INACTIVATION OF LIGNIN PEROXIDASE BY HYDROGEN-PEROXIDE DURING THE OXIDATION OF PHENOLS

The oxidation of phenols by lignin peroxidase (LiP) was characterized by a rapid decrease in enzyme activity. The initial oxidation rate of phenol decreased at moderately high (i.e., 400 mu M) concentrations of H2O2 Similar results were obtained with several phenols. However, LiP was not inactivated during the oxidation of veratryl alcohol (VA). Th e apparent second-order rate constants for the reaction of compound II with phenol and VA at pH 3.5 were very similar, about 2.1 X 10(4) and 4.7 X 10(4) M(-1) s(-1), respectively. However, unlike VA, phenols co uld not convert compound III back to ferric enzyme. The visible absorp tion spectra of compound II and III were observed during oxidation of VA and phenols, respectively. These results suggest that the inactivat ion of LiP during the oxidation of phenols was mainly due to the accum ulation of compound III, which was attributed to the inability of phen ols or phenoxyl radicals to revert compound III to ferric enzyme. All of these results also suggested that the inactivation mechanism of LiP during oxidation of phenols was different from that during oxidation of anisyl alcohol, since anisyl alcohol was neither a substrate of com pound II nor could it revert compound III [K. Valli et al. (1990) Bioc hemistry 29, 8535-8539 and R. S. Koduri and M. Tien (1994) Biochemistr y 33, 4225-4230]. (C) 1995 Academic Press, Inc.