Kinetic analysis of lignin peroxidase: explanation for the mediation phenomenon by veratryl alcohol.

We investigated the role of veratryl alcohol in lignin peroxidase-catalyzed oxidation of anisyl alcohol with pre-steady-state and steady-state kinetic methods. Veratryl alcohol has been proposed to act as a redox mediator for substrates that are not directly oxidized by the enzyme. Alternatively, its mediation activity has also been attributed to its ability to protect the enzyme from H2O2-dependent inactivation. As previously reported, veratryl alcohol was able to stimulate the oxidation of anisyl alcohol. However, this stimulation is not due to mediation or protection of the enzyme. The stimulation can be attributed to the relative reactivity of anisyl alcohol with compounds I and II of lignin peroxidase. We found that anisyl alcohol reacts with compound I, but not with compound II. Therefore, inclusion of veratryl alcohol or another substrate, which reacts with compound II, is essential for completion of the catalytic cycle.