a microcalorimetry study of the binding of nickel ion by human growth hormone

a binding study of nickel ions by a new recombinant human growth hormone (hgh), produced as an injected drug, has been done at 27˚c in nacl solution (50 mm) using an isothermal titration calorimetry. there is a set of three identical and non-interacting binding sites for nickel ions. the intrinsic dissociation equilibrium constant and the molar enthalpy of binding are 40 μm and -16.5 kj/mol, respectively. thermodynamic parameters of nickel ion binding are compared to the other metal ions. the molar entropy of binding is 29.3 j k-1 mol-1 for ni2+, less than cu2+ and more than other metal ions, means that the disorder of the protein structure due to the binding of nickel ions is more than to the other ion metals, except cu2+. it is expected that nickel ions can prevent from the aggregation of the protein.