Machida K, Tanaka T, Fujita K, Taniguchi M
Department of Biology, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan.
J Bacteriol. 1998 Sep;180(17):4460-5. doi: 10.1128/JB.180.17.4460-4465.1998.
The mechanism of farnesol (FOH)-induced growth inhibition of Saccharomyces cerevisiae was studied in terms of its promotive effect on generation of reactive oxygen species (ROS). The level of ROS generation in FOH-treated cells increased five- to eightfold upon the initial 30-min incubation, while cells treated with other isoprenoid compounds, like geraniol, geranylgeraniol, and squalene, showed no ROS-generating response. The dependence of FOH-induced growth inhibition on such an oxidative stress was confirmed by the protection against such growth inhibition in the presence of an antioxidant such as alpha-tocopherol, probucol, or N-acetylcysteine. FOH could accelerate ROS generation only in cells of the wild-type grande strain, not in those of the respiration-deficient petite mutant ([rho0]), which illustrates the role of the mitochondrial electron transport chain as its origin. Among the respiratory chain inhibitors, ROS generation could be effectively eliminated with myxothiazol, which inhibits oxidation of ubiquinol to the ubisemiquinone radical by the Rieske iron-sulfur center of complex III, but not with antimycin A, an inhibitor of electron transport that is functional in further oxidation of the ubisemiquinone radical to ubiquinone in the Q cycle of complex III. Cellular oxygen consumption was inhibited immediately upon extracellular addition of FOH, whereas FOH and its possible metabolites failed to directly inhibit any oxidase activities detected with the isolated mitochondrial preparation. A protein kinase C (PKC)-dependent mechanism was suggested to exist in the inhibition of mitochondrial electron transport since FOH-induced ROS generation could be effectively eliminated with a membrane-permeable diacylglycerol analog which can activate PKC. The present study supports the idea that FOH inhibits the ability of the electron transport chain to accelerate ROS production via interference with a phosphatidylinositol type of signal.
就法尼醇（FOH）对活性氧（ROS）生成的促进作用，研究了其诱导酿酒酵母生长抑制的机制。在最初30分钟的孵育过程中，经FOH处理的细胞中ROS生成水平增加了五至八倍，而用其他类异戊二烯化合物（如香叶醇、香叶基香叶醇和角鲨烯）处理的细胞则未表现出ROS生成反应。在存在抗氧化剂（如α-生育酚、普罗布考或N-乙酰半胱氨酸）的情况下，对这种生长抑制的保护作用证实了FOH诱导的生长抑制对这种氧化应激的依赖性。FOH只能在野生型大菌株的细胞中加速ROS生成，而不能在呼吸缺陷型小突变体（[rho0]）的细胞中加速ROS生成，这说明了线粒体电子传递链作为其来源的作用。在呼吸链抑制剂中，用米酵菌素可有效消除ROS生成，米酵菌素可抑制辅酶QH2被复合物III的Rieske铁硫中心氧化为半醌自由基，但用抗霉素A则不能，抗霉素A是一种电子传递抑制剂，在复合物III的Q循环中，其作用是将半醌自由基进一步氧化为辅酶Q。在细胞外添加FOH后，细胞的氧气消耗立即受到抑制，而FOH及其可能的代谢产物未能直接抑制用分离的线粒体制剂检测到的任何氧化酶活性。由于FOH诱导的ROS生成可用可激活蛋白激酶C（PKC）的膜通透性二酰甘油类似物有效消除，因此提示存在一种PKC依赖性机制来抑制线粒体电子传递。本研究支持这样一种观点，即FOH通过干扰磷脂酰肌醇类型的信号来抑制电子传递链加速ROS生成的能力。
