Peroxyl radicals are potential agents of lignin biodegradation

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 li kely to be relevant to ligninolysis in sound wood, where enzymes cannot pen etrate, only if it employs a small, diffusible lipid radical as the proxima l oxidant of lignin, Here we show that a non-phenolic beta-O-4-linked ligni n model dimer was oxidized to products indicative of hydrogen abstraction a nd electron transfer by three different peroxyl radical-generating systems: (a) MnP/Mn(II)/linoleic acid, (b) arachidonic acid in which peroxidation w as initiated by a small amount of H2O2/Fe(II), and (c) the thermolysis in a ir of either 4,4'-azobis(4-cyanovaleric acid) or 2,2'-azobis(2-methylpropio namidine) dihydrochloride. Some quantitative differences in the product dis tributions were found, but these were attributable to the presence of elect ron-withdrawing substituents on the peroxyl radicals derived from azo precu rsors. Our results introduce a new hypothesis: that biogenic peroxyl radica ls may be agents of lignin biodegradation, (C) 1999 Federation of European Biochemical Societies.