A Conceptual Mathematical Model of the Dynamic Self-Organisation of Distinct Cellular Organelles

Formation, degradation and renewal of cellular organelles is a dynamic process based on permanent budding, fusion and inter-organelle traffic of vesicles. These processes include many regulatory proteins such as SNAREs, Rabs and coats. Given this complex machinery, a controversially debated issue is the definition of a minimal set of generic mechanisms necessary to enable the self-organization of organelles differing in number, size and chemical composition. We present a conceptual mathematical model of dynamic organelle formation based on interacting vesicles which carry different types of fusogenic proteins (FP) playing the role of characteristic marker proteins. Our simulations (ODEs) show that a de novo formation of non-identical organelles, each accumulating a different type of FP, requires a certain degree of disproportionation of FPs during budding. More importantly however, the fusion kinetics must indispensably exhibit positive cooperativity among these FPs, particularly for the formation of larger organelles. We compared different types of cooperativity: sequential alignment of corresponding FPs on opposite vesicle/organelles during fusion and pre-formation of FP-aggregates (equivalent, e.g., to SNARE clusters) prior to fusion described by Hill kinetics. This showed that the average organelle size in the system is much more sensitive to the disproportionation strength of FPs during budding if the vesicular transport system gets along with a fusion mechanism based on sequential alignments of FPs. Therefore, pre-formation of FP aggregates within the membranes prior to fusion introduce robustness with respect to organelle size. Our findings provide a plausible explanation for the evolution of a relatively large number of molecules to confer specificity on the fusion machinery compared to the relatively small number involved in the budding process. Moreover, we could speculate that a specific cooperativity which may be described by Hill kinetics (aggregates or Rab/SNARE complex formation) is suitable if maturation/identity switching of organelles play a role (bistability).     

Effect of unsaturated fatty acids on the biosynthesis of glucose-repressed enzymes in yeast

In anaerobically glucose-grown yeast isocitrate lyase (EC 4.1.3.1.), malate synthase (EC 4.1.3.2.) and malate dehydrogenase (EC 1.1.1.37.) are repressed by glucose. 24 h cultures still contain 0.3–0.4% glucose in the medium, which is enough to completely repress these activities. Aeration of these cells, in buffer containing acetate, initiates the formation of the three enzymes. Within 16 h, the specific activities of these enzymes increase about 140, 120 and 70-fold, respectively. Glucose-6-phosphate dehydrogenase activity was not altered. When the yeast was grown anaerobically, but with a supplement of an unsaturated fatty acid in the medium, synthesis of the three enzymes was much faster and the specific activities after 16 h of derepression were considerably higher. A relationship exists between the number of double bonds in the unsaturated fatty acid molecule and its capability to stimulate enzyme synthesis: linolenic acid is more effective than linoleic acid, which, in turn, is much more effective than oleic acid. Increasing periods of aeration with glucose of anaerobically grown cells prior to derepression results in an increasing stimulation of enzyme synthesis on subsequent derepression. Anaerobic incubation of yeast in the presence of an unsaturated fatty acid in advance to derepression also increased the velocity of enzyme formation. It is suggested that during the aeration period with glucose and during anaerobic incubation with an unsaturated fatty acid a more active protein synthesizing apparatus was formed.     

American and korean ginseng tissue cultures: Growth,chemical analysis,and plantlet production

Summary Roots, stems, or leaves of American (Panax quinquefolium) and Korean (Panax ginsing) ginseng were grown as callus or supension tissue cultures. Tissue cultures ofP. ginseng would occasionally form plantlets. The fundamental chemical composition, inorganic analysis, and saponin (panaquilin) content of American and Korean ginseng plants and tissue cultures were determined. The crude saponin content is very similar to, but approximately one-half (1.3%, fresh weight) of that present in ginseng roots. Two-dimensional thin layer chromatographic analysis revealed minor differences in the panaquilins present in American and Korean ginseng tissue cultures. The sapogenin, panaxadiol, was isolated from Korean ginseng callus.     

