Peroxynitrite scavenging by ferryl sperm whale myoglobin and human hemoglobin

Abstract

Globins protect from the oxidative and nitrosative cell damage. Here, kinetics of peroxynitrite scavenging by ferryl sperm whale myoglobin (Mb Fe(IV) O) and human hemoglobin (Hb Fe(IV) O), between pH 5.8 and 8.3 at 20.0 °C, are reported. In the absence of CO 2, values of the second-order rate constant for peroxynitrite scavenging by Mb Fe(IV) O and Hb Fe(IV) O (i.e., for Mb Fe(III) and Hb Fe(III) formation; k on) are 4.6 × 10 4 M −1 s −1 and 3.3 × 10 4 M −1 s −1, respectively, at pH 7.1. Values of k on increase on decreasing pH with p K a values of 6.9 and 6.7, this suggests that the ONOOH species reacts preferentially with Mb Fe(IV) O and Hb Fe(IV) O. In the presence of CO 2 (=1.2 × 10 −3 M), values of k on for peroxynitrite scavenging by Mb Fe(IV) O and Hb Fe(IV) O are essentially pH-independent, the average k on values are 7.1 × 10 4 M −1 s −1 and 1.2 × 10 5 M −1 s −1, respectively. As a whole, Mb Fe(IV) O and Hb Fe(IV) O, obtained by treatment with H 2O 2, undertake within the same cycle H 2O 2 and peroxynitrite detoxification.