Biopolymers and cell. 1988. Volume 4. № 4. 171 - 177

V. I. Ivanov, E. E. Mlnyat

CHANGES IN STABILITY OF Z FORM DEPENDING ON IONIC STRENGTH, COMPARISON BETWEEN THE THEORY AND EXPERIMENT

Summary

    The polyelectrolyte theory for the B — Z transition has been tested with poly[d(G-m5C)] by changing the non-electrostatic contribution to the free energy difference between the B and Z forms. The non-electrostatic term was varied by addition of ethanol, a non-electrolyte. The experiments confirmed a bell-shaped dependence of the Z form stability on counterion concentration, the maximum B form stability being at 0.1 M NaCl. In accordance with the theory the widths of the Z-to-B transition at low ionic strengths (<0.01), when expressed in logarithms, are equal. A value of 3.6 kcal/mol was obtained for the free energy of the B/Z junction in poly[d(G-m5C)]. These findings make it possible to believe that an explanation of the low ionic strength reverse Z to B transition, based on an idea of pushing out the contaminating polyvalent ions by Na+, is unlikely.