Oxidative decomposition of malonic acid as basis for the action of manganese peroxidase in the absence of hydrogen peroxide.

Manganese peroxidase (MnP) from the ligninolytic basidiomycetes Phlebia radiata and Nematoloma frowardii was found to decompose malonate oxidatively in the absence of H2O2 in a reaction system consisting of the enzyme, sodium malonate and MnCl2. The enzymatic oxidation resulted in a substantial decrease in malonate concentration and the formation of CO2, oxalate, glyoxylate and formate. Simultaneously with the decomposition of malonate, Mn(II) was oxidized to Mn(III) leading to high transient concentrations of the latter. MnP action in the absence of H2O2 started slowly after a lag period of 3 h. The lag period was considerably shortened after a single addition of Mn(III). Superoxide dismutase and catalase inhibited the enzymatic reaction partly, ascorbate completely. ESR studies demonstrated the formation of a carbon-centered radical during the course of the reaction. We propose that the latter generates peroxides that can be used by MnP to oxidize Mn(II) to Mn(III).