.Phys. G30 (2004) S139-S150. We review recent developments in the field of microscopic transport model calculations for ultrarelativistic heavy ion collisions. In particular, we focus on the strangeness production, for example, the phi-meson and its role as a messenger of the early phase of the system evolution. Moreover, we discuss the important e ects of the (soft) field properties on the multiparticle system. We outline some current problems of the models as well as possible solutions to them
The wide-area deployment of WiFi hot spots challenges IP access providers. While new profit models are sought after by them, profitability as well as logistics for large-scale deployment of 802.11 wireless technology are still to be proven. Expenditure for hardware, locations, maintenance, connectivity, marketing, billing and customer care must be considered. Even for large carriers with infrastructure, the deployment of a large-scale WiFi infrastructure may be risky. This paper proposes a multi-level scheme for hot spot distribution and customer acquisition that reduces financial risk, cost of marketing and cost of maintenance for the large-scale deployment of WiFi hot spots.
Despite the apparent stability of the wage bargaining institutions in West Germany, aggregate union membership has been declining dramatically since the early 90's. However, aggregate gross membership numbers do not distinguish by employment status and it is impossible to disaggregate these sufficiently. This paper uses four waves of the German Socioeconomic Panel in 1985, 1989, 1993, and 1998 to perform a panel analysis of net union membership among employees. We estimate a correlated random effects probit model suggested in Chamberlain (1984) to take proper account of individual specfic effects. Our results suggest that at the individual level the propensity to be a union member has not changed considerably over time. Thus, the aggregate decline in membership is due to composition effects. We also use the estimates to predict net union density at the industry level based on the IAB employment subsample for the time period 1985 to 1997. JEL - Klassifikation: J5
The paper analyses the financial structure of German inward FDI. From a tax perspective, intra-company loans granted by the parent should be all the more strongly preferred over equity the lower the tax rate of the parent and the higher the tax rate of the German affiliate. From our study of a panel of more than 8,000 non-financial affiliates in Germany, we find only small effects of the tax rate of the foreign parent. However, our empirical results show that subsidiaries that on average are profitable react more strongly to changes in the German corporate tax rate than this is the case for less profitable firms. This gives support to the frequent concern that high German taxes are partly responsible for the high levels of intracompany loans. Taxation, however, does not fully explain the high levels of intra-company borrowing. Roughly 60% of the cross-border intra-company loans turn out to be held by firms that are running losses. JEL - Klassifikation H25 , F23 .
This paper is a draft for the chapter German banks and banking structure of the forthcoming book The German financial system . As such, the paper starts out with a description of past and present structural features of the German banking industry. Given the presented empirical evidence it then argues that great care has to be taken when generalising structural trends from one financial system to another. Whilst conventio nal commercial banking is clearly in decline in the US, it is far from clear whether the dominance of banks in the German financial system has been significantly eroded over the last decades. We interpret the immense stability in intermediation ratios and financing patterns of firms between 1970 and 2000 as strong evidence for our view that the way in which and the extent to which German banks fulfil the central functions for the financial system are still consistent with the overall logic of the German financial system. In spite of the current dire business environment for financial intermediaries we do not expect the German financial system and its banking industry as an integral part of this system to converge to the institutional arrangements typical for a market-oriented financial system. This Version: March 25, 2003
Initiated by the seminal work of Diamond/Dybvig (1983) and Diamond (1984), advances in the theory of financial intermediation have sharpened our understanding of the theoretical foundations of banks as special financial institutions. What makes them "unique" is the combination of accepting deposits and issuing loans. However, in recent years the notion of "disintermediation" has gained tremendous popularity, especially among American observers. These observers argue that deregulation, globalisation and advances in information technology have been eroding the role of banks as intermediaries and thus their alleged uniqueness. It is even assumed that ever more efficiently organised capital markets and specialised financial institutions that take advantage of these markets, such as mutual funds or finance companies, will lead to the demise of banks. Using a novel measurement concept based on intermediation and securitisation ratios, the present article provides evidence which shows that banking disintermediation is indeed a reality for the US financial system. This seems to indicate that American banks are not all that "unique"; they can be replaced to a considerable extent. Moreover, many observers seem to believe that what has happened in the US reflects a universal trend. However, empirical results reported in this paper indicate that such a trend has not manifested itself in other financial systems, and in particular, not in Germany or Japan. Evidence on the enormous structural differences between financial systems and the lack of unequivocal signs of convergence render any inferences from the American experience to other financial systems very problematic.
Abstract: It is commonplace in the debate on Germany's labor market problems to argue that high unemployment and low wage dispersion are related. This paper analyses the relationship between unemployment and residual wage dispersion for individuals with comparable attributes. In the conventional neoclassical point of view, wages are determined by the marginal product of the workers. Accordingly, increases in union minimum wages result in a decline of residual wage dispersion and higher unemployment. A competing view regards wage dispersion as the outcome of search frictions and the associated monopsony power of the firms. Accordingly, an increase in search frictions causes both higher unemployment and higher wage dispersion. The empirical analysis attempts to discriminate between the two hypotheses for West Germany analyzing the relationship between wage dispersion and both the level of unemployment as well as the transition rates between different labor market states. The findings are not completely consistent with either theory. However, as predicted by search theory, one robust result is that unemployment by cells is not negatively correlated with the within cell wage dispersion.
This paper evaluates the effects of Public Sponsored Training in East Germany in the context of reiterated treatments. Selection bias based on observed characteristics is corrected for by applying kernel matching based on the propensity score. We control for further selection and the presence of Ashenfelter's Dip before the program with conditional difference-in-differences estimators. Training as a first treatment shows insignificant effects on the transition rates. The effect of program sequences and the incremental effect of a second program on the reemployment probability are insignificant. However, the incremental effect on the probability to remain employed is slightly positive. JEL - Klassifikation: H43 , C23 , J6 , J64 , C14
Central wage bargaining and local wage flexibility : evidence from the entire wage distribution
(1998)
We argue that in labor markets with central wage bargaining wage flexibility varies systematically across the wage distribution: local wage flexibility is more relevant for the upper part of the wage distribution, and flexibility of wages negotiated under central wage bargaining affects the lower part of the wage distribution. Using a random sample of German social-security accounts, we estimate wage flexibility across the wage distribution by means of quantile regressions. The results support our hypothesis, as employees with low wages have significantly lower local wage flexibility than high wage employees. This effect is particularly relevant for the lower educational groups. On the other hand, employees with low wages tend to have a higher wage flexibility with respect to national unemployment.
The Box-Cox quantile regression model using the two stage method introduced by Chamberlain (1994) and Buchinsky (1995) provides an attractive extension of linear quantile regression techniques. However, a major numerical problem exists when implementing this method which has not been addressed so far in the literature. We suggest a simple solution modifying the estimator slightly. This modification is easy to implement. The modified estimator is still [square root] n-consistent and its asymptotic distribution can easily be derived. A simulation study confirms that the modified estimator works well.
This paper investigates the magnitude and the main determinants of share price reactions to buy-back announcements of German corporations. For our comprehensive sample of 224 announcements that took place between May 1998 and April 2003 we find average cumulative abnormal returns around -7.5% for the thirty days preceding the announcement and around +7.0 % for the ten days following the announcement. We regress post-announcement abnormal returns with multiple firm characteristics and provide evidence which supports the undervaluation signaling hypothesis but not the excess cash hypothesis or the tax-efficiency hypothesis. In extending prior empirical work, we also analyze price effects from initial statements of firms that they intend to seek shareholder approval for a buy-back plan. Observed cumulative abnormal returns on this initial date are in excess of 5% implying a total average price effect between 12% and 15% from implementing a buy-back plan. We conjecture that the German regulatory environment is the main reason why market variations to buy-back announcements are much stronger in Germany than in other countries and conclude that initial statements by managers to seek shareholders’ approval for a buy-back plan should also be subject to legal ad-hoc disclosure requirements.
This paper shows that abnormal stock price returns around open market repurchase announcements are about four times higher in Germany than in the US (12% versus 3%). We hypothesize that this observation can be explained by country differences in repurchase regulation. Our empirical evidence indicates that German managers primarily buy back shares to signal an undervaluation of their firm. We demonstrate that the stringent repurchase process prescribed by German law attributes a higher credibility to such a signal than lax US regulations and thereby corroborate our hypothesis.
This paper analyzes empirically the distribution of unemployment durations in West- Germany before and after the changes during the mid 1980s in the maximum entitlement periods for unemployment benefits for elderly unemployed. The analysis is based on the comprehensive IAB employment subsample containing register panel data for about 500.000 individuals in West Germany. We analyze two proxies for unemployment since the data do not precisely measure unemployment in an economic sense. We provide a theoretical analysis of the link between the durations of nonemployment and of unemployment between jobs. Our empirical analysis finds significant changes in the distributions of nonemployment durations for older unemployed individuals. At the same time, the distribution of unemployment durations between jobs did not change in response to the reforms. Our findings are consistent with an interpretation that many firms and workers used the more bene cial laws as a part of early retirement packages but those workers who were still looking for a job did not reduce their search effort in response to the extension of the maximum entitlement periods. This interpretation is consistent with our theoretical model under plausible assumptions. JEL: C24, J64, J65
This paper examines intraday stock price effects and trading activity caused by ad hoc disclosures in Germany. The evidence suggests that the observed stock prices react within 90 minutes after the ad hoc disclosures. Trading volumes take even longer to adjust. We find no evidence for abnormal price reactions or abnormal trading volume before announcements. The bigger the company that announces an ad hoc disclosure, the less severe is the abnormal price effect following the announcement. The number of analysts is negatively correlated to the trading volume effect before the ad hoc disclosure. The higher the trading volume on the last trading day before the announcement, the greater is the price effect after the ad hoc disclosures and the greater the trading volume effect. Keywords: ad hoc disclosure rules, intraday stock price adjustments, market efficiency.
We show that multi-bank loan pools improve the risk-return profile of banks’ loan business. Banks write simple contracts on the proceeds from pooled loan portfolios, taking into account the free-rider problems in joint loan production. Thus, banks benefit greatly from diversifying credit risk while limiting the efficiency loss due to adverse incentives. We present calibration results that the formation of loan pools reduce the volatility in default rates, proxying for credit risk, of participating banks’ loan portfolios by roughly 70% in our sample. Under reasonable assumptions, the gain in return on equity (in certainty equivalent terms) is around 20 basis points annually.
Global reserves of coal, oil and natural gas are diminishing; global energy requirements however are dramatically increasing. Renewable energy sources lower the threat to the earth’s climate but are not able to meet the energy consumption in major urban areas. The opinion of many experts is that the future will be dominated by hydrogen. However, this gas is essentially totally manufactured from fossil fuels and is hence of limited abundance – not to mention the hazards involved in its utilisation. - A novel energy concept involving solar and thus carbon-independent hydrogen-based technology necessitates an intermediate storage vehicle for renewable energy. This future energy carrier should be simple to manufacture, be available to an unlimited degree or at least be suitable for recycling, be able to store and transport the energy without hazards, demonstrate a high energy density and release no carbon dioxide or other climatically detrimental substances. - Silicon successfully functions as a tailor-made intermediate linking decentrally operating renewable energy-generation technology with equally decentrally organised hydrogen-based infrastructure at any location of choice. In contrast to oil and in particular hydrogen, the transport and storage of silicon are free from potential hazards and require a simple infrastructure similar to that needed for coal.
This paper compares the accuracy of credit ratings of Moody s and Standard&Poors. Based on 11,428 issuer ratings and 350 defaults in several datasets from 1999 to 2003 a slight advantage for the rating system of Moody s is detected. Compared to former research the robustness of the results is increased by using nonparametric bootstrap approaches. Furthermore, robustness checks are made to control for the impact of Watchlist entries, staleness of ratings and the effect of unsolicited ratings on the results.
National borders in Europe have been opening since 1992 and the Union is expanding to embrace more countries prompting enterprises to consider alternative and more attractive locations outside their home country to handle part of their activities (Van Dijk and Pellenbarg, 2000; Cantwell and Iammarino, 2002). International relocation is becoming more and more popular even for small and medium-sized firms that are involved in a growing internationalisation process, mirroring the path of multinational enterprises. Italy, like other industrialised countries, is experiencing a fragmentation of the production chain: firms tend to shift high labour-intensive manufacturing activities to areas characterised by an abundance of low-cost labour (i.e. Central Eastern Europe, India, South East Asia, Latin America, Russia and Central Asia). The internationalisation process by Italian district SMEs has assumed significant dimensions. It has become a relevant topic in recent economic debate because of its consequences for the local context and, in particular, the implication for the survival of the Italian district model (see, among others, Becattini, 2002; Rullani, 1998 and Cor, 2000). The purpose of the paper is twofold: it aims at (i) identifying the managerial approaches to the internationalisation process adopted by the Italian district SMEs and by the Industrial District (ID) itself and (ii) at investigating whether the international delocalisation to the South Eastern European countries (SEECs) constitutes a threat or an opportunity for the Italian district model. The paper is organised as follows. The general introduction is followed by a description of the evolution of the internationalisation processes in Italy over the last three decades. Section three presents a discussion of the internationalisation strategies adopted by Italian SMEs. Section four focuses on the internationalisation process of the Italian industrial districts SMEs. A review of the studies on the subject is offered in section five. Section six presents a qualitative study on the internationalisation process as undergone by sports shoes manufacturers in the Montebelluna district, in north-east Italy. This study shows different managerial strategies to the internationalisation process and emphasises that the motivations can evolve over time, from originally cost-saving to increasingly market-oriented or global strategies. On the basis of a literature review, section seven investigates whether internationalisation constitutes a threat (i.e. loss of jobs and knowledge) or an opportunity (i.e. enlargement of the ID, update district s competitiveness) for the district model. Finally, some summarising remarks in section eight conclude the paper.
