Glycosylation of Membrane Sterol Associated with Cell Differentiation

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Haploid myxoamoebae of Physarum polycephalum conjugate in pairs to form diploid zygotes and differentiate into plasmodia. During the course of differentiation, an expression of a nonpolar glycoconjugate in membrane fraction was detected. This substance was purified and structural studies were performed by GC, GC/MS, FAB/MS, NMR and enzymatic hydrolysis, ant the substance has been identified as poriferasterol monoglucoside (published in J. Biol. Chem. 262, 16719-16723).UDP-glucose:poriferasterol glucosyltransferase which synthesizes poriferasterol monoglucoside was also expressed during a differentiation from myxoamoebae to plasmodia. The enzyme activity was not detected in the amoeboid cells, but after conjugation, the enzyme activity appeared and increased. The enzyme was partially purified and characterized, and its molecular weight was determined to be 72,000, and pH optimum was 7.0. It catalyzed the glucose transfer from UDP-glucose to sitosterol and campesterol as well as to poriferasterol, but stigmasterol which is C-24 epimer of poriferasterol was a poor substrate for this enzyme reaction. Apparent Km values were 1.2 x 10^<-4>M for UDP-glucose and 4.8 x 10^<-6>M for poriferasterol, respectively. (Biochim. Biophys. Acta 992, 412-415).Colonia strain of Physarum polycephalum is a mutant which differentiates from myxoamoebae to plasmodia without nuclear DNA change. The poriferasterol monoglucoside and its synthesizing enzyme were detected in both stages, myxoamoebae and plasmodia, in this mutant strain.Changes in phospholipid composition and phospholipase D activity were also observed during a differentiation from myxoamoebae to diploid plasmodia in both, wild-typed and mutant strains (Biochim. Biophys. Acta,in press). Sterol contents were examined and compared, then the major one was determined to be poriferasterol (Cell Struct. Funct. 12, 519-524).