The Role of Enzymes and Mediators in White-Rot Fungal Degradation of Lignocellulose

White-rot fungi can selectively and efficiently degrade lignin through the action of secreted enzymes. Major lignin-degrading enzymes include lignin peroxidase (LiP), manganese peroxidase (MnP) and laccase. LiP and MnP require hydrogen peroxide (H 2 O 2 ) for their activities, but they are inactivated by a high concentration of H 2 O 2 . There are various H 2 O 2 —producing enzymes in white-rot fungi. LiP is able to oxidize both phenolic and non-phenolic lignin substructures, whereas MnP and laccase are only able to degrade phenolic lignin substructures. An unsaturated fatty acid or a thio-containing compound enables MnP to degrade non-phenolic lignin substructures. Several in vitro studies reveal that some enzymes can synergistically degrade lignin. As lignin-degrading enzymes are too bulky to penetrate plant cell walls for lignin degradation, the role of various small organic/inorganic compounds, serving as redox mediators for lignin-degrading enzymes in lignin degradation, is discussed in detail.