Biopolymers and cell. 1990. Volume 6. № 4. 43 - 47

G. M. Mrevlishvili, G. N. Lapiashvili, T. J. Mdzinarashvili, M. Z. Gorgoshidze, M. G. Kharatishvili, N. E. Yakobashvili

ENERGETICS OF THE B-TO-Z and Z-HELIX-TO-COIL TRANSITIONS IN WATER SOLUTIONS OF POLY(DG-DC)

Summary

    Differential scanning calorimetry, CD- and UV-spectroscopy were used to study thermo¬dynamics 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.