A model of the transient kinetics of laccase-catalyzed oxidation of phenol at micromolar concentrations

• The transient kinetics of the laccase-catalyzed oxidation of aqueous phenol was modeled.
• Phenol concentrations were in the micromolar to sub-micromolar range.
• Inactivation of the enzyme during the oxidation reaction was insignificant.
• The 4-parameter model was validated over wide ranges of phenol and enzyme concentrations.
• The model could be simplified to a 3 parameter model with only minor loss in accuracy.

Oxidoreductase enzymes have the potential to be used to catalyze the oxidation of aromatic trace contaminants in wastewaters. The feasibility of this approach can be explored by modeling transient kinetics, particularly in the low substrate concentration range, where the model may be used to predict the quantity of enzyme and time required to achieve a particular level of conversion of a target compound. Laccase from Trametes versicolor was selected as a candidate enzyme due to its wide substrate specificity and its use of molecular oxygen as an oxidant. Phenol was selected as a target substrate. A four-parameter kinetic model was developed based on the known reactions of laccase. The model was applied to 30 sets of data collected from batch reactions conducted at pH 5 and 25 °C over a three hour period. Initial phenol concentrations ranged from 0.5 to 50 μM and applied enzyme concentrations ranged from 0.12 to 2.5 μM. The model demonstrated its utility for predicting the quantities of enzyme and reaction times required to achieve desired levels of oxidation of phenol for varying initial concentrations. A three-parameter simplified version of the kinetic model was also developed to facilitate calibration and mathematical solution of its equations.