Over the past decade, a variety of studies have shown that other sectors in addition to high technology industries can provide a basis for regional growth and income and employment opportunities. In addition, design-intensive, craft-based, creative industries which operate in frequently changing, fashion-oriented markets have established regional concentrations. Such industries focus on the production of products and services with a particular cultural and social content and frequently integrate new information technologies into their operations and outputs. Among these industries, the media and, more recently, multimedia industries have received particular atte ntion (Brail/ Gertler 1999; Egan/ Saxenian 1999). Especially, the film (motion picture) and TV industries have been the focus of a number of studies (e.g. Storper/ Christopherson 1987; Scott 1996). For the purpose of this paper, cultural products industries are defined as those industries which are involved in the commodification of culture, especially those operations that depend for their success on the commercialization of objects and services that transmit social and cultural messages (Scott 1996, p. 306). Empirical studies on the size, structure and organizational attributes of the firms in media-related industry clusters have revealed a number of common characteristics (Scott 1996; Brail/ Gertler 1999; Egan/ Saxenian 1999). Most firms in these industries are fairly young, often existing for only a few years. They also tend to be small in terms of employment. Often, regional clusters of specialized industries are the product of a local growth process which has been driven by innovative local start-ups. In their early stages, many firms have been established by teams of persons rather than by individual entrepreneurs and have heavily relied on owner capital. Another important feature which distinguishes these industries from others is that they concentrate in inner-city instead of suburban locations (Storper/ Christopherson 1987; Eberts/ Norcliffe 1998; Brail/ Gertler 1999). In this study, I provide evidence that the Leipzig media industry shows similar tendencies and characteristics as those displayed by the multimedia and cultural products industry clusters in Los Angeles, San Francisco and Toronto, albeit at a much smaller scale. Cultural products industries are characterized by a strong tendency towards the formation of regional clusters despite the fact that in some sectors, such as the multimedia industry, technological opportunities (i.e. internet technologies) have seemingly reduced the necessity of proximity in operations between interlinked firms. In fact, it seems that regional concentration tendencies are even more dominant in cultural products industries than in many industries of the old economy . Cultural products industries have formed particular regional clusters of suppliers, producers and customers which are interlinked within the same commodity chains (Scott 1996; Les- 2 lie/ Reimer 1999). These clusters are characterized by a deep social division of labor between vertically-linked firms and patterns of interaction and cooperation in production and innovation. Within close networks of social relations and reflexive collective action, they have developed a strong tendency towards product- and process-related specialization (Storper 1997; Maskell/ Malmberg 1999; Porter 2000). In the context of the rise of a new media industry cluster in Leipzig, Germany, I discuss those approaches in the next section of this paper which provide an understanding of complex industrial clustering processes. Therein socio-institutional settings, inter-firm communication and interactive learning play a decisive role in generating regional innovation and growth. However, I will also emphasize that interfirm networks can have a negative impact on competitiveness if social relations and linkages are too close, too exclusive and too rigid. Leipzig's historical role as a location of media-related businesses will be presented in section 3. As part of this, I will argue the need to view the present cluster of media firms as an independent phenomenon which is not a mere continuation of tradition. In section 4 the start-up and location processes are analyzed which have contributed to the rise of a new media industry cluster in Leipzig during the 1990's. Related to this, section 5 will discuss the role and variety of institutions which have developed in Leipzig and how they support specialization processes. This will be interpreted as a process of reembedding into a local context. In section 6, I will discuss how media firms have become over-embedded due to their strong orientation towards regional markets. This will be followed by some brief conclusions regarding the growth potential of the Leipzig media industry.
There are few changes in the history of human existence comparable to urbanization in scope and potential to bring about biologic change. The transition in the developed world from an agricultural to an industrial-urban society has already produced substantial changes in human health, morphology and growth (Schell, Smith and Bilsborough, 1993, p.1). By the year 2000, about 50% of the world s total population will be living crowded in urban areas and soon thereafter, by the year 2025 as the global urban population reaches the 5 billion mark more of the world s population will be living in urban areas. This has enormous health consequences. By the close of the twenty-first century, more people will be packed into the urban areas of the developing world than are alive on the planet today (UNCHS (Habitat), 1996, p.xxi). Africa presents a particularly poignant example of the problems involved, as it has the fastest population and urban growth in the world as well as the lowest economic development and growth and many of the poorest countries, especially in Tropical Africa. Thus it exemplifies in stark reality many of the worst difficulties of urban health and ecology (Clarke, 1993, p.260). This essay is therefore concerned to analyse the trends of urbanization in Africa. This is followed by an overview of the environmental conditions of Africa s towns and cities. The subsequent section explores the links between the urban environment and health. Although the focus is with physical hazards it is important to note that the social milieu is also vital in the reproduction of health. The paper concludes by providing some policy recommendations.
Characterised as the mighty capital of the eurozone (Sassen 1999, 83), Frankfurt is said to be a rising world city primarily due to its financial centre. This is reflected in the use of such common catchphrases as Bankfurt and Mainhattan for the city, as well as its reference in scientific publications. As Ronneberger and Keil (1995, 305) state, for instance, a service economy [...] mastered by the finance sector forms the basis for the continuing integration of Frankfurt into the international market. Frankfurt is the most important German as well as European financial centres. Thirteen of the 30 largest German banks and about two thirds of Germany s foreign banks are seated here. Frankfurt s stock exchange (ranked 4th in the world) is by far the biggest in Germany with a turnover-share of more than 80%. Its derivatives exchange (Eurex) aims to become the biggest in the world. As the host city for the European Central Bank, it is also the centre of European monetary policy. As a major node in the global financial network today, Frankfurt s specific functions within this network will be investigated in this paper. Unlike most other predominant national financial centres, Frankfurt has not continuously held this position in Germany s since the middle ages: It re-gained it s position from Berlin only after World War II. In contrast to the static phenomenon financial centre which is well covered in the literature emergence and development of financial centres is not as well understood. The study of the development of the financial centre Frankfurt after World War II gives insights into the dynamics of the self-reinforcing mechanisms within financial centres; the second topic covered in the paper. The paper is organised as follows: the remainder of this chapter looks at the method used in this study and the theory of financial centres with an emphasis on the basic approaches to the emergence of financial centres. After that it is asked whether Frankfurt meets the basic requirements for the concept of path dependence, i.e. that there are self-reinforcing mechanisms. After a positive answer to that, the development of Frankfurt as a financial centre is discussed as well as its role as a node in the world (financial) system today in chapter two. Chapter three provides some more or less speculative remarks about Frankfurt s future; the last chapter briefly summarises the findings of the paper.
One of the most important but less understood phenomena in the beginning of the 21st century has been a shift toward knowledge-based economic activity in the comparative advantage of modern industrialized countries. Two broad trends has been observed in the global economy. That is, the output from the world's science and technology system has been growing rapidly and the nature of investment has been changed (MILLER, 1996). The relative proportions of physical and intangible investment have changed considerably with the relative increase of intangible investments since the 1980s. In addition, there has been increased complementarity between physical and intangible investments and more important role of high technology in both kinds of investment (MILLER, 1996). Even in the newly industrialized countries, the growth of technology intensive industries, the increase of R&D activities and the growth of the knowledge intensive producer services have been common feature in recent years. In this change of the structure of productive assets, the role of knowledge is well recognized as the most fundamental resources in recent years (OECD, 1996; WORLD BANK, 1998). The development of information and communication technology (ICT) and globalisation trend have promoted this shift toward knowledge-based economy.
The globalisation of contemporary capitalism is bringing about at least two important implications for the emergence and significance of business services. First, the social division of labour steadily increases (ILLERIS 1996). Within the complex organisation of production and trade new intermediate actors emerge either from the externalisation of existing functions in the course of corporate restructuring policies or from the fragmentation of the production chain into newly defined functions. Second, competitive advantages of firms increasingly rest on their ability to innovate and learn. As global communication erodes knowledge advantages more quickly, product life cycles shorten and permanent organisational learning results to be crucial for the creation and maintenance of competitiveness. Intra- and interorganisational relations of firms now are the key assets for learning and reflexivity (STORPER 1997). These two aspects of globalisation help understand why management consulting - as only one among other knowledge intensive business services (KIBS) - has been experiencing such a boost throughout the last two decades. Throughout the last ten years, the business has grown annually by 10% on average in Europe. Management consulting can be seen first, as a new organisational intermediate and second, as an agent of change and reflexivity to business organisations. Although the KIBS industry may not take a great share of the national GDP its impact on national economies should not be underestimated. Estimations show that today up to 80% of the value added to industrial products stem from business services (ILLERIS 1996). Economic geographers have been paying more attention to KIBS since the late 1970s and focus on the transformation of the spatial economy through the emerging business services. This market survey is conceived as a first step of a research programme on the internationalisation of management consulting and as a contribution to the lively debate in economic geography. The management consulting industry is unlimited in many ways: There are only scarce institutional boundaries, low barriers to entry, a very heterogeneous supply structure and multiple forms of transaction. Official statistics have not yet provided devices of grasping this market and it may be therefore, that research and literature on this business are rather poor. The following survey is an attempt to selectively compile existing material, empirical studies and statistics in order to draw a sketchy picture of the European market, its institutional constraints, agents and dynamics. German examples will be employed to pursue arguments in more depth.
During the 1980s and early 1990s, the importance of small firm growth and industrial districts in Italy became the focus of a large number of regional development studies. According to this literature, successful industrial districts are characterized by intensive cooperation and market producer-user interaction between small and medium-sized, flexibly specialized firms (Piore and Sabel, 1984; Scott, 1988). In addition, specialized local labor markets develop which are complemented by a variety of supportive institutions and a tradition of collaboration based on trust relations (Amin and Robins, 1990; Amin and Thrift, 1995). It has also been emphasized that industrial districts are deeply embedded into the socio-institutional structures within their particular regions (Grabher, 1993). Many case studies have attempted to find evidence that the regional patterns identified in Italy are a reflection of a general trend in industrial development rather than just being historical exceptions. Silicon Valley, which is focused on high technology production, has been identified as being one such production complex similar to those in Italy (see, for instance, Hayter, 1997). However, some remarkable differences do exist in the institutional context of this region, as well as its particular social division of labor (Markusen, 1996). Even though critics, such as Amin and Robins (1990), emphasized quite early that the Italian experience could not easily be applied to other socio-cultural settings, many studies have classified other high technology regions in the U.S. as being industrial districts, such as Boston s Route 128 area. Too much attention has been paid to the performance of small and medium-sized firms and the regional level of industrial production in the ill-fated debate regarding industrial districts (Martinelli and Schoenberger, 1991). Harrison (1997) has provided substantial evidence that large firms continue to dominate the global economy. This does not, however, imply that a de-territorialization of economic growth is necessarily taking place as globalization tendencies continue (Storper, 1997; Maskell and Malmberg, 1998). In the case of Boston, it has been misleading to define its regional economy as being an industrial district. Neither have small and medium-sized firms been decisive in the development of the Route 128 area nor has the region developed a tradition of close communication between vertically-disintegrated firms (Dorfman, 1983; Bathelt, 1991a). Saxenian (1994) found that Boston s economy contrasted sharply with that of an industrial district. Specifically, the region has been dominated by large, vertically-integrated high technology firms which are reliant on proprietary technologies and autarkic firm structures. Several studies have tried to compare the development of the Route 128 region to Silicon Valley. These studies have shown that both regions developed into major 2 agglomerations of high technology industries in the post-World War II period. Due to their different traditions, structures and practices, Silicon Valley and Route 128 have followed divergent development paths which have resulted in a different regional specialization (Dorfman, 1983; Saxenian, 1985; Kenney and von Burg, 1999). In the mid 1970s, both regions were almost equally important in terms of the size of their high technology sectors. Since then, however, Silicon Valley has become more important and has now the largest agglomeration of leading-edge technologies in the U.S. (Saxenian, 1994). Saxenian (1994) argues that the superior performance of high technology industries in Silicon Valley over those in Boston is based on different organizational patterns and manufacturing cultures which are embedded in those socio-institutional traditions which are particular to each region. Despite the fact that Saxenian (1994) has been criticized for basing her conclusions on weak empirical research (i.e. Harrison, 1997; Markusen, 1998), she offers a convincing explanation as to why the development paths of both regions have differed.1 Saxenian s (1994) study does not, however, identify which structures and processes have enabled both regions to overcome economic crises. In the case of the Boston economy, high technology industries have proven that they are capable of readjusting and rejuvenating their product and process structures in such a way that further innovation and growth is stimulated. This is also exemplified by the region s recent economic development. In the late 1980s, Boston experienced an economic decline when the minicomputer industry lost its competitive basis and defense expenditures were drastically reduced. The number of high technology manufacturing jobs decreased by more than 45,000 between 1987 and 1995. By the mid 1990s, however, the regional economy began to recover. The rapidly growing software sector compensated for some of the losses experienced in manufacturing. In this paper, I aim to identify the forces behind this economic recovery. I will investigate whether high technology firms have uncovered new ways to overcome the crisis and the extent to which they have given up their focus on self-reliance and autarkic structures. The empirical findings will also be discussed in the context of the recent debate about the importance of regional competence and collective learning (Storper, 1997; Maskell and Malmberg, 1998). There is a growing body of literature which suggests that some regional economies During the 1980s and early 1990s, the importance of small firm growth and industrial districts in Italy became the focus of a large number of regional development studies. According to this literature, successful industrial districts are characterized by intensive cooperation and market producer-user interaction between small and medium-sized, flexibly specialized firms (Piore and Sabel, 1984; Scott, 1988). In addition, specialized local labor markets develop which are complemented by a variety of supportive institutions and a tradition of collaboration based on trust relations (Amin and Robins, 1990; Amin and Thrift, 1995). It has also been emphasized that industrial districts are deeply embedded into the socio-institutional structures within their particular regions (Grabher, 1993). Many case studies have attempted to find evidence that the regional patterns identified in Italy are a reflection of a general trend in industrial development rather than just being historical exceptions. Silicon Valley, which is focused on high technology production, has been identified as being one such production complex similar to those in Italy (see, for instance, Hayter, 1997). However, some remarkable differences do exist in the institutional context of this region, as well as its particular social division of labor (Markusen, 1996). Even though critics, such as Amin and Robins (1990), emphasized quite early that the Italian experience could not easily be applied to other socio-cultural settings, many studies have classified other high technology regions in the U.S. as being industrial districts, such as Boston s Route 128 area. Too much attention has been paid to the performance of small and medium-sized firms and the regional level of industrial production in the ill-fated debate regarding industrial districts (Martinelli and Schoenberger, 1991). Harrison (1997) has provided substantial evidence that large firms continue to dominate the global economy. This does not, however, imply that a de-territorialization of economic growth is necessarily taking place as globalization tendencies continue (Storper, 1997; Maskell and Malmberg, 1998). In the case of Boston, it has been misleading to define its regional economy as being an industrial district. Neither have small and medium-sized firms been decisive in the development of the Route 128 area nor has the region developed a tradition of close communication between vertically-disintegrated firms (Dorfman, 1983; Bathelt, 1991a). Saxenian (1994) found that Boston s economy contrasted sharply with that of an industrial district. Specifically, the region has been dominated by large, vertically-integrated high technology firms which are reliant on proprietary technologies and autarkic firm structures. Several studies have tried to compare the development of the Route 128 region to Silicon Valley. These studies have shown that both regions developed into major 2 agglomerations of high technology industries in the post-World War II period. Due to their different traditions, structures and practices, Silicon Valley and Route 128 have followed divergent development paths which have resulted in a different regional specialization (Dorfman, 1983; Saxenian, 1985; Kenney and von Burg, 1999). In the mid 1970s, both regions were almost equally important in terms of the size of their high technology sectors. Since then, however, Silicon Valley has become more important and has now the largest agglomeration of leading-edge technologies in the U.S. (Saxenian, 1994). Saxenian (1994) argues that the superior performance of high technology industries in Silicon Valley over those in Boston is based on different organizational patterns and manufacturing cultures which are embedded in those socio-institutional traditions which are particular to each region. Despite the fact that Saxenian (1994) has been criticized for basing her conclusions on weak empirical research (i.e. Harrison, 1997; Markusen, 1998), she offers a convincing explanation as to why the development paths of both regions have differed.1 Saxenian s (1994) study does not, however, identify which structures and processes have enabled both regions to overcome economic crises. In the case of the Boston economy, high technology industries have proven that they are capable of readjusting and rejuvenating their product and process structures in such a way that further innovation and growth is stimulated. This is also exemplified by the region s recent economic development. In the late 1980s, Boston experienced an economic decline when the minicomputer industry lost its competitive basis and defense expenditures were drastically reduced. The number of high technology manufacturing jobs decreased by more than 45,000 between 1987 and 1995. By the mid 1990s, however, the regional economy began to recover. The rapidly growing software sector compensated for some of the losses experienced in manufacturing. In this paper, I aim to identify the forces behind this economic recovery. I will investigate whether high technology firms have uncovered new ways to overcome the crisis and the extent to which they have given up their focus on self-reliance and autarkic structures. The empirical findings will also be discussed in the context of the recent debate about the importance of regional competence and collective learning (Storper, 1997; Maskell and Malmberg, 1998). There is a growing body of literature which suggests that some regional economies an develop into learning economies which are based on intra-regional production linkages, interactive technological learning processes, flexibility and proximity (Storper, 1992; Lundvall and Johnson, 1994; Gregersen and Johnson, 1997). In the next section of this paper, I will discuss some of the theoretical issues regarding localized learning processes, learning economies and learning regions (see, also, Bathelt, 1999). I will then describe the methodology used. What follows is a brief overview of how Boston s economy has specialized in high technology production. The main part of the paper will then focus on recent trends in Boston s high technology industries. It will be shown that the high technology economy consists of different subsectors which are not tied to a single technological development path. The various subsectors are, at least partially, dependent on different forces and unrelated processes. There is, however, tentative evidence which suggests that cooperative behavior and collective learning in supplierproducer- user relations have become important factors in securing reproductivity in the regional structure. The importance of these trends will be discussed in the conclusions.
