Utilization and metabolism of methyl-sterol derivatives in the yeast mutant strain GL7.
Utilization and metabolism of methyl-sterol derivatives in the yeast mutant strain GL7.
复制标题
酵母突变株GL7中甲基甾醇衍生物的利用和代谢。
作者：
T. Buttke;K. Bloch
在四环核的不同位置修饰的硬脂酸被测试作为酿酒酵母菌株GL 7 erg 12血红素3的生长补充剂。3 β-胆甾烷醇或δ 7-3 β-胆甾烯醇的衍生物在C-4处带有单一α-取向的甲基或偕二甲基基团，支持突变体的生长，而4 β-甲基甾醇则不支持。营养活性的烷基衍生物被代谢为4-脱甲基甾醇，而4 β-甲基衍生物被掺入不变，这表明酵母的C-4脱甲基酶对α-取向的甲基具有特异性。看来，4-去甲基甾醇是强制性的增长，这种生物体。胆固醇的C-4甲基衍生物不支持生长，这表明δ 5双键阻止了相邻C-4的去甲基化。在其他实验中，14种α-甲基甾醇是有效的生长补充剂，而3种α-甲基胆固醇完全没有活性。去除胆固醇的C-19甲基（19-非胆固醇）使甾醇作为甾醇源的有效性降低。酵母的甾醇特异性似乎是特别严格的取代基，增加大量的类固醇核的A环。
Sterols modified at various positions of the tetracyclic nucleus were tested as growth supplements for Saccharomyces cerevisiae strain GL7 erg12 heme3. Derivatives of 3 beta-cholestanol or delta 7-3 beta-cholestenol bearing either a single alpha-oriented methyl group of a gem-dimethyl group at C-4 supported the growth of the mutant whereas 4 beta-methyl sterols did not. The nutritionally active alkyl derivatives were metabolized to 4-demethyl sterols while 4 beta-methyl derivatives were incorporated unchanged, indicating that the C-4 demethylase of yeast is specific for alpha-oriented methyl groups. It appears that 4-demethyl sterols are obligatory for growth of this organism. C-4 methyl derivatives of cholesterol did not support growth, suggesting that the delta 5 double bond blocks demethylation at the adjacent C-4. In other experiments, 14 alpha-methyl sterols were effective growth supplements, while 3 alpha-methylcholesterol was totally inactive. Removal of the C-19 methyl group of cholesterol (19-noncholesterol) rendered the sterol somewhat less effective as a sterol source. The sterol specificity for yeast appears to be particularly strict with regard to substituents that add bulk to the A ring of the steroid nucleus.