USE OF COMPETITIVE INHIBITION OF SUBSTRATE-BINDING TO CYTOCHROME P450 IN DETERMINATION OF SPECTRAL DISSOCIATION-CONSTANTS FOR SUBSTRATES WITH MULTIPLE TYPES OF BINDING, AS ILLUSTRATED WITH 1-BUTANOL

A method is described, which allows (a) the detection of competitive inhibition of binding to cytochrome P450 between two substrates which elicit the same type of spectral change, and (b) the estimation of dissociation constants for one type of spectral binding of a substrate which exhibits multiple interaction with cytochrome P450. This method was used to investigate the interaction of 1-butanol with the type I binding site of cytochrome P450 in liver microsomes from female mice. 1-Butanol was found to competitively inhibit the binding of ethylmorphine, and has an apparent dissociation constant for type I binding of 30 mM. © 1979.