Manganese peroxidase and its role in the degradation of wood lignin

White-rot wood-rotting and litter-decomposing fungi produce lignin-degrading enzymes the most common of which are lignin peroxidase (UP), manganese peroxidase (MnP) and laccase. According to literature and our own results, MnP and laccase are common ligninolytic enzymes whereas LiP is less common. Molecular properties of MnPs produced by several fungi are well known. MnP oxidizes Mn(II) to Mn(III), which in chelated form is a powerful oxidizing system, and when amended with unsaturated lipids is also able to mineralize up to 16 % of C-14-labelled synthetic lignin to (CO2)-C-14. The results obtained until now indicate that the mineralization of lignin may occur outside the fungal cell wall. This points to the key role of MnP in lignin degradation. MnP in a mixture of Tween 80, Mn2+, Mn-chelating organic acid and hydrogen peroxide generating system resulted both in depolymerization of milled pine wood, and polymerization of the insoluble part of pine wood, but depolymerization was the most prominent reaction. Many suitable fungi for biopulping produce MnP whereas the production of UP does not seem to be necessary in this application. The role of laccase is unclear. However, selective lignin degradation and efficiency in biopulping require a proper balance between lignin and cellulose degradation, and therefore also thorough studies to clarify the significance of cellulose and hemicellulose degradation in lignin-selective fungi are needed.