Biosynthesis of Galactocerebrosides and Glucocerebrosides in Glial Cell Lines

UDP-galactose:ceramide galactosyltransferase (CGalT, EC 2.4.1.45) and UDP-glucose:ceramide glucosyltransferase (CGlcT, EC 2.4.1.80) were determined in the glial cell lines G26-20, G26-24, C6, and C6TK-. The enzymatic assay for CGalT in cultured glial cells was complicated by a rapid conversion of UDP-galactose to UDP-glucose, due to the elevated UDP-galactose-4'-epimerase activity in certain glial cell clones. It seems that mechanisms regulating UDP-galactose-4'-epimerase activity and levels of UDP sugars in the glial cell lines differ from those in brain tissue. Compared with the maximum activity of CGalT in the myelinating rat brain, the enzyme activities in the oligodendroglioma clonal cell lines G26-20 and G26-24 were 16-30 times lower. On the other hand, CGalT levels in G26-20 and G26-24 cells were comparable to the values found in young rat brain before myelination starts. No CGalT activity could be detected in C6 or C6TK- cells by the method used in this study, whereas CGlcT activity was found in all glial cell lines tested and its levels were close to the values observed in the young rat brain.