androstane-3-17-dione--(5alpha)-isomer and aniline

The interaction of microsomal membrane-bound cytochrome P-450 with substrates was studied spectrophotometrically at various pH-values. The binding of type I compounds, hexobarbital and androstanedione, with cytochrome P-450, as determined by the magnitude of the type I spectral change of microsomes, was markedly enhanced at alkaline pH compared to that at acid pH. The pH-dependent spectral change could be reversed by changing the pH. The maximum absorption change (delta Amax) increased with increasing the pH, while the spectral dissociation constant (Ks) decreased. A similar pH-dependent binding reaction was also observed using a non-dissociative type I compound, cyclohexane. On the contrary, the absorbance magnitude between peak and trough in the aniline- or alcohol-induced difference spectrum of microsomes was enhanced by decreasing the pH, indicating easy complex formation of type II and reverse type I compounds with cytochrome P-450 in the acid rather than the alkaline region.

Topics: Aniline Compounds; Animals; Cytochrome P-450 Enzyme System; Ethanol; Etiocholanolone; Hexobarbital; Hydrogen-Ion Concentration; Kinetics; Male; Microsomes, Liver; Rats; Rats, Inbred Strains; Spectrophotometry