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Uncoupling of Substrate-Level Phosphorylation in Escherichia coli during Glucose-Limited Growth

机译：葡萄糖限制生长过程中大肠杆菌中底物水平磷酸化的解偶联

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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.
机译：大肠杆菌的呼吸链包含三种不同的细胞色素氧化酶。尽管细胞色素bo氧化酶和细胞色素bd-I氧化酶已被很好地表征，并已被证明有助于质子移位，但生理数据表明细胞色素bd-II氧化酶具有非电功能。但是，最近，这种观点受到了体外生化分析的挑战，该分析表明，细胞色素bd -II氧化酶的活性确实以H〜（+）/ e〜（？）化学计量比为1促进了质子移位。认为这种明显的差异是由于两个替代的分解代谢途径的活动所致：用于乙酸盐生产的丙酮酸氧化酶途径和以甲基乙二醛为中间体生产乳酸的途径。这些途径的ATP产量低于迄今一直被认为在能量有限的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）。将这些替代途径包括在生长中的大肠杆菌菌株的通量分析中以计算分解代谢的ATP合成速率，表明细胞色素bd -II氧化酶具有电学功能，与H〜（+）/ e〜（？）相容此分析首次显示了在能量受限的生长条件下大肠杆菌中底物水平磷酸化的绕开程度。

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