Kinetics of Substrate Reaction in the Course of Hydroperoxide-Mediated Inactivation of Cytochrome P450 1A1

Abstract

A schematic kinetic model is proposed for the hydroperoxide-mediated substrate reaction and cytochrome P450 inactivation. From the model, the relationships between the product concentration at infinite time (P infinity), the apparent rate constant of P450 inactivation (A), and the substrate concentrations are predicted, and the predictions were experimentally 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 proportional to cumene hydroperoxide (CuOOH) concentration, but P infinity is independent of H2O2 concentration, indicating different effects of CuOOH and H2O2 in P450 inactivation. The apparent rate constant (A) is proportional to the reciprocal of the substrate concentrations, suggesting substrate protection of P450 from hydroperoxide inactivation. The model also suggests that a second CuOOH molecule may compete with substrate for binding to the P450 substrate binding site. Simulated kinetics of production formation vs time are quite consistent with the experimental kinetics.

CYP2D6 Allelic Variants *34, *17-2, *17-3, and *53 and a Thr309Ala Mutant Display Altered Kinetics and NADPH Coupling in Metabolism of Bufuralol and Dextromethorphan and Altered Susceptibility to Inactivation by SCH 66712

“…6). In addition, we observed decreased enzyme activity in reactions with CuOOH (data not shown), consistent with inactivation of CYP2D6 by CuOOH, as has been reported with other P450s such as 2B1, 3A4, 1A1, and so forth (Yao et al, 1993;Yu et al, 1996;He et al, 1998). Coupling of NADPH Consumption to Substrate Metabolism.…”

Subsequent Products After Antioxidant Actions of β-Carotene and α-Tocopherol Have NoSalmonellaMutagenicity

“…Both CYP and N-hydroxy-Trp-P-2 have been recognized to be sensitive to reactive oxygen species such as hydroperoxides. 41,42) These hydroperoxides probably inactivated S9 enzymes and W or decomposed the activated Trp-P-2.…”