EFFECT OF SUPEROXIDE AND SUPEROXIDE-DISMUTASE ON LIGNIN PEROXIDASE-CATALYZED VERATRYL ALCOHOL OXIDATION

We have shown that superoxide (O-2(-)) is produced during the oxidatio n of veratryl alcohol by lignin peroxidase (LiP) by the reaction of th e veratryl alcohol cation radical with hydrogen peroxide (D. B. Barr, M. M. Shah, and S. D. Aust, 1993, J. Biol. Chem. 268, 241-244). Compou nd III, an inactive form of peroxidases can be formed by reaction of t he ferric enzyme with O-2(-). We therefore studied the effects of OI a nd superoxide dismutase (SOD) on the veratryl alcohol oxidase activity of LiP. SOD enhanced the rate of veratryl alcohol oxidation by LiP an d veratryl alcohol oxidation was inhibited by the addition of KO2. Upo n the addition of KO2, activity was also preceded by a lag period. Und er steady-state turnover conditions (i.e., for veratryl alcohol oxidat ion), the addition of KO2 resulted in the formation of LiP compound II I. Compound II of LiP was observed following a time period that correl ated with the lag prior to veratryl aldehyde formation. The extent of the lag preceding veratryl aldehyde formation increased with increasin g concentrations of KO2 and decreased with increasing concentrations o f veratryl alcohol. It was postulated that during the lag period the v eratryl alcohol cation radical reacted with compound III to regenerate the native enzyme. In this process the veratryl alcohol cation radica l was reduced to veratryl alcohol, and thus, no veratryl aldehyde was detected during the lag period. (C) 1994 Academic Press, Inc.