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pH-dependent interaction of microsomal cytochromeP-450 with substrates. I. Effect of pH upon the interaction of exogenous substrates with membrane-bound cytochromeP-450

Chemico-Biological Interactions
Publication Date
DOI: 10.1016/0009-2797(81)90175-7


Abstract 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 (ΔA max) increased with increasing the pH, while the spectral dissociation constant ( K s) 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.

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