Thermodynamics of Binding Copper(II) Ion by Human Growth Hormone

Abstract

The interaction of human growth hormone (hGH) with divalent copper ions in aqueous solution was studied using different methods. The binding isotherm for hGH-Cu²⁺ was obtained by two techniques of potentiometric, using a Cu²⁺-selective membrane electrode and isothermal titration calorimetry. There is a set of three identical and non-interacting binding sites. The intrinsic association equilibrium constant is 117 mM^–1 and the molar enthalpy of binding is –16.7 kJ/mol. Although the binding process of copper ions to the surface of protein do not change the secondary structure of hGH significantly, however, thermodynamic stability of the protein decreases considerably due to the binding of metal ions.