Evaluation of oxidative enzymes for efficient oxidation of aniline and phenolic pollutants

Tyrosinases, laccases, and peroxidases are three important groups of oxidative enzymes. A characteristic feature of these enzymes is their ability for the oxidation of aniline and phenolic compounds. Literature review reveals some overlap between the organic substrates of these enzymes, but how exactly they are different and how much they have in common from both substrate structure and rate of oxidation points of views. Can they complete functional efficiency of each other when co-immobilized in a multi-enzymes system? To address these questions, edible mushroom (Agaricus bisporus) tyrosinase, Neurospora crassa laccase, and horseradish peroxidase were examined for the oxidation of azo derivatives of anilines and phenols. These substances were selected because their enzymatic degradation is of interest to environmentalists and can be followed spectrophotometrically. Experiments showed that tyrosinase and laccase had limitations in oxidizing these substances, especially anilines, while peroxidase oxidized all the selected compounds. However, substrates carrying electron-withdrawing substituents had slower oxidation. Co-immobilization of tyrosinase and laccase would be effective against phenolic compounds, but phenols oxidation proceeds faster (between 100 and 500 times) if peroxidase and H₂O₂ are used. Combination of peroxidase and H₂O₂, instead of co-immobilization of tyrosinase, laccase, and peroxidase, seems to be more promising for the removal of organic pollutants from contaminated water resources.