Biopolym. Cell. 1990; 6(4):43-47.
Structure and Function of Biopolymers
Energetics of the B-to-Z and Zhelix-to-coil transitions in water solutions of Poly(DG-DC)
1Mrevlishvili G. M., 1Lapiashvili G. N., 1Mdzinarashvili T. J., 2Gorgoshidze M. Z., 2Kharatishvili M. G., 1Yakobashvili N. E.
  1. Department of Macromolecular Physics, State University of Tbilisi
    Tbilisi, USSR
  2. Institute of Physics, Academy of Sciences of the Georgian SSR
    Tbilisi, USSR

Abstract

Differential scanning calorimetry, CD- and UV-spectroscopy were used to study thermodynamics of the B-Z and Z-helix-coil transitions of poly(dG-dC). The experiments were performed under conditions of 0.5 mM water solutions of sodium cacodylate (pH 6.5) + 1 mM MgCl2 + 0.02 mM EDTA. The reversible transition of the polymer observed calorimetrically at 76 °C was identified as B-Z transition. The left-handed helix-coil transition was observed at 97 °C. The enthalpy of B-Z transition is small. A//Cai = 0.2 ± 0.02 kcal/mole bp, indicating a fine energy balance between the DNA left- and right-handed conformations in water solutions. The enthalpy of Z-helix-coil transition is A//Cai=10.1 ± l.l kcal/mole bp.

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