Nitrosylmyoglobin as antioxidant—kinetics and proposed mechanism for reduction of hydroperoxides

Abstract

Nitrosylmyoglobin (MbFe^IINO), which is believed to have a protective role during ischemia and reperfusion injury, was oxidized by tert-butyl hydroperoxide (t-BuOOH), and by hydrogen peroxide (H₂O₂) to the nitrite anion and metmyoglobin (MbFeIII). Further characterization of the reaction of MbFeIINO with excess of t-BuOOH was investigated with respect to reaction stoichiometry, temperature and pH dependence. It was found that the reaction between MbFe^IINO with excess of t- BuOOH followed a simple stoichiometry and had moderate pH and temperature dependence with the activation parameters ΔH^‡ = 57.4 ± 1.4 kJmol^-1 and ΔS^‡ = - 2112.0 ± 5.1 Jmol^-1K^-1, which is consistent with an associative reaction mechanism. Moreover, t-BuOOH-induced oxidation of MbFe^IINO did not result in any detectable formation of the hypervalent myoglobin (Mb) species, i.e. perferrylmyoglobin, (.MbFe^IV=O) or ferrylmyoglobin (MbFe^IV=O), and hereby differed from H₂O₂-induced oxidation of MbFe^IINO, which results in the formation of MbFe^IV=O. Based on the obtained results and on published data, different mechanisms for the reaction of the MbFe^IINO with t-BuOOH and H₂O₂ are proposed.

• myoglobin
• nitrosylmyoglobin
• NO
• antioxidant
• peroxide