Kinetic and spectroscopic characterization of an intermediate peroxynitrite complex in the nitrogen monoxide induced oxidation of oxyhemoglobin.

Stopped-flow spectroscopy studies of the nitrogen monoxide mediated oxidation of oxyhemoglobin in the pH range 5-10.5 show that an intermediate can be characterized at alkaline pH. The rate of decay of this species to methemoglobin increases significantly with decreasing pH such that it does not accumulate in quantities large enough to be observed under neutral or acidic conditions. Kinetic and spectroscopic properties of this intermediate support its assignment as a methemoglobin peroxynitrite complex.