[Comparative study of DNA interactions with daunomycin and proflavine in a solution].

The comparative investigations of DNA complexes with daunomycin and proflavine were proceeded by the technique of spectrophotometry, viscometry and flow birefringence for two ionic strengths of environment (mu). According to the spectrophotometry data there is an unique type of ligand binding with DNA for mu = 0.1. The intrinsic viscosity and optical anisotropy of DNA-daunomycin complex increase nonlinearly together with its equilibrium rigidity as the amount of the binding ligand (r) rises, contrary to the behaviour of the same characteristics of DNA-proflavine complexes. The discussion of the experimental data within a scope of different models of binding reveals the best agreement with the intercalation model. Evaluation of the angels between the orientation planes of chromophore and aminoglucose residue of a daunomycin molecule and the axis of DNA double-helix was performed. Apart from intercalation there is a process of external binding of daunomycin with DNA in the low ionic strength (mu = 0.001) solutions which arises mainly at higher values of r. This type of binding weakens the long-range electrostatic interactions (and also to a certain extent the short-range ones) in DNA chain that determine the behaviour of the parameters under study.