%0 Journal Article %A MAGDI R. I. SOLIMAN %A H. DOUGLAS JOHNSON %A ADELBERT E. WADE %T THE INTERACTIONS OF INDUCERS, INHIBITORS, AND SUBSTRATES OF DRUG-METABOLIZING ENZYMES WITH RAT LIVER CYTOCHROME P-450 %D 1974 %J Drug Metabolism and Disposition %P 87-96 %V 2 %N 1 %X The interactions of drug-metabolizing enzyme inducers, inhibitors, and substrates with washed liver microsomes and a solubilized cytochrome P-450 were investigated using spectral shift techniques. Results indicate that the microsomal enzyme inducer, phenobarbital, binds to microsomes and to soluble cytochrome P-450, is readily displaced by hexobarbital (type I substrate) or aniline (type II substrate), and does not greatly inhibit the interaction of substrates with cytochrome P-450. On the other hand, enzyme inhibitors such as SKF 525-A and 2,4-dichloro-6-phenylphenoxyethylamine (DPEA) bind to microsomes and to soluble cytochrome P-450, are not readily displaced by substrates, and greatly inhibit the interactions of substrates with cytochrome P-450. Barbital, which is not metabolized appreciably, does not bind to microsomes or to soluble cytochrome P-450, nor does it affect the binding of other substances. Aniline and DPEA added to solubilized cytochrome P-450 produced a modified type II spectral shift. The Ks for aniline binding was much higher than that observed with washed microsomes, whereas the Ks for DPEA was identical in both systems. Nicotinamide (a type II compound). SKF 525-A, and hexobarbital (type I compounds) produced typical difference spectra with soluble cytochrome P-450. Puromycin, a potent type II binder to microsomal cytochrome P-450, failed to produce a spectral shift when added to soluble cytochrome P-450. These results suggest that type I and type II binding sites are inter-related, that drug binding affects both sites, and that the extent of mutual displacement between two drugs is governed by their dissociation constants regardless of the type of difference spectrum produced. Copyright © 1974 by The American Society for Pharmacology and Experimental Therapeutics %U https://dmd.aspetjournals.org/content/dmd/2/1/87.full.pdf