DNA conformational equilibrium in the presence of Zn2+ ions in neutral and alkaline solutions

Effect of Zn2+ ions on DNA transition from B-form to a metallized form (m-DNA) in Tris and tetraborate buffers at pH 8.5 has been studied by visible and differential UV-spectroscopy and by thermal denaturation. The results have been compared to those obtained at pH 6.5 in cacodylate buffer. It was found that in alkaline solutions Zn2+ ions induced a hypochromicity of the DNA absorption in the whole spectral range monitored, which was attributed to DNA transition from B- to the m-form. Complete metallization occurred only upon heating the DNA solutions containing more than ∼2 × 10−4 M of Zn2+ ions. Phase diagrams of the DNA-zinc complexes at pH 6.5 and 8.5 have been obtained for the first time. The m-DNA form showed higher thermal stability compared to B-DNA.