Mn(II) oxidation is the principal function of the extracellular Mn-peroxidase from Phanerochaete chrysosporium

Abstract

The manganese peroxidase (MnP), from the lignin-degrading fungus Phanerochaete chrysosporium, an H 2O 2-dependent heme enzyme, oxidizes a variety of organic compounds but only in the presence of Mn(II). The homogeneous enzyme rapidly oxidizes Mn(II) to Mn(III) with a pH optimum of 5.0; the latter was detected by the characteristic spectrum of its lactate complex. In the presence of H 2O 2 the enzyme oxidizes Mn(II) significantly faster than it oxidizes all other substrates. Addition of 1 m equivalent of H 2O 2 to the native enzyme in 20 m m Na-succinate, pH 4.5, yields MnP compound II, characterized by a Soret maximum at 416 nm. Subsequent addition of 1 m equivalent of Mn(II) to the compound II form of the enzyme results in its rapid reduction to the native Fe 3+ species. Mn(III)-lactate oxidizes all of the compounds which are oxidized by the enzymatic system. The relative rates of oxidation of various substrates by the enzymatic and chemical systems are similar. In addition, when separated from the polymeric dye Poly B by a semipermeable membrane, the enzyme in the presence of Mn(II)-lactate and H 2O 2 oxidizes the substrate. All of these results indicate that the enzyme oxidizes Mn(II) to Mn(III) and that the Mn(III) complexed to lactate or other α-hydroxy acids acts as an obligatory oxidation intermediate in the oxidation of various dyes and lignin model compounds. In the absence of exogenous H 2O 2, the Mn-peroxidase oxidized NADH to NAD +, generating H 2O 2 in the process. The H 2O 2 generated by the oxidation of NADH could be utilized by the enzyme to oxidize a variety of other substrates.