Sialosyltransferase activity and specificity in the biosynthesis in vitro of sialosylgalactosylceramide (GM4) and sialosyllactosylceramide (GM3) by rat astrocytes, neuronal perikarya, and oligodendroglia.
Total homogenates of astrocytes, neuronal perikarya, and oligodendroglia isolated from rat brain exhibited sialosyltransferase activity in the biosynthesis in vitro of GM3 from lac-cer and CMP-NeuNAc. This activity was highest in neuronal perikarya. In contrast, only oligodendroglia were found to be capable of catalyzing the transfer of NeuNAc from CMP-NeuNAc to gal-cer to form GM4. This activity was about three fold higher in oligodendroglia from 10-day-old rat brain than in those from 60-day-old animals; an intermediate activity was observed in oligodendroglia from 20-day-old rats. Purified preparations of myelin from 14-day-old rat cerebrum, cerebellum, and spinal cord did not show activity in the synthesis of either GM3 or GM4.