ACCELERATION OF PEROXYNITRITE OXIDATIONS BY CARBON-DIOXIDE

Stopped-flow kinetic studies of the isomerization of peroxynitrite to give nitrate have been performed in carbonate-enriched buffers using p H jump and carbonic anhydrase as probes, The data are consistent with the reaction of CO2 and the peroxynitrite anion rapidly forcing an uns table nitrosoperoxycarbonate anion adduct, O=N-OOCO2- (1). The CO2 cat alysis of the isomerization of peroxynitrite is not accompanied by the formation of nitrite, hydrogen peroxide, or other hydroperoxidic mate rial like peroxycarbonate, The reaction proceeds via the transient for mation of an oxidant or oxidants that is (are) capable of promoting el ectrophilic nitration reactions. We propose that O=N-OOCO2- rearranges to give a nitrocarbonate anion, O2N-OCO2- (2) which, in turn, may ser ve as the proximal oxidant in biological systems that produce peroxyni trite. At least four different mechanistic classes of reactions that h ave been ascribed to peroxynitrite can be envisioned to involve 2: (a) hydrolysis to nitrate, (b) one-electron or (c) two-electron oxidation s, and (d) electrophilic nitration. Given the fast reaction of peroxyn itrite with carbon dioxide and the ubiquitous presence of the latter, the role of CO2 cannot be neglected in complex peroxynitrite reactions in vitro and in vivo. (C) 1996 Academic Press, Inc.