Taking shareholder protection seriously? : Corporate governance in the United States and Germany
(2003)
The paper undertakes a comparative study of the set of laws affecting corporate governance in the United States and Germany, and an evaluation of their design if one assumes that their objective were the protection of the interests of minority outside shareholders. The rationale for such an objective is reviewed, in terms of agency cost theory, and then the institutions that serve to bound agency costs are examined and critiqued. In particular, there is discussion of the applicable legal rules in each country, the role of the board of directors, the functioning of the market for corporate control, and (briefly) the use of incentive compensation. The paper concludes with the authors views on what taking shareholder protection seriously, in each country s legal system, would require.
This memorandum describes the approach of the U.S. Securities and Exchange Commission (the "SEC") in monitoring and, where appropriate, regulating the use of research reports by investment banking firms in connection with securities transactions. The memorandum addresses the historical system of regulation, which continues in large measure to apply. It also examines the new initiatives taken, following a number of prominent corporate, accounting and banking scandals and a significant decline in U.S. and international capital markets, to supplement the current system in what some have dubbed the "post-Enron era".
Recent empirical work shows that a better legal environment leads to lower expected rates of return in an international cross-section of countries. This paper investigates whether differences in firm-specific corporate governance also help to explain expected returns in a cross-section of firms within a single jurisdiction. Constructing a corporate governance rating (CGR) for German firms, we document a positive relationship between the CGR and firm value. In addition, there is strong evidence that expected returns are negatively correlated with the CGR, if dividend yields and price-earnings ratios are used as proxies for the cost of capital. Most results are robust for endogeneity, with causation running from corporate governance practices to firm fundamentals. Finally, an investment strategy that bought high-CGR firms and shorted low-CGR firms would have earned abnormal returns of around 12 percent on an annual basis during the sample period. We rationalize the empirical evidence with lower agency costs and/or the removal of certain governance malfunctions for the high-CGR firms.
The corporate convergence debate is usually presented in terms of competing efficiency and political claims. Convergence optimists assert that an economic logic will promote convergence on the most efficient form of economic organization, usually taken to be the public corporation governed under rules designed to maximize shareholder value. Convergence skeptics counterclaim that organizational diversity is possible, even probable, because of path dependent development of institutional complementarities whose abandonment is likely to be inefficient. The skeptics also assert that existing elites will use their political and economic advantages to block reform; the optimists counterclaim that the spread of shareholding will reshape politics.
The venture capital market and firms whose creation and early stages were financed by venture capital are among the crown jewels of the American economy. Beyond representing an important engine of macroeconomic growth and job creation, these firms have been a major force in commercializing cutting edge science, whether through their impact on existing industries as with the radical changes in pharmaceuticals catalyzed by venture-backed firms commercialization of biotechnology, or by the their role in developing entirely new industries as with the emergence of the internet and world wide web. The venture capital market thus provides a unique link between finance and innovation, providing start-up and early stage firms - organizational forms particularly well suited to innovation - with capital market access that is tailored to the special task of financing these high risk, high return activities.
This article presents a structural overview of corporate disclosure in Germany against the background of a rapidly evolving European market. Professor Baums first makes the theoretical case for mandatory disclosure and outlines the standard, regulatory elements of market transparency. He then turns to German law and illustrates both how it attempts to meet the principle, theoretical demands of disclosure and how it should be improved. The article also presents in some detail the actual channels of corporate disclosure used in Germany and the manner in which German law now fits into the overall development of the broader, European Community scheme, as well as the contemplated changes and improvements both at the national and the supranational level.
The paper was submitted to the conference on company law reform at the University of Cambridge, July 4th, 2002. Since the introduction of corporation laws in the individual German states during the first half of the 19th century, Germany has repeatedly amended and reformed its company law. Such reforms and amendments were prompted in part by stock exchange fraud and the collapse of large corporations, but also by a routine adjustment of law to changing commercial and societal conditions. During the last ten years, a series of significant changes to German company law led one commentator to speak from a "company law in permanent reform". Two years ago, the German Federal Chancellor established a Regierungskommission Corporate Governance ("Government Commission on Corporate Governance") and instructed it to examine the German Corporate Governance system and German company law as a whole, and formulate recommendations for reform.
On April 24, 2001 the European Commission presented a proposal for a Directive1 introducing supplementary supervision of financial conglomerates (the Proposed Directive). The Proposed Directive requires a closer coordination among supervisory authorities of different sectors of the financial industry and leads to changes in the number of existing Directives relating to the supervision of credit institutions, insurance undertakings and investment firms.
It is an established policy in the United States to separate commercial banking (the business of taking deposits and making commercial loans) from other commercial activities. The separation of banking and commercial activities is achieved by federal and state banking laws, which enumerate the powers that banks may exercise, the activities that banks may engage in, and the investments that banks may lawfully make, and expressly exclude banks from certain activities or relationships. Some of these provisions could be circumvented if a nonbank company could carry on banking activities through a banking subsidiary and nonbanking activities either itself or through a nonbanking subsidiary.
The institutionalization and internationalization of shareholdings, the globalization of capital markets and the rapid development of information technologies have placed our corporate law system under increasing pressure to adapt to the ever changing requirements of the market. For this reason, in May 2000, the German government called together a group of industrialists, representatives of shareholder associations and institutional investors, trade unionists, politicians and scholars to form an expert Panel with the task of reviewing the German corporate governance system. This Government Panel on Corporate Governance prepared a questionnaire on key issues in the field, and solicited responses and input from numerous national and international experts and institutions. In July 2001, the Commission presented its 320 page report (available at www.ottoschmidt. de/corporate_governance.htm) to the German Chancellor. The Report made nearly 150 recommendations for amendments or changes to existing provisions of German law and also set forth proposals on how the German corporate governance system should be further developed in order to maintain a normative framework that is suitable and attractive not only for companies, but also for domestic and foreign investors. In order that the Panel s proposals may receive careful consideration from a diverse audience, it seems very useful to keep a wider public informed of the Panel s recommendations. Therefore, also on behalf of the Panel, I very much appreciate that the international law firm Shearman & Sterling has taken the initiative to have the summary of the Panel s recommendations translated into English.
The road to shareowner power
(1999)
A dramatic rise in shareowner power and improvements in corporate governance tan be achieved in the next few years by expanding the role of proxy advisory firms. This will require changing the way such firms are paid. They are now paid directly by investors who buy their advice; but this arrangement suffers from a free-rider problem. Instead, they should be paid by each corporation about which they are advising, in accordance with shareholder vote so as to preclude management influence. This arrangement would make it economically feasible for advisory firms to expand their services, becoming proactive like relational investors. Any proxy advisor other than the market leader Stands to gain tremendously by initiating this new System. lt would eliminate the natura1 monopoly feature of the current System, and spread the tost more equitably across all shareowners. lt would also enable proxy advisory ftrms to market their Services to individual investors via the internet.
Shareholder voting is back on the agenda of public debate for several reasons. One is the investors’ internationalization of capital investments and the raising of funds globally by companies. It can be predicted that considering the growing together of capital markets the trend to international investments will increase not least because the introduction of the Euro will create a uniform European stock market. This leads to the question how the law deals with this development and its problems. The EU Commission has commissioned a comparative study dealing, inter alia, with shareholders’ representation at general meetings in the EU member states.1 The aim is to simplify the operating regulations for public limited companies in the EU. Furthermore, the internationalization of shareholdings leads the investors to ask how their interests are protected abroad. Are the mechanisms of shareholder protection sufficient for foreign investors? In particular the formation of transnational companies like Daimler-Chrysler will change corporate governance systems. It remains to be seen whether and how foreign institutional investors will use measures of - in this case - German corporate law to control the management. From a microeconomic point of view the question is what specific features of a given corporate governance system might contribute to better performance of firms. The following remarks will however, be confined to one specific aspect of corporate governance only, the exercise of shareholders’ voting rights at the general meeting.
I analyze the most powerful shareholders in Germany to illustrate the concentration of control over listed corporations. Compared to other developed economies, the German stock market is dominated by large shareholders. I show that 77% of the median firm’s voting rights arecontrolled by large blockholders. This corresponds to 47% of the market value of all firms listed in Germany’s official markets. About two thirds of this amount is controlled by banks, industrial firms, holdings, and insurance companies. I show that due to current legislation it is clear for neither group who ultimate exerts control over the shareholding firm itself. For the remaining blockholders, only blocks controlled by voting pools and individuals can be traced back to the highest level of ownership. In the aggregate, both groups control only 5.6% of all reported blocks. The German government controls 8%, and it is not clear who ultimately is responsible for the consequences of decisions.
We first analyze legal provisions relating to corporate transparency in Germany. We show that despite the new securities trading law (WpHG) of 1995, the practical efficacy of disclosure regulation is very low. On the one hand, the formation of business groups involving less regulated legal forms as intermediate layers can substantially reduce transparency. On the other hand, the implementation of the law is not practical and not very effective. We illustrate these arguments using several examples of WpHG filings. To illustrate the importance of transparency, we show next that German capital markets are dominated by few large firms accounting for most of the market’s capitalization and trading volume. Moreover, the concentration of control is very high. First, 85% of all officially listed AGs have a dominant shareholder (controlling more than 25% of the voting rights). Second, few large blockholders control several deciding voting blocks in listed corporations, while the majority controls only one block.
The article describes the legal structure of the Daimler-Chrysler merger. It asks why this specific structure rather than another cheaper way was chosen. This leads to the more general question of the pros and cons of mandatory corporate law as a regulatory device. The article advocates an "optional" approach: The legislator should offer various menus or sets of binding rules among which the parties may choose. (JEL: ...)
The previous proposal for a company law directive on takeovers in 1990 was rejected in Germany almost unanimously for several different reasons. The new "slimmed down" draft proposal, in the light of the subsidiarity principle, takes the different approaches to investorprotection in the various member states better into account. Notably, the most controversial principle of the previous draft, viz. the mandatory bid rule as the only means of investorprotection in case of a change of control, has been given up. Therefore a much higher degree of acceptance seems likely. The Bundesrat (upper house) and the industry associations have already expressed their consent; the Bundestag (Federal Parliament) will deal with the proposal shortly. The technique of a "frame directive" leaves ample leeway for the member states. That will shift the discussion back to the national level and there will lead to the question as to how to make use of this leeway (cf. II, III, below) rather than to a debate about principles as in the past. It seems likely that criticism will confine itself to more technical questions (cf. IV, below).
The corporate governance systems in Europe differ markedly. Economists tend to use stylized models and distinguish between the Anglo-American, the German and the Latinist model.1 In this view, for instance, the Austrian, Dutch, German, and Swiss systems are said to be variations of one model. For lawyers the picture is of course, much more detailed as particular rules may vary even where common principles prevail. Many comparative studies on these differences have been undertaken meanwhile.2 I do not want to add another study but to treat a different question. Are there as a consequence of growing internationalization, globalization of markets and technological change, also tendencies of convergence of our corporate governance systems? My answer will be in two parts. As corporate governance systems are traditionally mainly shaped by legislation, the first part will analyze the influence of the economic and technological change on the rule-setting process itself. How does this process react to the fundamental environmental change? That includes a short analysis of the solution of centralized harmonizing of company law within the EU as well as the question of whether EU-wide competition between national corporate law legislators can be observed or be expected in the future. The second part will then turn to the national level. It deals with actual tendencies of convergence or, more correctly, of approach by the German corporate governance system to the Anglo-American one.
Universal banking means that banks are permitted to offer all of the various kinds of financial services. This includes classical banking activities like the credit and deposit business, as well as investment services, placement and brokerage of securities, and even insurance activities, trading in real estate and others. German universal banks also hold stock in nonfinancial firms and offer to vote their clients' shares in other firms. This paper deals with universal banks and their role in the investment business, more specifically, their links with investment companies and their various roles as shareholders and providers of financial services to such companies. Banks and investment companies have, as financial intermediaries, one trait in common: they both transform capital of investors (depositors and shareholders of investment funds, respectively) into funds (loans and equity or debt securities, respectively) that are channeled to other firms. So why should a regulation forbid to combine these transformation tasks in one institution or group, and why should the law not allow banks to establish investment companies and provide all kinds of financial services to them in addition to their banking services? German banking and investment company law have answered these questions in the affirmative. This paper argues that the existing regulation is not a sound and recommendable one. The paper is organized as follows: Sections II - V identify four areas where the combination of banking and investment might either harm the shareholders of the investment funds and/or negatively affect other constituencies such as the shareholders of the banking institution. These sections will at the same time explore whether there are institutional or regulatory provisions in place or market forces at work that adequately protect investors and the other constituencies in question. Concluding remarks follow (VI.).
For the German observer the idea of a Company repurchasing its own shares seems to resemble the picture of a snake eating its own tail. It appears to be highly unnatura1 and one wonders how the tail tan possibly be eatable for the snake. Not in the United States. Although repurchases have once been subject to the most stubbornly fought conflict in US Company law only some modest disclosure requirements and safeguards against overt market manipulation exist today. Large repurchases are an almost everyday event and there is an increasing tendency. The aggregate value of shares repurchased by NYSE listed companies has increased from $ 1 .l billion in 1975 to $ 6.3 billion in 1982 to $ 37.1 billion in 1985*. Few examples may illustrate this practice further: Within three years Ford Motor Corp. repurchased 30 million shares for $ 1.2 billion. In 1985 Phillips Petroleum Corp. was faced with two hostile bids and took several defensive Steps, one of which was to tender for 20 million of its own shares at a total tost of $ 1 billion. And by the end of 1988 Exxon Corp. retired 28 percent of its shares that had once been outstanding at an aggregate tost of $ 14.5 billion. The Situation in Germany is completely different. As it will be shown under German law repurchases are severely restricted and do appreciable amount at all. not take place at an In contrast to German law the United Kingdom does not prohibit repurchases but requires companies to comply with such complex rules that US companies would regard simply as limiting their economic freedom. Therefore UK companies very seldom repurchase their own shares, too. This Paper deals with repurchases by quoted companies, in particular the UK public Company and the more or less German equivalent, the Aktiengesellschaft (AG). It seeks to ascertain the reasons why companies might want to engage in those activities. Moreover, it tries to analyse the Problems which may arise from repurchases and the safeguards which the UK and German legal Systems provide for these Problems.This Paper deals with repurchases by quoted companies, in particular the UK public Company and the more or less German equivalent, the Aktiengesellschaft (AG). It seeks to ascertain the reasons why companies might want to engage in those activities. Moreover, it tries to analyse the Problems which may arise from repurchases and the safeguards which the UK and German legal Systems provide for these Problems.
