[Purification and characterization of GM2 synthase, UDP-N-acetylgalactosamine:GM3 beta-N-acetylgalactosaminyl-transferase from rat liver].

A UDP-N-acetylgalactosamine: ganglioside GM3 beta-N-acetylgalactosaminyltransferase which catalyzes the conversion of ganglioside GM3 to GM2 has been purified over 6,000-fold from a Triton X-100 extract of rat liver microsomes by affinity chromatography on UDP-hexanolamine-Sepharose and GM3-acid Sepharose. The purified enzyme is composed of two non-identical subunits with apparent molecular weights of 70,000 and 64,000 on sodium dodecyl sulfate polyacrylamide gel electrophoresis. The enzyme has a pH optimum of pH 6.7-6.9 and requires divalent cations such as Ni2+ or Mn2+. Studies on substrate specificity indicates that GM3 containing N-acetylneuraminic acid and GM3 containing N-glycolylneuraminic acid were both good acceptors. The oligosaccharide of GM3, sialyllactose was also a good acceptor, which indicates that the preferred acceptor substrate has the general structure NeuAc alpha 2- or NeuGc alpha 2-3Gal beta 1-4Glc-O-R, in which the nature of the R moiety has relatively little effect on activity.