Kinetics of soluble and immobilized horseradish peroxidase-mediated oxidation of phenolic compounds

Horseradish peroxidase (HRP) is an intensively used enzyme in biochemical and medical analyses. It is also proposed for wastewater processing. A bioprocess monitoring method based on co-oxidation of phenol-4-sulfonic acid (PSA) and 4-aminoantipyrine (4-AAP) by immobilized HRP was recently described. In this work a mathematical model that describes a set of reactions that occur in phenol/4-AAP/HRP system upon addition of hydrogen peroxide has been used for the evaluation of the PSA/4-AAP/HRP system by estimating and comparing the apparent kinetic parameters for different reaction systems. The parameters thus obtained were compared for three phenolic compounds (phenol, p-chlorophenol and PSA) and for immobilized HRP in the PSA/4-AAP system. The model was able to capture distinctive features of the system, such as increasing initial reaction rates for increasing concentrations of H2O2; a plateau upon reactant exhaustion; and decreasing initial reaction rates at high H2O2 concentrations. The performance of the PSA/4-AAP/HRP system expressed as the initial reaction rate was found to be less than 12% that of the conventional phenol/4-AAP/HRP system. The estimated parameters for the kinetic model provided the basis for the mechanistic explanation for the lower performance observed in the system containing PSA.