Reductive activity of a manganese-dependent peroxidase from phanerochaete chrysosporium

A manganese-dependent peroxidase (MnP) from Phanerochaete chrysosporium catalyzed the reduction of cytochrome c in a reaction mixture containing H₂O₂, Mn(II)-tartrate, and p-hydroquinone. Electron spin resonance studies have shown that the hydroquinone-dependent reductive activity of MnP is due to the benzosemiquinone formed upon the one-electron oxidation of p-hydroquinone by Mn(III)-tartrate, which is formed upon the oxidation of Mn(II) by MnP. The reductive activity increased linearly with an increase in the concentration of p-hydroquinone. The reductive activity was also observed using other hydroquinones such as methylhydroquinone, 2,5-dimethylhydroquinone, and trimethyihydroquinone. The apparent K_m values for Mn(II) and H₂O₂ for the hydroquinone-dependent reductive activity were similar to those for oxidative reactions of MnP. A stoichiometry study showed that about 1.5 mol of cytochrome c was reduced per mole of H₂O₂ consumed. The stoichiometry decreased with an increase in the concentration of H₂O₂. The optimal pH for the reductive activity was 5.0, approximately the physiological pH of the fungus. The reduction of cytochrome c was also observed using a quinone and cellobiose:quinone oxidoreductase isolated from the extracellular medium of the fungus.