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 water-ethanol solutions at different metal ion concentrations was studied by IR-spectroscopy. At sufficiently high DNA concentrations, DNA interaction 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. Binding constants and cooperativity of the metal ion binding rise, and the non-monotonous dependencies of the binding degree, r, on the concentration of free metal ions, Cf, become pronounced. Binding isotherms take the S-like form similar to van der Waals isotherms for phase transitions of the liquid-vapour type. Cu2+ and Ca2+ ion binding to DNA in water-ethanol solutions also results in compacting of DNA macromolecule. The process is characterised by a high positive cooperativity and has a phase transition character.