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Reactivity of hydrogen sulfide with peroxynitrite and other oxidants of biological interest

Abstract:

Hydrogen sulfide (H2S) is an endogenously generated gas that can also be administered exogenously. It modulates physiological functions and has reported cytoprotective effects. To evaluate a possible antioxidant role, we investigated the reactivity of hydrogen sulfide with several one- and two-electron oxidants. The rate constant of the direct reaction with peroxynitrite was (4.8 ± 1.4) × 103 M-1 s-1 (pH 7.4, 37°C). At low hydrogen sulfide concentrations, oxidation by peroxynitrite led to oxygen consumption, consistent with a one-electron oxidation that initiated a radical chain reaction. Accordingly, pulse radiolysis studies indicated that hydrogen sulfide reacted with nitrogen dioxide at (3.0 ± 0.3) × 106 M-1 s -1 at pH 6 and (1.2 ± 0.1) × 107 M -1 s-1 at pH 7.5 (25 °C). The reactions of hydrogen sulfide with hydrogen peroxide, hypochlorite, and taurine chloramine had rate constants of 0.73 ± 0.03, (8 ± 3) × 107, and 303 ± 27 M-1 s-1, respectively (pH 7.4, 37 °C). The reactivity of hydrogen sulfide was compared to that of low-molecular-weight thiols such as cysteine and glutathione. Considering the low tissue concentrations of endogenous hydrogen sulfide, direct reactions with oxidants probably cannot completely account for its protective effects. © 2010 Elsevier Inc. All rights reserved.