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Interaction between species in a marine ecosy stem is described by expressions for food consumption and grazing mortality which are consistent with each other and with the Beverlon and Holt model of the population dynamics ofindividual species. A model of primary production is introduced in order to make possible an account of nutricnt circlliation (as examplified by phosphorus) within and nutrient flow through the system. It is demonstrated in an application to North Sea fishencs that recent changes in total yield can be described in some detail under the terms of the model as a function of fishing mortality alone. The composition of the North Sea fauna in the virgin state is discussed and also the conditions under which total yield could be increased above the 1970 level.
Until recently, up to thirteen specics of the scincid genus, Scincus, were recognized, but examination of some 590 individuals frorn a wide range of localities suggests that only three or four are valid. Of these, S. mitranus is confined to eastern and southern Arabia and S. hemprichii probably to southwest Arabia. The remaining forms constitute the S. scincus complex, which may consist in North Africa of two largely allopatric species, S. scincus and S. albifasciatus, although evidence for this is not conclusive. The S. scincus complex is represented in southwest Asia by two forms : S. scincus meccensis in southern Jordan, northwest and west Arabia and S. s. conirostris in southern and eastern Arabia, Iraq and southwest Iran. Scincus appears to have evolved Erom a primitive scincine, very similar to members of the Eumeces schneideri group, especially E. (schneideri) algariensis; it does not seem to be directly related to the sympatric genus Scincopus. Within Scincus, the S. scincus complex is the least specialized component of the genus and both S. rnitranus and S. hemprechii may have been independently derived from it, or from a closely related form. Possibly the whole range of the genus was once occupied by a S. scincus-like species and its distribution was subsequently restricted by the onset of less desertic conditions leaving reduced populations in North Africa, southwest Arabia and southeast Arabia that gave rise to the S. scincus complex, S. hemprichii and S. mitranus respectively. A renewed expansion of arid areas could then have enabled the S. scincus complex to invade southwest Asia. Some of the characters of its most eastern subspecies, S. s. conirostris, may have arisen, or been maintained, by character displacement through contact with S. mitranus.
As we have shown in a recent paper, the principle of competition between "statistical" and "chemical" mixing represents a molecular thermodynamic approach to all known types of phase separation. This principle is effective if the contributions of two independent spontaneous processes enter into the thermodynamic potential by which the resulting equilibrium state of the system is determined. This is equivalent with the statement that two different forms of entropy exist which are not interchangeable, and for which the law of increasing entropy independently must be valid. As "cooperativity" is introduced by this principle, critical phenomena may be described by simple equilibrium models in which only nearest-neighbour interactions are considered.
Starting from the molar Gibbs free energy GM of the most simple binary equilibrium model z = 1 with nearest-neighbour pairs, nonclassical critical-point exponents α = 0.33 of the molar heat capacity, β = 0.33 of the coexistence curve, γ = 1.33 of the isothermal compressibility, and δ = 4.33 of the critical isotherm, are derived, which are consistent with the well-known exponent in equalities. These non-classical critical-point exponents are independent of the chemical nature of the particles because they are obtained by applying thermodynamic arguments on the coupling constant τ, by which the contribution of "statistical mixing" to GM is weighted.
Phasentrennung als Folge der Konkurrenz zwischen "statistischer" und "chemischer" Vermischung
(1977)
The fact that common thermodynamic conditions are valid for all known types of critical phases (liquid-liquid, liquid-gas, and "gas-gas") suggests that a common principle for the interpretation of material phase instability from a molecular point of view must exist. In this paper we show that the principle of competition between "statistical mixing" (i. e. random mixing) and "chemical mixing" (i. e. mixing effected under the influence of chemical interactions) can give this common inter pretation. If the equilibrium states resulting from both types of mixing are sufficiently different, phase separation occurs. We refer to our earlier papers (since 1972) in which we have applied this principle to describe liquid-liquid phase equilibria by "chemical" models, using the equilibrium constants of exchange equilibria between nearest-neighbour complexes as a measure of "chemical" mixing. In this paper we show that the well-known reduced gas-liquid coexistence curve, T/Tc =f(q/qc), can accurately be fitted by a very simple "mixture" model of molecules A with "vacan cies", provided that the contributions of both statistical and chemical mixing are incorporated into the formula for GE. From a discussion of the application to "gas-gas" phase equilibria in the hyper critical region it results that the weight factor r, by which the contribution of statistical mixing enters into GE, must depend on the density of the gas mixture. Phase separation can only occur if, by increasing pressure, the contributions to GE of statistical and chemical mixing have reached the same order of magnitude. From an attempt to apply the same principle to solid-liquid equilibria it is shown under which external conditions a critical point for this type of phase transition can be expected.