Until the late 1980s, asset securitisation was an US-American finance technique. Meanwhile this technique has been used also in some European countries, although to a much lesser extent. While some of them have adopted or developed their legal and regulatory framework, others remain on earlier stages. That may be because of the lack of economic incentives, but also because of remaining regulatory or legal impediments. The following overview deals with the legal and regulatory environment in five selected European countries. It is structured as follows: First, this finance technique will be described in outline to the benefit of the reader who might not be familiar with it. A further part will report the recent development and the underlying economic reasons that drive this development. The main part will then deal with international aspects and give an overview of some legal and regulatory issues in five European legislations. Tax and accounting questions are, however, excluded. Concluding remarks follow.
The following descriptive overview of the German corporate governance system and the current debate is structured as follows. Part II will give some information on the empirical background. Part III will describe the formal legal setting as well as actual practices in some key areas. Part IV will then deal with some issues of the current debate.
In my following remarks I will focus on a differente which we find in German law as well as in other legislations, the differente b e t w e e n entrepreneurial investments among firms and merely financial investments. Whereas OUT law of groups of companies o f Konzernrecht contains quite an elaborated set of rules, the rules governing financial investments, especially Cross-border financial investments, seems to be somewhat underdeveloped.
In early 1991 the United States Treasury Department of the Bush Administration recommended in ib proposal for Modemizing The FinancialSystem l that, in addition to other remarkable breaks with the traditional United States financial Services framework, the current bank holding Company structure be replaced with a new financial Services holding Company that would reward banks with the ability to engage in a broad new range of financial activities through separate afbliates, including full-service securities, insurance, and mutual fund activities. The Treaaury Department pointed out that commercial banking and investment banking are complementary Services and that the Glass-Steagall Separation was unnecessary. The Treasury Department gave many reasons for the need for financial modernization and why such a modemized System would work better. As an example that demonstrates the advantages of the System proposed by the Treasury Department, the proposal pointed to the German banks and called the German model of a universal banking System the most liberal banking System in the world. -What makes the German universal banking System so unique and desirable? The following outline of the history and the current structure of the Getman banking System is intended to give readers a background tc determine whether the German banking System could be a model for the System of the future.
The task of this Paper as originally described in the outline of the current project was to compare the German banking System, as one type of relationship banking , with the Japanese main bank System. This was, of course, not simply meant in the sense of a mere description and comparison of different institutions. A meaningful contribution rather has to look at the functions of a given banking System as a provider of capital or other financial Services to their client firms, has to ask in what respect the one or the other System might be superior or less efficient, and has to analyze the reasons for this. Such a thorough analysis would have to answer questions like, for instance, to what extent investment is financed by (lang or short term-)bank loans, whether German banks have, because of specific institutional arrangements like own equity holdings, seats on Company boards or other links with their borrowers, informational or other advantages that make bank finance eheaper or easier available; how such banks behave with respect to financial distress and bankruptcy of their client firms, and what their exact role in corporate governance is. While preparing this Paper I found that in Order to give reliable answers to these questions there had to be several other conferences comparable to the present one that had to focus exclusively on our domestic System. Hence what this Paper only tan provide for at this moment is a short overview of the German banking System and its special t r a i t s ( Universalbankensystem and Group Banking ; part I), describe and analyse some aspects of bank lending to firms (Part II), and the role of German banks as delegated monitors in widely held firms (Part Ill). A description of the historical development of the specific links between banks and industry and their impact on the economic growth of Germany during the period of the industrialization and later on would be specifically interesting within the framework of a Conference that discusses the lessons and relevante of banking Systems for developing market economies and for transforming socialist economies. However, historical remarks had to be omitted completely, not least because of lack of own knowledge, time and space, but also because this history is already well documented and available in English publications, too.
Other than in Belgium, German banks may hold even controlling equity participations in industrial firms (and such firms may own banks) and do so to a large extent. Vis-a-vis the European development this leads to two questions: From the perspective of the (Belgian and other) competitors of these banks, whether their own domestic System might be disadvantageous to them. And from a public interest perspective, which advantages and drawbacks are connected with the different regulations in Europe. The article first informs about the legal framework and some statistical facts. Then the various and different reasons why banks acquire and hold shares on own account are analyzed. The following Parts deal with the various public policy arguments whether equity links between banks and industrial firms should be prohibited or not (safety and soundness of banking; autonomie de Ia fonction bancaire ; abuse of confidential information and conflicts of interest; antitrust considerations; negative and positive impacts on the respective firm). In its last part the article deals with recent proposals in the German political debate to limit stockholdings of banks. The article argues that a step-by-step approach to the Single Problems and issues (conflict of interests; anticompetitive effects etc.) should be preferred to a general limitation of stock ownership of banks.
The corporate governance Systems in the U.K. and in Germany differ markedly. German large firms have a two-board structure, they are subject to employee codetermination, their managements are not confronted with public hostile takeover bids, and banks play a major role in corporate governance, through equity stakes, through proxies given to them by small investors, and through bankers positions on the supervisory boards of these firms. One of the main issues of corporate governance in large firms, the Problem of shareholders passivity in monitoring management in Berle-Means type corporations, is thus addressed by an institutional Provision, the role of the banks, rather than by a market-oriented Solution as we find it in the U.K. with its market for corporate control through the threat of hostile takeovers. These two different approaches to corporate governance have been compared several times recently, and it was argued that a bank-based or institutional Solution has clear advantages and should be preferred. Cosh, Hughes and Singh, for example, argue at the conclusion of their discussion of takeovers and short-termism in the U.K. that the institutional shareholder [in the UK] should take a much more active and vigorous part in the internal governance of corporations. . . . In Order for such a proposal to be effective both in disciplining inefficient managements and promoting long-term investments, far reaching changes in the internal workings and behaviour of the financial institutions would be required. The financial institutions would need to pool their resources together, set up specialised departments for promoting investment and innovations - in other words behave like German banks. The following remarks seek to continue this discussion from the German perspective. The article will first attempt to evaluate the monitoring potential of our domestic bank or institution-oriented corporate governance System and then, in a further patt, compare it with that of a market-oriented Solution. lt will be argued that both Systems focus on different Problems and have specific advantages and drawbacks, and that there are still quite a few puzzles to be solved until all pros and cons of each of these monitoring devices tan be assessed. The perception that both Systems focus on different Problems suggests combining institutional monitoring with a market for corporate control rather than considering them to be contrasting and incompatible approaches. The article is organized as follows. Section II will describe the legal structure of the large corporation in Germany in more detail. Section Ill explains why a market for corporate control by the threat of public hostile takeover bids does not exist in Germany. Section IV then Shows how corporate governance in publicly held corporations with small investors is organized instead, and deals with the role of banks in corporate governance in these firms. Section V of the atticle then will try to compare the monitoring potential of a marketoriented and our bank or institution-oriented corporate governance System. Concluding remarks follow.
The hypothesis that oxidative stress plays a role in the pathogenesis of Alzheimer’s disease (AD) was tested by studying oxidative damage, acitvities of antioxidant enzymes and levels of reactive oxygen species (ROS) in several models. To this end, mouse models transgenic for mutant presenilin (PS1M146L) as well as mutant amyloid precursor protein (APP) and human post mortem brain tissue from sporadic AD patients and age-matched controls were studied. Aging leads to an upregulation of antioxidant enzyme activities of Cu/Zn-superoxide dismutase (Cu/Zn-SOD), glutathione peroxidase (GPx) and glutathione reductase (GR) in brains from C57BL/6J mice. Simultaneously, levels of lipid peroxidation products malondialdehyde MDA and 4-hydroxynonenal HNE were reduced. Additionally, pronounced gender effects were observed, as female mice display better protection against oxidative damage due to higher activity of GPx. Hence, antioxidant enzymes provide an important contribution to the protection against oxidative damage. In PS1M146L transgenic mice oxidative damage was only detectable in 19-22 months old mice, arguing for an additive effect of aging and the PS1 mutation. Both HNE levels in brain tissue as well as mitochondrial and cytosolic levels of ROS in splenic lymphocytes were increased in PS1M146L mice. Antioxidant defences were unaltered. In PDGF-APP and PDGF-APP/PS1 trangenic mice no changes in any of the parameters studied were observed in any age group. In contrast, Thy1-APP transgenic mice display oxidative damage as assessed by increased HNE levels. Reduced activity of Cu/Zn-SOD may explain this observation. Additionally, gender modified this effect, as female APP transgenic mice display higher b-secretase cleavage of APP and simultaneously increased HNE levels and reduced Cu/Zn-SOD activity earlier than male mice, i.e. from an age of 3 months and before the formation of Ab plaques. Reduced Cu/Zn-SOD activity was also found in another APP transgenic mouse model, in APP23 mice. In post mortem brain tissue from sporadic AD patients activities of Cu/Zn-SOD and GPx were however increased, and changes were most pronounced in temporal cortex. Simultaneously, levels of HNE but not MDA were elevated. Additionally, in vitro stimulation of lipid peroxidation led to increased MDA formation in samples from AD patients, indicating that increased activity of Cu/Zn-SOD and GPx are insufficient to protect against oxidative damage. Furthermore, the observed changes were subject to a gender effect, as samples from female AD patients showed increased activities of Cu/Zn-SOD and GPx as well as increased HNE levels, indicating that brain tissue from females is more sensitive towards oxidative damage. Levels of soluble Ab1-40 were positively correlated with with MDA levels and activities of Cu/Zn-SOD and GPx. Additionally, levels of lipid peroxidation products MDA and HNE are gene-dose-dependently modulated by the Apolipoprotein E4 allele, the most important genetic risk factor for AD known so far. While MDA levels were negatively correlated with MMSE scores, a measure for cognitive function, HNE levels were highest in AD patients with moderate cognitive impairment. Hence, increased HNE levels may play an important role in neurodegenerative events at an early disease stage. In summary, oxidative damage, as assessed by increased HNE levels, could be detected in sporadic AD patients and in different transgenic mouse models. The results of this thesis therefore support the further research of pharmacological targets aiming at augmentation of antioxidant defences for therapy or prophylaxis of Alzheimer’s disease.
The cytochrome bc1 complex is a cornerstone in bioenergetic electron transfer chains, where it carries out tasks as diverse as respiration, photosynthesis, and nitrogen fixation. This homodimeric multisubunit membrane protein has been studied extensively for several decades and the enzyme mechanism is described with the modified protonmotive Q cycle. Still, the molecular and kinetic description of the catalytic cycle is not complete and questions remain regarding the bifurcation of electron transfer at the quinol oxidation (Qo) site, substrate occupancy, pathways of proton conduction, and the nature of the Rieske protein domain movement. We used competitive inhibitors to study the molecular architecture at the Qo site with X-ray crystallography. The structure of the enzyme with the substrate analog 5-n-heptyl-6-hydroxy-4,7-dioxobenzothiazole (HHDBT) bound at the Qo site was determined at 2.5 Å resolution. Spectroscopic studies showed that HHDBT is negatively charged when bound at the active site. Mechanistic interpretations from inhibitor binding are in line with single occupancy model for quinol oxidation and structural analysis supports the proposed proton transfer pathway. For functional insight into the enzyme mechanism, redox-sensitive protonation changes were studied by Fourier transform infrared spectroscopy. The protein purification procedure was optimized for less delipidation and the isolated enzyme was more active. Furthermore, two new phospholipids were identified in the X-ray structures, including a cardiolipin. Strikingly, conserved lipid binding cavities were observed in structural comparison with homologous enzymes. The functional role of tightly bound phospholipids will be discussed. Finally, the Qo site is a target for various compounds of agricultural and pharmaceutical importance. Importantly, the X-ray structures permit detailed analysis of the molecular reasons for acquired resistance to and treatment failure of Qo site inhibitors, such as atovaquone, that is used to treat malaria and pneumonia, as discussed herein.
The cytochrome bc1 complex or ubiquinol:cytochrome c oxidoreductase (QCR) catalyses electron transfer from ubiquinol to cytochrome c in respiration and photosynthesis coupled to a vectorial proton transport across the membrane, in which the enzyme resides. In both bacteria and eukaryotic organisms, QCR participates in supramolecular assembly of membrane proteins that comprise the respiratory or photosynthetic chain. In the present work, proton transfer pathways, substrate binding and the supramolecular assembly of the respiratory chain in yeast were probed by structure-based site-directed mutagenesis and characterization of the variants. Both active sites centre P, the place of quinol oxidation, and centre N, where quinone reduction takes place, lack direct access to the bulk solvent necessary for proton release and uptake. Based on the X-ray structure, proton transfer pathways were postulated. Analysis at centre P showed, that E272 and Y132 of cytochrome b are important for QCR catalysis as indicated by increased superoxide production and lowered Cyc1p reductase activity in these variants. Pre-steady state heme reduction kinetics in combination with stigmatellin resistance indicated that charge and length of the side chain at position 272 are crucial for efficient docking of the ISP to form the enzyme substrate complex and for electron bifurcation at centre P. Variants of Y312 and F129, both residues of cytochrome b, showed an increased Km indicating participation of these residues in coordination of ubiquinol or the possible intermediate semiquinone anion radical. F129 proved to be crucial for a functional Q-cycle as indicated by respiratory negative growth phenotype and a lowered H+/e- stoichiometry of F129 variants. At centre N, the postulated CL/K and E/R proton transfer pathways are located at opposite sites of the bound ubiquinone. Variants in the surface residues R218 (cytochrome b) and E52 (Qcr7) of the E/R pathway and E82 (Qcr7) of the CL/K pathway showed instability upon purification indicating an important role of these residues for QCR integrity. The slowed down centre N reduction kinetics in H85 (CL/K), R218 and N208 (both E/R) variant was attributed to a destabilised semiquinone anion consistent with the observed decreased sensitivity towards the site-specific inhibitor antimycin and an increased Km. Variants of residues of both pathway, E82Q and R218M, exhibited a decreased H+/e- stoichiometry indicating a crucial role of both residue for maintaining a working Q-cycle and supporting the proposed protonation of the substrate via the Cl/K and the E/R pathway. Long-range interaction between centre N and centre P were observed by altered reduction kinetics of the high potential chain and increased superoxide production in the centre N variants. The role of the cation-pi-interaction between F230 of Cyt1p and R19 of cytochrome c in binding of the redox carrier to QCR was analysed. In F230L hydrophobic interaction were partially lost as was deduced from the ionic strength dependence of Cyc1p reductase activity and Cycp1 binding, as detected by ionic strength sensitive Kd and Km for Cyc1p. The decreased enzymatic rate of F230W could be explained by a disturbed binding of Cyc1p to the variant enzyme. F230 may influence the heme mid point potential and thereby the electron transfer rate to Cyc1p. Reduction of Cobp via both centre P and centre N was disturbed suggesting an interaction between high and low potential chain. Supramolecular association between QCR and cytochrome c oxidase (COX) in yeast mitochondria was probed by affinity chromatography of a his-tagged QCR in the presence of the mild detergent digitonin. In comparison to purification with laurylmaltoside, the presence of both QCR and COX subunits was detected in the elution fractions by SDS-PAGE, Cyc1p reductase and TMPD oxidase activity assays and immunoblot analysis. The CL-dependent formation of the supercomplex between QCR and COX was analysed by replacement variants in the CL-binding site of QCR in CL containing and CL free environment. With an increasing number of replacements of the three lysines the CL-binding pocket supercomplex formation was not abolished, when CL is present as shown by BN-PAGE analysis. This was supported by the synergetic decrease in enzyme activity for both enzymes upon increased number of replacements. In the CL-free environment, no supracomplex formation was observed for a wildtype CL binding site. By replacements of two lysines in the CL-binding pocket, supercomplex formation could be recovered as revealed by BN-PAGE. This indicates, that CL may serve as a charge neutralizer for the lysines near the presumed interaction domain between complex III and complex IV. The obtained results for centre P provide new information of residues critical for stabilisation of ubiquinol and controlling electron short circuit reactions. The observations for centre N variants clearly support the proposed two proton transfer pathways and the role of the bound phospholipids in centre N kinetics. Variants in the Cyc1p binding site suggest a role for F230 both in Cyc1p binding and electron transfer. Clear interaction between the high and low potential chain in both Cyt1p and centre N variants strongly support long-range interactions in the complex. Studies on the supramolecular association of complex III and complex IV indicate a new role of Cl in stabilising a supracomplex.
