Veratryl alcohol-mediated indirect oxidation of pentachlorophenol by lignin peroxidase

The oxidation of pentachlorophenol (PCP) by lignin peroxidase (LiP) is characterized by a rapid loss of activity during which time the enzyme is quickly converted to compound III, an inactive form of the enzyme. We investigated the indirect oxidation of PCP by LiP using veratryl alcohol (VA) as a mediator. The oxidation of VA to veratryl aldehyde by LiP was inhibited by PCP. Inhibition was characterized by lag period followed by the same rate of VA oxidation. The lag period before VA oxidation was increased by increasing concentrations of PCP. During the lag period, PCP was oxidized and the extent of PCP oxidation increased with increasing concentrations of VA. The enzyme stayed as compound II during PCP oxidation in the presence of VA, suggesting that VA has a protective role in the LiP catalysis. The kinetics of PCP oxidation in the presence of VA were similar to those of VA oxidation. All these results suggest that PCP is oxidized indirectly via the veratryl alcohol cation radical. 2,3,5,6-Tetrachloro-p-benzoquinone was a stoichiometric product during PCP oxidation in both the presence and the absence of VA. An equivalent amount of inorganic chloride was formed by oxidative 4-dechlorination during PCP oxidation in the presence of VA. The increase in the rate and extent of PCP oxidation by VA results from mediation of PCP oxidation and reversion of inactive compound III to native enzyme, both by the veratryl alcohol cation radical.