L. Flohé and J. R. Harris (eds.), Peroxiredoxin Systems, 83-113. © 2007 Springer.

than the heme- or selenium-containing peroxidases, but in some cases the k+1 values (bimolecular rate constant for oxidation of reduced E by ROOH) are comparable, the overall range being 2 x 103-4 x 107 M-1

and the individual Prx. For the reduction of peroxynitrite k+1 values of 1 x 106 up to 7 x 107 M-1s-1 have been measured. The net forward rate constants k+2 for the reductive part of the cycle range between 2 x 104-1 x 107 M-1s-1. These kinetic characteristics qualify the peroxiredoxins as moderately efficient devices to detoxify hydroperoxides, which is pivotal to organisms devoid of more efficient peroxidases, and as most relevant to the detoxification of peroxynitrite. In higher organisms, their specific role is seen in the regulation of signalling cascades that are modulated by H2O2, lipid hydroperoxides or peroxynitrite

Keywords: Peroxiredoxin, Peroxynitrite, Peroxide, Oxidative stress, Kinetics

Abbreviations: Peroxiredoxins (Prxs), hydrogen peroxide (H2O2), peroxidatic cysteine residue (Cp), resolving cysteine residue (CR), cysteine sulfenic acid (Cys-SOH), superoxide anion (O2^-), nitric oxide (•NO), nitrate (NO-), hydroxyl radical (•OH), nitrogen dioxide (^NO2), carbonate radical (CO3^-), peroxynitrous acid (ONOOH), peroxynitrite anion (ONOO-), thiolate anion (RS-), thiol (RSH), cytosolic trypare-doxin peroxidase (cTXNPx), alkyl hydroperoxide reductase (Ahp), thioredoxin peroxidase (TPx), horseradish peroxidase (HRP), glutathione peroxidase 1 (GPxl), MnnI-meso-tetrakis[(N-butyl)pyridinium-2-yl] porphyrin (MnnITB-2-PyP), dihydrorho-damine 123 (DHR)

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