Aristololactam-beta-D-glucoside. A new DNA binding monofunctional intercalating alkaloid.

The binding of aristololactam-beta-D-glucoside to DNA is characterized by hypochromism and bathochromism in the absorption band, quenching of the fluorescence intensity, increase in the positive and negative ellipticity of DNA, enhancement of thermal transition temperature, sign and magnitude of thermodynamic parameters, increase of the contour length of sonicated rod-like DNA and induction of the unwinding-rewinding process of covalently closed superhelical DNA. Binding parameters determined from absorbance and fluorescence titration by Scatchard analysis, according to an excluded-site model, indicate a very high affinity towards DNA. The binding of the alkaloid is an exothermic process with Gibbs free energy of -7.4 kcal/mol, van't Hoff enthalpy of -13.8 kcal/mol and entropy of -21.5 cal/degree/mol at 25 degrees. On the basis of these observations it is concluded that aristololactam-beta-D-glucoside binds to DNA by a mechanism of intercalation.