KINETICS OF SUBSTRATE REACTION IN THE COURSE OF HYDROPEROXIDE-MEDIATED INACTIVATION OF CYTOCHROME-P450 1A1

A schematic kinetic model is proposed for the hydroperoxide-mediated s ubstrate reaction and cytochrome P450 inactivation. From the model, th e relationships between the product concentration at infinite time (P- infinity), the apparent rate constant of P450 inactivation (A), and th e substrate concentrations are predicted, and the predictions were exp erimentally examined. The reciprocal of P-infinity is proportional to the reciprocal of the substrate concentration in both CuOOH- and H2O2- supported substrate reactions. The reciprocal of P-infinity is proport ional to cumene hydroperoxide (CuOOH) concentration, but P-infinity is independent of H2O2 concentration, indicating different effects of Cu OOH and H2O2 in P450 inactivation. The apparent rate constant (A) is p roportional to the reciprocal of the substrate concentrations, suggest ing substrate protection of P450 from hydroperoxide inactivation. The model also suggests that a second CuOOH molecule may compete with subs trate for binding to the P450 substrate binding site. Simulated kineti cs of production formation vs time are quite consistent with the exper imental kinetics.