DEPOLYMERIZATION OF A SYNTHETIC LIGNIN INVITRO BY LIGNIN PEROXIDASE

Lignin peroxidases, although believed to catalyze the first step of fungal ligninolysis in vivo, have never been demonstrated to depolymerize unmodified lignin in vitro. It is shown here that crude Phanerochaete chrysosporium lignin peroxidase, in the presence of H2O2 and veratryl alcohol, will catalyze the partial fragmentationof a C-14-beta-labeled synthetic hardwood lignin in Na acetate (pH 4.5)/N,N-dimethylformamide, 9:1. Gel permeation chromatography of the treated lignin demonstrated that fragments with molecular weights as low as ca. 170 were products of this reaction. Determinations of total C-14 showed that 25-30% of the radiolabel originally present was converted to volatile products during enzymatic oxidation. No evidence for depolymerization was found in control reactions from which lignin peroxidase or H2O2 had been omitted, and little change in the lignin was discernible in reactions that lacked veratryl alcohol.