Typical range of kcat/Km (rate constants) for reactions between H2O2 (hydrogen peroxide) and the dehydratases and mononuclear enzymes and half-time for enzyme inactivation by H2O2

Range kcat/Km 10^3 to 10^4M^−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 top paragraphPubMed ID23712352
Primary Source [76] Anjem, A. & Imlay, J. A. Mononuclear iron enzymes are primary targets of hydrogen peroxide stress. J. Biol. Chem. 287, 15544–15556 (2012). doi: 10.1074/jbc.M111.330365. [92] Jang, S. & Imlay, J. A. Micromolar intracellular hydrogen peroxide disrupts metabolism by damaging iron-sulfur enzymes. J. Biol. Chem. 282, 929–937 (2007). DOI: 10.1074/jbc.M607646200PubMed ID22411989, 17102132
Method Primary source [76] abstract: "This study tested whether nonredox metalloenzymes are commonly charged with iron in vivo and are primary targets of oxidative stress because of it. Indeed, three sample mononuclear enzymes, peptide deformylase, threonine dehydrogenase, and cytosine deaminase, were rapidly damaged by micromolar hydrogen peroxide in vitro and in live Escherichia coli. The first two enzymes use a cysteine residue to coordinate the catalytic metal atom it was quantitatively oxidized by the radical generated by the Fenton reaction." Primary source [92] abstract: "An Escherichia coli strain that cannot scavenge hydrogen peroxide has been used to identify the cell processes that are most sensitive to this oxidant. Low micromolar concentrations of H2O2 completely blocked the biosynthesis of leucine."
Comments P.446 Box 2 top paragraph: "However, the rate constants for reactions between H2O2 and the dehydratases and mononuclear enzymes are typically in the range of 10^3 to 10^4 M^−1×s^−1 (primary sources), which means that the half-time for enzyme inactivation by H2O2 must be as short as 20 minutes."
Entered by Uri M
ID 112945