pH-dependent interaction of microsomal cytochrome P-450 with substrates. I. Effect of pH upon the interaction of exogenous substrates with membrane-bound cytochrome P-450.
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.
D000814:Aniline Compounds / Q000378:metabolism; D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D000431:Ethanol / Q000378:metabolism; D005043:Etiocholanolone / Q000031:analogs & derivatives / Q000378:metabolism; D006591:Hexobarbital / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013053:Spectrophotometry
D000814:Aniline Compounds; D000431:Ethanol; C006576:androstane-3,17-dione; D003577:Cytochrome P-450 Enzyme System; D005043:Etiocholanolone; D006591:Hexobarbital; C023650:aniline