Application of a simple calorimetric data analysis on the binding study of calcium ions by human growth hormone

A simple graphical linear method was introduced for isothermal titration calorimetric data analysis in the protein-ligand interaction. The number of binding sites, the dissociation binding constant and the molar enthalpy of binding site can be obtained by using this new isothermal titration calorimetric data analysis method. The method was applied to the study of the interaction of human growth hormone (hGH) with divalent calcium ion at 27 degrees C in NaCl solution, 50 mM. hGH has a set of three identical and independent binding sites for Ca2+. The intrinsic dissociation equilibrium constant and the molar enthalpy of binding are 52 mu M and -17.4, respectively. Results obtained by this new calorimetric data analysis are in good agreement with results obtained using our previous method.