Biosynthesis of glycoproteins in Candida albicans: Biochemical characterization of dolichol phosphate glucose synthase

A mixed membrane fraction isolated from C. albicans yeast cells catalyzed the transfer of glucose from UDP-Glc into three classes of endogenous acceptors: glucolipid, glycoprotein and lipid-linked oligosaccharides. About 80 of the total radioactivity transferred into these products corresponded to the glucolipid which was identified as dolichol phosphate glucose by several criteria. The remainder was detected in about equal proportions in the other two fractions. Conditions that stimulated or inhibited glucolipid synthesis did not affect the extent of glycoprotein labeling. The synthesis of dolichol phosphate glucose exhibited a K_mof 104 M UDP-Glc and was stimulated by Mg²⁺but not by Mn²⁺or Ca²⁺. The latter cations were, however, better stimulators of glycoprotein labeling than Mg²⁺. Most nucleotides strongly inhibited the synthesis of dolichol phosphate glucose, UMP being a competitive inhibitor with a K_iof 100 M. The dolichol phosphate glucose synthase reaction was reversed about 57 by 0.62 mM UDP but not by UMP.