Proton NMR study of the interaction of benzo(a)pyrene with rat liver microsomal cytochrome P-450

1H nuclear magnetic resonance longitudinal relaxation time (T1) measurements were used to study the interaction of 1,3,6-H-benzo(a)pyrene (1,3,6-H-BaP) with microsomal cytochrome P-450 from livers of phenobarbital- and beta-naphthoflavone-treated rats. Upon addition of various amounts of cytochrome P-450 to solutions of BaP, the T1 values for the three BaP protons decreased. When the hemeprotein was converted to its carbon monoxyferrous derivative in the presence of BaP, the T1 values of the BaP protons increased. The paramagnetic contributions to the observed T1 values were calculated and resulted in distance estimates of greater than 6 A for the three BaP protons in both cases.