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The results presented here strongly indicate that ubiquitination of the recombinant human alpha1 GlyR at the plasma membrane of Xenopus oocytes is involved in receptor internalisation and degradation. Ubiquitination of the human alpha1 GlyR has been demonstrated by radio-iodination of plasma membrane-boundalpha1 GlyRs, whose subunits differed in molecular weight by additional 7, 14 or 21 kDa, corresponding to the molecular weights of one, two and three conjugated ubiquitin molecules, respectively, and by co-isolation of the non-tagged human alpha1 GlyR through hexahistidyl-tagged ubiquitin. Ubiquitin conjugated GlyRs where prominent at the plasma membrane, but could be hardly detected in total cell homogenates, indicating that ubiquitination takes place exclusively at the plasma membrane. Ubiquitination of the alpha1 GlyR at the plasma membrane was no longer detectable when the ten lysine residues of the cytoplasmic loop between transmembrane segments M3 and M4 were replaced by arginines. Despite this proteolytic cleavage continued to take place at the same extent as with the wild type alpha1 GlyR, suggesting that removal of GlyRs from the plasma membrane and routing to lysosomes for degradation were not dependent on ubiquitination. Also replacing a tyrosine in position 339, which was speculated to be part of an additional endocytosis motif, did not lead to a significant reduction of cleavage of the GlyR alpha1 subunits. However, a mutant lacking both, ubiquitination sites and 339Y, was significantly less processed. These results may suggest that the GlyR alpha1 subunit harbors at least two endocytosis motifs, which may act independently to regulate the density of alpha1 GlyR. Apparently, each of the two signals may be capable of compensating entirely the loss of the other. Part two of this Dissertation demonstrates that the correct topology of the glycine receptor alpha1 subunit depends critically on six positively charged residues within a basic cluster, RFRRKRR, located in the large cytoplasmic loop following the C-terminal end of M3. Neutralization of one or more charges of this cluster, but not of other charged residues in the M3-M4 loop, led to an aberrant translocation into the endoplasmic reticulum lumen of the M3-M4 loop. However, when two of the three basic charges located in the ectodomain linking M2 and M3 were neutralized, in addition to two charges of the basic cluster, endoplasmic reticulum disposition of the M3-M4 loop was prevented. We conclude that a high density of basic residues C-terminal to M3 is required to compensate for the presence of positively charged residues in the M2-M3 ectodomain, which otherwise impair correct membrane integration of the M3 segment. Part three of this Dissertation describes my contribution (blue native PAGE analysis of metabolically labeled alpha7 and 5HT3A receptors and the examination of the glycosylation state of metabolically labeled alpha7 subunits) to a work on the limited assembly capacity of Xenopus oocytes for nicotinic alpha7 subunits. While 5HT3A subunits combined efficiently to pentamers, alpha7 subunits existed in various assembly states including trimers, tetramers, pentamers, and aggregates. Only alpha7 subunits that completed the assembly process to homopentamers acquired complex-type carbohydrates and appeared at the cell surface. We conclude that Xenopus oocytes have a limited capacity to guide the assembly of alpha7 subunits, but not 5HT3A subunits to homopentamers. Accordingly, ER retention of imperfectly assembled alpha7 subunits rather than inefficient routing of fully assembled alpha7 receptors to the cell surface limits surface expression levels of alpha7 nicotinic acetylcholine receptors. Part four of this Dissertation describes my contribution (the biochemical analysis of the human P2X2 and P2X6 subtypes) to studies on the quaternary structure of P2X receptors. Armaz Aschrafi, the main author of the paper showed that subsequent to isolation under non-denaturing conditions from Xenopus oocytes the His-rP2X2 protein migrated on blue native PAGE predominantly in an aggregated form. The only discrete protein band detectable could be assigned to homotrimers of the His-rP2X2 subunit. Because of the exceptional assembly-behaviour of the rP2X2 protein compared to the rP2X1, rP2X3, rP2X4 and rP2X5 proteins, its human orthologue was investigated in the same manner. In contrast to rP2X2 subunits, hP2X2 subunits migrated under virtually identical conditions in a single defined assembly state, which could be clearly assigned to a trimer. P2X6 subunits represent the sole P2X subtype that is unable to form functional homomeric receptors in Xenopus oocytes. The blue native PAGE analysis of metabolically labeled hP2X6 receptors and the examination of the glycosylation state revealed that hP2X6 subunits form tetramers and aggregates that are not exported to the plasma membrane of Xenopus oocytes.
Electric charge correlations were studied for p+p, C+C, Si+Si, and centrality selected Pb+Pb collisions at sqrt[sNN]=17.2 GeV with the NA49 large acceptance detector at the CERN SPS. In particular, long-range pseudorapidity correlations of oppositely charged particles were measured using the balance function method. The width of the balance function decreases with increasing system size and centrality of the reactions. This decrease could be related to an increasing delay of hadronization in central Pb+Pb collisions.
