Conformations of adducts and kinetics of binding to DNA of the optically pure enantiomers of anti-benzo(a)pyrene diol epoxide

Kinetic flow dichroism studies indicate that the (+) enantiomer of 7 beta, 8 alpha-dihydroxy-9 alpha, 10 alpha-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene physically bound at intercalative-type sites in double-stranded DNA undergoes covalent binding reactions to form adducts at external binding sites. The conformation of the non-covalent complex derived from the (-) stereoisomer is also intercalative in nature, but the conformations of the covalent adducts are heterogeneous and are characterized by both intercalative-type and external conformations. It is suggested that the distinctly higher biological activity of the (+) enantiomer relative to the activity of the (-) enantiomer may be related to the preponderance of 7,8,9-triol benzo(a)pyrene residues covalently linked to deoxyguanine and located at external binding sites in the DNA adducts.