Manganese peroxidase (EC 1.11.1.13, Mn(II):hydrogen-peroxide oxidoreductase, MnP) also require H2O2 as an oxidant in the Mn-dependent catalyzing reaction in which Mn2+ is converted to Mn3+ by MnP. Mn3+ then oxidizes phenolic rings to phenoxyl radicals, which leads to decomposition of compounds. Both LiPs and MnPs are heme-containing glycoproteins [49, 101, 102]. But LiPs are not as widespread as MnPs, and major difference between MnPs and LiPs in lignin degradations are as LiPs generally oxidize nonphenolic lignin substructures and MnPs oxidize phenolic

rings of lignin [49]. MnPs have an important role in lignin depolymerization, chloro — lignin, and demethylation of lignin. Therefore, MnPs have a very essential role in biological pretreatment of lignocellulosic biomass. So far, many researchers have reported that P. chrysosporium, Pleorotus ostreatu, Trametes sp., and several other species, which belong to Meruliaeiae, Coriolaceae, and Polyporaceae produce MnP [32].

MnPs contain one molecule of heme as iron protoporhyrin IX and comprise with 357 amino acid residues, three sugar residues (Glc Nac, Glc Nac at Asn 131, and a single mannose at Ser 336), two structural calcium ions, a substrate Mn2+ and 478 solvent molecules. For MnP, the acidic amino acids, aspartic acid, and two glutamic acids have been proposed as manganese-binding residues [32, 98]. MnPs act on its substrate almost similar to LiPs action. Thus, the native form of MnP is oxidized by addition of H2O2 to form MnP I complex (Fig. 1.3). Then this catalytic cycle involves in the oxidation of Mn2+ to Mn3+ by MnP I and MnP II complexes. Finally, Mn3+ oxidizes the lignin compounds by diffusing into the lignifled cell wall and attacks it from inside. Indeed, MnP I can directly involve in the oxidation of phenolic compounds such as 2,6-dimethoxyphenol, guaiacol, and phenolic tetrameric lignin model compounds. This oxidation reaction clearly elucidates that MnP oxidizes the phenolic part of the lignin indirectly via Mn ions. But MnP naturally does not oxidize aromatic compounds of lignin directly as LiP. Because they do not have tryptophan residue, required for electron transfer to non-phenolic substrates [98,103]. Recently, MnPs have been isolated from Bjerkandera sp. BOS55 and P eryngii that are found to be oxidized Mn2+ as well as aromatic compounds [98]. Hence, it is very clear that addition of Mn2+ may play further enhancement in the bio-oxidation of phenolic compounds of lignin and may induce MnP production in fungi.