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.