Alteration of cholesterol synthesis in rat liver as induced by 4-methyl-5-hydroxy valeric acid

Summary The rate of cholesterogenesis in rat liver, measured by the incorporation of labelled acetate or mevalonate into cholesterol, was significantly supressed by the use of 4-methyl-5-hydroxy valeric acid sodium salt. This effect cannot be explained by changes in HMG CoA reductase activity.     

Effect of mecloqualone on the oxygen and glucose uptake by brain tissue in vitro

Resumen La mecloqualona inhibe in vitro, la respiración de cortes y homogenizados de cerebro, incrementando el consumo de glucosa; este último efecto no se produce cuando al medio de incubación se añaden 100 mM de potasio.     

Adaptation to intermittent fasting as a factor modifying the radiation resistance of mice

Summary Mice adapted to intermittent food intake (24 h fasting:24 h feeding) for 2–3 weeks exhibit a higher resistance to whole-body gamma irradiation. This is manifested by increased survival of animals and a more effective recovery of blood leukocyte counts.     

Effects of sphingolipids on erythroblastic maturation in the mouse

Summary The changes effected by injection of an extract of phospholipids obtained from the plasma of normal human donors (PLE) or an emulsion of commercially available sphingolipids on erythropoiesis in the mouse were studied. The parameters followed were⁵⁹Fe uptake by the erythroid tissue and the number of circulating reticulocytes. It was found that in the 12–24-h period following administration of PLE or purified sphingomyelin a significant increase in⁵⁹Fe uptake by circulating RBC and by their hemic fraction takes place. This change was associated with a higher⁵⁹Fe utilization by the bone marrow and with an increase in the number of circulating reticulocytes.Acknowledgments. This work was supported by a grant from the Consejo Nacional de Investigaciones científícas y Técnicas de la República Argentina. We thank Isabel Zingariello and Maria Amalia Nicastro for excellent technical assistance.     

Effect of streptozotocin diabetes on adenosine-5′-triphosphate,oxygen consumption and steroidogenesis in testis mitochondria from rats

Summary The activity of the enzyme cleaving the side-chain of cholesterol (rate limiting step in steroidogenesis) was considerably reduced in experimentally induced diabetes. This result was accompained by both an increase in oxygen consumption and an increase in ATP synthesis. Insulin treatment prevented them.     

Studies on the structure of collagen V. The site of binding of trivalent iron on collagen

Zusammenfassung Die Reaktion zwischen Kollagen und Fe^III wurde studiert. Es zeigte sich, dass das Eisen an die Sequenzen des Typs Ala-Asp-Gly gebunden wird. Weiter wurde gefunden, dass 1 mol Ratten-Tropokollagen 1 mol Cystein als Sequenz Cys-Ala-Asp-Gly enthält.

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S. Bump, Z. Deyl andJ. Rosmus, Communication IV, Experientia23, 518 (1967).     

Dynamics of singularities in a constrained elastic plate

Large deformations of thin elastic plates usually lead to the formation of singular structures which are either linear (ridges) or pointlike (developable cones). These structures are thought to be generic for crumpled plates, although they have been investigated quantitatively only in simplified geometries. Previous studies have also shown that a large number of singularities are generated by successive instabilities. Here we study, experimentally and numerically, a generic situation in which a plate is initially bent in one direction into a cylindrical arch, then deformed in the other direction by a load applied at its centre. This induces the generation of pairs of singularities; we study their position, their dynamics and the corresponding resistance of the plate to deformation. We solve numerically the equations describing large deformations of plates; developable cones are predicted, in quantitative agreement with the experiments. We use geometrical arguments to predict the observed patterns, assuming that the energy of the plate is given by the energy of the singularities.     

Coevolution with viruses drives the evolution of bacterial mutation rates

Bacteria with greatly elevated mutation rates (mutators) are frequently found in natural and laboratory populations, and are often associated with clinical infections. Although mutators may increase adaptability to novel environmental conditions, they are also prone to the accumulation of deleterious mutations. The long-term maintenance of high bacterial mutation rates is therefore likely to be driven by rapidly changing selection pressures, in addition to the possible slow transition rate by point mutation from mutators to non-mutators. One of the most likely causes of rapidly changing selection pressures is antagonistic coevolution with parasites. Here we show whether coevolution with viral parasites could drive the evolution of bacterial mutation rates in laboratory populations of the bacterium Pseudomonas fluorescens. After fewer than 200 bacterial generations, 25% of the populations coevolving with phages had evolved 10- to 100-fold increases in mutation rates owing to mutations in mismatch-repair genes; no populations evolving in the absence of phages showed any significant change in mutation rate. Furthermore, mutator populations had a higher probability of driving their phage populations extinct, strongly suggesting that mutators have an advantage against phages in the coevolutionary arms race. Given their ubiquity, bacteriophages may play an important role in the evolution of bacterial mutation rates.