Lignin-modifying enzyme

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Lignin-modifying enzymes (LMEs) are various types of enzymes produced by fungi that catalyze the breakdown of lignin, a biopolymer commonly found in the cell walls of plants. The terms ligninases and lignases are older names for the same class, but the name "lignin-modifying enzymes" is now preferred, given that these enzymes are not hydrolytic but rather oxidative (electron withdrawing) by their enzymatic mechanisms. LMEs include peroxidases, such as lignin peroxidase (EC 1.11.1.14), manganese peroxidase (EC 1.11.1.13), versatile peroxidase (EC 1.11.1.16), and many phenoloxidases of the laccase type.

LMEs have been known to be produced by many species of so-called white rot basidiomycetous fungi, including: Phanerochaete chrysosporium, Ceriporiopsis subvermispora, Trametes versicolor, Phlebia radiata, Pleurotus ostreatus and Pleurotus eryngii.

LMEs are produced not only by wood-white rotting fungi but also by litter-decomposing basidiomycetous fungi such as Agaricus bisporus (common button mushroom), and many Coprinus and Agrocybe species. The brown-rot fungi, which are able to colonize wood by degrading cellulose, are not able to produce LMEs.

Some results on LME-type of peroxidases have also been reported for some species of filamentous bacteria such as Streptomyces viridosporus T7A, Streptomyces lavendulae REN-7 and Clostridium stercorarium.

However, efficient lignin and lignin-like polymer degradation is only achieved by fungal LME peroxidases, and laccases in combinations with organic charge transfer mediator compounds. Laccases are more widely distributed enzymes belonging to the multicopper oxidase (MCO) superfamily encompassing all three domains of life (bacteria, archaea, eukarya).

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