, Volume 29, Issue 11-12, pp 627-638

Ganglioside GD3 biosynthesis in normal and mutant mouse embryos

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Abstract

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 atpH 6.0 using 0.1% detergent Triton CF-54. TheK m values for GM3 and CMP-sialic acid were 55 and 80 µM, respectively. TheV max 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 µM (40%) and from 150 to 300 µM (65%). The rate of GD3 formation was similar in whole embryos and in embryo head and body regions. GD3 synthase activity int w1/t w1 mutant mouse embryos, which express defects in neuronal differentiation, was only 40% of that in normal wild-type (+/+) embryos. Enzyme activity in heterozygous (+/t w1) 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.

This work was supported by NIH Grant NS 24826.