[Interaction of Cu2+ and Ca2+ ions with DNA immobilized in polyacrylamide gel]

Interaction of cupric and calcium ions with DNA entrapped in acrylamide gel was studied by means of ion-exchange method. Ion-exchangers on the basis of DNA were obtained by polymerization of acrylamide with and without warming-up. Samples of DNA with different degrees of denaturation were also used for preparation of ion-exchangers. It was demonstrated that ion-exchange capacity is determined by the number of phosphate groups of DNA entrapped in gel. Cu2+ and Ca2+ ion-exchange equilibrium on the macromolecules of immobilized DNA was studied at different temperatures. Ion-exchange equilibrium constant alpha Cu2+ Ca2+ was shown to vary from 1,9 to 8,2 an increase of selectivity for Cu2+ ions taking place under conditions favouring denaturation of DNA. Stoichiometric ratio between the quantity of the phosphate groups and the number of equivalents of Cu2+ and Ca2+ was observed in all the experiments. Lack of over-equivalent absorption of CuCl2 on the DNA molecules indicates that chloride ions do not participate in charge neutralization within the Cu2+.DNA complex. It means that Cu2+ ions interact with phosphate groups of DNA coordinate simultaneously with DNA bases only.