[Effect of the nature of a monovalent counterion on the secondary structure of DNA is aqueous solutions].

Doxyribonucleates (DNMe) and deoxyribonucleic acid (DNA) were prepared by the ion-exchange method from Na+-salt from chicken erythrocyte DNA (DNS). (Here Me+ means Rb+, CS+, Na+, or NH4+). It was found that in aqueous solutions of DNMe in which the concentration of nucleic phosphorus was 8-10(5) mole/1 and the supporting electrolyte contained as an impurity only, the secondary structure of DNA was partly restored. This was confirmed by low values of the atomic extinction coefficient (epsilon260(p) = 6800 1/mole-cm and by high values of the hyperchromicity coefficients (1-28). The melting temperatures, as well as the width of the melting transition calculated from the melting curves, did not depend on the nature of Me+. Abnormally high melting temperatures for aqueous solutions of DNMe were noted. It was shown that the DNS - DNA transition was accompanied by spectrum changes that are typical of the denaturation process.