The NO-mediated Oxidation of Oxymyoglobin and Oxyhemoglobin

The rapid reaction of nitrogen monoxide with oxyhemoglobin (oxyHb) is of particular interest, because it significantly reduces the half-life of NO in vivo and is the cause of increased blood pressure observed when extracellular hemoglobin-based blood substitutes are administered [16]. 

The second-order rate constants, obtained from the linear plots of the observed pseudo-first-order rate constants against oxyMb or oxyHb concentrations, are pH 

Averaged spectra were collected (62 scans 320, 480, 640, 800, and 1280 ms after mixing. 

Further mechanistic studies showed that no free peroxynitrite is formed during the reactions of NO with the oxy-forms of these proteins, and that nitrate is formed quantitatively, at both pH 7.0 and pH 9.0 [18]. Analysis of the proteins after ten cycles of oxidation by NO and reduction by ascorbic acid indicated that fewer than 1% of the tyrosine residues are nitrated. These results show that when peroxynitrite is coordinated to the heme of myoglobin or hemoglobin, it rapidly iso-merizes to nitrate, and thus cannot nitrate the tyrosine residues of the globin. 

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Herold, S., Exner, M., Nauser,T., Kinetic and mechanistic studies of the NO -mediated oxidation of oxymyoglobin and oxyhemoglobin, Biochemistry 40 (2001), p. 3385-3395... 

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