The enzyme quinol:fumarate reductase (QFR) from the anaerobic e-proteobacterium Wolinella succinogenes is part of the anaerobic respiratory system of this organism. It couples the reduction of fumarate to succinate to the oxidation of menaquinol to menaquinone. W. succinogenes uses fumarate as terminal electron acceptor and can use various substrates (e.g., formate or molecular hydrogen) as electron donors. The concerted catalytic substrate turnover of either a hydrogenase or a formate dehydrogenase in conjunction with QFR contributes to the generation of an electrochemical potential gradient across the bacterial plasma membrane, which is used for the phosphorylation of ADP with inorganic phosphate, Pi, to ATP. In addition to an FAD (in subunit A) and three iron-sulfur clusters (in subunit B), QFR binds a low- and a high-potential heme b group in its transmembrane subunit C, as was ultimately shown in the crystal structure at 2.2 Å resolution (Lancaster et al., 1999, Nature 402, 377– 385). Both hemes are part of the electron transport chain between the two catalytic sites of this redox enzyme. The midpoint potentials of the hemes are well established but their assignment to the distal and proximal positions in the structure had not yet been determined. Furthermore, QFR from W. succinogenes has been proposed to exhibit a novel coupling mechanism of transmembrane electron and proton transfer, which has been described in the so-called “E-pathway” hypothesis (Lancaster, 2002, Biochim. Biophys. Acta 1565, 215–231). The aim of this project was to characterize the relationship between structure and function of QFR and to investigate the details of the proposed coupling mechanism (“Epathway”) with the help of computer-based electrostatic calculations on the QFR wild-type (WT) coordinates, and electrochemically induced FTIR and VIS difference spectroscopy on the QFR WT and available variant enzymes (in particular enzyme variant E180Q, in which the glutamic acid at position C180 has been replaced by a glutamine). 1.) It was demonstrated in this study that the diheme-containing QFR exhibits stable and reproducible electrochemically induced FTIR difference bands in the midinfrared range from 1800 cm-1 to 1000 cm-1 that reflect transitions from the reduced to the oxidized state of the enzyme. The spectral features that were observed in the FTIR difference spectra are fully reversible when changing from a reductive to an oxidative reference potential at the working electrode and vice versa. This indicates that the underlying redox reactions of the enzyme at the gold grid working electrode are also fully reversible under the applied experimental conditions. The same reversible spectral redox behavior in the visible range could also be ascertained for the Soret- and a-band of the two heme b groups of QFR. This behavior allowed to reliably determine the heme b midpoint potentials of QFR at various pH values. Analysis of the FTIR difference spectra in the amide I range yields evidence for structural reorganizations of the polypeptide backbone upon the electrochemically induced redox reaction. 2.) The redox titrations of the high- and low-potential heme b of QFR as simulated by multiconformation continuum electrostatics (MCCE) calculations showed a very high level of agreement with respect to the experimentally observed midpoint potentials of the heme b groups at pH 7. As determined with the help of the theoretical calculations, prominent features governing the differences in redox potential between the two hemes are the higher loss of reaction field energy for the proximal heme and the stronger destabilization of the oxidized form of the proximal heme due to several buried and ionized Arg and Lys residues. The explicit incorporation of crystallographically identified water molecules in the calculations had a noticeable effect on the absolute values of the determined midpoint potentials, although the relative difference of the two obtained midpoints did not change significantly. The results of the electrostatic calculations clearly showed that the lowpotential heme corresponds to the distal position bD in the structure, and that the high-potential heme is identical to the proximal heme bP. This assignment could previously not be achieved unequivocally with experimental methods. 3.) In addition, the currently discussed mechanism of coupled electron and proton transfer in the QFR of W. succinogenes (i.e., the “E-pathway” hypothesis) is further supported by the results of this study. The simulations of intermediate states of electron transfer via the heme b groups show that the protonation state of the key amino acid residue Glu C180 depends on the redox states of the heme groups as suggested in the “E-pathway” hypothesis. This result yields a possible mechanism for the coupling of transient transmembrane proton transfer via Glu C180 to the electron transfer via the heme b groups, since Glu C180 could be part of a “proton wire” and its redox-dependent protonation state could serve as the regulatory element of the “E-pathway”. Furthermore, the results of simulated heme reduction indicate that the side chain of Glu C180 also changes its conformation with respect to the redox state of the hemes. Both major results concerning the role of Glu C180, the change of protonation as well as the reorientation of the side chain upon reduction of the heme groups, are consistent with the results from electrochemically induced FTIR difference spectroscopy: Of particular interest was the spectral range above 1710 cm-1, where C=O stretching vibrations of protonated COOH carboxyl groups absorb, because those groups can act as proton donors, respectively acceptors, and can be involved in intra-protein proton transfer reactions. It was possible to observe signals of such protonated carboxyl groups originating from QFR enzyme, which either change their protonation state and/or experience an environmental change in the course of the induced redox reaction. This finding was supported by the fact that the relevant FTIR difference signals are sensitive to an isotopic hydrogen/deuterium (1H/2H) exchange via the buffer solution, since they were shifted towards lower wavenumbers in D2O. Furthermore, it could be shown with the help of site-directed mutagenesis that the acidic residue Glu C180, which is located in the membranespanning, diheme-containing subunit C of QFR, is contributing to the redox dependent signal of protonated carboxyl groups. The observed residual signal in the FTIR double-difference spectrum of QFR wild-type and enzyme variant E180Q (Glu C180 has been replaced with a Gln residue) could be interpreted as a protonation/deprotonation event that is superimposed by an environmental effect on the specific C=O vibration. This result strongly supports the proposed “E-pathway” of coupled transmembrane electron and proton transfer in the QFR enzyme, which states that residue Glu C180 is an essential constituent of a transient redox-controlled transmembrane proton transfer pathway. 4.) As a second possible constituent of the suggested “E-pathway”, the ring C propionate of the distal heme was found to be unusually fully protonated in all simulated redox states, indicating a possible role as a transient proton donor/acceptor in the “E-pathway”. Similarly to Glu C180, experimental evidence from FTIR difference spectroscopy on a modified QFR with 13C-labeled heme propionates was obtained, which indicates an involvement of at least one of the two propionates of heme bD in proton transfer. The observed signals can tentatively be interpreted as a redox-coupled (de)protonation of the ring C propionate of bD, which is possibly xiii superimposed by a conformational or environmental change of the specific propionate. 5.) Also the observation of a strong redox Bohr effect for both heme b groups in QFR is in line with the proposed “E-pathway” hypothesis, as this effect yields a possible and well-established mechanism for the coupling of proton transfer and redox changes of the heme groups. The comparison of the observed effect in QFR WT and E180Q together with the results from FTIR spectroscopy and MCCE calculation indicate that the ring C propionate of the distal heme is dominating the pHdependence of the midpoint potential of bD, and that the corresponding group for bP is Glu C180. The origin of the redox Bohr effect for bP in the enzyme variant E180Q (which is dramatically changed with respect to the WT) could not be identified unequivocally, but the observation of this redox Bohr effect in the variant implies the presence of other protolytic groups, which interact with heme bP and which may be necessary for a functional “E-pathway”.
Die vorliegende Arbeit soll einen Beitrag zur Erforschung der Verarbeitungsmechanismen des Gehirns leisten. Die Erregung des komplexen Systems "Hirn" liefert Antworten, deren Analyse zu einem besseren Verständnis dieser Informationsverarbeitung führt. Zu diesem Zweck wurde das Gehirn mit unterschiedlichen visuellen Stimuli angeregt und die hirnelektrischen Signale gemessen, die von Nervenzellgruppen (Multiunits) im visuellen Kortex der Katze ausgesandt wurden.Die verwendeten Stimuli waren ein Streifenmuster sowie eine Zufallspunktverteilung, deren Kohärenz beliebig geändert werden konnte. Darüber hinaus wurden die Antworten auf eine Vielzahl von Stimuli analysiert, die nur aufgrund des Bewegungskontrastes zwischen punktdefiniertem Objekt und Hintergrund zu erkennen sind (Shape-from-Motion- (SFM-) Stimuli). Die aufgenommenen Daten wurden mit Hilfe einer umfangreichen Signalanalyse untersucht. So wurden in Abhängigkeit von der Stimulusbedingung die Anzahl der Nervenimpulse pro Zeiteinheit (Feuerraten), Synchronisation, Frequenzverteilung sowie Kopplung von Aktionspotenzialen und LFPDaten analysiert. Die Experimente im ersten Teil dieser Arbeit untersuchten den Einfluss von Kohärenz auf die Verarbeitung von Bewegungsinformation im primären visuellen Areal (A17) und im posteromedialen lateralen suprasylvischen Sulcus (Area PMLS) der Katze. Es konnte gezeigt werden, dass Multiunits in A17 und PMLS sowohl auf Streifenmuster als auch auf Zufallspunktverteilungen antworten und dass die Stärke der Antwort als eine Funktion der Stimulusrichtung variiert. Die Vorzugsrichtung ist in beiden Arealen weitgehend unabhängig von der Art des verwendeten Stimulus, was darauf hindeutet, dass die Stimulusrichtung für Streifenmuster und Zufallspunktmuster in diesen Arealen durch einen einheitlichen Mechanismus bestimmt wird. Bei einer Abnahme der Stimuluskohärenz zeigen die Multiunits eine Abnahme der Feuerrate, wobei im Vergleich zu PMLS in A17 eine stärkere Abnahme der Kohärenz nötig ist, um die gleiche Abnahme der Feuerrate zu erreichen. Dieses Ergebnis konnte durch die unterschiedlichen Größen der rezeptiven Felder der beiden Areale erklärt werden und ist ein weiterer Hinweis darauf, dass eine wichtige Funktion von PMLS in der Analyse von Bewegung und räumlich verteilter Information liegt. Da beide Areale keine signifikante Änderungen der Feuerrate bei Inkohärenzniveaus von mehr als 50% zeigten, scheinen sie nicht in der Lage zu sein, die Bewegungsrichtung eines inkohärenten Zufallspunktmusters nahe der psychophysischen Detektionsschwelle von 95% auf der Basis von Feuerraten zu erkennen. Die Korrelation der Aktionspotenziale unterschiedlicher Multiunits zeigte bereits bei einer geringen Abnahme der Stimuluskohärenz eine monotone Verbreiterung des zentralen Maximums in den Korrelogrammen beider Areale. Die Stärke der Synchronisation hingegen war kaum beeinflusst. Darüberhinaus kam es zu einer Verschiebung der Leistung im lokalen Feldpotential (LFP) von hohen hin zu niedrigen Frequenzbereichen. Diese Verschiebung wurde auch für die Kopplung zwischen LFP und Akvi tionspotenzialen nachgewiesen. Diese Resultate unterstützen die Theorie, dass präzise Synchronisation und hochfrequente Oszillationen ein Mechanismus für die Bindung kohärenter Objekte sind. Sie zeigen darüber hinaus, dass Synchronisation auch nicht kohärente Stimuli binden kann und dass die Verschiebung im LFP hin zu niedrigeren Frequenzen wichtig für die Integration verteilter Information über einen größeren visuellen Raum sein kann. Da bei hohen Inkohärenzniveaus keine präzise Synchronisation mehr nachgewiesen werden konnte, kann jedoch auch die Synchronisation nicht als alleiniger Mechanismus zum Erkennen einer Bewegungsrichtung eines inkohärenten Zufallspunktmusters herangezogen werden. In den Experimenten im zweiten Teil dieser Arbeit wurde untersucht, wie das Gehirn SFM-Stimuli verarbeitet. Die Auswertungen der Feuerraten haben gezeigt, dass Multiunits in PMLS sowohl auf helligkeitsdefinierte Kontrastbalken als auch auf SFM-Balken reagieren. Die Stärke der Antwort hängt von der Kombination von Stimulus und Hintergrund und von der relativen Bewegungsrichtung zueinander ab. Während ähnliche Feuerraten für Balken mit hohem Kontrast relativ zum Hintergrund und für punktdefinierte Balken gefunden wurde, die sich über einen dunklen Hintergrund bewegten, führte ein statischer Zufallspunkthintergrund zu einer starken Abnahme der von dem SFM-Balken hervorgerufenen Antwort. Ein in die Gegenrichtung bewegter Hintergrund sowie ein reduziertes Kohärenzniveau des Zufallspunkthintergrundes führten dazu, dass die Multiunits auf den SFM- Balken nicht mehr mit einer Zunahme der Feuerraten reagierten. Um die hemmende Wirkung des Hintergrundes aufzuheben, musste der Hintergrund auf einer Fläche des visuellen Feldes, die der Größe des rezeptiven Feldes entsprach, abgedeckt werden. Dieses Ergebnis zeigt, dass die Feuerraten für diese Art Stimulus nicht wesentlich von Arealen außerhalb des rezeptiven Feldes beeinflusst werden. Zur weiteren Analyse der Fähigkeit von PMLS, SFM-Balken nur aufgrund des Bewegungskontrastes zwischen punktdefiniertem Objekt und Hintergrund zu erkennen, wurde mit Hilfe von zwei Tuningkurven-Stimuli, bei denen sich die Bewegungsrichtung der Punkte innerhalb des Balkens um 90° unterschied, die Vorzugsrichtung der Multiunits bestimmt. Die Auswertung ergab, dass sich die gemessene Vorzugsrichtung der Multiunit um 45° drehte, obwohl sich die Bewegungsrichtung des Balkens selbst nicht änderte. Darüber hinaus wurden verschiedene SFM-Stimuli untersucht, die alle dieselbe Bewegungsrichtung des Balkens, jedoch unterschiedliche Bewegungsrichtungen der Punkte innerhalb des Balkens aufwiesen. Wenn PMLS die Bewegung des SFM-Objekts statt der Bewegung der einzelnen Punkte verarbeitet, sollte die Feuerrate für alle diese Bedingungen identisch sein. Die Ergebnisse zeigen jedoch, dass sich die durch die verschiedenen SFM-Stimuli hervorgerufenen Feuerraten verringerten, je weiter sich die Punkte, die den Balken bildeten, von der Bewegungsrichtung des Balkens – und damit von der Vorzugsrichtung der Multiunit – weg bewegten. Durch dieses Ergebnis konnte gezeigt werden, dass Multiunits in PMLS nicht in der Lage sind, die Richtung von kinetisch definierten Balken zu analysieren und statt dessen nur die Bewegung der einzelnen Komponenten erfassen.
