title: In vitro biosynthesis of the tetrasialoganglioside GQ1b.
abstract: A sialyltransferase activity which catalyzes the synthesis of the tetrasialoganglioside GQ1b (N-acetylneuraminyl-N-acetylneuraminylgalactosyl-N-acetylgalactosaminyl [N-acetylneuraminyl-N-acetylneuraminyl]-galactosylglucosylceramide) from added trisialoganglioside GT1b (N-=acetylneuraminylgalactosyl-N-acetylgalactosaminyl [N-acetylneuraminyl-N-acetylneuraminyl]galactosylglucosylceramide) and CMP-N-acetyl[4-14C]neuraminic acid has been demonstrated using a membrane fraction of embryonic chick brain. Optimum enzymatic activity was obtained using the detergent Triton CF-54 at a pH of 6.6. Enzyme activity appeared unaffected by Ca2+, Mg2+, Mn2+, EDTA, or histone. A slight elevation in activity was seen in the presence of Hg2+. When the disialoganglioside GD1b (galactosyl-N-acetylgalactosaminyl [N-acetylneuraminyl-N-acetylneuraminyl]galactosylglucosylceramide) was used as the glycolipid substrate, approximately 15% of the radioactive label was found in GQ1b. When this GQ1b was subjected to a periodate oxidation-borohydride reduction, the distribution of radioactive label was consistent with GQ1b being the major tetrasialoganglioside product and that its synthesis could proceed via the sequence GD1b-GT1b-GQ1b.
mesh_terms: D000818:Animals; D001921:Brain / Q000201:enzymology*; D002413:Cations, Divalent; D002462:Cell Membrane / Q000201:enzymology; D002642:Chick Embryo; D003902:Detergents / Q000494:pharmacology; D005732:Gangliosides / Q000096:biosynthesis*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009438:Neuraminic Acids / Q000378:metabolism; D012799:Sialyltransferases / Q000378:metabolism*; D013347:Subcellular Fractions / Q000201:enzymology; D014166:Transferases / Q000378:metabolism*
chemical_list: D002413:Cations, Divalent; D003902:Detergents; D005732:Gangliosides; D009438:Neuraminic Acids; C082013:tetrasialoganglioside GQ1b; D014166:Transferases; D012799:Sialyltransferases