Oxidation of oxymyoglobin by nitric oxide through dissociation from cobalt nitrosyls

Add time:08/28/2019    Source:sciencedirect.com

Kinetic evaluation of the oxidation of oxymyoglobin (MbO2) to metmyoglobin (Mb+) by bis(dimethylglyoximato)cobalt nitrosyl [Co(NO)(DMGH)2] has established that the mechanism of this transformation involves initial dissociation of nitric oxide from Co(NO)(DMGH)2, followed by direct oxidation of MbO2 by nitric oxide. Nitrate formation accompanies the production of Mb+ and is proposed to arise from isomerization of the initially formed peroxynitrite ion. By comparative kinetic determinations with nitrosyl transfer from the cobalt nitrosyl reagent to deoxyhemoglobin, the rate constant for oxidation of MbO2 by nitric oxide is calculated to be 31 X 106 M−1sec−1 at 10.0°C in phosphate-buffered media at pH 7.0. Bis(dimethylglyoximato)cobalt(II), the cobalt complex formed by nitric oxide dissociation from Co(NO)(DMGH)2, is an effective trap for dioxygen liberated from MbO2. The resulting μ-peroxo- or μ-superoxo-dicobaloxime(III) oxidizes deoxymyoglobin to metmyoglobin at a rate that is competitive with oxidation induced by Co(NO)(DMGH)2.

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