Inhibition of peroxynitrite-mediated oxidation of glutathione by carbon dioxide.

Peroxynitrite reacts with CO2 to from an adduct containing a weak O--O bond that can undergo homolytic and/or heterolytic cleavage to give other reactive intermediates. Because the peroxynitrite/CO2 reaction is fast and physiological concentrations of CO2 are relatively high, peroxynitrite-mediated oxidations of biological species probably involve the peroxynitrite-CO2 adduct and its subsequent reactive intermediates. We have examined the reaction of glutathione with peroxynitrite in the presence and absence of added bicarbonate. In the presence of added bicarbonate, CO2 competes with glutathione for peroxynitrite, resulting in a markedly decreased consumption of glutathione compared with that observed in the absence of added bicarbonate. However, the consumption of glutathione still is much higher than predicted from the assumption that the glutathione-peroxynitrite reaction is the only reaction that can consume glutathione in this system. These results suggest that glutathione partially, but not completely, traps intermediate(s) derived from the peroxynitrite and CO2 reaction. Some rate constants for the trapping of the intermediates are estimated by simulating the reactions, and possible mechanisms for the reaction of peroxynitrite with glutathione in the presence of added bicarbonate are discussed.