Copper(II)-DNA denaturation. II. The model of DNA denaturation.

Abstract

AbstractIn a continuing study of the denaturation of DNA as brought abought about by Cu(II) ions, results are presented for the dependence of Tm and τ (the terminal relaxation time) on ionic strength, pH, reactant concentrations, and temperature. Maximum stability of the double helix, as reflected by the longest relaxation times and highest Tm values, was observed between pH 5.3 and 6.2. Outside this range both Tm and τ decreased sharply. A second, faster relaxation time was deduced from the kinetic cureves. The apparent activation energies of the rapid and slow (“terminal”) relaxations were found to be 12 and 55 kcal/mole, respectively. Several lines of evidence led to the conclusions that (1) the rate‐determining step in DNA denaturation, when occurring in the transition region, is determined by chemical events and (2) the interactions which are disrupted kinetically in the rate‐determining step are those which account for the major portion of the thermal (Tm) stability of helical DNA.