EVIDENCE FOR VERATRYL ALCOHOL AS A REDOX MEDIATOR IN LIGNIN PEROXIDASE-CATALYZED OXIDATION

We have examined the hypothesis that veratryl alcohol (VA) may act as a redox mediator in Lignin peroxidase (LiP)-catalyzed oxidations. The oxidation of chlorpromazine (CPZ) by this system was used to evaluate this hypothesis. Chlorpromazine can be oxidized by one electron to for m a stable cation radical (CPZ(.+)). This cation radical can be oxidiz ed by another electron to the sulfoxide (CPZSO). These oxidation steps are easily monitored, making CPZ a useful chemical to investigate red ox mediation by VA. Lignin peroxidase oxidized CPZ to CPZ(.+) whether or not VA was present. The inclusion of VA, however, stimulated CPZ ox idation to CPZ(.+) and subsequent oxidation of CPZ(.+) to CPZSO. In th e absence of VA, the initial rates of CPZ oxidation by LiP were CPZ co ncentration-dependent. However, when saturating concentrations of VA w ere added, the oxidation of CPZ and CPZ(.+) became independent of CPZ concentration. When the oxidation of VA to veratryl aldehyde was conce ntrations of CPZ produced a lag in veratryl aldehyde appearance propor tional to the concentration of CPZ. Conversely, increasing concentrati ons of VA never inhibited CPZ oxidation. Transient-state kinetic studi es indicated that both VA and CPZ reduced the compound I and compound II forms of LiP. However, when saturating concentrations of VA were ut ilized, LiP turnover was independent of CPZ concentration. We suggest these data demonstrate that VA may act as a redox mediator for the ind irect oxidation of compounds by LiP.