title: Peroxyl radicals are potential agents of lignin biodegradation.
abstract: Past work has shown that the extracellular manganese-dependent peroxidases (MnPs) of ligninolytic fungi degrade the principal non-phenolic structures of lignin when they peroxidize unsaturated fatty acids. This reaction is likely to be relevant to ligninolysis in sound wood, where enzymes cannot penetrate, only if it employs a small, diffusible lipid radical as the proximal oxidant of lignin. Here we show that a non-phenolic beta-O-4-linked lignin model dimer was oxidized to products indicative of hydrogen abstraction and electron transfer by three different peroxyl radical-generating systems: (a) MnP/Mn(II)/linoleic acid, (b) arachidonic acid in which peroxidation was initiated by a small amount of H(2)O(2)/Fe(II), and (c) the thermolysis in air of either 4,4'-azobis(4-cyanovaleric acid) or 2,2'-azobis(2-methylpropionamidine) dihydrochloride. Some quantitative differences in the product distributions were found, but these were attributable to the presence of electron-withdrawing substituents on the peroxyl radicals derived from azo precursors. Our results introduce a new hypothesis: that biogenic peroxyl radicals may be agents of lignin biodegradation.
authors.affiliation: Institute for Microbial and Biochemical Technology, USDA Forest Products Laboratory, Madison, WI 53705, USA.
authors.forename: A N
authors.initials: AN
authors.lastname: Kapich
authors.forename: K A
authors.initials: KA
authors.lastname: Jensen
authors.forename: K E
authors.initials: KE
authors.lastname: Hammel
mesh_terms: D001230:Aspergillus / Q000201:enzymology; D001673:Biodegradation, Environmental; D002851:Chromatography, High Pressure Liquid; D008401:Gas Chromatography-Mass Spectrometry; D008031:Lignin / Q000378:metabolism*; D008956:Models, Chemical; D010544:Peroxidases / Q000378:metabolism*; D020075:Phanerochaete / Q000201:enzymology; D011994:Recombinant Proteins / Q000378:metabolism; D013997:Time Factors
chemical_list: D011994:Recombinant Proteins; D008031:Lignin; D010544:Peroxidases; C051129:manganese peroxidase