VERATRYL ALCOHOL-MEDIATED INDIRECT OXIDATION OF PHENOL BY LIGNIN PEROXIDASE

Veratryl alcohol (VA) oxidation by lignin peroxidase (LiP) was inhibit ed by phenol. The enzyme was quickly converted to compound III, an ina ctive intermediate. However, as soon as VA began to be oxidized, compo und II was observed. The lag period before VA oxidation was affected b y the concentrations of both phenol and VA. The addition of VA increas ed the extent of phenol oxidation and the kinetics of phenol oxidation in the presence of VA were similar to those of VA oxidation. Previous ly it was shown that the VA cation radical (VA(.+)) was responsible fo r the conversion of compound III back to ferric enzyme [D. P. Barr and S. D. Aust (1994) Arch. Biochem. Biophys. 312, 511-515]. Here we obse rved that the reversion of compound III to active ferric enzyme in the presence of VA was prevented by addition of phenol, suggesting that V A(.+) oxidizes phenol to phenoxyl radical. This hypothesis was also su pported by the observation that O-2 consumption during VA oxidation wa s inhibited by the addition of phenol. All of these results suggested that VA was first oxidized by LiP to VA(.+) and then it oxidized pheno l to phenoxyl radical while VA(.+) was reduced back to VA. Activity wa s lost as compound III accumulated since the VA(.+) was consumed by th e oxidation of phenol. After all of the phenol was oxidized, VA(.+) be came available to convert compound III back to ferric enzyme. (C) 1995 Academic Press, Inc.