title: Ganglioside biosynthesis in rat liver. Characterization of UDPgalactose--glucosylceramide galactosyltransferase and UDPgalactose-GM2 galactosyltransferase.
abstract: The conditions for the quantitative determination of UDP-Gal:glucosylceramide galactosyltransferase and of UDP-Gal:GM2 galactosyltransferase in Golgi-enriched preparations of rat liver were optimized. Triton X-100 was the detergent routinely used as octyl glucoside acted as a galactose acceptor forming octyl lactoside. Manganese ions were required for full activity, but Co2+ and Mg2+ could substitute to some extent. The nucleotide pyrophosphatase activity of the Golgi preparations which interfered with the GL2-synthase assay was inhibited by addition of 20 mM IMP; the latter is without appreciable effect on the rate of GL2 synthesis. Apparent Km values for UDP-Gal were 130 microM and 140 microM with Gl2-synthase and Gm1-synthase, respectively. That for glucosylceramide was 80 microM with GL2-synthase; for GM2 it was 10 microM with GM1-synthase. Competition experiments with variable concentrations of the lipid acceptors showed that the two synthase activities are independent catalytic entities. The specific activity of GM1-synthase exceeds that of GL2-synthase by a factor of ca. 25 under the optimized conditions used here.
mesh_terms: D000818:Animals; D002384:Catalysis; D055598:Chemical Phenomena; D002621:Chemistry; D003902:Detergents / Q000494:pharmacology; D005260:Female; D005700:Galactosyltransferases / Q000378:metabolism*; D051147:Ganglioside Galactosyltransferase; D005732:Gangliosides / Q000096:biosynthesis*; D006056:Golgi Apparatus / Q000378:metabolism; D007700:Kinetics; D008099:Liver / Q000201:enzymology / Q000378:metabolism*; D011755:Pyrophosphatases / Q000037:antagonists & inhibitors; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D003902:Detergents; D005732:Gangliosides; D005700:Galactosyltransferases; C039090:UDPgalactose-glucosylceramide galactosyltransferase; D051147:Ganglioside Galactosyltransferase; D011755:Pyrophosphatases; C021899:nucleotide pyrophosphatase