Interactions of histone amino acid: lysine with copper(II) ions and adenosine 5′-triphosphate as well as in a metal-free system
Thermodynamic stability and mode of coordination were studied in the binary system of copper(II)/lysine, ternary system of copper(II)/ATP/lysine, and compared to the intermolecular interaction in the metal-free ATP/lysine system. In the system ATP/Lys, groups P β and P γ from ATP, participate in the interaction with the amino acid, while group P α from ATP is involved as reaction center only at high pH. The endocyclic nitrogens from the nucleotide N(1) and N(7) take part in the interactions only below physiological pH. In the binary complexes, oxygens from carboxylic group and nitrogen from the α-NH2 amino group are involved in coordination. However, introduction of the second ligand, ATP, into the system Cu(II)/Lys changes the amino acid coordination in alkaline medium. In protonated mixed-ligand complexes, the α, β, and γ oxygens of the phosphate from ATP coordinate, but at higher pH, only α oxygens coordinate in Cu(ATP)(Lys). Although Cu(II) ions do not coordinate nitrogen from ATP in the ternary system, the presence of metal ions excludes interaction of these atoms over the whole pH range studied.
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