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 (Mb{single bond}Fe(IV){double bond, long}O) and human hemoglobin (Hb{single bond}Fe(IV){double bond, long}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 Mb{single bond}Fe(IV){double bond, long}O and Hb{single bond}Fe(IV){double bond, long}O (i.e., for Mb{single bond}Fe(III) and Hb{single bond}Fe(III) formation; k_on) are 4.6 × 10⁴ M^-1 s^-1 and 3.3 × 10⁴ M^-1 s^-1, respectively, at pH 7.1. Values of k_on increase on decreasing pH with pK_a values of 6.9 and 6.7, this suggests that the ONOOH species reacts preferentially with Mb{single bond}Fe(IV){double bond, long}O and Hb{single bond}Fe(IV){double bond, long}O. In the presence of CO₂ (=1.2 × 10^-3 M), values of k_on for peroxynitrite scavenging by Mb{single bond}Fe(IV){double bond, long}O and Hb{single bond}Fe(IV){double bond, long}O are essentially pH-independent, the average k_on values are 7.1 × 10⁴ M^-1 s^-1 and 1.2 × 10⁵ M^-1 s^-1, respectively. As a whole, Mb{single bond}Fe(IV){double bond, long}O and Hb{single bond}Fe(IV){double bond, long}O, obtained by treatment with H₂O₂, undertake within the same cycle H₂O₂ and peroxynitrite detoxification.