Do the extracellular enzymes cellobiose dehydrogenase and manganese peroxidase form a pathway in lignin biodegradation?

The extracellular enzyme manganese peroxidase is believed to degrade lignin by a hydrogen peroxide-dependent oxidation of Mn(II) to the reactive speci es Mn(III) that attacks the lignin, However, Mn(III) is not able to directl y oxidise the non-phenolic lignin structures that predominate in native lig nin, We show here that pretreatment of a non-phenolic lignin model compound with another extracellular fungal enzyme, cellobiose dehydrogenase, allows the manganese peroxidase system to oxidise this molecule. The mechanism be hind this effect is demethoxylation and/or hydroxylation, i.e. conversion o f a nonphenolic structure to a phenolic one, mediated by hydroxyl radicals generated by cellobiose dehydrogenase, This suggests that cellobiose dehydr ogenase and manganese peroxidase may act in an extracellular pathway in fun gal lignin biodegradation, Analytical techniques used in this paper are rev erse-phase high-pressure liquid chromatography, gas chromatography connecte d to mass spectroscopy and UV-visible spectroscopy. (C) 2000 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All righ ts reserved.