Evidence from cell-free systems for differences in the sterol biosynthetic pathway of Rhizoctonia solani and Phytophthora cinnamomi.
Evidence from cell-free systems for differences in the sterol biosynthetic pathway of Rhizoctonia solani and Phytophthora cinnamomi.
复制标题
来自无细胞系统的证据表明立枯丝核菌和肉桂疫霉的甾醇生物合成途径存在差异。
作者：
S. Wood;D. Gottlieb
合成甾醇的立枯丝核菌和非合成甾醇的肉桂疫霉菌的无细胞制剂在[2(-14)C]甲氧戊酸和碘乙酰胺的存在下孵育，将甲戊酸转化为标记的甲戊酸5-磷酸、甲伐他酸5-焦磷酸和焦磷酸异戊烯。在没有碘乙酰胺的情况下，但在厌氧条件下，相同的制剂将甲戊酸转化为标记的香叶醇、法尼醇和角鲨烯，前两种化合物可能是它们的焦磷酸盐。当两种微生物的无细胞制剂在[1(-14)C]焦磷酸异戊烯存在下好氧培养时，从肉桂假单胞菌反应混合物中只回收标记的香叶醇、法尼醇和角鲨烯，而在芦荟反应混合物中存在标记的香叶醇、法尼醇、角鲨烯、环氧化角鲨烯、羊毛甾醇和麦角甾醇。当这些相同的制剂与14C标记的角鲨烯一起孵育时，标记的角鲨烯环氧化物、羊毛甾醇和麦角甾醇都从R.solani反应混合物中被回收。相反，肉桂假单胞菌的制剂不能将角鲨烯进一步转化为沿着甾醇途径的产物；相反，标记的部分角鲨烯被转化为水溶性产物，这表明该生物体中可能存在角鲨烯的降解过程。肉桂类固醇生物合成途径的阻断似乎发生在角鲨烯环氧化水平上。
Cell-free preparations of both Rhizoctonia solani, a sterol-synthesizing fungus, and Phytophthora cinnamomi, a non-sterol-synthesizing fungus, incubated in the presence of [2(-14)C]mevalonate and iodacetamide, converted the mevalonate into labelled mevalonate 5-phosphate, mevalonate 5-pyrophosphate and isopentenyl pyrophosphate. In the absence of iodoacetamide, but under anaerobic conditions, the same preparations converted the mevalonate into labelled geraniol, farnesol and squalene, the first two compounds presumably as their pyrophosphates. When cell-free preparations of both organisms were incubated aerobically in the presence of [1(-14)C]isopentenyl pyrophosphate, only labelled geraniol, farnesol and squalene were recovered from the P. cinnamomi reaction mixture, whereas labelled geraniol, farnesol, squalene, squalene epoxide, lanosterol and ergosterol were present in the R. solani reaction mixture. When these same preparations were incubated in the presence of 14C-labelled squalene, labelled squalene epoxide, lanosterol and ergosterol were recovered from the R. solani reaction mixture. In contrast, the P. cinnamomi preparation was unable to convert the squalene into products further along the sterol pathway; instead, a portion of the labelled squalene was converted into water-soluble products, indicating the possible existence of a squalene-degradation process in this organism. It appears that the block in the sterol biosynthetic pathway of P. cinnamomi occurs at the level of squalene epoxidation.