Sexual reproduction in yeasts has a survival function by providing an alternative to the vegetative processes when conditions are no longer conducive for growth. If both sexes are in the correct physiological state (usually under starvation conditions), then initiation of copulation involves the mutual induction of a sexual response. This response is mediated by diffusible compounds and by physical contact. Initial cell contacts between opposite mating types can be disrupted easily, but stronger intercellular bonds form later that result in the fusion of two cells into one. Union between mates involves mixing of parental gene pools. The new diploid organism or its subsequent offspring might be better equipped to survive in a new environment because they may contain new combinations of parental genes. Hence, sex is more advantageous to the survival of the species than it is to the individual organism. The purpose of this review is to compare the steps in the mating process in three species of yeasts. The various physiological factors, events and regulatory phenomena that are part of the mating process will be described for Hansenuta wingei, Schizosaccharomyces pombe and Saccharomyces cerevisiae in Sections II, III and IV, respectively. Then, in Section V, the similarities and differences among these yeast systems will be discussed. Emphasis in this article will be on recent observations since reviews of earlier work are available for each mating system (for H. wingei: Crandall and Brock, 1968; Crandall and Caulton, 1975; for Schizosacch. pombe: Leupold, 1970; Gutz et at., 1974; for Sacch. cerevisiae: Fowell, 1969a, b; Bilinski et at., 1975; Sena et at., 1975). For a comprehensive review of conjugation in all yeasts, fungi and other micro-organisms, consult Crandall (1977). The three yeasts to be reviewed here are quite diverse in terms of their ecological niches, metabolism, morphology and life cycles. Therefore, for a better understanding of the physiology of sexual reproduction in these organisms, it is necessary first to consider these characteristics. A more detailed description of each yeast is given in Lodder (1970).
The NAD analogue [3-(3-acetylpyridinio)-propyl] adenosine pyrophosphate forms enzymically inactive complexes with glyceraldehyde-3-phosphate dehydrogenase from yeast and rabbit skeletal muscle. In the latter enzyme four mol of the analogue are bound with equal affinity inhibiting the enzyme in a competitive way: KI = 0.3 mM as compared to the dissociation constant KD=O.6 mм.
The brominated derivative [3- (3-bromoacetylpyridinio) -propyl] adenosine pyrophosphate is covalently bound to both enzymes causing irreversible loss of enzymic activity. Complete inactivation of the enzyme from muscle requires two moles of the analogue per mol of tetramer. The remaining two sites are still able to bind two mol of NAD+ without regain of enzymic activity. In the case of the yeast enzyme four mol of the analogue are bound. Inactivation of the rabbit muscle enzyme is accompanied by the disappearance of two out of four highly reactive sulfhydryl groups; in the yeast enzyme the four active site cysteine residues are still able to react with DTNB1 the reactivity being diminished significantly.
Hybrid formation between the native enzymes from yeast and skeletal muscle is not affected by the modification of the enzyme. Similarly the sedimentation properties of the covalently modified enzyme are indistinguishable from those of the native molecule. This indicates that both the native and the irreversibly inhibited enzyme are identical regarding their quaternary structure.
In einer mehrjährigen Grabungskampagne hat das Niederösterreichische Landesmuseum in Pitten, N.Ö., ein ausgedehntes Gräberfeld freigelegt, in dem Schichten mehrerer Epochen entdeckt wurden. Die anthropologische Bearbeitung der frühmittelalterlichen Skelette dieses Gräberfeldes wird mithin vorgelegt. Insgesamt standen 137 Skelette, davon 32 männliche, 44 weibliche und 61 kindliche zur Verfügung. Ihr Erhaltungszustand war größtenteils gut, sodaß eine große Zahl von Individualdaten nach den standartisierten anthropologischen Methoden erhoben werden konnte, aus denen die gruppenstatistischen Parameter berechnet wurden. Wesentlich mehr Einzelmerkmale deuten auf eine nähere Verwandtschaft der Pittener Population mit denen von Mikulcice, Lupka und Pobedin (CSSR) hin, als mit den awarenzeitlichen Gruppen von Zwölfaxing (NÖ), Feherto-A, Allätyan-Tulant und Adorjan (Ungarn), mit denen sich nur wenige Ähnlichkeiten fanden. Dieses Ergebnis wurde noch durch das Resultat einer Varianzanalyse erhärtet. Typisch mongoloide Schädel, wie sie in geringer Zahl im awarenzeitlichen Gräberfeld von Zwölfaxing festgestellt wurden, scheinen in unserer Serie nicht auf. Einige Merkmale mit mongoloider Tendenz finden sich zwar bei einem weiblichen Schädel, doch reichen unsere Kentnisse über die Variabilität der Pittener Population nicht aus, um ihn mit Sicherheit zu den Mongoliden stellen zu können. Die morphologisch-metrische Gesamtbeurteilung über die mögliche rassische Zugehörigkeit des vorliegenden untersuchten Teiles des Pittener Gräberfeldes bestätigt mit großer Wahrscheinlichkeit die, auf Grund der kulturellen Beigaben vermutete slawische Herkunft dieser Population. Demographische Berechnungen und Untersuchungen über Beziehungen innerhalb des Gräberfeldes wie Familien- oder Sippenähnlichkeiten, Unterschiede bezüglich der beiden Haupt-Bestattungsrichtungen N-S u. W-O, konnten keine Ergebnisse bringen, da das Gräberfeld teilweise zerstört war, bzw. großteils gar nicht gehoben werden konnte. Die in den wichtigen Merkmalen auswertbare Schädelserie war außerdem zu klein um noch sinnvolle Unterteilungen durchführen zu können.
A single procedure for the preparation of lactate dehydrogenase (EC 1.1.1.27), the mitochondrial and cytoplasmic forms of malate dehydrogenase (EC 1.1.1.37), adenylate kinase (EC 2.7.4.3) and pyruvate kinase (EC 2.7.1.40) from pig heart is described. The five enzymes are obtained in preparative amounts in homogenous form with specific activities equal to or higher than those pre viously reported. Some molecular properties of pig heart pyruvate kinase are determined.