PDF(Pubmed)
Abstract：
The terminal oxidases of bacterial aerobic respiratory chains are redox-active electrogenic enzymes that catalyze the four-electron reduction of O2 to 2H2O taking out electrons from quinol or cytochrome c. Living bacteria often deal with carbon monoxide (CO) which can act as both a signaling molecule and a poison. Bacterial terminal oxidases contain hemes; therefore, they are potential targets for CO. However, our knowledge of this issue is limited and contradictory. Here, we investigated the effect of CO on the cell growth and aerobic respiration of three different Escherichia coli mutants, each expressing only one terminal quinol oxidase: cytochrome bd-I, cytochrome bd-II, or cytochrome bo3. We found that following the addition of CO to bd-I-only cells, a minimal effect on growth was observed, whereas the growth of both bd-II-only and bo3-only strains was severely impaired. Consistently, the degree of resistance of aerobic respiration of bd-I-only cells to CO is high, as opposed to high CO sensitivity displayed by bd-II-only and bo3-only cells consuming O2. Such a difference between the oxidases in sensitivity to CO was also observed with isolated membranes of the mutants. Accordingly, O2 consumption of wild-type cells showed relatively low CO sensitivity under conditions favoring the expression of a bd-type oxidase.
摘要：
细菌需氧呼吸链的末端氧化酶是氧化还原活性的产电酶，可催化O2的四电子还原为2H2O，从喹啉或细胞色素c中取出电子。活细菌通常处理一氧化碳（CO），一氧化碳既可以充当信号分子，也可以充当毒药。细菌末端氧化酶含有血红素；因此，它们是CO的潜在目标。然而,我们对这个问题的了解是有限和矛盾的。这里,我们研究了CO对三种不同的大肠杆菌突变体的细胞生长和有氧呼吸的影响，每个只表达一个末端喹啉氧化酶：细胞色素bd-I，细胞色素bd-II，或者细胞色素bo3.我们发现在仅含bd-I的细胞中加入CO后，对生长的影响最小，而仅bd-II和仅bo3菌株的生长均严重受损。始终如一，仅含bd-I的细胞对CO的有氧呼吸的抵抗程度很高，与消耗O2的仅bd-II和仅bo3细胞显示的高CO敏感性相反。在突变体的分离膜中也观察到了氧化酶对CO敏感性的这种差异。因此，在有利于bd型氧化酶表达的条件下，野生型细胞的O2消耗显示出相对较低的CO敏感性。
