Ganglioside GD3 biosynthesis in normal and mutant mouse embryos.
CMP-sialic acid:GM3 sialyltransferase (GD3 synthase; EC 2.4.99.8) was characterized in a membrane-enriched preparation (P2 pellet) from mouse embryos at embryonic day 12 (E-12). Gangliosides GD3 and GM3 were the major radiolabeled products of the reaction. Optimum GD3 synthase activity was obtained at pH 6.0 using 0.1% detergent Triton CF-54. The Km values for GM3 and CMP-sialic acid were 55 and 80 microM, respectively. The Vmax value was calculated as 622 pmol/mg protein/hr. Ganglioside GD3, as end product, induced a two-step reduction of enzyme activity in the range of concentrations from 0 to 34 microM (40%) and from 150 to 300 microM (65%). The rate of GD3 formation was similar in whole embryos and in embryo head and body regions. GD3 synthase activity in tw1/tw1 mutant mouse embryos, which express defects in neuronal differentiation, was only 40% of that in normal wild-type (+/+) embryos. Enzyme activity in heterozygous (+/twl) embryos was similar to that in +/+ embryos. These findings suggest that the reduced GD3 synthase activity in the mutants might arise as a consequence of failed nervous system development and might reflect a secondary rather than a primary effect of the mutation.
Novikov
A M
AM
Department of Biology, Boston College, Chestnut Hill, Massachusetts 02167.
Seyfried
T N
TN
D000818:Animals; D005314:Embryonic and Fetal Development; D004790:Enzyme Induction; D005260:Female; D005679:G(M3) Ganglioside / Q000096:biosynthesis; D005732:Gangliosides / Q000096:biosynthesis*; D005804:Genes, Lethal; D007700:Kinetics; D051379:Mice; D008817:Mice, Mutant Strains / Q000196:embryology* / Q000235:genetics / Q000378:metabolism; D009420:Nervous System / Q000196:embryology; D009436:Neural Tube Defects / Q000196:embryology / Q000201:enzymology / Q000235:genetics; D012799:Sialyltransferases / Q000172:deficiency / Q000378:metabolism*; D013379:Substrate Specificity
D005679:G(M3) Ganglioside; D005732:Gangliosides; C026226:ganglioside, GD3; D012799:Sialyltransferases; C043662:alpha-N-acetylneuraminate alpha-2,8-sialyltransferase