Microbial degradation of lignin: Role of lignin peroxidase, manganese peroxidase, and laccase

Abstract

Lignin peroxidase (LiP), laccase (LA) and manganese peroxidase (MnP) of white-rot basidiomycetes such as Phanerochaete chrysosporium, Coliorus versicolor, Phlebia radiata and Pleurotus eryngii catalyze oxidative degradation of lignin substructure model compounds and synthetic lignins (DHPs). Side chain-and aromatic ring cleavage products of both phenolic and non-phenolic substrates oxidized by LiP were isolated and characterized by NMR and MS. The cleavage mechanism was elucidated by using O. Recent studies suggested that LiP is capable of oxidizing lignin directly at the protein surface via a long-range electron transfer process. LA and MnP, which oxidize phenolic but not non-phenolic moieties, generally degrade lignin stepwise from phenolic moieties. However, recent studies indicated that MnP and LA can degrade both phenolic and non-phenolic aromatic moieties of lignin with some special mediators. (1), 4-ethoxy-3-methoxyphenylglycerol-β-guaiacyl ether; (2), 4-ethoxy-3-methoxyphenylglycerol-β, γ-cyclic carbonate; (3), 4-ethoxy-3-methoxyphenylglycerol-β-methyl oxalate; (4), 4-ethoxy-3-methoxyphenylglycerol-β-mucorate. As the case of the degradation of β-O-4 lignin substructure model dimers by LiP, the cyclic carbonates and formate ester of arylglycerols, and arylglycerol were isolated from degradation products of the DHP by LiP ; the chemical structures of the products were identified by GC-MS. These results indicated that the lignin polymer is really degraded by the LiP of white-rot fungi.Active sites of LiP to substrates. Doyle and his group 19) recently found that by cultivating wood-rotting fungi in an agar medium containing several phenolic compounds, such as gallic acid, tannic acid, and hydroquinone, that white-rot fungi produced a large darkened zone around the mycerial mat, but no zone of darkening was associated with the growth of brown-rot fungi. Davidson et al. 37) subsequently investigated the reaction using 210 species of wood-rotting fungi, and concluded that the white-rotting type coincides with Bavendamm's reaction in general, and that the reaction is helpful in identifying fungi. The enzyme responsible for Bavendamm's reaction was extensively studied in the next 10 years, and characterized to be laccase (LA). 38) LA, p-diphenol oxidase (EC 1.10.3.2) has been isolated and characterized as a blue, copper containing oxidase from a lac tree (Rhus spp) and several fungi. White rot fungi constitutively produce laccase during primary metabolism. 39)1. Degradation of β-1 model compounds. Kawai et al. 40) found that phenolic β-1 model compounds are degraded by LiP of P. chrysosporium and LA of C. versicolor via similar pathways. 1-(3,5-Dimethoxy-4-hydroxyphenyl)-2-(3,5-dimethoxy-4-ethoxyphenyl)-propane-1,3-diol (1, Fig. 6) was converted by LA of C. versicolor to 1-(3,5-dimethoxy-4-hydroxyphenyl)-2-(3,5-dimethoxy-4-ethoxyphenyl)-3-hydroxypropanone (2)by Cα oxidation, 2-(3,5-dimethoxy-4-ethoxyphenyl)-3-hydroxypropanal (5), 2,6-dimethoxy-p-hydroquinone (4) and its benzoquinone (3) by alkyl-ph...

Phenolic acids act as signaling molecules in plant-microbe symbioses

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Paper pulp delignification using laccase and natural mediators

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Agroindustrial Wastes as Substrates for Microbial Enzymes Production and Source of Sugar for Bioethanol Production

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