Modelling the transient kinetics of laccase-catalyzed oxidation of four aqueous phenolic substrates at low concentrations

Laccase catalyzes the oxidation of aqueous phenolic substrates by oxygen. To assess the feasibility of using this enzyme to oxidize aqueous phenols at low concentrations, a five-parameter kinetic model was developed based on previous work to predict the transient kinetics of reactions catalyzed by laccase from Trametes versicolor. The model was calibrated against data collected at pH 5.0 and 25 °C for batch reactions of triclosan, cumylphenol, and estradiol. Phenol data arising from an earlier study was used for comparison. The kinetic model, which incorporated a term for enzyme inactivation, accurately simulated the time course of reactions of all four compounds for ranges of substrate and laccase concentrations that spanned up to 5 orders of magnitude. Furthermore, it was demonstrated that the model made accurate predictions far outside of the range of its calibration. The utility of the model for assessing the feasibility of using laccase to catalyze the oxidation of substrates over a range of reactant concentrations was demonstrated. Modelling and experimental results showed that estradiol, cumylphenol and triclosan can be oxidized through the catalytic action of laccase at aqueous substrate concentrations in the micromolar to nanomolar concentration range, while using substantially less enzyme than required for phenol.