Swammerdam Institute of Life Sciences, University of Amsterdam, Amsterdam, The Netherlands.
Appl Environ Microbiol. 2012 Oct;78(19):6908-13. doi: 10.1128/AEM.01507-12. Epub 2012 Jul 27.
The respiratory chain of Escherichia coli contains three different cytochrome oxidases. Whereas the cytochrome bo oxidase and the cytochrome bd-I oxidase are well characterized and have been shown to contribute to proton translocation, physiological data suggested a nonelectrogenic functioning of the cytochrome bd-II oxidase. Recently, however, this view was challenged by an in vitro biochemical analysis that showed that the activity of cytochrome bd-II oxidase does contribute to proton translocation with an H(+)/e(-) stoichiometry of 1. Here, we propose that this apparent discrepancy is due to the activities of two alternative catabolic pathways: the pyruvate oxidase pathway for acetate production and a pathway with methylglyoxal as an intermediate for the production of lactate. The ATP yields of these pathways are lower than those of the pathways that have so far always been assumed to catalyze the main catabolic flux under energy-limited growth conditions (i.e., pyruvate dehydrogenase and lactate dehydrogenase). Inclusion of these alternative pathways in the flux analysis of growing E. coli strains for the calculation of the catabolic ATP synthesis rate indicates an electrogenic function of the cytochrome bd-II oxidase, compatible with an H(+)/e(-) ratio of 1. This analysis shows for the first time the extent of bypassing of substrate-level phosphorylation in E. coli under energy-limited growth conditions.
大肠杆菌的呼吸链包含三种不同的细胞色素氧化酶。虽然细胞色素 bo 氧化酶和细胞色素 bd-I 氧化酶已经得到很好的描述，并被证明有助于质子转移，但生理数据表明细胞色素 bd-II 氧化酶的功能是非电活性的。然而，最近的一项体外生化分析挑战了这一观点，该分析表明细胞色素 bd-II 氧化酶的活性确实有助于质子转移，其 H(+)/e(-)比为 1。在这里，我们提出这种明显的差异是由于两种替代的分解代谢途径的活性：用于生成乙酸盐的丙酮酸氧化酶途径和以甲基乙二醛为中间产物生成乳酸盐的途径。这些途径的 ATP 产率低于迄今为止一直被认为在能量限制生长条件下催化主要分解代谢通量的途径（即丙酮酸脱氢酶和乳酸脱氢酶）。在生长大肠杆菌菌株的通量分析中纳入这些替代途径，以计算分解代谢 ATP 合成率，表明细胞色素 bd-II 氧化酶具有电活性功能，与 H(+)/e(-)比为 1 兼容。该分析首次表明，在能量限制生长条件下，大肠杆菌中底物水平磷酸化的绕过程度。
