Ion-exchange properties of immobilized DNA

Abstract

Results of investigations of the ion-exchange properties of ion exchangers obtained by immobilization of DNA gels in polyacrylamide gel (PAAG) are given. The exchange capacity of ion exchangers, under defined conditions, is determined exclusively by phosphate DHA groups and constitutes 0.05 to 0.17 meq/g. The following series of cations has been obtained when ordered according to their degree of binding with DNA: Cu 2+ > Zn 2+ > Ca 2+ > Mg 2+ ⪢ Li + K + ≈ Na + The positions of Cu 2+ and Zn 2+ in the series are explained by their chelation with the nitrogen bases of DNA. This is also evidenced by an increase in the degree of binding of Cu 2+ in parallel with the perturbation of the secondary structure of DNA in the ion exchanger. At 25° C, conversion to the H 3O − form is accompanied by hydrolysis of DNA and by complete elution of DNA from PAAG. At 4°C, when hydrolysis can be neglected, about 24% of phosphate groups becomes inaccessible to the H 3O + ion, an effect attributable to the formation of compact structures caused by protonation. The influence of the ion exchange capacity and the 1,4-dioxane content in solution on the exchange of ions of alkali metals has also been investigated. The results obtained are consistent with the familiar data on the influence of metal ions on the secondary structure of DNA. It is shown that investigations of DNA-based ion exchangers for determining the binding constants and for elucidating the mechanism of interaction between DNA and metal ions are promising.