Effect of superoxide and superoxide dismutase on lignin peroxidase-catalyzed veratryl alcohol oxidation.

We have shown that superoxide (O2.-) is produced during the oxidation of veratryl alcohol by lignin peroxidase (LiP) by the reaction of the veratryl alcohol cation radical with hydrogen peroxide (D. B. Barr, M. M. Shah, and S. D. Aust, 1993, J. Biol. Chem. 268, 241-244). Compound III, an inactive form of peroxidases can be formed by reaction of the ferric enzyme with O2.-. We therefore studied the effects of O2.- and superoxide dismutase (SOD) on the veratryl alcohol oxidase activity of LiP. SOD enhanced the rate of veratryl alcohol oxidation by LiP and veratryl alcohol oxidation was inhibited by the addition of KO2. Upon the addition of KO2, activity was also preceded by a lag period. Under steady-state turnover conditions (i.e., for veratryl alcohol oxidation), the addition of KO2 resulted in the formation of LiP compound III. Compound II of LiP was observed following a time period that correlated with the lag prior to veratryl aldehyde formation. The extent of the lag preceding veratryl aldehyde formation increased with increasing concentrations of KO2 and decreased with increasing concentrations of veratryl alcohol. It was postulated that during the lag period the veratryl alcohol cation radical reacted with compound III to regenerate the native enzyme. In this process the veratryl alcohol cation radical was reduced to veratryl alcohol, and thus, no veratryl aldehyde was detected during the lag period.