Effect of propionate and pyruvate on citrulline synthesis and ATP content in rat liver mitochondria.

Propionate inhibits citrullinogenesis when succinate (plus rotenone) or glutamate are the oxidizable substrates used. Propionate decreases the intramitochondrial concentration of carbamylphosphate by decreasing the ATP content. When the energy supply for citrullinogenesis is provided by an influx of exogenous ATP, propionate is no longer an inhibitor. Pyruvate inhibits citrullinogenesis with glutamate but not with succinate (plus rotenone) as oxidizable substrates. Propionate and pyruvate deplete mitochondrial ATP but probably by different mechanisms.     

Bionomies comparées de deux souches (Marocaine et Américaine) d’Ooencyrtus kuvanae [Hym.: Encyrtidae], parasite oophage deLymantria dispar [Lep.: Lymantriidae]

Résumé Des adultes d’Ooencyrtus kuvanae (Howard) sortis d’œufs deLymantria dispar (L.) récoltés au Maroc et aux états-Unis ont été élevés séparément mais simultanément dans les mêmes conditions abiotiques. On a évalué chez ces adultes des caractéristiques bionomiques telles que la longévité, la proportion de ♀ fécondes, la fécondité réelle moyenne, la durée de la période de ponte et le pourcentage d’œufs viables développés par parthénogenèse. Chez la progéniture, on a évalué la survie des larves et la proportion de ♀. Aucune différence significative entre les 2 souches n’est apparue. Des croisements entre les 2 souches ont donné une descendance comportant des proportions équivalentes de ♀.O. kuvanae avait été introduit au Maroc en 1926 depuis les états-Unis. Ainsi, 50 années d’acclimatation de ce parasite au Maroc (soit près de 500 générations) n’ont pas modifié ses potentialités et n’ont pas suffi à induire chez lui une nouvelle race géographique.

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Summary Adults ofOoencyrtus kuvanae (Howard) were recovered from eggs ofLymantria dispar (L.) collected in Morocco and in the U.S.A. They were reared separately and simultaneously under identical laboratory conditions. Various biological characteristics of adults from both sources were compared including longevity, proportion of fertilized versus unfertilized females, fecundity, duration of the oviposition period, and the percentage of viable eggs produced by virgin females. Also the survival of the larvae and the sex ratio of the 2 cultures were evaluated. Crossbreeding individuals of the 2 cultures resulted in a similar proportion of females in the progeny. In general there were no significan differences found between the 2 cultures.O. kuvanae had been introduced in Morocco in 1926 from the U.S.A. The adaptation of this parasite to conditions in Morocco during the ensuring 50 years since its establishment (about 500 generations) did not appear to modify the biotic potential of this species nor was it sufficient to induce the development of a new geographic race.

     

Analysis of the conformation of polypeptides : the combined use of energy computations and nuclear magnetic resonance studies.

This review surveys current approaches to the problem of determining the solution conformation of polypeptides. The basic principles of energy computations are described. The utility, problems, and limitations of various theoretical methods are summarized: conformational energy mapping, energy minimization, scanning of selected local conformations, statistical predictive schemes. The need for combining the calculations with experimental studies is pointed out. The information content of various physico-chemical methods is compared for this purpose. The analysis of nmr coupling constants is discussed in more detail. In combination with energy computations, it can furnish specific information on local aspects of the conformation. Examples of such combined studies on small peptides are summarized.     

Luminance artifacts of cathode-ray tube displays for vision research.

Phosphor persistence, video bandwidth, DC restoration and high-voltage regulation affect the appearance of images presented on cathode-ray tubes (CRTs), potentially resulting in differences between nominal and actual stimuli. We illustrate these effects by measuring physical parameters of horizontal and vertical static and counter-phase flickering gratings, and we illustrate problems for vision research by measuring contrast sensitivity to these gratings. We also measured the extent to which calibration protocols actually result in the monitor being calibrated over its entire area regardless of image size. The results of our physical measurements indicate substantial differences between gratings that nominally differ only as to orientation. Consistent with these differences, our psychophysical measurements indicate different sensitivities when the bars of the gratings are parallel or orthogonal to raster lines, regardless of the retinal orientation of the gratings. The results of our calibration check show that only a small region around the target area of calibration can be regarded as effectively linearized, and only if the size of the test image used during the check is similar to the size of the calibration patch. Overall, our results indicate potentially severe problems with the use of CRTs in vision research, and we discuss some published results that are likely to have been affected by these problems.     

Ultrastructure of Weddellomyces epicallopisma (Dothideales, Dacampiaceae, Ascomycota), especially of its ascospores]

An ultrastructural study of Weddellomyces epicallopisma (ascomata wall, asci, ascospores and vegetative hyphae), the first done on the family Dacampiaceae, confirms most of the observations made in light microscopy. Moreover it shows that ascospores are provided with an endospore (not visible in light microscope) and that the structure of the ascospore septum is more complex. The similarity of the wall structure between the ascospore and the hyphoid appendages, developed on the upper part of the ascoma, is emphasized.     

The exosome of Trypanosoma brucei.

The yeast exosome is a complex of at least 10 essential 3'-5' riboexonucleases which is involved in 3'-processing of many RNA species. An exosome-like complex has been found or predicted to exist in other eukaryotes but not in Escherichia coli. The unicellular parasite Trypanosoma brucei diverged very early in eukaryotic evolution. We show here that T.brucei contains at least eight exosome subunit homologs, but only a subset of these associate in a complex. Accordingly, the T.brucei exosome is smaller than that of yeast. Both free and complex-associated homologs are essential for cell viability and are involved in 5.8S rRNA maturation. We suggest that the exosome was present in primitive eukaryotes, and became increasingly complex during subsequent evolution.     

Low responsiveness of six-rowed genotypes to androgenesis in barley does not have a pleiotropic basis.

A heterozygous mutant for the two- and six-rowed character was isolated in the barley cultivar Igri through application of sodium azide to isolated microspore cultures and posterior regeneration. Six-rowed and two-rowed homozygotic plants were subsequently identified in the self-pollinated M2 progenies of the original heterozygous M1. Detailed molecular markers confirmed the isogenic nature of this recovered mutant and the original cultivar Igri. A comparative study of the anther culture response of this six-rowed induced mutant vs. diploid 'Igri' was performed to assess whether the two- or six-rowed gene influences anther culture response in barley through a pleiotropic effect or via linkage disequilibrium. No significant differences for any of the recorded variables throughout the in vitro regeneration process were detected between the 'Igri' six-rowed mutant and any of their two-rowed isogenic lines. This suggests that row-type association with anther culture response in barley cultivars is due to the effect of a tight linkage with other genes directly responsible for androgenic response.