title: Phenolic mediators enhance the manganese peroxidase catalyzed oxidation of recalcitrant lignin model compounds and synthetic lignin.
abstract: Fungal oxidative enzymes, such as peroxidases and laccases, are the key catalysts in lignin biodegradation in vivo, and consequently provide an important source for industrial ligninolytic biocatalysts. Recently, it has been shown that some syringyl-type phenolics have potential as industrial co-oxidants or mediators, in laccase-catalyzed modification of lignocellulosic material. We have now studied the effect of such mediators with ligninolytic peroxidases on oxidation of the most recalcitrant lignin model compounds. We found that they are able to enhance the manganese peroxidase (MnP) catalyzed oxidation reactions of small non-phenolic compounds, veratryl alcohol and veratrylglycerol β-guaiacyl ether (adlerol), which are not usually oxidized by manganese peroxidases alone. In these experiments we compared two peroxidases from white-rot fungi, MnP from Phlebia sp. Nf b19 and versatile peroxidase (VP) from Bjerkandera adusta under two oxidation conditions: (i) the Mn(III) initiated mediated oxidation by syringyl compounds and (ii) the system involving MnP-dependent lipid peroxidation, both with production of (hydrogen) peroxides in situ to maintain the peroxidase catalytic cycle. It was found that both peroxidases produced α-carbonyl oxidation product of veratryl alcohol in clearly higher yields in reactions mediated by phenoxy radicals than in lipid-peroxyl radical system. The oxidation of adlerol, on the other hand, was more efficient in lipid-peroxidation-system. VP was more efficient than MnP in the oxidation of veratryl alcohol and showed its lignin peroxidase type activity in the reaction conditions indicated by some cleavage of Cα-Cβ-bond of adlerol. Finally, the mediator assisted oxidation conditions were applied in the oxidation of synthetic lignin (DHP) and the structural analysis of the oxidized polymers showed clear modifications in the polymer outcome, e.g. the oxidation resulted in reduced amount of aliphatic hydroxyls indicated by (31)P NMR.
authors.affiliation: Department of Chemistry, Laboratory of Organic Chemistry, University of Helsinki, Finland. Electronic address: paula.nousiainen@helsinki.fi.
authors.forename: Paula
authors.initials: P
authors.lastname: Nousiainen
authors.affiliation: Department of Chemistry, Laboratory of Organic Chemistry, University of Helsinki, Finland.
authors.forename: Jussi
authors.initials: J
authors.lastname: Kontro
authors.affiliation: Department of Chemistry, Laboratory of Organic Chemistry, University of Helsinki, Finland.
authors.forename: Helmiina
authors.initials: H
authors.lastname: Manner
authors.affiliation: Department of Food and Environmental Sciences, Division of Microbiology and Biotechnology, University of Helsinki, Finland.
authors.forename: Annele
authors.initials: A
authors.lastname: Hatakka
authors.affiliation: Department of Chemistry, Laboratory of Organic Chemistry, University of Helsinki, Finland.
authors.forename: Jussi
authors.initials: J
authors.lastname: Sipilä
mesh_terms: D001487:Basidiomycota / Q000201:enzymology*; D001592:Benzyl Alcohols / Q000378:metabolism; D020536:Enzyme Activators / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000378:metabolism; D008031:Lignin / Q000378:metabolism*; D015227:Lipid Peroxidation; D008345:Manganese / Q000378:metabolism; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000378:metabolism*; D010636:Phenols / Q000378:metabolism*
chemical_list: D001592:Benzyl Alcohols; D020536:Enzyme Activators; D010636:Phenols; D008345:Manganese; D008031:Lignin; D006861:Hydrogen Peroxide; D010544:Peroxidases; C051129:manganese peroxidase; C042197:veratryl alcohol
keywords: Dehydrogenation polymer; Lignin model compounds; Manganese peroxidase; Oxidation; Phenolic mediators; Versatile peroxidase