The oxidative and nitrosative chemistry of the nitric oxide/superoxide reaction in the presence of bicarbonate.

The primary product of the interaction between nitric oxide (NO) and superoxide () is peroxynitrite (ONOO-), which is capable of either oxidizing or nitrating various biological substrates. However, it has been shown that excess NO or 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. Since ONOO- reacts not only with NO and but also with CO2, the effects of bicarbonate () 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 were formed with DEA/NO [NaEt2NN(O)NO] and xanthine oxidase, respectively. The presence of 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 CO2 does not affect the scavenging of ONOO- by either NO or. However, an increase in the rate of DHR oxidation by ONOO- in the presence of suggests that a CO2-ONOO- adduct does play a role in the interaction of NO or 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 CO2 adduct of ONOO- to form nitrosating species which have similar oxidation chemistry and reactivity with and NO.

The reaction of S-nitrosoglutathione with superoxide.

The nitric oxide (NO)-dependent S-nitrosation of thiols to generate S-nitrosothiols has been proposed as an important pathway for the metabolism of NO in vivo. Although it has been suggested that these S-nitrosated compounds are resistant to decomposition by reactive oxygen metabolites (ROMs), very little information is available regarding the interaction between S-nitrosothiols and ROMs. We found that S-nitrosoglutathione (GSNO) rapidly reacted with O2- to generate glutathione disulfide and equimolar quantities of nitrite and nitrate. The reaction was second order with respect of GSNO and first order with respect of O2- with a rate equation of -d[GSNO]/dt = 2k3[GSNO]2[O2-], where k3 = 3 - 6 x 10(8) M-2s-1. In addition, the reaction of GSNO with O2- generated a strong oxidant as an intermediate capable of oxidizing dihydrorhodamine in the absence of the apparent generation of NO. We conclude that O2- may act as a physiological modulator of S-nitrosation reactions by directly promoting the decomposition of S-nitrosothiols.

The reaction of S-nitrosoglutathione with superoxide.

The nitric oxide (NO)-dependent S-nitrosation of thiols to generate S-nitrosothiols has been proposed as an important pathway for the metabolism of NO in vivo. Although it has been suggested that these S-nitrosated compounds are resistant to decomposition by reactive oxygen metabolites (ROMs), very little information is available regarding the interaction between S-nitrosothiols and ROMs. We found that S-nitrosoglutathione (GSNO) rapidly reacted with O2- to generate glutathione disulfide and equimolar quantities of nitrite and nitrate. The reaction was second order with respect of GSNO and first order with respect of O2- with a rate equation of -d[GSNO]/dt = 2k3[GSNO]2[O2-], where k3 = 3 - 6 x 10(8) M-2s-1. In addition, the reaction of GSNO with O2- generated a strong oxidant as an intermediate capable of oxidizing dihydrorhodamine in the absence of the apparent generation of NO. We conclude that O2- may act as a physiological modulator of S-nitrosation reactions by directly promoting the decomposition of S-nitrosothiols.