Reactions of oxymyoglobin with NO, NO2, and NO2- under argon and in air.
Oxymyoglobin under argon reacts with NO2- and NO2 (N2O4) to produce metmyoglobin in a spectrally clean process with clear isosbestic points. In both cases, the reactant is NO2-. The second-order rate constant for NO2- or N2O4 is the same: d(Mb+)/dt = k(MbO2)(NO2-) where k = 0.21 +/- 0.02 L mol-1 S-1. The reaction of MbO2 with NO under argon is a complex process and entails the generation of Mb+ and OONO- (peroxynitrite) in the first step. The latter (lambda MAX, 302 nm) was poorly resolved from more intense protein absorption in the 300-nm region. However, at pH 9, the change in absorbance corresponded exactly to a quantitative production of the OONO-ion. Hydroxy radicals from it were trapped with ethylene-1, 2-(13) C. The initial step is followed in sequence by the rapid formation of MbNO+. The iron(III)-nitrosyl adduct hydrolyzes slowly to MbII and NO2- (k = 8.0 +/- 0.8 x 10(-5) S-1. MbII then rapidly associates with NO, and MbNO is the final product of this reaction. Oxymyoglobin is inert to NO3-. In contrast to the results under argon, in air the reactions of MbO2 with NO2-, NO, and NO2 (N2O4) all proceed in the same autocatalytic fashion with kAVE (for the autocatalytic rates) approximately equal to 9 +/- 5 L mol-1 s-1. Nitrite is the initial reactant in all cases. Isosbestic points are not observed in the visible spectrum, and additional porphyrin iron-ligated species are intermediates. Based upon work with iron porphyrins.
Wade
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Environmental Toxicology Graduate Program, University of California, Riverside 92521, USA.
Castro
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D000388:Air; D000818:Animals; D001128:Argon; D006736:Horses; D007700:Kinetics; D009206:Myocardium / Q000378:metabolism; D009211:Myoglobin / Q000737:chemistry*; D009566:Nitrates / Q000737:chemistry; D009585:Nitrogen Dioxide / Q000737:chemistry*; D009609:Nitrous Oxide / Q000737:chemistry*
D009211:Myoglobin; D009566:Nitrates; C017595:oxymyoglobin; C039642:peroxynitric acid; D001128:Argon; D009609:Nitrous Oxide; D009585:Nitrogen Dioxide