Kinetic study of the transient phase of a second-order chemical reaction coupled to an enzymic step: application to the oxidation of chlorpromazine by peroxidase-hydrogen peroxide.

Peroxidase-hydrogen peroxide assay with chlorpromazine as substrate was kinetically analysed as a system of a chemical reaction of second-order coupled to an enzymic step. This system follows a mechanism defined as enzymic-chemical second-order with substrate regeneration (EzC2-S.R.). The rate constant of the chemical step and the enzymic reaction rate have been evaluated from the progress curves of the accumulation of the cation radical intermediate (CPZ+.) and the non-linear regression analysis of these curves. The presteady-state rate of the accumulation of the cation radical intermediate (CPZ+.) and the level of the steady-state plateau were dependent on the rate constant of the chemical step and the enzyme concentration. The rate constant of the chemical reaction was dependent on the proton, buffer and chlorpromazine concentrations.