Biopolym. Cell. 2009; 25(3):218-225.
Molecular Biophysics
Phase diagram of Ni2+ ions complexes with polyU·polyA·polyU
1Sorokin V. A., 1Valeev V. A., 1Usenko E. L.
  1. B. I. Verkin Institute for Low Temperature Physics and Engineering, NAS of Ukraine
    47, Prospekt Lenina, Kharkiv, Ukraine, 61103


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 polyU·polyA·polyU (A2U) on Ni2+ ion concentration (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 (ΔH3→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.
Keywords: polynucleotides, metal ions, conformational transitions


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