Influence of glyoxylic acid on properties of isolated mitochondria]

Glyoxalate is an effector of oxidative phosphorylation in isolated mitochondria : it slows down State 3 but does not affect State 4 respiration. This report presents the findings of our study on the mechanism of action of glyoxalate ; these findings are listed below. The inhibition of Stage 3 respiration by glyoxalate does not set in immediately, can be reversed in part by the addition of an uncoupling agent or a dithiol, is non-competitive against succinate and can be demonstrated with substrates requiring the involvement of other membrane transport systems. Glyoxalate prevents the increased oxygen uptake stimulated by 2,4-DNP or Sr++. Glyoxalate also inhibits phosphate transport and this inhibition can account for most of the effect observed. The inhibition of State 3 respiration is paralleled by a decrease in the mitochondrial accumulation of succinate : this decrease could arise from a direct effect of glyoxalate on dicarboxylic acid transport or could be the result of an inhibiton of the phosphate transport system, which is connected with the former. The decrease in the respiratory rate of uncoupled mitochondria placed in a phosphate free medium demonstrates that the effector acts directly at the substrate transport or/and electron transfer level. Phosphate, by delaying the respiratory inhibiton due to glyoxalate, has a protecting effect on mitochondrial functions. Glyoxalate is thus acting at several mitochondrial sites. It acts presumably by forming hemimercaptals, blocking sulfhydryl groups. Its effects can be accounted for by the unfolding of such (hemicercaptal) groups under the influence of ADP, Pi, uncoupling or others agents which bring about conformational changes in the internal mitochondrial membrane.     

Effects of Conformism on the Cultural Evolution of Social Behaviour

Models of cultural evolution study how the distribution of cultural traits changes over time. The dynamics of cultural evolution strongly depends on the way these traits are transmitted between individuals by social learning. Two prominent forms of social learning are payoff-based learning (imitating others that have higher payoffs) and conformist learning (imitating locally common behaviours). How payoff-based and conformist learning affect the cultural evolution of cooperation is currently a matter of lively debate, but few studies systematically analyse the interplay of these forms of social learning. Here we perform such a study by investigating how the interaction of payoff-based and conformist learning affects the outcome of cultural evolution in three social contexts. First, we develop a simple argument that provides insights into how the outcome of cultural evolution will change when more and more conformist learning is added to payoff-based learning. In a social dilemma (e.g. a Prisoner’s Dilemma), conformism can turn cooperation into a stable equilibrium; in an evasion game (e.g. a Hawk-Dove game or a Snowdrift game) conformism tends to destabilize the polymorphic equilibrium; and in a coordination game (e.g. a Stag Hunt game), conformism changes the basin of attraction of the two equilibria. Second, we analyse a stochastic event-based model, revealing that conformism increases the speed of cultural evolution towards pure equilibria. Individual-based simulations as well as the analysis of the diffusion approximation of the stochastic model by and large confirm our findings. Third, we investigate the effect of an increasing degree of conformism on cultural group selection in a group-structured population. We conclude that, in contrast to statements in the literature, conformism hinders rather than promotes the evolution of cooperation.     

Spatial organization of transport domains and subdomain formation in the plasma membrane of Chara corallina

Pattern formation mechanisms in developing organisms determine cellular differentiation and function. However, the components that interact during the manifestation of a spatial pattern are in general unknown. Characean algae represent a model system to study pattern formation. These algae develop alternating acid and alkaline transport domains that influence the pattern of growth. In the present study, it will be demonstrated that a diffusion mechanism is implicated in acid and alkaline domain formation and this growth pattern. Experiments on the characean growth pattern were performed that resulted in pronounced, however, unpredictable modifications in the original pattern. A major component involved in this pattern-forming mechanism emerged from the nonlinear kinetics of the H⁺-ATPase that is located in the plasma membrane of these algae. Based on these kinetics, a mathematical model was developed and numerically analyzed. As a result, the contribution of a diffusional component to the characean acid/alkaline pattern appeared most likely.This work was supported by the Deutsche Forschungsgemeinschaft (grant #571 1/1) to JF.     

Experimentelle Untersuchungen über die Stoffaufnahme durch Pinocytose während der Vitellogenese des Amphibienoocyten

Summary Female newts (Triton alpestris) are treated with an iron-III-dextran complex (Myofer Hoechst) in order to demonstrate the uptake of this substance into the oocytes. In animals, sacrificed 24 or 48 hours after the injection, iron as well as a polysaccharide are detectable cytochemically in the older stages of the oocytes. The iron is visualized by Prussian blue and Turnbull blue reaction, the dextran by the PAS reaction.The uptake of Myofer into the egg, the transport within the cytoplasm and the incorporation of iron into the yolk bodies are also studied by means of electron microscopy. Myofer particles are found at the surface of the plasmalemm of the oocyte. Such particles appear to enter the plasmalemm by means of pinocytosis. Pinocytotic vesicles are shown to unite and to form cytosomes which in turn are incorporated into the previtelline globules and into the developing yolk bodies. During incorporation into the yolk bodies the Myofer particles aggregate so that they appear larger and more dense than in the cytosomes. This aggregation of the Myofer particles can be also demonstrated by differences in the results obtained with the two histochemical methods for the detection of iron. The process involved in the uptake of an unspecific substance into the oocyte and in the formation of yolk platelets are discussed.

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Mit dankenswerter Unterstützung durch die Deutsche Forschungsgemeinschaft.

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Auszugsweise vorgetragen auf dem II. Europäischen Anatomen-Kongreß in Brüssel, September 1963 (Wartenberg 1963).