The cytochrome P450s metabolize a wide variety of xenobiotic and endogenous compounds. Biochemical, biophysical and computational approaches were applied to examine the structure-function relationships which govern the interactions of P450s with substrates, membrane lipids and microsomal proteins. The kinetics of CO binding to P450 was used as a probe of P450 conformation and dynamics, to define the effect of various drugs and carcinogens on P450s. Of particular interest is the finding that human P450 3A4, which metabolizes a variety of structurally dissimilar drugs, can assume alternate conformations. In contrast, the alcohol-inducible and carcinogen-metabolizing P450 2E1, which metabolizes a more narrow range of substrates, is more conformationally homogeneous. Ethanol, which stabilizes this P450, was found to reduce the CO binding rate and modulate its substrate interactions.We employed molecular modeling to generate a three dimensional structure of human P450 1A2. The active site structure was consistent with the relative inhibitory potencies of several flavonoids as well as three class 1B antiarrhythmics which inhibit this P450. We are currently employing this model to discover new P450 1A2 inhibitors. - Carcinogen metabolism, Computational methods, Cyotochrome P, 0, Drug Metabolism, Homology modeling, protein structure, Drug Metabolism, - Neither Human Subjects nor Human Tissues