DEGRADATION OF NONPHENOLIC BETA-O-4 TYPE LIGNIN CARBOHYDRATE COMPLEX MODEL COMPOUNDS BY LIGNIN PEROXIDASE FROM THE WHITE-ROT FUNGUS PHANEROCHAETE-CHRYSOSPORIUM

Non-phenolic beta-O-4 type lignin carbohydrate complex (LCC) model com pounds (1) in erythro- and threo-forms were oxidized by lignin peroxid ase (LiP) from the white-rot fungus Phanerochaete chrysosporium Burds. 4-O-Ethylvanillin produced as a result of the enzymatic C-alpha-C-bet a bond and C-alpha-ether bond eleavages of 1 was determined by gas chr omatography-mass spectrometry. The initial reaction rates of formation of the cleavage product from the diastereomeric isomers of 1 were com pared with those of the diastereomeric beta-O-4 model compounds (2), v eratryl alcohol xyloside (3), and veratryl alcohol (4). The reaction r ates decreased in the following order: 4>3 approximate to 2>1. The amo unts of the benzaldehyde products produced from LCC model substrate 1 were decreased by addition of oxalate into the LiP system. However, ox alate added was concomitantly decomposed to carbon dioxide. It is note worthy that, in contrast to the smaller reaction rates of the formatio n of benzaldehydes from the LCC model substrates (1 and 3), the LCC mo del substrates were more effective than the corresponding non-sugar an alogs (2 and 4) in decomposing the oxalate. The inhibition of the form ation of the cleaved product by oxalate was explained as such that the cation radical intermediates of LCC model substrates formed by the on e-electron oxidation oxidized oxalate to CO2, and was concomitantly re duced back to the substrates level.