In vitro biosynthesis of an isomer of brain trisialoganglioside, GT1a.
A sialyltransferase activity which catalyzes the synthesis of the trisialoganglioside GT1a from added disialoganglioside TD1a and CMP-N-acetylneuraminic acid has been demonstrated using a particulate fraction of 9-day-old embryonic chick brains. The enzyme exhibited optimum activity with the detergent Triton CF-54 and showed a broad pH optimum of 6.0 to 7.2. Ca2+ inhibited the reaction, whereas Mn2+, Mg2+, and EDTA had no effect. Slight elevations in activity were seen in the presence of Hg2+ or histone. The apparent Km for GD1a leading to GT1a was estimated to be 10(-3) M. When the monosialoganglioside, GM1, was used as the glycolipid substrate under conditions optimum for the synthesis of GR1a from GD1a, approximately 65% of the radioactive label was found in GD1a. However, about 50% of the remaining radioactivity was found in GT1a. The results suggest that the synthesis of GR1a could proceed via the sequence GM1 yields GD1a yields GT1a.
D000818:Animals; D001921:Brain / Q000201:enzymology*; D002413:Cations, Divalent; D002642:Chick Embryo; D003902:Detergents / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D005732:Gangliosides / Q000096:biosynthesis*; D007700:Kinetics; D012799:Sialyltransferases / Q000378:metabolism*; D014166:Transferases / Q000378:metabolism*
D002413:Cations, Divalent; D003902:Detergents; D005732:Gangliosides; D004492:Edetic Acid; D014166:Transferases; D012799:Sialyltransferases