[Interactinos of DNA with low molecular weight ligands of various structures. I. Complexes of DNA with actinomycin and its simple analogs].

The DNA complexes with actinomycin D and its simple analogues have been investigated by means of spectrophotometry, viscometry and flow birefringence methods. The number of binding sites per base pair of ligand on DNA depends on the nature of substitute in 1.9 position of the phenoxasone chromophore. It has been shown that phenoxasone derivatives without aminogroup in 2 position complex with DNA as in the case of simple actinomycin analogues. The intrinsic viscosity and optical anisotropy of DNA-analogues complexes increase linerly with increasing quantity of bound ligand. This testifies that the binding of the compounds under investigation to DNA molecule is of intercalation type. The character of variation of hydrodynamical and optical parameters of DNA molecule by its binding with actinomycin differs qualitatively from that observed by the binding with analogues. The experimental data obtained for DNA-actinomycin complexes can be interpreted only by suggesting a specific secondary structure alteration of the DNA molecule. It has been shown that the simple actinomycin analogues can not be used as an appropriate model for investigation of DNA-actinomycin complexes structure.