The extracellular enzyme manganese peroxidase is believed to degrade lignin by a hydrogen peroxide-dependent oxidation of Mn(II) to the reactive species Mn(III) that attacks the lignin. However, Mn(III) is not able to directly oxidise the non-phenolic lignin structures that predominate in native lignin. 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 behind this effect is demethoxylation and/or hydroxylation, i.e. conversion of a nonphenolic structure to a phenolic one, mediated by hydroxyl radicals generated by cellobiose dehydrogenase. This suggests that cellobiose dehydrogenase and manganese peroxidase may act in an extracellular pathway in fungal lignin biodegradation. Analytical techniques used in this paper are reverse-phase highpressure liquid chromatography, gas chromatography connected to mass spectroscopy and UV-visible spectroscopy. ß

This review concerns basic research on cellulases and cellulose-specific carbohydrate-binding modules (CBMs). As a background, glycosyl hydrolases are also briefly reviewed. The nomenclature of cellulases and CBMs is discussed. The main cellulase-producing organisms and their cellulases are described. Synergy, enantioseparation, cellulases in plants, cellulosomes, cellulases and CBMs as analytical tools and cellulase-like enzymes are also briefly reviewed.

Bmax, maximum binding capacity; BMCC, bacterial microcrystalline cellulose; CBH, cellobiohydrolase; CBM, carbohydrate-binding module; CBM-FITC, carbohydrate-binding module labelled with fluorescein isothiocyanate; CBM1, carbohydrate-binding module of family 1; FITC, fluorescein isothiocyanate; KD, dissociation constant; RP-HPLC, reversed phase HPLC; S1-S3, Secondary cell wall layers 1-3.