Glycosylation of Membrane Sterol Associated with Cell Differentiation

多头绒泡菌（Physarumpolycephalum）的单倍体黏阿米巴成对结合形成二倍体合子并分化为原质团。在分化过程中，检测到膜组分中非极性糖缀合物的表达。该物质被纯化，并通过GC、GC/MS、FAB/MS、NMR和酶水解进行结构研究，该物质已被鉴定为多孔甾醇单葡糖苷（发表于J. Biol. Chem. 262，16719-16723）。在变形细胞中未检测到酶活性，但接合后，酶活性出现并增加。对该酶进行了部分纯化和表征，其分子量为72，000，最适pH为7.0。它催化葡萄糖从UDP-葡萄糖转化为谷甾醇和菜油甾醇以及多孔甾醇，但作为多孔甾醇的C-24差向异构体的豆甾醇是该酶反应的不良底物。UDP-葡萄糖的表观Km值为1.2 × 104 <-4>M，多孔甾醇的表观Km值为4.8 × 104 <-6>M。（Biochim. Biophys.多头绒泡菌的科洛尼亚菌株是一种突变体，其从粘阿米巴分化为疟原虫，而没有核DNA变化。在该突变株中，在粘阿米巴和疟原虫两个阶段中都检测到多孔甾醇单葡糖苷及其合成酶。在野生型和突变株中，在从粘阿米巴分化为二倍体疟原虫的过程中也观察到磷脂组成和磷脂酶D活性的变化（Biochim. Biophys. Acta，in press）.甾醇含量进行了检查和比较，然后确定主要的是多孔甾醇（细胞结构功能。12，519-524）。

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).