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Phase diagram of Ni2+ ions complexes with polyU×polyA×polyU

Author(s): Sorokin V. A. | Valeev V. A. | Usenko E. L.

Journal: Biopolymers and Cell
ISSN 0233-7657

Volume: 25;
Issue: 3;
Start page: 218;
Date: 2009;
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Keywords: polynucleotides | metal ions | conformational transitions

Aim. To investigate Ni2+ ion effect on the conformational equilibrium of the three-stranded polynucleotide polyU×polyA×polyU and to ascertain thermodynamic parameters of the metal complex formation. Methods. The differential UV spectroscopy and thermal denaturation. Results. Dependences of conformational transition (Tm) of poly U×polyA×polyU (A2U) on Ni2+ ion con- centration (up to 0.001 M) under conditions close to physiological ones (0.1 M Na+, pH 7) were obtained. At [Ni2+] < 3×10–4 M two branches are observed in the phase diagram, corresponding to A2U → polyA×polyU (AU) + polyU (3→2) and AU→polyA + polyU (2→1) transitions. Only A2U→polyU + polyA + polyU (3→1) transition is realized at higher Ni2+ concentrations and upon A2U heating. Effective binding constants are determined for Ni2+ ions with AU (850 M–1) and A2U (1300 M–1) as well as 3→2 transition enthalpy (DH3→2 = 4±1 kcal/mol×triplet). Conclusions. By the equilibrium binding theory the thermodynamic nature of (Tm)2→3 different behavior in the phase diagram of AU in the presence of Mg2+ and Ni2+ ions was determined. A larger difference of the magnesium affinity to A2U and AU as compared with that to AU and poly A results in (Tm)2→3 decrease whereas the opposite ratio of Ni2+ ion binding constants induces its increasing
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