Interaction between ellagic acid and calf thymus DNA studied with flow linear dichroism UV-VIS spectroscopy

The interaction between ellagic acid and DNA has been characterized with re spect to the geometry of the ellagic acid-DNA complex, and the active form of ellagic acid has been identified. Optical spectroscopic methods have bee n employed to examine the interaction between double-stranded calf thymus D NA and ellagic acid in low-ionic-strength aqueous solutions at pH values of 5.5, 7.0, and 8.8. Based on normal absorption titration and how linear dic hroism experiments, it is confirmed that the neutral form of ellagic acid p resent at pH 5.5 binds to double-stranded DNA. It is found that the plane o f the ellagic acid chromophore is positioned at an angle relative to the DN A helix axis, which is in accordance with intercalation of ellagic acid in DNA. It is concluded that at higher values of pH no or a very limited amoun t of ellagic acid binds to DNA. These results prove that the direct interac tion between ellagic acid and DNA must be taken into account when evaluatin g the mechanism underlying the observed biological effects of this plant ph enol. (C) 1999 Academic Press.