Steady-state oxidation model by horseradish peroxidase for the estimation of the non-inactivation zone in the enzymatic removal of pentachlorophenol

Abstract

A theoretical model for the rate of oxidation of pentachlorophenol (PCP) catalyzed by horseradish peroxidase (HRP), was investigated to account for the influence of hydrogen peroxide (H 2O 2) concentration on the catalytic activity. To evaluate the maximum allowable H 2O 2 concentration, a relatively simple steady-state model was developed based on the Ping-Pong Bi-Bi mechanism considering the effect of excess H 2O 2. Several sets of experimental data obtained from batch reactions using an equimolar concentration of H 2O 2 and PCP were used to estimate the kinetic parameters by a nonlinear regression method. The model profiles acquired using the estimated parameters were in good agreement with experimental data at different initial enzyme and substrate concentrations. The best-fitted parameters were used to predict the initial rate of the enzyme reaction. The model prediction was coincident with the experimental results of other studies, indicating that the proposed model could be used for the optimization of reaction conditions. The maximum allowable H 2O 2 concentration to prevent H 2O 2 inhibition was calculated from the proposed model equation: [H 2O 2] 0,max = K m H 2O 2 K i [ PCP] 0 K m PCP +[ PCP] 0 . Using this equation, a curve depicting the non-inactivation zone for the two substrates (hydrogen peroxide and PCP) was plotted and it could be used for experimental design and optimal process operation. To minimize enzyme inactivation by H 2O 2, it was determined that the concentration of H 2O 2 should be lower than 2.78 mM, regardless of the stoichiometric ratio.