Biomedical subjects
Publications and source records attributed to J Picard.
The uptake of large neutral aminoacids across the blood brain of mouse is increased by previously intraperitonealy given ethanol. The uptake of small neutral, acid and basic aminoacids is not modified. Observed increase is correlated with octanol-water istribution coefficient.
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Pulse chase experiments disclosed relationships between different pools of proteoglycans from arterial wall, isolated by subcellular fractionation or by sequential extraction procedure with guanidinium hydrochloride solutions. The results are consistent with the presence in microsomes of proteoglycans which are the precursors of more soluble proteoglycans, and suggests that polysaccharide chain sulfation occurs soon in microsomal fractions and proceeds during polymerization.
Hexosaminyltransferase and glucuronyltransferase are well known for their role in the biosynthesis of proteoglycans. These two enzymes are characterized in rough and smooth membranes, obtained following subcellular fractionation of aortic media-intima. They require the presence of Mn2+ or Mg2+ for activity. The optimum concentration for these two cations is 5 mM. The optimum pH for hexosaminyltransferase and glucuronyltransferase is approximately 6.8 in Tris buffer, and their optimum temperature is 30 degrees C. Hexosaminyltransferase has an apparent Km of 0.27 nM. Glucuronyltransferase has an apparent Km of 0.21 nM. Uptake of labeled sugars by endogenous proteoglycans is inhibited by puromycin. Hexosaminyltransferase and glucuronyltransferase are present in both rough and smooth submicrosomal fractions. The different endogenous glycosaminoglycans are labeled during our incubation experiments. The greatest incorporation is noted for hyaluronic acid and heparan sulfate; the least is seen for chondroitin sulfate. The results obtained in vitro for incorporation of labeled precursors into endogenous proteoglycans are consistent with those observed during the study in vivo of the turnover of these macromolecules.
The human serum butyrylcholinesterase was rapidly purified with an affinity technique on meta-aminophenyltrimethylammonium-agarose; the ionic strength was 0.25 and the specific elution was achieved with 9-amino-10-methylacridinium. After ion exchange on DEAE-cellulose and molecular filtration, an enzyme purified more than ten thousand times was obtained.
A new procedure for the fractionation of glycosaminoglycans by electrophoresis on Pevikon has been described. Mixtures of glycosaminoglycans were fractionated by preparative electrophoresis on Pevikon in pyridine formate or glycine-HCl buffers. By this procedure, 200 mg of a mixture of hyaluronic acid, heparan sulphate, dermatan sulphate and chondroitin sulphate isolated from arterial wall could be successfully separated without loss of material. The purified fractions were analysed by enzymatic and chemical procedures. The molar ratios of uronic acid to hexosamine and of sulphate to hexosamine and the amino acid content of each glycosaminoglycan have been determined. The peptidic content (less than 1%) is represented by five amino acids, viz. serine, glycine, alanine, aspartic acid, and glutamic acid.
The interaction of insulin with its receptors was studied in liver plasma membranes of the young non-obese hereditary diabetic mouse (KK strain). Under identical conditions of preparation and incubation, the membranes of the KK mouse bind only 55-70% as much insulin per mg of protein as those of the control mouse (Swiss albino). Scatchard analysis suggests that this decrease in binding is due to a decrease in the number of receptor sites in the membrane of the diabetic mouse. However, the membranes of diabetic and control mice do not exhibit significant differences in hexosamine and sialic acid contents, enzyme activities, and protein and glycoprotein analysis. The decrease in insulin receptors in the KK mouse seems to correlate with the insulin resistance which they exhibit.
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Glycosaminoglycans (GAG) from brains, intestines, livers and skin of rats were analyzed by electrophoretic and enzymatic methods. Variations in GAG distribution have been studied in rats fed on a vitamin-A-deficient diet and on a diet supplemented with an excessive quantity of vitamin A. Hypervitaminosis A resulted in a decrease in GAG isolated from connective and hepatic tissues. The incorporation of labeled sulfate into the GAG of these tissues has been studied. Hypervitaminosis A resulted in a decrease in sulfate incorporation into the GAG isolated from connective tissues. A large increase in sulfate incorporation into the GAC of the digestive tract is observed for vitamin-A-treated rats. A decrease is noted for vitamin-A-deficient rats. It was suggested that these variations in distribution and specific activity of GAG could be due to different effects of vitamin A. Vitamin A seems to be required either for the release of lysosomal enzymes or for the sulfatation and elongation of certain glucidic chains in the biosynthesis of sulfated GAG.
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