Mn-dependent peroxidase from the lignin-degrading white rot fungus Phlebia radiata

A homogeneous Mn-dependent peroxidase (MnP) was purified from the extracellular culture fluid of the lignin-degrading white rot fungus Phlebia radiata by anion exchange chromatography. The enzyme had a molecular weight of 49,000 and pI 3.8. It was a glycoprotein, containing carbohydrate moieties accounting for 10% of the molecular weight. Mn-peroxidase was capable of oxidizing phenolic compounds in the presence of H₂O₂, whereas the effect on nonphenolic lignin model compounds was insignificant. MnP contained protoporphyrin IX as a prosthetic group. During enzymatic reactions H₂O₂ converted the native MnP to compound II. Mn²⁺ was essential in completing the catalytic cycle by returning the enzyme to its native state. The oxidation of ultimate substrates was dependent on superoxide radicals, O₂⁻ and probably on Mn³⁺ generated during the catalytic cycle. MnP exhibited high activity of NADH oxidation without exogenously added H₂O₂. It was shown to produce H₂O₂ at the expense of NADH.