Peroxynitrite scavenging by ferryl sperm whale myoglobin and human hemoglobin

Globins protect from the oxidative and nitrosative cell damage. Here, kinetics of peroxynitrite scavenging by ferryl sperm whale myoglobin (MbFe(IV)O) and human hemoglobin (HbFe(IV)O), between pH 5.8 and 8.3 at 20.0 °C, are reported. In the absence of CO2, values of the second-order rate constant for peroxynitrite scavenging by MbFe(IV)O and HbFe(IV)O (i.e., for MbFe(III) and HbFe(III) formation; kon) are 4.6 × 104 M−1 s−1 and 3.3 × 104 M−1 s−1, respectively, at pH 7.1. Values of kon increase on decreasing pH with pKa values of 6.9 and 6.7, this suggests that the ONOOH species reacts preferentially with MbFe(IV)O and HbFe(IV)O. In the presence of CO2 (=1.2 × 10−3 M), values of kon for peroxynitrite scavenging by MbFe(IV)O and HbFe(IV)O are essentially pH-independent, the average kon values are 7.1 × 104 M−1 s−1 and 1.2 × 105 M−1 s−1, respectively. As a whole, MbFe(IV)O and HbFe(IV)O, obtained by treatment with H2O2, undertake within the same cycle H2O2 and peroxynitrite detoxification.