UDP-galactose-ceramide galactosyltransferase in rat brain myelin subfractions during development.
The localization and activity of the enzyme UDP-galactose-hydroxy fatty acid-containing ceramide galactosyltransferase is described in rat brain myelin subfractions during development. Other lipid-synthesizing enzymes, such as cerebroside sulphotransferase, UDP-glucose-ceramide glucosyltransferase and CDP-choline-1,2-diacylglycerol cholinephosphotransferase, were also studied for comparison in myelin subfractions and microsomal membranes. The purified myelin was subfractionated by isopycnic sucrose-density-gradient centrifugation. Four myelin subfractions, three floating respectively on 0.55 M- (light-myelin fraction), 0.75 M- (heavy-myelin fraction) and 0.85 M-sucrose (membrane fraction), and a pellet, were isolated and purified. At all ages, 70--75% of the total myelin proteins was found in the heavy-myelin fraction, whereas 2--5% of the protein was recovered in the light-myelin fraction, and about 7--12% in the membrane fraction. Most of the galactosyltransferase was associated with the heavy-myelin and membrane fractions. Other lipid-synthesizing enzymes studied appeared not to associate with purified myelin or myelin subfractions, but were enriched in the microsomal-membrane fraction. During development, the specific activity of the microsomal galactosyltransferase reached a maximum when the animals were about 20 days old and then declined. By contrast the specific activity of the galactosyltransferase in the heavy-myelin and membrane fractions was 3--4 times higher than that of the microsomal membranes in 16-day-old animals. The specific activity of the enzyme in the heavy-myelin fraction sharply declined with age. Chemical and enzymic analyses of the heavy-myelin and membrane myelin subfractions at various ages showed that the membrane fraction contained more proteins in relation to lipids than the heavy-myelin fraction. The membrane fraction was also enriched in phospholipids compared with cholesterol and contrined equivalent amounts of 2':3'-cyclic nucleotide 3'-phosphohydrolase compared with heavy- and light-myelin fractions. The membrane fraction was deficient in myelin basic protein and proteolipid protein and enriched in high-molecular-weight proteins. The specific localization of galactosyltransferase in heavy-myelin and membrane fractions at an early age when myelination is just beginning suggests that it may have some role in the myelination process.
D000818:Animals; D001921:Brain / Q000187:drug effects / Q000201:enzymology* / Q000254:growth & development; D004533:Egtazic Acid / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D005700:Galactosyltransferases / Q000378:metabolism*; D051147:Ganglioside Galactosyltransferase; D066298:In Vitro Techniques; D050356:Lipid Metabolism; D009185:Myelin Proteins / Q000378:metabolism; D009186:Myelin Sheath / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D051381:Rats; D013347:Subcellular Fractions / Q000201:enzymology / Q000378:metabolism
D009185:Myelin Proteins; D004533:Egtazic Acid; D005700:Galactosyltransferases; C511215:Ugt8 protein, rat; D051147:Ganglioside Galactosyltransferase