[Calorimetric study of Ca2+ and Mn2+ ions' effect on DNA helix-coil transition].

Using the method of differential scanning calorimetry, the DNA helix-coil transition studied in solutions (10(-3) M Na+, 10(-3) M tris HCl, pH 7.0) containing divalent metal ions (Mn2+ and Ca2+) at relative metal ion concentrations (Me/PDNA) ranging from 0.2 to 20. Dependences of the melting temperature and enthalpy on the ion relative concentration were stated. The fine structure of melting curves in DNA+Me complexes was observed. The resolution degree of this structure was shown to increase in the range of moderate ion concentrations. The data obtained were compared with values determined by UV-spectroscopy. Association constants were defined for Mn2+ and Ca2+ binding to DNA by the ligand theory.