Binding isotherm determination by isothermal titration calorimetry -: Interaction between Cu2+ and myelin basic protein

A simple method for determination of binding isotherm in the protein-ligand interaction was introduced using isothermal titration calorimetric data. This general method was applied to the study of the interaction of myelin basic protein (MBP) from bovine central nervous system with divalent copper ion at 27degreesC in Tris buffer solution at pH=7.2. The binding isotherm for copper-MBP interaction is easily obtained by carrying out titration calorimetric experiment in two different concentrations of MBP. MBP has two binding sites for copper ion, which show positive cooperativity in its sites. The intrinsic association equilibrium constants are 0.083 and 1.740 muM(-1) in the first and second binding sites, respectively. Hence, occupation of the first site has produced an appreciable enhancement 21 of the binding affinity of the second site. The molar enthalpies of binding are -13.5 and -14.8 kJ mol(-1) in the first and second binding sites, respectively.