Fluorescence energy transfer measurements of the complexes of aflatoxin B1 and cytochromes P-450

Abstract The distances between the heme of cytochrome P-450 and the substrate, aflatoxin B 1 , in the complex of aflatoxin B 1 and each of two species of cytochrome P-450 were determined by fluorescence energy transfer measurements. Cytochromes P-450 used were cytochrome P-450 I-d and cytochrome P-450 II-a prepared from hepatic microsomes of polychlorinated biphenyl-treated rats; the main metabolic products of aflatoxin B 1 were aflatoxin Q 1 and aflatoxin M 1 , respectively. The distances between the heme and the substrate were calculated to be 6.9nm and 4.7nm in cytochrome P-450 I-d and cytochrome P-450 II-a, respectively. The results suggest that the difference in the metabolic products of aflatoxin B 1 is due to the difference in the conformation of the enzyme-substrate complexes.