Specific features of Zn²⁺, Co²⁺ and Ni²⁺ ion binding to DNA in alkaline solutions

Dependence of DNA metallization degree during B-DNA transition into the metallized (m) form on DNA concentration has been studied by visible and differential UV-spectroscopy in the presence of Zn(2+), Co(2+) and Ni(2+) ions in tetraborate buffer (pH 8.5) with and without ethidium bromide. Constants of Mt(2+) binding to double stranded DNA were calculated. The obtained binding constants corresponded to the formation of inter-strand metal bridges stabilizing m-form. Thermodynamic origin of higher efficiency of Zn(2+) ions in DNA metallization compared to Co(2+) and Ni(2+) was revealed. Increase of the DNA helix-coil transition temperature by up to 10°С upon formation of m-form in the presence of Zn(2+) ions was observed and rationalized. Furthermore, a strong cooperative decrease (up to 30°С) of the temperature of В→m transition induced by heating in the presence of Zn(2+) was found and its nature was explained.