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 accepters: 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-m of 104 mu 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 Ki of 100 mu M. The dolichol phosphate glucose synthase reaction was reversed about 57% by 0.62 mM UDP but not by UMP.