Linear dichroism studies of conformations of carcinogen-dna adducts application to covalent complexes derived from the reactions of the two enantiomers of 9, 10-epoxy-9, 10, l l,12-tetrahydrobenzo(E)pyrene with dna

The conformations of the adducts derived from the covalent binding of the two enantiomeric forms of 9, 10-epoxy-9, 10, ll, 12-tetrahydrobenzo(e)pyrene (BePE) with native DNA were investigated by the electric linear dichroism technique. Both enantiomers give rise to two major adducts, one of which appears to be a quasi-intercalative site (I) while the other one is an external binding site (II). While the overall linear dichroism spectra are similar, in the case of the (-) enantiomer there is a greater contribution of site II adducts. These results are markedly different from the ones obtained with the two enantiomers of a”i;’-benzo(a)pyrene- 7, 8-diol-9, 10-epoxide (BaPDE), where the (+) enantiomer gives rise almost exclusively to site II binding, while the (-) enantiomer gives rise to both site I and site II covalent binding. The differences in the heterogeneity of binding between BePE and anfi-BaPDE enantiomers may be due to the absence of hydroxyl groups in BePE which, in the case of BaPDE, are an important factor in determining the stereoselective properties of the covalent binding to double-stranded DNA.