Pfeiffer S, Gorren A C, Schmidt K, Werner E R, Hansert B, Bohle D S, Mayer B
Institut für Pharmakologie und Toxikologie, Karl-Franzens-Universität Graz, Universitätsplatz 2, A-8010 Graz, Austria.
J Biol Chem. 1997 Feb 7;272(6):3465-70. doi: 10.1074/jbc.272.6.3465.
Peroxynitrite, the reaction product of nitric oxide (NO) and superoxide (O-2) is assumed to decompose upon protonation in a first order process via intramolecular rearrangement to NO3-. The present study was carried out to elucidate the origin of NO2- found in decomposed peroxynitrite solutions. As revealed by stopped-flow spectroscopy, the decay of peroxynitrite followed first-order kinetics and exhibited a pKa of 6.8 +/- 0.1. The reaction of peroxynitrite with NO was considered as one possible source of NO2-, but the calculated second order rate constant of 9.1 x 10(4) M-1 s-1 is probably too small to explain NO2- formation under physiological conditions. Moreover, pure peroxynitrite decomposed to NO2- without apparent release of NO. Determination of NO2- and NO3- in solutions of decomposed peroxynitrite showed that the relative amount of NO2- increased with increasing pH, with NO2- accounting for about 30% of decomposition products at pH 7.5 and NO3- being the sole metabolite at pH 3.0. Formation of NO2- was accompanied by release of stoichiometric amounts of O2 (0.495 mol/mol of NO2-). The two reactions yielding NO2- and NO3- showed distinct temperature dependences from which a difference in Eact of 26.2 +/- 0.9 kJ mol-1 was calculated. The present results demonstrate that peroxynitrite decomposes with significant rates to NO2- plus O2 at physiological pH. Through formation of biologically active intermediates, this novel pathway of peroxynitrite decomposition may contribute to the physiology and/or cytotoxicity of NO and superoxide.
过氧亚硝酸根是一氧化氮（NO）和超氧阴离子（O₂⁻）的反应产物，假定它在质子化后通过分子内重排以一级反应过程分解为硝酸根（NO₃⁻）。本研究旨在阐明过氧亚硝酸根分解溶液中发现的亚硝酸根（NO₂⁻）的来源。如停流光谱法所示，过氧亚硝酸根的衰减遵循一级动力学，其pKa为6.8±0.1。过氧亚硝酸根与NO的反应被认为是NO₂⁻的一种可能来源，但计算得出的二级反应速率常数9.1×10⁴ M⁻¹ s⁻¹可能太小，无法解释生理条件下NO₂⁻的形成。此外，纯过氧亚硝酸根分解为NO₂⁻，没有明显释放出NO。对过氧亚硝酸根分解溶液中NO₂⁻和NO₃⁻的测定表明，NO₂⁻的相对量随pH升高而增加，在pH 7.5时，NO₂⁻约占分解产物的30%，而在pH 3.0时，NO₃⁻是唯一的代谢产物。NO₂⁻的形成伴随着化学计量的O₂释放（0.495 mol/mol的NO₂⁻）。产生NO₂⁻和NO₃⁻的两个反应表现出不同的温度依赖性，据此计算出活化能（Eact）相差26.2±0.9 kJ mol⁻¹。目前的结果表明，在生理pH条件下，过氧亚硝酸根以显著的速率分解为NO₂⁻和O₂。通过形成生物活性中间体，过氧亚硝酸根这种新的分解途径可能对NO和超氧阴离子的生理学和/或细胞毒性有贡献。
