Spectral and kinetic studies on the interaction between oxyhaemoglobin and peroxynitrite: a comparison with hydrogen peroxide.

Interaction between oxyhaemoglobin and peroxynitrite was studied using stopped-flow rapid-scan spectrophotometry. The influence of pH, peroxynitrite concentration and temperature on the pseudo-first-order rate constants was studied and the activation energy calculated. The kinetic curve for the oxyhaemoglobin-peroxynitrite reaction showed that a fast reaction occurred in the initial seconds, followed by a slow process of decrease in absorbance. The biphasic reaction kinetics of oxyhaemoglobin with peroxynitrite or hydrogen peroxide demonstrated the existence of an intermediary species. For the first time a rapid-scan stopped-flow spectrophotometry study is presented, yielding spectral and kinetic data of the reaction.