The Oxidative and Nitrosative Chemistry of the Nitric Oxide/Superoxide Reaction in the Presence of Bicarbonate

Abstract The primary product of the interaction between nitric oxide (NO) and superoxide ([figure]) is peroxynitrite (ONOO − ), which is capable of either oxidizing or nitrating various biological substrates. However, it has been shown that excess NO or[figure]can further react with ONOO − to form species which mediate nitrosation. Subsequently, the controlled equilibrium between nitrosative and oxidative chemistry is critically dependent on the flux of NO and[figure]. Since ONOO − reacts not only with NO and[figure]but also with CO 2 , the effects of bicarbonate ([figure]) on the biphasic oxidation profile of dihydrorhodamine-123 (DHR) and on the nitrosation of both 2,3-diaminonaphthalene and reduced glutathione were examined. Nitric oxide and [figure] were formed with DEA/NO [NaEt 2 NN(O)NO] and xanthine oxidase, respectively. The presence of [figure] did not alter either the oxidation profile of DHR with varying radical concentrations or the affinity of DHR for the oxidative species. This suggests that the presence of CO 2 does not affect the scavenging of ONOO − by either NO or[figure]. However, an increase in the rate of DHR oxidation by ONOO − in the presence of [figure] suggests that a CO 2 -ONOO − adduct does play a role in the interaction of NO or[figure]with a product derived from ONOO − . Further examination of the chemistry revealed that the intermediate that reacts with NO is neither ONOO − nor cis -HOONO. It was concluded that NO reacts with both trans -HOONO and a CO 2 adduct of ONOO − to form nitrosating species which have similar oxidation chemistry and reactivity with[figure]and NO.