DNA INTERACTION WITH BIOLOGICALLY-ACTIVE METAL-IONS - COOPERATIVITY OF METAL-ION BINDING AT COMPACTING OF DNA

The interaction of Cu2+, Mn2+ and Ca2+ ions with DNA in aqueous and wa ter-ethanol solutions at different metal ion concentrations was studie d by IR-spectroscopy. At sufficiently high DNA concentrations, DNA int eraction with Cu2+, Ca2+ and Mn2+ ions results in compacting of DNA in the aqueous solutions. This process shows a very high cooperativity. In the presence of alcohol, DNA condensation takes place at much lower concentrations of metal ions used than in pure aqueous solution. Bind ing constants and cooperativity of the metal ion binding rise, and the non-monotonous dependencies of the binding degree, r, on the concentr ation of free metal ions, C-f, become pronounced. Binding isotherms ta ke the S-like form similar to van der Waals isotherms for phase transi tions of the liquid-vapour type. Cu2+ and Ca2+ ion binding to DNA in w ater-ethanol solutions also results in compacting of DNA macromolecule . The process is characterised by a high positive cooperativity and ha s a phase transition character.