Rate constant (kcat/Km) for inactivation of dehydratases and mononuclear enzymes by O2− (superoxide) and half-time for enzyme inactivation by O2-

Range kcat/Km >10^6M^−1×s^−1: half-time for enzyme inactivation 20min
Organism Bacteria Escherichia coli
Reference Imlay JA. The molecular mechanisms and physiological consequences of oxidative stress: lessons from a model bacterium. Nat Rev Microbiol. 2013 Jul11(7):443-54. doi: 10.1038/nrmicro3032. p.446 Box 2 bottom paragraphPubMed ID23712352
Primary Source [82] Flint, D. H., Tuminello, J. F. & Emptage, M. H. The inactivation of Fe-S cluster containing hydro-lyases by superoxide. J. Biol. Chem. 268, 22369–22376 (1993).PubMed ID8226748
Method Primary source abstract: "[Investigators] report in this paper that highly purified Escherichia coli dihydroxy-acid dehydratase, fumarase A, fumarase B, and mammalian aconitase are inactivated by O2- with second order rate constants in the range of 10^(6) to 10^(7) M^-1×s^-1."
Comments P.446 Box 2 bottom paragraph: "The rate of endogenous O2− formation is probably slightly lower [than H2O2](~5μM/s)[BNID 112943]. The titre (20 μM) and rate constant (10^9M^−1×s^−1) of superoxide dismutases (SODs) mean that steady-state O2− levels are ~0.2 nM, or fewer than one molecule per cell. But it is necessary for O2− to be this scarce: the rate constants for inactivation of dehydratases and mononuclear enzymes by O2− exceed 10^6M^−1×s^−1 (primary source), so this steady-state level of O2− should also cause an inactivation half-time of as little as 20 minutes."
Entered by Uri M
ID 112950