EPIMERASE-CATALYZED GLUCOSE-GALACTOSE INTERCONVERSION IN DEVELOPING MOUSE BRAIN

Mice aged from 2 to 32 days were injected i.p. with [14C6]glucose and sacrificed at 1, 2 and 4 h post-injection. Free and bound glucose and galactose were reisolated from brain, and their radioactivity was determined, as well as the integrity of the hexose carbon chain. A 10-15-fold increase in the free galactose to free glucose ratio was observed between 16 and 22 days post-partum. Lower values were observed for bound sugar ratios. These changes coincide with increased brain UDP-galactose-4-epimerase activity and with active myelination. The incorporation of radiocarbon in myelin was determined by subcellular fractionation of brain 24 h after i.p. injection of [14C6]glucose. Optimal incorporation of radiocarbon was observed at 16 days post-partum and is consistent with a primary role for UDP-galactose-4-epimerase in myelin biosynthesis. These results also support the hypothesis that the sharply increased brain requirements for galactose during myelination are met by in situ conversion of dietary milk glucose th galactose through the UDP-galactose-4-epimerase pathway. © 1969.