Kinetic Flow Dichroism Study of Conformational Changes in Supercoiled DNA Induced by Ethidium Bromide and Noncovalent and Covalent Binding of Benzo(a)pyrene Diol Epoxide

摘要

The dynamic conformational changes due to the noncovalent intercalative binding of ethidium bromide and racemic (BPDE), and the covalent binding of BPDE to supercoiled phiX174 DNA, have been studied by gel electrophoresis and a novel application of a kinetic flow linear dichroism technique. The kinetic flow dichromism spectra indicate that the noncovalent BPDE-DNA complexes are intercalative in nature, while the covalent adducts are characterized by a very different conformation in which the long axes of the pyrenyl residues are oriented at a large angle with respect to the average orientation of the planes of the DNA bases. These results suggest that conformations of carcinogen-DNA adducts, other than intercalative ones, can causes the unwinding of superhelical DNA. The flow dichroism method is capable of following kinetically changes not only in the shapes, and thus conformations of supercoiled DNA molecules, but also in the conformations of drugs or carcinogens causing these changes. Reprints.