Zinser E, Paltauf F, Daum G
Institut für Biochemie und Lebensmittelchemie, Technische Universität Graz, Austria.
J Bacteriol. 1993 May;175(10):2853-8. doi: 10.1128/jb.175.10.2853-2858.1993.
Organelles of the yeast Saccharomyces cerevisiae were isolated and analyzed for sterol composition and the activity of three enzymes involved in sterol metabolism. The plasma membrane and secretory vesicles, the fractions with the highest sterol contents, contain ergosterol as the major sterol. In other subcellular membranes, which exhibit lower sterol contents, intermediates of the sterol biosynthetic pathway were found at higher percentages. Lipid particles contain, in addition to ergosterol, large amounts of zymosterol, fecosterol, and episterol. These sterols are present esterified with long-chain fatty acids in this subcellular compartment, which also harbors practically all of the triacylglycerols present in the cell but very little phospholipids and proteins. Sterol delta 24-methyltransferase, an enzyme that catalyzes one of the late steps in sterol biosynthesis, was localized almost exclusively in lipid particles. Steryl ester formation is a microsomal process, whereas steryl ester hydrolysis occurs in the plasma membrane and in secretory vesicles. The fact that synthesis, storage, and hydrolysis of steryl esters occur in different subcellular compartments gives rise to the view that ergosteryl esters of lipid particles might serve as intermediates for the supply of ergosterol from internal membranes to the plasma membrane.
对酿酒酵母的细胞器进行了分离，并分析了其甾醇组成以及参与甾醇代谢的三种酶的活性。质膜和分泌囊泡是甾醇含量最高的组分，其中麦角甾醇是主要的甾醇。在其他甾醇含量较低的亚细胞膜中，甾醇生物合成途径的中间体所占百分比更高。脂质颗粒除了含有麦角甾醇外，还含有大量的酵母甾醇、粪甾醇和表甾醇。这些甾醇在这个亚细胞区室中与长链脂肪酸酯化存在，该区域还几乎包含了细胞中所有的三酰甘油，但磷脂和蛋白质含量很少。甾醇δ24-甲基转移酶是一种催化甾醇生物合成后期步骤之一的酶，几乎只定位于脂质颗粒中。甾醇酯的形成是一个微粒体过程，而甾醇酯的水解发生在质膜和分泌囊泡中。甾醇酯的合成、储存和水解发生在不同的亚细胞区室这一事实，使人认为脂质颗粒中的麦角甾醇酯可能作为甾醇从内膜供应到质膜的中间体。
