Biopolym. Cell. 1988; 4(4):171-177.
Structure and Function of Biopolymers
Changes in stability of Z form depending on ionic strength, comparison between the theory and experiment
1Ivanov V. I., 1Minyat E. E.
  1. Institute of Molecular Biology, Academy of Sciences of the USSR
    Moscow, USSR

Abstract

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.

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