Peroxidase Inactivation by Covalent Modification with Phenoxyl Radical during Phenol Oxidation

Abstract

The mechanism-based inactivation of peroxidases limits the usefulness of these versatile enzymes. In this study, we propose a dominant inactivation mechanism for peroxidase during phenol oxidation. Two peroxidases, Coprinus cinereus peroxidase (CiP) and horseradish peroxidase isozyme C (HRPC) showed much higher inactivation rates after simultaneous addition of phenol and hydrogen peroxide, whereas addition of hydrogen peroxide alone or polymeric products had relatively little impact on peroxidase activity. During the oxidation of a phenol substrate, the molecular weights of polypeptides originating from inactivated peroxidases were slightly increased, and a large fraction of CiP and HRPC hemes remained intact even after phenoxyl radical coupling. Our study strongly supports the hypothesis that the inactivation of a peroxidase during the oxidation of phenolic compounds occurs by a covalent modification of the peroxidase polypeptide chain with a phenoxyl radical. These findings will elucidate the method of inactivation for peroxidase and other heme proteins