Heterogeneity of liver microsomal cytochrome P-450: the spectral characterization of reactants with reduced cytochrome P-450.

The aerobic metabolism of benzphetamine by liver microsomes, during a cytochrome P-450-catalyzed mixed-function oxidation reaction, results in the formation of an easily detected spectral complex with an absorption band maximum at 456 nm. Electron paramagnetic resonance studies, as well as studies with the chemical reductant, sodium dithionite, or the oxidant, potassium ferricyanide, indicate that the spectral complex results from the formation of a product adduct with reduced cytochrome P-450. The spectral properties of this product complex of cytochrome P-450 have been compared to those observed with carbon monoxide, metyrapone, and ethylisocyanide. The reaction of these reagents to specific pools of microsomal cytochrome P-450 permits the identification of at least two major and two minor types of cytochrome P-450 in liver microsomes prepared from phenobarbital-treated rats.