Proton-translocating NADH:ubiquinone oxidoreductase (complex I) transports two electrons from NADH to membranal ubiquinone: in this process protons are translocated across the membrane, producing 40% of the total proton gradient between matrix side and intermembrane space. Mitochondrial complex I contains at least 46 subunits in mammals, and has a molecular weight of around 1000 kDa. Electronic microscopy analysis showed that complex I has an L-form, which consists of two domains: a peripheral “arm” (hydrophilic domain) and a membrane “arm” (hydrophobic domain). The peripheral domain, which protrudes into the matrix, contains one non-covalently bound flavin mononucleotide (FMN) and the iron-sulfur clusters N1a, N1b, N2, N3, N4 and N5 as redox active groups. They transport electrons from NADH to ubiquinone. Cluster N2 is supposed to be the immediate electron donor to ubiquinone by virtue of its highest and pH dependent redox midpoint potential (Em,7 –150 mV). The exact location of the tetra-nuclear cluster N2 is still object of discussion. The TYKY and the PSST subunits contain three binding motifs for tetranuclear clusters which are formed by twelve cysteins. In an effort to investigate the “ubiquinone reduction module” of complex I, in the first part of this work site directed mutagenesis of the TYKY and PSST subunits has been carried out. Mutant strains were characterised in terms of complex I content, catalytic activity and EPR signature of cluster N2. The second part of this work was aimed at developing a substrate inducible version of the internal alternative NADH:ubiquinone oxidoreductase (NDH2i). A substrate inducible NDH2i is expected to offer a “switch” between complex I activity dependent (no NDH2i activity) and independent (NDH2i activity) cell growth, by changing between activating and non-activating substrates. This strategy would allow the screening for two types of complex I mutants, which is a prerequisite for realising a random PCR mutagenesis of single subunits of complex I, that allows the production of a high number of point mutations in relatively short time. Y. lipolytica complex I deficiency mutant strains could be easily identified, by virtue of their inability to survive under complex I dependent growth conditions (no NDH2i activity). By this way, amino acids that have an important role for complex I structure or function could be identified by subsequent sequence analysis. Each of the twelve cysteines that form the above mentioned three binding motifs for iron-sulfur cluster have been mutagenised. In mutant mitochondrial membranes, no assembled complex I could be detected. From these data one may conclude that the mutagenised 6 SUMMARY 92 cysteines play an important role for complex I stability, or that are a prerequisite for complex I assembly in Y. lipolytica, but there is not direct evidence indicating that any of the four mutagenised residues acts as a ligand. Two aspartates in the PSST subunit, Asp-99 and Asp-115, were found to be essential for complex I catalytic activity. EPR spectroscopic analysis indicated that the electron transfer to N2 cluster was not blocked and implied that this was not the reason for the loss of catalytic activity. From these data it can be concluded that D99 and D115 play a vital role for complex I NADH:ubiquinone reductase activity, but are not ligands for cluster N2 and that their position is not close enough to the cluster to influence directly its electromagnetic environment. Three mutations, identified in the PSST and TYKY homologous subunits of patients affected with Leigh syndrome (V119M in PSST, P78L and R101H in TYKY) were reconstructed in the obligate aerobic yeast Y. lipolytica. This approach may help to understand the aetiology of the Leigh syndrome, in terms of the ability of complex I to oxidize NADH and to transport electrons. In fact, all three mutations showed effects on electron transport, reducing the VMax by about 50%. Mutant V119M in the PSST subunit, which had a lethal effect in two patients that were homozygous for this mutation, affects a fully conserved residue. Overall, the results from site directed mutagenesis carried out so far support the theory that the “catalytic core ” (N2 cluster and quinone binding site) of complex I has been evolved from the electron transfer module of the [Ni-Fe] hydrogenases. In fact, mutagenesis of residues that are fully conserved between complex I and [Ni-Fe] hydrogenases, showed dramatic effects on complex I in terms of assembly (cysteine mutants) or catalytic activity (D99-D115). Differently, changing aspartate 174 and glutamic acid 185 (not fully conserved, Fig 4.1A) had little or no effect on the Michaelis-Menten parameters and N2 EPR signal. In recent years Y. lipolytica has been developed as a yeast genetic system to study mitochondrial complex I. The present work introduced the promoter for the isocitrate lyase (pICL1) as a useful tool for the substrate selective expression of the internal version of the alternative NADH:ubiquinone oxidoreductase (pICL1-NDH2i). This allows to rescue complex I deficiencies “in vivo” selectively by growth on acetate (or ethanol) medium. The integration of the pICL1-NDH2i construct into the genome of Y. lipolytica and subsequent deletion of nuclear-coded subunits like PSST, TYKY and 49 kDa, would contribute to further develop this organism as a useful genetic model for studying subunits of mitochondrial complex I by site directed mutagenesis.
Stability, unfolding and refolding of the outer membrane protein porin from Paracoccus denitrificans was investigated using genetic and spectroscopic methods. Structural and functional activity studies on wild type and mutant porins: The site-directed mutants were constructed based on conserved residues and evidences on the role of certain amino acids from previous studies with OmpF. Secondary structure analysis of wild type and mutants E81Q, W74C, E81Q/D148N, E81Q/D148N/W74C by FTIR and CD spectroscopy are in line with the fact that porins are predominantly ß-sheet structure. The functional activity studies by black lipid bilayer techniques showed that the wild type and mutants W74C, E81Q/D148N, E81Q/D148N/W74C have a conductance of 3.25 nS. For mutant E81Q conductance of 1.25nS was more predominant over 3.25 nS. The activity of the mutants was observed to be far less than the wild type. This indicates that structural similarities does not implies similar functional activity. Thermal stability analysis of porin in detergent micelles and reconstituted into liposomes: Thermal stability analysis of wild type and mutants in detergent micelles showed changes in secondary and quaternary structure. It was found that wild type porin unfolds into aggregated structure with a high transition temperature of 86.2 °C. For mutants E81Q, W74C, E81Q/D148N the transition temperature was found to be 84.2 °C, 80.3 °C and 80.2 °C respectively. Functional activity assays at high temperatures revealed that the protein tends to loose its activity on heating up to 50 °C. This shows that structural stability does not imply functionality in the case of porins. Thermal stability analysis of porin reconstituted into liposomes showed that there was no change in the secondary and quaternary structure of the protein up to 100 °C, revealing that the protein becomes more thermostable when it is reconstituted into liposomes. Refolding of aggregated porin: This study shows that disaggregation of ß-sheet membrane protein porin is possible by changing its chemical and thermodynamic parameters. An increase of the solution pH to 12 or above results in opening up of the aggregated protein into unordered structure, as observed by FTIR and CD spectroscopy. This unordered structure could be refolded into native-like structure forming trimers. The secondary structure of the refolded protein deviated slightly from the native one. The thermal stability analysis of the native-like refolded proteins showed that the unfolding pattern is entirely different when compared to the native porins. pH dependent unfolding of porin: Thermal stability of porin at different pH values showed that the protein is stable in a pH range of 1-11. At pH 12 and above the protein unfolds into unordered structure instead of aggregating. The high pH unfolding of porin is a reversible process. The secondary structure of the refolded protein varied slightly from the native-one. Whereas thermal stability was entirely different. This shows that even though the unfolding of porin at high pH is reversible, it results in changes in local interaction between the amino acids resulting in a difference in stability. Unfolding in presence of urea and guanidinium hydrochloride (GuHCl): Denaturation of porin in the presence of chemical denaturants like urea and GuHCl showed that porin unfold into unordered structure. The unfolding is a reversible process. Unfolded protein was refolded into detergent micelles and liposomes. Refolding into detergent micelles was faster compared to refolding into liposomes, as seen by kinetic gel shift assays. The refolding into liposomes showed the presence of intermediates similar to those reported for OmpF. This study shows the difference in thermal stability of the outer membrane protein porin from Paracoccus denitrificans in detergent micelles and native-like liposomes. It suggests various unfolding pathways, which can be further investigated for unfolding and refolding kinetics. This report also suggests that it is possible to refold a heat-aggregated protein.
Dutch nominalised infinitives have been notoriously difficult to analyse, partly because they seem to show mixed verbal and nominal properties interspersed across the structure. In this paper, it is argued that at least two types of such infinitives should be distinguished, one which contains a high level of verbal functional structure, and one that differs at least in not projecting TP. On the basis of this distinction it is possible to show that Dutch nominalised infinitives have much more predictable properties than could previously be identified. They show evidence of conforming to a model of analysing mixed categories in terms of category switch within the constituent. In order to account for the seemingly interspersed nature of nominal and verbal properties in Dutch nominalised infinitives I propose that Dutch of-phrases (van-phrases) may merge inside the VP, provided they have access to nominal functional structure for feature checking. I will show that if D° is filled by a special type of non-deictic demonstratives van-phrases may even occur in SpecDP.
Results were presented from Brownian dynamics simulations for cyt c molecules approximated as spherical particles with diameter 2R ' 3.3 nm interacting with a charged planar membrane surface. Using the well-known Ermak-McCammon algorithm of ref. [36, 37] for solving the Langevin equations (see Chapter 2), a new computer program in C++ was developed. An overview of the way it is implemented is given in Chapter 3. The program in its current state is able to compute the trajectories (translation and rotation) of hundreds of spherical particles in systems with typical dimensions of 103 − 1003 nm3 . As explained in the introductory Chapter 1 the motivation for studying the dynamics of cyt c molecules in such systems came from the progress in the research of photosynthetic bacteria, e.g. While the internal processes of energy transduction (light harvesting, channelling to RC, charge separation) are quite well understood, the dynamics of soluble cyt c as an electron transporter in this context is not yet clear. In many textbooks one can find illustrations where a single cyt c is responsible for the electron transport between two integral membrane proteins (the reaction centre RC and the bc1 complex). But as pointed out in publications like refs. [49], [59], [60], [61] or [62] biological cells are crowded with different molecules. Consequently, one can assume that the electron transport between two integral membrane proteins is not simply taken on by one single cyt c molecule. Instead it is likely that many of these particles are located in a cyt c pool above the membrane and that they perform the electron transport in turns. Thus, it is desirable to have a simulation package that is able to compute the trajectories of many proteins. Note that the detailed processes of electron transfer and binding to membrane proteins are not modelled here. The details of these processes are quite complicated so that we refrained from including them in the coarse-grained simulations. Here, the actual binding is simply defined by a particle distance zb from the membrane which marks the beginning of the attractive potential. ...
Hinreichend kalte und dichte Quarkmaterie ist ein Farbsupraleiter. Ähnlich wie Elektronen in einem gewöhnlichen Supraleiter bilden Quarks Cooper-Paare. Während bei Elektronen der Austausch von Phononen zu einer Anziehung führt, ist im Falle von Quarks der Antitriplett-Kanal der starken Wechselwirkung attraktiv. Arbeiten in den letzten Jahren haben verschiedene Phasen von farbsupraleitender Quarkmaterie untersucht und sich dabei vor allem auf Phasen konzentriert, m denen der Gesamtspin eines Cooper-Paares verschwindet. In der vorliegenden Dissertation habe ich hauptsächlich Farbsupraleiter diskutiert, deren Cooper-Paare im Spin-Triplett-Kanal kondensieren, d.h. die Cooper-Paare haben den Gesamtspin 1. Diese Art von Supraleiter ist möglicherweise relevant für Systeme in der Natur, wie z.B. das Innere von Neutronensternen. Denn bei der Spin-0-Farbsupraleitung wird vorausgesetzt, dass die Fermi-Impulse zweier Quark-Flavor gleich ist oder zumindest hinreichend klein, was für realistische Systeme, also für nicht zu große Dichten, fragwürdig ist. Diese Einschränkung gibt es im Falle von Spin-1-Farbsupraleitern nicht, da hier Quarks des gleichen Flavors Cooper-Paare bilden. Ich habe in meiner Dissertation die verschiedenen möglichen Phasen eines Spin-1-Farbsupraleiters systematisch klassifiziert. Dies wurde mit Hilfe von gruppen-theoretischen Methoden durchgeführt, basierend auf der Tatsache, dass die Farbsupraleitung durch das theoretische Konzept der spontanen Symmetriebrechung beschrieben werden kann. Ähnlich wie bei supraflüssigem Helium-3 gibt es eine Vielzahl theoretisch möglicher Phasen. Ich habe die physikalischen Eigenschaften von vier dieser Phasen untersucht, nämlich der polaren und planaren Phasen sowie der A- und CSL-(color-spin-locked)Phasen. Mit Hilfe der QCD-Lückengleichung wurde die Energielücke sowie die kritische Temperatur bestimmt. Es stellt sich heraus, dass die Energielücke eines Spin-1-Farbsupraleiters um 2-3 Größenordnungen kleiner ist als die eines Spin-0-Farbsupraleiters, d.h. sie liegt im Bereich von 10 - 100 keV. Zwei besondere Eigenschaften der Energielücke werden diskutiert, nämlich eine 2-Lücken-Struktur, die in zwei der untersuchten Fälle auftritt, sowie mögliche Anisotropien, insbesondere Nullstellen der Lückenfunktion. Die Berechnung der kritischen Temperatur zeigt, dass es durchaus farbsupraleitende Materie in einer Spin-1-Phase im Innern von Neutronensternen geben kann, da die Temperatur von alten Neutronensternen im Bereich von einigen keV oder sogar darunter liegt. Darüber hinaus wurde die Frage untersucht, ob ein Farbsupraleiter auch ein gewöhnlicher Supraleiter ist. In diesem Zusammenhang ist die Frage von Interesse, ob ein Spin-1-Farbsupraleiter gewöhnliche Magnetfelder aus seinem Innern verdrängt, was sicherlich Auswirkungen auf die Observablen eines Neutronensterns hätte. Tatsächlich stellt sich heraus, dass ein Spin-1-Farbsupraleiter, im Gegensatz zu einem Spin-0-Farbsupraleiter, einen elektronmagnetischen Meissner-Effekt aufweist. Dieses Ergebnis wurde mit Hilfe von gruppentheoretischen Überlegungen vorausgesagt und mit Hilfe einer detaillierten Berechnung der Photon-Meissner-Massen bestätigt.
