Synthesis of Gluco‐ and Galactocerebrosides in Bovine Neurones and Oligodendroglia

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Abstract
Oligodendroglial and neuronal perikarya were isolated from fresh and frozen bovine brain and used to investigate the synthesis of cerebrosides from UDP-hexoses and ceramides. The radioactive cerebrosides produced were identified by TLC of the intact lipids on borate-silica gel and by a chromatography of the liberated hexoses. Incubation of either neuronal or oligodendroglial homogenates with UDP-galactose (UDP-gal) and mixed ceramides (hydroxy plus nonhydroxy fatty acids) leads to the synthesis of hydroxy fatty acid galactocerebroside. This lipid is also formed by both neuronal and oligodendroglial homogenates if the UDP-gal is replaced by UDP-glucose (UDP-glu). Formation of glucocerebroside were observed only in the presence of neuronal homogenates and UDP-glu. EM examination of the isolated cell preparations showed that, although the oligodendroglia are relatively pure, the neurons are contaminated with oligodendroglia, which may account for some of the hydroxy fatty acid galactocerebroside synthesis. When unlabeled UDP-gal is included in the incubations containing cell homogenates, mixed ceramides and labeled UDP-glu, galactocerebroside formation is greatly reduced, but there is comparatively little effect on glucocerebroside synthesis. Experiments using D-[14C]galactose 1-phosphate and UDP D-[6-3H]glucose simultaneously showed the rate of formation of tritiated cerebroside is much greater than that of the 14C-labeled compound. Galactocerebroside is formed from UDP-glu and ceramide by epimerization of the UDP hexose to UDP-gal rather than by synthesis of UDP-gal from galactose 1-phosphate and UDP-glu.