Glyoxylate-Supported Reactions Catalyzed by Mn Peroxidase of Phanerochaete chrysosporium: Activity in the Absence of Added Hydrogen Peroxide

Mn peroxidases are H2O2-utilizing hemeproteins secreted by the lignin-degrading fungus Phanerochaete chrysosporium. We show here that glyoxylate is capable of supporting Mn peroxidase activity without added H2O2. This glyoxylate-supported activity is dependent upon Mn2+ and dioxygen. The involvement of superoxide is demonstrated by inhibition by superoxide scavenging agents, superoxide dismutase, or tetranitromethane. The addition of catalase resulted in dioxygen evolution, indicating that H2O2 is an intermediate in the reaction. Formate is one of the oxidation products of glyoxylate as detected by the formate dehydrogenase assay. The generation of H2O2 in the presence of Mn2+ and Mn peroxidase results in Mn3+ formation. Consequently, we show that the direct reaction between glyoxylate and Mn3+ also results in formate formation. The stoichiometry of this reaction approaches 1:1. Electron spin resonance, spin-trapping studies show formation of the formate radical CO2 in the reaction of Mn3+ and glyoxylate.