Journal of Biological Chemistry
Volume 279, Issue 47, 19 November 2004, Pages 48742-48750
Journal home page for Journal of Biological Chemistry

Metabolism and Bioenergetics
Are Respiratory Enzymes the Primary Sources of Intracellular Hydrogen Peroxide?*

https://doi.org/10.1074/jbc.M408754200Get rights and content
Under a Creative Commons license
open access

Endogenous H2O2 is believed to be a source of chronic damage in aerobic organisms. To quantify H2O2 formation, we have generated strains of Escherichia colithat lack intracellular scavenging enzymes. The H2O2 that is formed within these mutants diffuses out into the medium, where it can be measured. We sought to test the prevailing hypothesis that this H2O2 is primarily generated by the autoxidation of redox enzymes within the respiratory chain. The rate of H2O2 production increased when oxygen levels were raised, confirming that H2O2 is formed by an adventitious chemical process. However, mutants that lacked NADH dehydrogenase II and fumarate reductase, the most oxidizable components of the respiratory chain in vitro, continued to form H2O2 at normal rates. NADH dehydrogenase II did generate substantial H2O2 when it was when overproduced or quinones were absent, forcing electrons to accumulate on the enzyme. Mutants that lacked both NADH dehydrogenases respired very slowly, as expected; however, these mutants showed no diminution of H2O2 excretion, suggesting that H2O2 is primarily formed by a source outside the respiratory chain. That source has not yet been identified. In respiring cells the rate of H2O2 production was ∼0.5% the rate of total oxygen consumption, with only modest changes when cells used different carbon sources.

Cited by (0)

*

This study was supported by National Institutes of Health Grant GM49640. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Recipient of National Institutes of Health Training Grant GM07283.