Does the Oxidation of Nitric Oxide by oxyMyoglobin Share an Intermediate with the metMyoglobin-Catalyzed Isomerization of Peroxynitrite?

The reaction of nitric oxide with oxy-rnyoglobin (oxyMb) to form ferric myoglobin (metMb) and nitrate, and the metiqb-catalyzed isornerization of peroxynitrite to nitrate, have long been assumed to proceed via the same iron-bound peroxynitrite intermediate (metMb(OONO)). More recent research' showed that the metMb-catalyzed isomerization of peroxynitrite to nitrate produces detectable amounts of nitrogen dioxide and ferry! myoglobin (ferrylMB). This suggests a mechanism in which the peroxynitrite binds to the rnetMb, ferryiMb is transiently generated by dissociation of NO2, and nitrate is formed when the NO2 nitrogen attacks the ferrylMb oxo ligand. The presence of free NO2 and ferrylMb products reveals that small amounts of NO2 escape from myoglobin s interior before recombination can occur. Free NO2, and ferrylMb should also be generated in the reaction of oxyMb with NO, if the common intermediate metMb(OONO) is formed. However, this report presents a series of time-resolved IJV/vis spectroscopy experiments in which no ferrylMb was detected when oxyMb, and NO reacted. Th sensitivity of the methodology is such that as little as 10% of the ferrylMb, Predicted from the experiments ents with th metMban peroxynitrite should have been detectable. These results lead to the conclusion that the oxyMb + NO and metMbh + ONOO- reactions do not proceed via a common intermediate as previously thought. The conclusion has significant implications for researchers that propose a possible role of o,xvMb in intracellular NO regulation, because it means that toxic NO2 and ferrlMb are not generated during NO oxidation by this species.