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.