[Effect of divalent copper ions on heat denaturation of DNA].

Using the thermal denaturation method the effect of bivalent copper of (4-10(-6)-10(-3)) M concentrations on the helix-coil transition of DNA was studied in the solution of Na+ concentrations 10(-3)-10(-1) M. Unlike the previous studies, this paper makes allowance for the effect of impurity ions present in DNA and deionized water. It has been shown that in the region of low Cu2+ and Na+ concentrations, thermal stability increases, the melting range extends and the denaturation curves become asymmetric. At concentrations more than approximately 3-10(-5) M Cu2+, melting temperature starts to fall, and the range reduces to 1-1.5 degrees at [Cu2+] greater than or equal to 2-10(-4) M. As [Cu2+] reaches these values, the denaturation curve asymmetry and melting range increase again, which is due to the inversion of the relative stability of AT- and GC-pairs. Employing experimental and phase-transition-theory data for homopolymers, the constants of Cu2+ binding with phosphates and DNA bases were calculated. The concentration dependence of the DNA denaturation parameters was shown to be governed by the superposition of binding Cu2+ with phosphates and nucleic acid bases.