Destruction of cytochrome P-450 by allylisopropylacetamide is a suicidal process

Abstract

The destruction of cytochrome P-450 by allylisopropylacetamide (2-isopropyl-4-pentenamide) in microsomes from phenobarbital-pretreated rats has been shown to require oxygen, to be inhibited by NADP through inhibition of cytochrome P-450 reductase, and to be slightly stimulated by NADH. Glutathione (1 m m) does not inhibit destruction, but methyl 4,5-epoxy-2-isopropylpentanoate (5 m m), an analog of the epoxide of allylisopropylacetamide, does. The inactivation of cytochrome P-450 is both time dependent and saturable, although no more than approximately 40% of the microsomal enzyme appears to be normally destructible. However, mechanical perturbation of the microsomal suspension by rehomogenization initiates renewed destruction. Kinetic analysis shows that the destructive process is pseudo-first-order, with an apparent inactivation rate constant of 1.4 × 10 −3 s −1 and an apparent K m of 1.14 m m. Approximately 230 molecules of substrate are turned over for each destructive event. These results, in conjunction with previously reported data, clearly and unambiguously establish that inactivation of cytochrome P-450 by allylisopropylacetamide is a suicidal process.