Role of membrane sialic acid content in the adhesiveness of aged erythrocytes to human cultured endothelial cells

Following our previous observation that the oldest normal red blood cells were the most adherent to human cultured endothelial cells, we attempted to simulate this age-related adherence. Among all the membrane modifications experienced by erythrocytes during their life-span, loss of sialic acids has attracted considerable attention. Using two different preparations of neuraminidase, we performed a sialic acid depletion on the youngest erythrocytes to reach a sialic acid content similar to that observed in physiologically aged erythrocytes. These pretreated youngest cells displayed limited increase in the adhesiveness to endothelial cells, lower than that found with intact oldest cells. To obtain an adhesiveness of pretreated cells similar to that of naturally aged cells, it was necessary to exceed 80% of sialic acid depletion. At this extent of desialation, modifications of the electrophoretic pattern of glycophorins were observed as well as the appearance of peanut agglutinin reactivity which were never found in physiologically aged erythrocytes. Therefore, the sialic acid loss cannot be considered as being a single determinant factor of the naturally aged red cell adhesiveness.     

Mitotic recombination between dispersed but related rRNA genes of Schizosaccharomyces pombe generates a reciprocal translocation

Summary Recombination between dispersed yet related serine tRNA genes of Schizosaccharomyces pombe does occur during mitosis but it is approximately three orders of magnitude less frequent than in meiosis. Two mitotic events have been studied in detail. In the first, a sequence of at least 18 nucleotides has been transferred from the donor sup3 gene on the right arm of chromosome I to the related acceptor gene sup12 on the left arm of the same chromosome, thereby leading to the simultaneous change of 8 bp in the acceptor gene. This event must be explained in terms of recombination rather than mutation. It is assumed that it represents mitotic gene conversion, although it was not possible to demonstrate that the donor gene had emerged unchanged from the event. The second case reflects an interaction between sup9 on chromosome III and sup3 on chromosome I. Genetic and physical analysis allows this event to be described as mitotic gene conversion associated with crossingover. The result of this event is a reciprocal translocation. No further chromosomal aberrations were found among an additional 700 potential intergenic convertants tested. Thus intergenic conversion is much less frequently associated with crossingover than allelic conversion. However, the rare intergenic conversion events associated with crossingover provide a molecular mechanism for chromosomal rearrangements.     

Electron microscopic cytochemical localization ofα-hydroxyacid oxidase in rat liver

Summary The substrate specificity and the intraperoxisomal localization of -hydroxyacid oxidase in rat liver has been investigated cytochemically by the cerium technique and biochemically with a luminometric assay. Rat liver is fixed by perfusion with a low concentration (0.25%) of glutaraldehyde and vibratome sections are incubated for 60 min at 37°C in a medium containing 3 mM CeCl₃, 100 mM NaN₃ and 5 mM of an -hydroxyacid in 0.1M of one of the following buffers: Pipes, Mops, Na-cacodylate,Tris-maleate, all adjusted to pH 7.8. Ten different -hydroxyacids with a chain length between 2 and 8 carbon atoms were tested. The best results were obtained with glycolic, argininic andl--isocaproic acids. These cytochemical findings were confirmed also biochemically using purified peroxisomal fractions isolated by gradient centrifugation in metrizamide. The pattern of the intraperoxisomal localization of the enzyme was influenced markedly by the type of buffer used for the cytochemical incubation. Whereas in theTris-maleate medium both the cores and the matrix stained with the same intensity, with all other buffers the reaction in cores was more prominent. The staining of cores was abolished by pretreating sections inTris-maleate (pH 7.8) or alkaline pyrophosphate buffers. These observations establish the substrate specificity of -hydroxyacid oxidase in rat liver and demonstrate the delicate association of this enzyme with the crystalline cores and the matrix of peroxisomes in rat liver.Abbreviations -HAOX l-hydroxyacid oxidase - Argininic acid l--hydroxy--guanidinovaleric acid - Pipes piperazine-N,N-bis(2ethane sulfonic acid) - Mops 3(N-morpholino) propane sulfonic acid - Tris tris-(hydroxymethyl)-aminomethane - Luminol 5-amino-2,3 dihydrophthalazine-1,4-dione - GA glutaraldehyde     

Studies on Scenedesmus acutus growth. The incorporation of 14C-glucose by Scenedesmus acutus under light and dark periods

Qualitative and quantitative estimations of alcohol-extractable compounds from (14)C-glucose-incorporated Scendesmus acutus cells were performed at various intervals of time. After two hours of incubation with (14)C-glucose in light, amino acids were synthesized at 65% and sucrose at 26% of the total input label. In the dark incorporation, 30% of the total radioactivity was found in amino acids and 46% in sucrose. Leucine and valine were detected only during the oxidation of glucose in light. The concentration of serine increased more in the presence of light, as compared to dark. These results on the oxidation of glucose are discussed in this article.