OxyR system is calibrated when H2O2 reaches ~200nM: growth defects become evident at 400nM nM
||Bacteria Escherichia coli
||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
|| Seaver, L. C. & Imlay, J. A. Hydrogen peroxide fluxes and compartmentalization inside growing Escherichia coli. J. Bacteriol. 183, 7182–7189 (2001). DOI: 10.1128/JB.183.24.7182-7189.2001  Sobota, J. M. & Imlay, J. A. Iron enzyme ribulose-5-phosphate 3-epimerase in Escherichia coli is rapidly damaged by hydrogen peroxide but can be protected by manganese. Proc. Natl Acad. Sci. USA 108, 5402–5407 (2011). doi: 10.1073/pnas.1100410108.PubMed ID11717277, 21402925
||Primary source  abstract: "The rates of H(2)O(2) degradation by the two major scavenging enzymes, alkyl hydroperoxide reductase and catalase, were quantified." Primary source  abstract: "[Investigators] used a strain of Escherichia coli that lacks catalases and peroxidases to impose protracted low-grade H(2)O(2) stress. Physiological analysis indicated that the pentose-phosphate pathway, in particular, was poisoned by submicromolar intracellular H(2)O(2). Assays determined that ribulose-5-phosphate 3-epimerase (Rpe) was specifically inactivated. In vitro studies demonstrated that Rpe employs a ferrous iron atom as a solvent-exposed cofactor and that H(2)O(2) rapidly oxidizes this metal in a Fenton reaction."
||P.446 Box 2 top paragraph: "Because the half-time for repair of dehydratase clusters is about 5 minutes [BNID 112946], at any moment during aerobic growth a significant minority of the enzyme population is inactive. Any additional H2O2 stress will exacerbate the situation. Indeed, the OxyR system is calibrated to be activated when intracellular H2O2 reaches ~200 nM, and growth defects become evident when levels rise to 400 nM (primary sources)." P.446 left column bottom paragraph: "In fact, whenever the extracellular H2O2 concentration exceeds 200 nM, the rate of influx into E. coli exceeds the rate of endogenous H2O2 formation [primary source 38]. Therefore, when bacteria enter H2O2-containing environments, oxidative stress is likely to occur. This threat is sensed by OxyR, a transcription factor containing an active-site Cys residue that reacts rapidly with H2O2 (Refs 39, 40) (Fig. 2a). OxyR is normally inactive during routine aerobiosis, when the intracellular H2O2 concentration is ~50 nM. However, an intracellular concentration of ~200 nM is sufficient to drive OxyR into a disulphide-bonded form that actively promotes the transcription of a dozen operons around the chromosome."