Binding of pyrene to DNA, base sequence specificity and its implication

Solubilization as well as spectral studies of pyrene in natural DNA and synthetic deoxypolynucleotide solutions at neutral pH reveal at least two binding modes. Sites I are predominant in native DNA and in poly(dA-dT): poly(dA-dT) whereas sites II are found with denatured DNA and other polynucleotides such as poly(dA):poly(dT) and three different types of guanine containing copolymers which solubilize pyrene to a lesser extent. Spectral comparison with the covalent adducts of trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10- tetrahydro-benzo(a)pyrene (anti-BPDE) and the physical complexes of its tetraols lead to the suggestion of a base sequence specific binding model for this carcinogenic metabolite to account for the puzzling fact that although its physical binding is predominantly intercalative, the covalent adducts appear not to be intercalated. It is speculated that in neutral solutions, intercalation may have little, if any, to do with the chemical lesion of this metabolite to the guanine base of the DNA and may, on the contrary, provide an efficient pathway for detoxification.