Formation of peroxynitrite from reaction of nitroxyl anion with molecular oxygen

Peroxynitrite (ONOO-/ONOOH) is generally expected to be formed in vivo from the diffusion-controlled reaction between superoxide (O-2(.-)) and nitric oxide ((NO)-N-.). In the present paper we show that under aerobic conditions the nitroxyl anion (NO-), released from Angeli's salt (disodium diazen-1-ium-1,2,2-triolate, -ON=NO2-), generated peroxy-nitrite with a yield of about 65%. Simultaneously, hydroxyl radicals are formed from the nitroxyl anion with a yield of about 3% via a minor, peroxy-nitrite-independent pathway. Further experiments clearly underline that the chemistry of NO- in the presence of oxygen is mainly characterized by peroxynitrite and not by HO. radicals. Quantum-chemical calculations predict that peroxynitrite formation should proceed via intermediary formation of (NO)-N-. and O-2(.-), probably by an electron-transfer mechanism. This prediction is supported by the fact that H2O2 is formed during the decay of NO- in the presence of superoxide dismutase (Cu(II),Zn-SOD). Since the nitroxyl anion may be released endogenously by a variety of biomolecules, substantial amounts of peroxynitrite might be formed in vivo via NO- in addition to the "classical" (NO)-N-. + O-2(.-) pathway.