| Abstract
| - The strong oxidizing and nitrating agent peroxynitrite has been shown to diffuse into erythrocytesand oxidize oxyhemoglobin (oxyHb) to metHb. Because the value of the second-order rate constant forthis reaction is on the order of 104 M-1 s-1 and the oxyHb concentration is about 20 mM (expressed perheme), this process is rather fast and oxyHb is considered a sink for peroxynitrite. In this work, weshowed that the reaction of oxyHb with peroxynitrite, both in the presence and absence of CO2, proceedsvia the formation of oxoiron(iv)hemoglobin (ferrylHb), which in a second step is reduced to metHb andnitrate by its reaction with NO2•. In the presence of physiological relevant amounts of CO2, ferrylHb isgenerated by the reaction of NO2• with the coordinated superoxide of oxyHb (HbFeIIIO2•-). This reactionproceeds via formation of a peroxynitrato−metHb complex (HbFeIIIOONO2), which decomposes to generatethe one-electron oxidized form of ferrylHb, the oxoiron(iv) form of hemoglobin with a radical localizedon the globin. CO3•-, the second radical formed from the reaction of peroxynitrite with CO2, is alsoscavenged efficiently by oxyHb, in a reaction that finally leads to metHb production. Taken together, ourresults indicate that oxyHb not only scavenges peroxynitrite but also the radicals produced by itsdecomposition.
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