Der Einflug der Gro?trappe(Otis tarda L.) nach West-Europa im Winter 1969/70

Zusammenfassung Im Winter 1969/70 fand ein besonders starker Einflug der Großtrappe (Otis tarda L.) nach West-Europa statt. Daran dürften etwa 300 Vögel beteiligt gewesen sein, von denen mindestens der überwiegende Teil aus der DDR stammte, und die hauptsächlich in Nordwestdeutschland und in Holland auftraten; Einzelexemplare flogen bis Bayern, Frankreich, Schottland und Dänemark.Nach den Einflügen bei strengem Frost und hoher Schneelage im Dezember und Januar führten die überwinternden Großtrappen witterungsabhängige, zwischen W und E pendelnde, Wanderungen aus, die typische Randzugerscheinungen darstellten. Auf dem Rückzug bildete sich im März im östlichen Niedersachsen ein Zugstau aus.Die Großtrappen zeigten sich meistens einzeln, mehrfach jedoch auch in Trupps bis zu 5, gelegentlich bis zu 20 Exemplaren. Das Geschlechterverhältnis betrug 1 : 1,35 . Etwa 10% der eingeflogenen Großtrappen kamen um.Da nicht jeder strenge Winter so ausgedehnte Großtrappenwanderungen in Mitteleuropa bewirkt, dürfte die Ursache für den Einflug 1969/70 das ganz besonders frühe Einsetzen winterlicher Witterung gewesen sein, so daß ein latent vorhandener Wegzugtrieb noch ausgelöst werden konnte.Summary An account is given of an extremely large invasion of Western Europe by the great bustard (Otis tarda L.) in the winter 1969/70, in the course of which about 300 birds, mostly from the DDR, were observed in Northwestern Germany and in Holland; single birds reached Bavaria, France, Scotland and Denmark.After the arrival of the birds in frosty weather with quite a lot of snow in December and January, wheather-dependent migrations of the wintering great bustards, oscillating between E and W, were found and are interpreted as Randzug. The spring migration stopped for about a week in March in the eastern parts of Lower Saxony.The great bustards mainly occured singly, but also several times in flocks up to 5 and occasionally up to 20 birds. The ratio of sexes was 1 : 1,35 . About 10% of the invading great bustards died.Because not every hard winter leads to extended migrations of the great bustard in Central Europe, the reason for the invasion 1969/70 seems to be the very early beginning of frosty wheather, so that a latent existing tendency to migration was brought out.     

Isolated epithelial cells of the toad bladder. Their preparation, oxygen consumption, and electrolyte content

Epithelial cells of the toad bladder were disaggregated with EDTA, trypsin, hyaluronidase, or collagenase and were then scraped free of the underlying connective tissue. In most experiments EDTA was complexed with a divalent cation before the tissue was scraped. Q _OO2, sucrose and inulin spaces, and electrolytes of the isolated cells were measured. Cells disaggregated by collagenase or hyaluronidase consumed O₂ at a rate of 4 µl hr^-1 dry wt^-1. Q _OO2 was increased 50% by ADH (100 U/liter) or by cyclic 3'',5''-AMP (10 mM/liter). Na⁺-free Ringer''s depressed the Q _OO2 by 40%. The Q _OO2 of cells prepared by trypsin treatment or by two EDTA methods was depressed by Na⁺-free Ringer''s but was stimulated relatively little by ADH. Two other EDTA protocols produced cells that did not respond to Na⁺ lack or ADH. The intracellular Na⁺ and K⁺ concentrations of collagenase-disaggregated cells were 32 and 117 mEq/kg cell H₂O, respectively. Cation concentrations of hyaluronidase cells were similar, but cells that did not respond to ADH had higher intracellular Na⁺ concentrations. Cells unresponsive to ADH and Na⁺ lack had high sucrose spaces and low transcellular membrane gradients of Na⁺, K⁺, and Cl^-. The results suggest that trypsin and EDTA disaggregation damage the active Na⁺ transport system of the isolated cell. Certain EDTA techniques may also produce a general increase in permeability. Collagenase and hyaluronidase cells appear to function normally.     

Ein Schlafplatz der Amsel im Schilfrohr

Ohne Zusammenfassung