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首页> 美国卫生研究院文献>Journal of Bacteriology >Homeostatic regulation of intracellular hydrogen peroxide concentration in aerobically growing Escherichia coli.
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Homeostatic regulation of intracellular hydrogen peroxide concentration in aerobically growing Escherichia coli.

机译：在需氧生长的大肠杆菌中细胞内过氧化氢浓度的稳态调节。

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The exponential phase of aerobic growth is associated with risk of endogenous oxidative stress in which cells need to cope with an approximately 10-fold increase in the rate of H2O2 generation. We addressed this issue by studying the regulation of the intracellular concentration of H2O2 in aerobically growing Escherichia coli. Intracellular H2O2 was kept at an almost constant steady-state value of approximately 0.2 microM (variation, less than twofold) over a broad range of cell densities in rich medium. This regulation was achieved in part by a transient increase in the OxyR-dependent transcription of the catalase gene katG (monitored by using a katG::lacZ operon fusion) during exponential growth, directly correlated with the increased rate of H2O2 generation. The OxyR-regulated alkyl hydroperoxide reductase encoded by ahpFC did not detectably affect H2O2 or catalase activity levels. Induction of katG, ahpFC, and perhaps other genes prevented the accumulation of oxidatively modified lipids but may not have protected DNA: the spontaneous mutation rate was significantly increased in both wild-type and delta(oxy)R strains during exponential growth compared to that in these strains during lag or stationary phases. Strains lacking oxyR showed throughout growth an 8- to 10-fold-higher frequency of spontaneous mutation than was seen for wild-type bacteria. The ahpdelta5 allele also had a mutator effect half of that of delta(oxy)R in exponential and stationary phases and equal to that of deltaoxyR in lag phase, perhaps by affecting organic peroxide levels. These results show that oxyR-regulated catalase expression is not solely an emergency response of E. coli to environmental oxidative stress, but also that it mediates a homeostatic regulation of the H2O2 produced by normal aerobic metabolism. The activation of the oxyR regulon in this process occurs at much lower levels of H2O2 (approximately 10(-7)M) than those reported for oxyR activation by exogenous H2O2 (approximately 10(-5) M).
机译：有氧生长的指数期与内源性氧化应激的风险相关，在这种风险中，细胞需要应对H2O2生成速率的大约10倍的增长。我们通过研究需氧生长的大肠杆菌中细胞内H2O2浓度的调节解决了这个问题。在丰富的培养基中，广泛的细胞密度范围内，细胞内H2O2保持在几乎恒定的稳态值（约0.2 microM，变化小于两倍）。这种调节部分是通过指数增长期间过氧化氢酶基因katG的OxyR依赖性转录的瞬时增加（通过使用katG :: lacZ操纵子融合体进行监测）来实现的，该增加与H2O2生成速率的增加直接相关。由ahpFC编码的OxyR调节的烷基氢过氧化物还原酶没有可检测地影响H2O2或过氧化氢酶的活性水平。诱导katG，ahpFC以及其他基因阻止了氧化修饰脂质的积累，但可能没有保护DNA：与野生型和delta（oxy）R菌株相比，其指数生长期间的自发突变率显着提高。这些应变处于滞后或平稳阶段。缺乏oxyR的菌株在整个生长过程中显示出自发突变的频率比野生型细菌高出8到10倍。 ahpdelta5等位基因在指数期和固定期的突变效应也为delta（oxy）R的一半，而在滞后阶段则与deltaoxyR相同，这可能是由于影响了有机过氧化物的水平。这些结果表明，oxyR调节的过氧化氢酶表达不仅是大肠杆菌对环境氧化应激的紧急反应，而且还介导了正常有氧代谢产生的H2O2的稳态调节。在此过程中，oxyR调节剂的活化发生在H2O2的水平低得多（约10（-7）M），低于外源H2O2活化oxyR活化的报道水平（约10（-5）M）。

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