Biomedical subjects
Publications and source records attributed to O Gateau.
A sialyl transferase activity is found in purified mitochondria. It is not due to residual contamination and this enzymatic system is located in the outer mitochondrial membrane. This proves mitochondrial autonomy in regard to glyconconjugate sialylation.
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A higher level of N-acetylglucosamine incorporation by proteinic and polyprenic endogenous acceptors is observed after infection by Myxovirus. This phenomenon occurs in whole mitochondria as in outer mitochondrial membranes, where it is particularly obvious with proteinic endogenous acceptors. Under viral infection, no new N-acetylglucosaminylated polyprenol is detected. In the case of infected animals as in the case of control animals, compounds P1 (extracted by chloroform/methanol 2:1) are identified by thin layer chromatography as a N-acetylglucosamyl-pyrophosphoryl-dolichol and a N, N'-diacetylchitobiosyl-pyrophosphoryl-dolichol. In the case of infected animals, biosynthesis of proteinic acceptors and dolichol is not modified; therefore the increase of N-acetylglucosamine incorporation is not due to a modification of the endogenous acceptors level. By the use of exogenous dolichol-monophosphate we demonstrate that the increased transfer of [14C] N-acetylglucosamine into polyprenic acceptors is the result of a higher activity of the mitochondrial N-acetylglucosaminyltransferase after viral infection.
Mitochondria, and specially outer mitochondrial membranes, incorporate D-[14C]glucose from UDP-D-[14C]glucose into products extracted with organic solvents and into a residual precipitate, with a pH optimum of about 6.5 in (2-N-morpholino-ethane)-sulfonic acid (MES) buffer. The chloroform/methanol (2:1, v/v) extract contains two products. The major [14C]glucolipid is stable to mild alkali, but releases [14C]glucose upon mild acid hydrolysis. It is retained on DEAE-cellulose (acetate form) and is eluted with the same ionic strength as an hexosyldolichyl monophosphate diester. This [14C] glucolipid has the same chromatographic behaviour as dolichyl-mannosylphosphate in neutral, acidic and basic solvent systems; and its biosynthesis is greatly increased by exogenous dolichylmonophosphate. The other [14C]glucolipid is stable upon mild acid hydrolysis and is not retained on DEAE-cellulose. On silicic acid it is eluted with acetone. The biosynthesis of this compound is stimulated by exogenous ceramide. This glucolipid has the same chromatographic mobility in different solvent systems as glucosylceramide isolated from the liver of a patient with Gaucher's disease. Biosynthesis of these two glucolipids is inhibited by UDP, but only biosynthesis of dolichylglucosyl monophosphate is reversible with this nucleotide. The biosynthesis of these different glucosylated derivatives is stimulated by the addition of divalent cations (Mn2+, Mg2+). the effect of these two metal ions on dolichylglucosyl monophosphate and glucosylceramide formation is studied in different conditions.
Outer mitochondrial membranes catalyze the transfer of N-acetyl-glucosamine into polyprenic and proteinic endogenous acceptors. Different effectors (nucleotides, EGTA) are used, suggesting that there are two separate metabolic ways.
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There is in mitochondrial outer membrane a mannosyl-transferase which is able to catalyse the mannose transfer on a polyprenic acceptor, to give a mannosyl-phosphoryl-dolichol. This enzyme is stimulated by Mn2+, Mg2+ and dithiothreitol. It is inhibited by GDP, mersalyl and EGTA.
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Nocardia asteroides was grown in Sauton medium containing sodium [carboxy-14C]acetate. The biosynthesis of the peptidoglycan was inhibited by adding penicillin or phosphonomycin to the growth medium. These antibiotics give an accumulation of radioactive nucleotidic precursors of the peptidoglycan. In the presence of penicillin, there was an accumulation of uridine diphosphate-N-glycolylmuramyl peptide (UDP-MurNGlyc peptide) and of a mixture of uridine diphosphate-N-acetyl and N-glycolylmuramic acid (UDP-MurNAc) and UDP-MurNGlyc). In the presence of phosphonomycin, the biosynthesis of muramic acid was blocked and there was an accumulation of uridine diphosphate-N-acetylglucosamine (UDP-GlcNAc) and uridine diphosphate-N-glycolyglucosamine (UDP-GlcNGlyc). Thus the formation of a N-glycolyl group can be performed upon the neucleotidic derivatives of glucosamine and muramic acid. However in the peptidoglycan synthesized in vivo in the absence of antibiotic, only muramic acid was glycolyated. So, glycolylation seems to take place essentially on UDP-MurNAc. When the binding of peptide chain to muramic acid is achieved, all the muramic acid is glycolylated, then the polymerisation of glycan and peptidoglycan units by the mean of particulate enzymes is carried out on the N-glycolylated derivative of muramic acid. A cell-free preparation from Nocardia asteroides was obtained which can hydroxylate the acetyl group of UDP-MurNAc. The activity was localised in the soluble fraction. This system acts as a hydroxylase and requires the presence of NADPH.
Catalysing the transfer of oses and ose derivatives on various accepters, glucosyltransferases are of increasing importance in biology and pathology. Their sub-cellular localisation is now known together with the physico-chemical parameters of their activity and the importance of polyprenic intermediates. The first phenomenological studies concerning them are in favour of a mechanism of Bi-Bi type. For example, they may play a role in mucoviscidosis, virus diseases, vaccination and arthrosis.
Various uro-angiographic contrast media have been injected in the rabbit. The partition at the organ level and in subcellular fraction has been studied. Blood enzymatic inhibition with specific enzymatic systems is reported.