A new experimental setup, for pump-probe fs DFWM measurements, which is based on a femtosecond laser system, has been constructed. It allows for the investigation of molecular species in the gas phase at different temperatures, from ~30 K in a seeded supersonic jet up to ~500 K in a heat-pipe oven. In comparison to other RCS methods the employed fs DFWM technique is less complicated and gives much higher signal-to-noise ratio [BFZ86, FeZ95a, CKS89, CCH90, HCF91, WRM02, Rie02]. A general computer code for the simulation of fs DFWM spectra of nonrigid asymmetric top molecules has been developed. This new DFWM code in combination with a non-linear fitting routine allows one to determine rotational and centrifugal distortion constants and obtain information on the polarizability tensor components from the experimental spectra. Fs DFWM spectroscopy was successfully applied to the medium-sized molecules benzene and benzene-d6 in a gas cell and in a supersonic jet. The spectrum from a seeded expansion has been measured up to delay time of 3.9 ns (restricted by the length of the delay stage) with excellent signal-to-noise ratio (102-103). In that way 87 and 72 J-type transients have been recorded for benzene and benzene-d6, correspondingly. A relative accuracy on the order of 10-5 has been achieved for the rotational constant. From the room temperature experiments, precise values of centrifugal distortion constants DJ and DJK have been extracted. The literature data for cyclohexane have been revised and a new precise rotational constant B0 has been obtained, which is (+5.5 MHz) shifted from the one reported in the former Raman investigation by Peters et al. [PWW73]. Additionally, high-level ab initio calculations of cyclohexane have been carried out using a large number of basis sets at several levels of theory. In particular, the vibrational averaging effects have been examined in order to critically compare the experimentally determined and theoretically evaluated rotational constants. The contribution of highly symmetric vibrational modes to vibrational averaging effects was clarified. More structural information could be obtained from fs DFWM measurements of asymmetric top species, since different type of rotational recurrences can appear, and all three rotational constants (A, B, C) can be extracted. On the other hand the analysis of the asymmetric top spectra is no longer trivial. In fact the simple formula for rotational recurrence periods of symmetric top species (Tab. 2.1) can not be applied to asymmetric top molecules. Thus, in order to extract high-resolution data for asymmetric species, a complete fitting of the experimental spectra is necessary. The fs DFWM and (1+2') PPI method have been applied to the asymmetric top molecules pyridine in the ground (S0) and pDFB in the S0 and electronically excited (S1) states. By fitting the measured fs DFWM spectra the rotational and centrifugal distortion constants have been extracted with good precision and the value of the parametrized polarizability angle of pDFB was obtained. In this work, the first application of fs DFWM spectroscopy to a molecular cluster has been reported. Also, the chemical equilibrium between monomeric and dimeric species was studied. In particular formic and acetic acid have been investigated in a gas cell and in a supersonic expansion. Many spectral features have been observed and analized in the fs DFWM spectrum of formic acid vapor in a gas cell at room temperature. Most of them were attributed to rotational recurrences of the formic acid monomer, but also spectral feature originating from the formic acid dimer of O-H×××O/O×××H-O type have been detected and analyzed. From the fitted simulation, the rotational and centrifugal distortion constants, and parametrized polarizability angle were extracted for the dimeric structure of O-H×××O/O×××HO type. With the assumption of unperturbed monomers a center-of-mass distance of R = 2.990 ± 0.001 Å for the monomers within the dimer has been calculated from the spectroscopic results. This distance is 0.028 Å smaller than that reported from electron diffraction [ABM69]. Thus, the centers-of-mass distance was assigned as the main point of disagreement between results of fs DFWM and electron diffraction experiments. In contrast to formic acid, acetic acid shows strong recurrences from dimeric species even in the fs DFWM spectra at room temperature. This is explained in terms of different symmetry of the moments-of-inertia tensor, which modulates the intensity of RRs (the fs DFWM signal is in general stronger from symmetric species). Due to the symmetric nature of the acetic acid dimer, only the sum (B+C) of the rotational constants has been extracted. The changes of geometrical parameters upon dimer formation have been analyzed for, both, formic and acetic acid. A heat-pipe oven has been used in order to overcome the main drawback of fs DFWM spectroscopy – the square dependence of the signal intensity on the sample number density. Two-ring molecules (cyclohexylbenzene, para-cyclohexylaniline and nicotine) with low vapor pressure (<0.1 mbar) at room temperature have been investigated. From the analysis of the experimental and ab-initio results for CHB and pCHA a nearly perpendicular conformation of the aromatic vs. cyclohexane ring for both system is inferred. The enlargement of the benzene ring of CHB in the electronically excited state (S1) has been found to cause the smaller rotational constants in S1. This conclusion has been drawn from the comparison of the ground and electronically excited state experimental rotational constants in combination with ab-initio calculations. The extraction of precise structural information for nicotine was not possible due to it weak fs DFWM signal. However, the fact that fs DFWM technique can be applied to conformational analysis of molecular species in an equilibrium mixture opens other applications for this kind of spectroscopy. In general the results obtained in this work show that the fs DFWM technique, being an experimental implementation of RCS, provides one with an important tool for structural analysis of molecular species in the gas phase in particular for the species to which microwave spectroscopy can not be applied. It gives spectra with excellent signal-to-noise ratio even at low number density samples expanded in a seeded supersonic jet. It provides an alternative and innovative approach towards rotational Raman spectroscopy of large polyatomic molecules applicable under various experimental conditions (broad temperature and pressure range). With the introduction of femtosecond (10-15s) laser pulses (usually picosecond (10-12s) laser pulses were used in RCS) an improvement in time-resolution and therefore in precision for the rotational constants by more than one order of magnitude has been achieved. Molecular systems in the ground electronic state without permanent dipole moment and chromophore can be studied with high precision, providing thereby molecular benchmark systems for the electronic structure theory. As has been shown, the study of molecular clusters by fs DFWM spectroscopy is possible, but its potential are restricted by the square dependence of the fs DFWM signal from the sample number density, which is even more important for supersonic jet expansions. Here, the application of near-resonant and resonant FWM schemes should help in order to compensate for the low sample concentration. With the introduction of the heat pipe oven for fs DFWM experiments, the investigation of large nonvolatile molecules under equilibrium conditions is possible now. In our laboratory the first results on the structural analysis of different conformers of pyrrolidine in the gas phase have been obtained [MaR04]. This method can have even more prospects for the structural investigations of large molecular species in combination with new non-thermal gas phase sources for nonvolatile molecules, like laser desorption [CTL89], laser oblation [MHL83], electrospray [FMM90], laser induced liquid beam ion desorption [KAB96, Sob00] etc. A very recent application of the fs DFWM technique is the investigation of the influence of strong laser fields on molecular gas phase sample, which could range from active alignment [PPB03] over molecular deformation to field ionization [CSD03]. In regards to future development in fs DFWM spectroscopy for more complex molecules one has to take into account, how large amplitude motions such as the van der Waals vibrations or internal rotation (see section 6.4.2) affect the rotational coherences. In any case, femtosecond Degenerate Four-Wave Mixing as experimental implementation of Rotational Coherence Spectroscopy can be considered as an innovative, developing, and powerful method for the structural investigation of the molecular species, which are hard to study by classical frequency-resolved spectroscopy [FeZ95a, Dan01, Rie02].
Ruth First papers
(2001)
Scope and content: The collection includes personal material of First and her immediate family such as correspondence and financial records, papers relating to First's work as a journalist in South Africa, as a university lecturer, an anti-apartheid activist, and as an author and editor of numerous books and articles on Africa and other political topics. Also included are research papers and printed material relating to First and her family, collected both during her lifetime and after her death. System of arrangement: The collection is divided into individual deposits which have been presented separately to the Institute of Commonwealth Studies. As far as has been possible, the arrangement of the material within each deposit reflects the system of arrangement used by First, although much has been resorted. Throughout this catalogue the series into which the collection is divided are shown with the reference, title and date underlined. Orderable files are described without underlining.
Nitric oxide (NO) represents a short-lived mediator that pivotally drives keratinocyte movements during cutaneous wound healing. In this study, we have identified p68 DEAD box RNA helicase (p68) from a NO-induced differential keratinocyte cDNA library. Subsequently, we have analyzed regulation of p68 by wound-associated mediators in the human keratinocyte cell line HaCaT. NO, serum, growth factors and pro-inflammatory cytokines were potent inducers of p68 expression in the cells. p68 was constitutively expressed in murine skin, but rapidly down-regulated upon injury. The down-regulation appeared to be transient, as p68 protein expression increased again after the inflammatory phase of repair. However, p68 protein expression did not completely disappear during wound inflammation, as immunohistochemistry and cell fractiona tion analysis revealed a restricted localization of p68 in keratinocyte nuclei of the developing epithelium. In line, cultured human (HaCaT) and murine (PAM 212) keratinocyte cell lines showed a nuclear localization of the helicase. Moreover, confocal microscopy revealed a strong localization of p68 protein within the nucleoli of the keratinocytes. Functional analyses demonstrated that p68 strongly participates in keratinocyte proliferation and gene expression. Keratinocytes that constitutively overexpressed p68 protein were characterized by a marked increase in serum-induced proliferation and vascular endothelial growth factor (VEGF) expression, whereas down-regulation of endogenous p68 using small interfering RNA (siRNA) markedly attenuated serum-induced proliferation and VEGF expression. Altogether, our results suggest a tightly controlled expression and nucleolar localization of p68 in keratinocytes in vitro and during skin repair in vivo that functionally contributes to keratinocyte proliferation and gene expression.
Reliable communication in the central nervous system requires the precise control of the duration and the intensity of neurotransmitter action at specific molecular targets. After their release at the synapse, neurotransmitters activate pre- and/or postsynaptic receptors. To terminate synaptic transmission, neurotransmitters are in turn inactivated by either enzymatic degradation or active uptake into neuronal and/or glial cells by neurotransmitter transporters. In the present study, two types of membrane proteins involved in transcellular signal transduction were investigated, the P2X receptors, which are ATP-gated ion channels and the glutamate transporters of the EAAT family. The first part of this study is concerned with the targeting and anchoring of P2X receptors at specific locations. P2X receptors play a role of fast excitatory neurotransmission to extracellular ATP in both the peripheral and central nervous system. For several ligand-gated ion channel, like glycine receptors or nicotinic acetylcholine receptors, it is known that specific binding proteins exist, which are involved in receptor trafficking and anchoring of the receptors at appropriate sites on the synapse. Within the P2X family, amino acid homology is scattered over the protein sequence excepted of the cytoplasmic C-terminal tails, which do not share significant sequence similarity, indicating that they might provide peculiar properties to the respective receptor isoforms. Using GST fusion proteins containing the C terminal end of the P2X2A, P2X5 and P2X7 subunits as baits, ßIII tubulin was identified by MALDI-TOF mass spectrometry as a direct interacting partner of P2X2A. ßIII tubulin did not interact with P2X5 nor with P2X7. The tubulin binding motif of P2X2A could be confined to a 42 amino acid long region ranging from amino acid 371 to 412 of the complete P2X2A subunit. This domain, which includes a total of six serine residues and twelve proline residues, interestingly overlaps to a significant extent with a 69 amino acid long sequence, which is lacking in P2X2B, a splice variant of P2X2A. P2X2B receptors are known to desensitize - significantly faster than P2X2A receptors. The interaction of the P2X2A receptor with ßIII tubulin may contribute to receptor desensitization as well as tethering of the P2X2A receptor at specialized regions of the cell. In a second part of this work, the oligomeric state of two distantly related glutamate transporters, the human glial glutamate transporter hEAAT2, and the glutamate transporter ecgltP of E.coli was determined. Excitatory amino acid transporters (EAATs) buffer and remove synaptically released L-glutamate and maintain its concentration below neurotoxic levels. Mammalian glutamate transporter subunits are known to form homomultimers, but controversial numbers of subunits per transporter complex have been reported, ranging from 2-5. Both hEAAT2 and ecgltP proteins expressed at high levels in Xenopus laevis oocytes, from which they were purified in a [35S]methionine-labeled form under nondenaturing conditions by metal affinity chromatography. Blue native PAGE analysis revealed that both the hEAAT2 and ecgltP transporters exist exclusively as homogenous populations of homotrimers in Xenopus oocytes. The trimeric structure was corroborated by chemical crosslinking. Also, ecgltP purified as a recombinant protein from its natural host E.coli migrated as a trimeric protein on blue native PAGE gels. The conservation of the quaternary structure from prokaryotes to mammals assigns an important functional role to the trimeric structure. Glutamate transporters are known to exhibit a dual mode of operation by functioning both as glutamate Na+/K+/H+ co-transporters and as anion channels. It is intriguing to speculate that the EAAT monomer is responsible for the secondary active transport of glutamate, whereas a barrel-like arrangement of the three subunits forms a central anion pore mediating anion conductivity.
The detailed mechanism of the 20 S proteasome from Thermoplasma acidophilum is unknown. Substrates are degraded processively to small fragments without the release of intermediates, but the basis for this unique degradation mode remains obscure. The proteasome is a molecular machine, but how the different nanocompartments interplay and whether more than one substrate can be treated simultaneously has not been elucidated yet. To address these questions we had to disable the functionality of one aperture in order to dissect whether the other pore can compensate for the loss. As it is challenging to introduce mutations solely around one pore aperture of the highly symmetrical construct, we chose a novel approach by unique orientation of the proteasome at interfaces. For this purpose we purified recombinant 20 S proteasomes, where hexahistidine tags were fused either around the entrances or at the sides. According to electron microscopic studies we immobilized these constructs uniformly either end-on or side-on at metal-chelating interfaces (lipid vesicles, lipid monolayers and self-assembled thiol monolayers). Degradation of small fluorogenic peptides and large proteins like casein was analyzed. Small substrates were degraded with comparable activity by free and immobilized proteasomes, irrespective of their orientation. Thus it can be assumed that peptides can pass the sealed entrance of the 'dead-end' proteasome. However, larger substrates like fluorescently labeled casein were processed near the temperature optimum by side-on immobilized and soluble proteasomes with threefold activity compared to end-on immobilized proteasomes. Hence it can be concluded that one pore is sufficient for substrate entry and product release. In other words, the pore and antechamber can fulfil a triple function in the import and unwinding of substrates and the egress of products. With means of surface plasmon resonance the exact substrate/proteasome stoichiometry could be determined to ~1 for 'dead-end' proteasomes and ~2 for side-on immobilized (active and inactive) proteasomes. Most importantly, a fit with the Hill equation revealed positive cooperativity for side-on immobilized (Hill coefficient ~2) in contrast to end-on immobilized proteasomes (Hill coefficient ~1). Thus in case of soluble proteasomes two substrates bind presumably in opposite antechambers with positive cooperativity. The off-rate of casein as substrate is twofold for the active side-on immobilized proteasome in comparison to the end-on immobilized proteasome. The exact 2:1 stoichiometry of the off-rates equals the ratio of exit pathways amenable in case of side-on orientated versus 'dead-end' immobilized proteasomes. Thus crevices along the cylindrical body of the 20 S proteasome seem not to participate in the egress of small products. An inactive proteasome mutant displays a concentration-dependent off-kinetic against casein. Accordingly, the off-rate of the bisubstrate:proteasome complex can be attributed around half the value of the monosubstrate:proteasome complex. Consequently, substrates exit the inactive proteasome via the route of access due to obstruction of the trans side with an entering substrate. Hence the active proteasomes have to chop substrates down to small fragments prior to release through both pores. Thus the processive degradation mode might result from positive binding cooperativity. The on-rate constants for casein suggested that substrate association represents a two-step process comprising a rate-limiting translocation step and a fast binding step. As fluorescence cross-correlation revealed that two substrates can be co-localized in the proteasome and bind successively with increasing affinity (KD,1 = 8 µM versus KD,2 = 700 nM), an allosteric transition in the proteasome can be assumed. Combining our results with the data from other research groups led to a mechanistic model for the 20 S proteasome. Accordingly, the first substrate undergoes a slow translocation step, binds in the antechamber and diffuses subsequently to the catalytic centers, where it is degraded. By switching on the catalytic activity, the pores at both termini are dilated via conformational changes. Hence entry of the second substrate into the proteasome is facilitated due to omission of the rate-determining translocation step. The second substrate is either accommodated in the antechamber before it is processed (alternating degradation) or, most probably, is directly threaded into the central cavity (simultaneous degradation). As effusing peptides compete with entering proteins for binding in the antechamber, the pores are kept in an open state. After finishing digestion the pores are closed and a new degradation cycle can be reinitiated. In summary, substrate association with the proteasome underlies an ordered alternating binding mechanism in contrast to the random mode of degradation. Thus the two-stroke engine offers the advantage of speeding up degradation without enhancing complexity.