We argue that the shape of the system-size dependence of strangeness production in nucleus-nucleus collisions can be understood in a picture that is based on the formation of clusters of overlapping strings. A string percolation model combined with a statistical description of the hadronization yields a quantitative agreement with the data at sqrt s_NN = 17.3 GeV. The model is also applied to RHIC energies.
System-size dependence of strangeness production in nucleus-nucleus collisions at √sNN = 17.3 GeV
(2005)
Emission of pi, K, phi and Lambda was measured in near-central C+C and Si+Si collisions at 158 AGeV beam energy. Together with earlier data for p+p, S+S and Pb+Pb, the system-size dependence of relative strangeness production in nucleus-nucleus collisions is obtained. Its fast rise and the saturation observed at about 60 participating nucleons can be understood as onset of the formation of coherent partonic subsystems of increasing size. PACS numbers: 25.75.-q
Das vorliegende Werk umfasst auf 792 Seiten die „Methodenstandards“ als Handwerkszeug bei den Vogelbeobachtern. Einführend gibt das Handbuch eine Übersicht zu feldornithologischen Erfassungsmethoden, dann folgen die Ausführungen zu den wichtigsten Standard-Methoden: der Revierkartierung, der Punkt-Stopp-Zählung, der Linienkartierung.
Die Meteor-Reise 63 befasst sich mit zwei unterschiedlichen Themen. Zum einen soll die Klimageschichte des Agulhas-Stroms sowie die spätpleistozäne und holozäne Klimage-schichte rekonstruiert und werden. Der zweite Fahrtabschnitt befasst sich mit Biodiversi-tätsgradienten in der abyssalen Tiefsee des Atlantik. Die Reise Meteor 63 soll somit Grundlagenwissen zur marinen Umwelt der Tiefsee um Afrika liefern, sowie deren kurz- und langfristige Variabilität zu erklären helfen.
Bei einer Fischarten-Erfassung an der Elbe zwischen Arneburg und Sandau fanden Dipl.-Biol. J. Huth, G. Belkner und der Verfasser am 14.10.2004 in der Nähe des rechten Ufers zwischen Strom-km 409 und 410 an einem etwa 10 cm langen Barsch (Perca fluviatilis) ein etwa 2 cm langes Krebstier, das wie eine kleine Garnele aussah. Die Determination dieses Fundtieres durch Frau Dipl.-Biol. U. Michels ergab Atyaephyra desmaresti, die einzige in Deutschland vorkommende Süßwassergarnele.
Zum fünften Mal fand am 12. Juni 2004 im Kreis Höxter der "Tag der Artenvielfalt" statt. Diese inzwischen weltweit größte Feldforschungsaktion, bei der das Arteninventar verschiedenster Lebensräume im europäischen Raum zeitgleich von über 10.000 Wissenschaftlern und Hobbyforschern erfasst wird, war 1999 von der Zeitschrift GEO initiiert worden. Die Idee der Aktion ist, innerhalb eines Tages in einem definierten Gebiet so viele Arten wie möglich zu erfassen und damit zu zeigen, dass es eine große Artenfülle nicht nur beispielsweise im tropischen Regenwald, sondern auch "direkt vor der Haustür" gibt.
Tagging kausaler Relationen
(2005)
In dieser Diplomarbeit geht es um kausale Beziehungen zwischen Ereignissen und Erklärungsbeziehungen zwischen Ereignissen, bei denen kausale Relationen eine wichtige Rolle spielen. Nachdem zeitliche Relationen einerseits ihrer einfacheren Formalisierbarkeit und andererseits ihrer gut sichtbaren Rolle in der Grammatik (Tempus und Aspekt, zeitliche Konjunktionen) wegen in jüngerer Zeit stärker im Mittelpunkt des Interesses standen, soll hier argumentiert werden, dass kausale Beziehungen und die Erklärungen, die sie ermöglichen, eine wichtigere Rolle im Kohärenzgefüge des Textes spielen. Im Gegensatz zu “tiefen” Verfahren, die auf einer detaillierten semantischen Repr¨asentation des Textes aufsetzen und infolgedessen für unrestringierten Text m. E. nicht geeignet sind, wird hier untersucht, wie man dieses Ziel erreichen kann, ohne sich auf eine aufwändig konstruierte Wissensbasis verlassen zu müssen.
This article combines a brief introduction into a particular philosophical theory of "time" with a demonstration of how this theory has been implemented in a Literary Studies oriented Humanities Computing project. The aim of the project was to create a model of text-based time cognition and design customized markup and text analysis tools that help to understand ‘‘how time works’’: more precisely, how narratively organised and communicated information motivates readers to generate the mental image of a chronologically organized world. The approach presented is based on the unitary model of time originally proposed by McTaggart, who distinguished between two perspectives onto time, the so-called A- and B-series. The first step towards a functional Humanities Computing implementation of this theoretical approach was the development of TempusMarker—a software tool providing automatic and semi-automatic markup routines for the tagging of temporal expressions in natural language texts. In the second step we discuss the principals underlying TempusParser—an analytical tool that can reconstruct temporal order in events by way of an algorithm-driven process of analysis and recombination of textual segments during which the "time stamp" of each segment as indicated by the temporal tags is interpreted.