Oxalate-dependent reductive activity of manganese peroxidase from Phanerochaete chrysosporium.

The mechanism of oxalate-dependent reductive activity of a manganese-dependent peroxidase (MnP) from Phanerochaete chrysosporium was investigated. Ferric iron reduction was demonstrated in reaction mixtures containing Mn-peroxidase, Mn2+, oxalate, H2O2, ferric chloride, and 1,10-phenanthroline. Only catalytic amounts of H2O2 were required. Oxygen consumption was also observed in reaction mixtures containing Mn-peroxidase, Mn2+, oxalate, and H2O2 and was inhibited by the addition of ferric iron. Electron spin resonance studies, using the spin traps 5,5-dimethyl-1-pyrroline-N-oxide and alpha-4-pyridyl-1-oxide-N-t-butylnitrone were used to obtain evidence for the production of the formate radical (CO2.-) and superoxide (O2.-) in a reaction mixture containing Mn2+, oxalate and H2O2. It was concluded that both CO2.- (anaerobic conditions) and O2.- (aerobic conditions) could reduce ferric iron. The dismutation of some O2.- would produce H2O2 to provide a constant supply of H2O2.