Transmembrane proteins play crucial roles in biological systems as active or passive channels and receptors. Experimentally only few structures could be determined so far. Gaining structural insights enables besides a general understanding of biological mechanisms also further processing such as in drug design. Due to the lack of experimental data, reliable theoretical predictions would be of high value. However, for the same reason, missing data, the knowledge-based class of prediction methods that is well established for soluble proteins can not be applied. The goal of predicting transmembrane protein structures with ab initio methods demands locating the free energy minimum. Main difficulties here are, first, the computational costs of explicitly calculating all involved interactions and, second, providing an algorithm that is capable of finding the minimum within an extremely complex and rugged energy landscape. We have developed promising energy functions that describe the interactions of amino acids on a residue level, reducing computational costs while still containing most information on the atomistic level. We have also found a way to describe the interaction of the residues with its surrounding in a realistic manner by distinguishing residues exposed to the environment from those buried within helices using a sphere algorithm. The sphere algorithm can also be applied for a different purpose: one can measure how densely sidechains are packed for certain helical conformations, and thereby get an estimate of the sidechain entropy. In addition, overcrowding effects can be identified which are not well-described by the energy functions due to the pairwise calculation. To determine the absolute free energy minimum, we assume the helices to be located on an equidistance grid with slightly larger distances than to be expected. Optimizing the helices on the grid provides a starting point that should enable common minimizing algorithms, gradient-based or not, to find the absolute minimum beyond the grid. To simulate the dynamics of the helices on large time scales, we split them into rigid body dynamics and internal dynamics in terms of the dihedrals. The former one is well-known with its inherent problem of numerical drift and plenty of approaches to it, among which we have chosen the quaternions to represent the rotation of the rigid bodies. The latter one requires a detailed analysis of the torque size exerted on the dihedrals caused by the forces acting on the residues.
Die 5 Lipoxygenase (5 LO) ist das Schlüsselenzym in der Synthese von Leukotrienen. Sie wird auf transkriptioneller und posttranskriptioneller Ebene reguliert. Die Differenzierung myeloider Zelllinien mit 1,25-Dihydroxyvitamin D3 (1,25(OH)2D3) und transformierendem Wachstumsfaktor beta (TGFbeta) führt zu einer Erhöhung der 5 LO mRNA-, Protein-Bildung und der zellulären Enzymaktivität. Hier wurde gezeigt, dass dabei reife, nicht jedoch prä-mRNA der 5 LO im Zytosol und im Zellkern stark angereichert wird und dass beide Agentien in die mRNA-Prozessierung eigreifen. Obwohl die Bindung von VDR-Retinoid-X-Rezeptor (RXR)-Heterodimeren an Bindungsstellen im 5 LO-Promotor mittels DNAseI-Footprinting und EMSAs nachgewiesen wurde, konnten Reportergene unter der Kontrolle des 5 LO-Promotors in transienten und stabilen Transfektionen durch 1,25(OH)2D3/TGFbeta nicht stimuliert werden. Offensichtlich wird die Induktion der Expression der 5 LO durch 1,25(OH)2D3/TGFbeta durch Elemente außerhalb des Promotors vermittelt. In transienten Transfektionen führte der Einbau der kodierenden Sequenz der 5 LO in Luziferase-Plasmide bei Cotransfektion von VDR/RXR zu einer 5 fachen Induktion der Reportergen-Aktivität durch 1,25(OH)2D3/TGFbeta, was durch zusätzlichen Einbau der letzten vier Introns auf eine 13-fache Erhöhung gesteigert wurde. Der VDR zeigte einen Ligand-unabhängigen Effekt. Diese Reportergen-Effekte waren promotorunabhängig und von der kodierenden Sequenz gesteuert. RT-PCR-Analyse wies auf eine Deletion von Teilen der kodierenden Sequenz im Laufe der mRNA-Prozessierung hin, was durch 1,25(OH)2D3/TGFbeta verhindert wird. Auch Cotransfektion der TGFbeta-Effektoren Smads 3/4 führte in Abhängigkeit von der kodierenden Sequenz und in geringerem Maße von der 3'-UTR und den Introns J M, aber unabhängig vom Promotor, zu einer starken Erhöhung der Reportergenaktivität. Die 5 LO-Expression wird in den untersuchten Zellen vermutlich durch posttranskriptionelle Prozesse (Splicing, mRNA-Reifung) herunterreguliert, während 1,25(OH)2D3/TGFbeta die Expression der 5 LO durch eine Gegenregulation zu erhöhen, an der Komplexe beteiligt sind, die vermutlich Smads, VDR-RXR-Dimere, andere Transkriptionsfaktoren, Coaktivatoren, RNA-Polymerase II und Splicing-Faktoren enthalten. Hyperacetylierung des 5 LO-Promoters durch Inkubation mit mit dem Histondeacetylase-Inhibitor TsA führte zu einer transkriptionellen Aktivierung. Die kodierende Sequenz (und die Introns) wirkt diesem Effekt vermutlich durch die Rekrutierung von HDACs an VDR oder Smads, die direkt oder indirekt an die kodierende Region binden, entgegen.
The transporter associated with antigen processing (TAP) plays a pivotal role in the adaptive immune response against virus-infected or malignantly transformed cells. As member of the ABC transporter family, TAP hydrolyzes ATP to energize the transport of antigenic peptides from the cytosol into the lumen of the endoplasmic reticulum. TAP forms a heterodimeric complex composed of TAP1 and TAP2 (ABCB2/3). Both subunits contain a hydrophobic transmembrane domain and a hydrophilic nucleotide-binding domain. The aim of this work was to study the ATP hydrolysis event of the TAP complex and gain further insights into the mechanism of peptide transport process. To analyze ATP hydrolysis of each subunit I developed a method of trapping 8- azido-nucleotides to TAP in the presence of phosphate transition state analogs followed by photocross-linking, immunoprecipitation, and high-resolution SDS-PAGE. Strikingly, trapping of both TAP subunits by beryllium fluoride is peptide-specific. The peptide concentration required for half-maximal trapping is identical for TAP1 and TAP2 and directly correlates with the peptide-binding affinity. Only background levels of trapping were observed for low affinity peptides or in the presence of the herpes simplex viral protein ICP47, which specifically blocks peptide binding to TAP. Importantly, the peptideinduced trapped state is reached after ATP hydrolysis and not in a backward reaction of ADP binding and trapping. In the trapped state, TAP can neither bind nor exchange nucleotides, whereas peptide binding is not affected. In summary, these data support the model that peptide binding induces a conformation that triggers ATP hydrolysis in both subunits of the TAP complex within the catalytic cycle. The role of the ABC signature motif (C-loop) on the functional non-equivalence of the NBDs was investigated. The C-loops of TAP transporter contain a canonical C-loop (LSGGQ) for TAP1 and a degenerated ABC signature motif (LAAGQ) for TAP2. Mutation of the leucine or glycine (LSGGQ) in TAP1 fully abolished peptide transport. TAP complexes with equivalent mutations in TAP2 showed however still residual peptide transport activity. To elucidate the origin of the asymmetry of the NBDs of TAP, we further examined TAP complexes with exchanged C-loops. Strikingly, the chimera with two canonical C-loops showed the highest transport rate whereas the chimera with two degenerated C-loops had the lowest transport rate, demonstrating that the ABC signature motifs control the peptide transport efficiency. All single-site mutants and chimeras showed similar activities in peptide or ATP binding, implying that these mutations affect the ATPase activity of TAP. In addition, these results prove that the serine of the C-loop is not essential for TAP function, but rather coordinates, together with other residues of the C-loop, the ATP hydrolysis in both nucleotide-binding sites. To study the coupling between the ATP binding/hydrolysis and the peptide binding, the putative catalytic bases of the TAP complex were mutated to generate the so-called EQ mutants. The mutations did not influence the peptide-binding ability. Dimerization of the NBDs of EQ mutants upon ATP binding does not alter the peptide binding property. At 27°C, both ATP and ADP could induce the loss of peptide-binding ability (Bmax) only in the variants bearing a mutated TAP2. Further studies are required to deduce at which stage in the catalytic cycle the peptide-binding site is affected. In addition, mutation of the putative catalytic base of both subunits showed a magnesium-dependent peptide transport activity, demonstrating these mutants did not abolish the ATP hydrolysis. Thus, the function of this acidic residue as the catalytic base is not likely to be universe for all ABC transporters.
Abraham Lincoln
(1899)
Ligands of Iron-Sulphur Cluster N2: In this work the ubiquinone reducing catalytic core of NADH:ubiquinone oxidoreductase (complex I) from Y. lipolytica was studied by a series of point mutations replacing conserved histidines or arginines in the 49-kDa subunit. Although the missing 4th ligand of cluster N2 could not be found in the 49-kDa subunit of complex I, it was clearly demonstrated that iron-sulphur cluster N2 resides directly on the interface between the PSST and 49-kDa subunits. The results presented in this work show that residues in the 49-kDa subunit have strong influence on this redox centre and also on catalytic activity. The strong influence of Arg-141 and His-226 residues in 49-kDa subunit on this cluster can be deducted from complete loss of N2 signals in EPR spectra such as in case of mutants H226A and R141A. In the case of mutant H226M the EPR signal from cluster N2 was shifted and cluster N2 even lost the pH dependence of its redox midpoint potential and became more similar to the other so called 'isopotential' clusters. Specifically in the case of mutants R141M and R141K the characteristic signature of cluster N2 became undetectable in EPR spectra. However, specific dNADH:DBQ oxidoreductase activity that could be inhibited with the specific complex I inhibitors DQA and rotenone was not absolutely abolished but rather reduced. These reductions in complex I activity did not correspond to similar reductions in the specific EPR signal of cluster N2 as it was observed in the His-226 mutant series. No indications could be found that these mutations had modified the magnetic properties of cluster N2, resulting in different EPR spectra. From these observations it could be concluded that both mutants R141K and R141M virtually or entirely lack iron-sulphur cluster N2. The rates in complex I activity could be reconciled with electron transfer theory: After removal of a single redox centre in a chain, electron transfer rates are predicted to be still much faster than steady-state turnover of complex I. These results from mutants R141K, R141M and also the result from mutant H226M that protons are being pumped even if the redox midpoint potential of cluster N2 is not pH dependent questions the prominent role in the catalytic mechanism of complex I that has been ascribed to cluster N2. Histidine 91 and 95 were found to be absolutely essential for activity of complex I since in both mutants complex I was fully assembled and artificial NADH:HAR activity was parental whereas complex I specific dNADH:DBQ activity was abolished. The signal from cluster N2 in EPR spectra was parental for all His-91 and -95 mutants. Mutations at the C-terminal arginine 466 affected ubiquinone affinity and inhibitor sensitivity but also destabilised complex I. All these results provide further support for a high degree of structural conservation between the 49-kDa subunit of complex I and the large subunit of water soluble [NiFe] hydrogenases. Remodelling of Human Pathogenic 49-kDa Mutations in Y. lipolytica: Y. lipolytica has been proven a good system for studying complex I properties and thus also for studying defects that occur in humans. In this work pathogenic mutations in the 49-kDa subunit of complex I were recreated and studied. The P232Q mutant showed non-assembly of complex I and this is probably the cause why this mutation was lethal in patients. The mutants R231Q and S416P were parental for the content, artificial and also specific complex I activity, Km for DBQ and IC50 for DQA. From these results we can conclude that these two residues Arg-228 and Ser-413 in mammalian cells have specific structural importance for the 49-kDa subunit even if they are not directly involved in catalytic process.
Removal of apoptotic cells by macrophages or resident semi-professional phagocytes is a prominent principle with important implications for the pathophysiology of chronic inflammatory diseases, viral infections, or cancer. To characterize mechanisms which may determine the fate of apoptotic cells, I investigated chemokine expression in apoptotic promonocytic U-937 cells or PBMC. Exposure of U-937 cells to the anti-cancer drug etoposide (VP-16), an inducer of apoptosis in these cells, was associated with increased expression of the chemokines IL-8 and macrophage inflammatory protein 1alpha (MIP-1alpha). Upregulation of IL-8 mRNA expression by VP-16 was observed as early as 4 h after onset of treatment and was still detectable after 19h of exposure. A serine protease inhibitor prevented both VP-16-induced apoptosis and release of IL-8, whereas inhibition of p38 MAP-kinases reduced IL-8 secretion only. Moreover, I observed that incubation with 2-chlorodeoxyadenosine (CdA) upregulated release of IL-8 from adherent PBMC in parallel to induction of apoptosis. In these cells a modest but significant induction of TNF-alpha release by CdA was also detected. In addition, CdA augmented release of IL-8 from whole blood cultures. By facilitating adequate recruitment of phagocytes to sites of cell death, stress-induced upregulation of chemokines associated with apoptosis may contribute to mechanisms aiming at efficient removal of apoptotic cells.
This dissertation study argues that 'policy advice formation', as a discourse development, is a differentiated hybrid resultant from merger between comparative education and policy studies disciplines. Through discourse analysis based on John Creswell's format, this study identifies revisions, restatements and shifts in emphasis of theories, methodological models and challenge topics of comparative education and policy studies. Findings which display the development of policy advice formation' discourse. In conclusion, this study found differential patterns seemingly formed because of collaborative affects of standardization in education science knowledge expressed within discourse.