The oxidation reaction of pyrogallol red (PR) by H₂O₂ in the presence of lignin peroxidase (LiP) was studied at different concentrations of H₂O₂. Experiments showed that the oxidation products depended on the molar ratio of H₂O₂ to PR, suggesting that the LiP catalyzed oxidation products of PR should be controllable. This phenomenon was caused by the dual roles of H₂O₂, i.e., at lower concentrations it was an activator of LiP, while at higher concentrations it was an inhibitor. Veratryl alcohol (VA) could stimulate the oxidation of PR catalyzed by LiP, especially at higher molar ratios of H₂O₂ to PR, however, PR inhibited the LiP catalyzed oxidation of VA. The inhibition should be used to explain a phenomenon that no veratryl alcohol activity was detected in the culture of white rot fungi where dye was effectively decolorized. Kinetics analysis suggested that VA should accelerate the conversion of LiP(II) and/or LiP(III) to LiP, and therefore the catalytic cycle of LiP. Indirect oxidation of PR by the veratryl alcohol cationic radical was also contributed to the increase in the oxidation rate of PR.

Key words: lignin peroxidase, pyrogallol red, oxidative degradation, veratryl alcohol, inhibition