A pulse radiolysis investigation of the reactions of myeloperoxidase with superoxide and hydrogen peroxide

Abstract

Using pulse radiolysis, the rate constant for the reaction of ferric myeloperoxidase with O 2 − to give compound III was measured at pH 7.8, and values of 2.1 · 10 6 M −1 · s −1 for equine ferric myeloperoxidase and 1.1 · 10 6 M −1 · s −1 for human ferric myeloperoxidase were obtained. Under the same conditions, the rate constant for the reaction of human ferric myeloperoxidase with H 2O 2 to give compound I was 3.1 · 10 7 M −1 · s −1. Our results indicate that although the reaction of ferric myeloperoxidase with O 2 − is an order of magnitude slower than with H 2O 2, the former reaction is sufficiently rapid to influence myeloperoxidase-dependent production of hypochlorous acid by stimulated neutrophils.