Thermodynamic Studies on the Interaction of Nickel with Human Serum Albumin

The interaction of human serum albumin with divalent nickel ion was studied by equilibrium dialysis, isothermal titration calorimetry (ITC), differential scanning calorimetry (DSC) and circular dichroism (CD) in 30 mmol/ L Tris buffer, pH = 7.0. There is a set of 8 identical binding sites for nickel binding on the protein at two temperatures of 300 K and 310 K. The cooperativity in the binding is observed at 310 K. The Hill coefficients at 300 K and 310 K are 0.97 and 1.25, respectively. The interaction between nickel ions and HSA is exothermic. A value of -36.5 kJ for enthalpy of interaction (1: 1 stoichiometry) was obtained. The secondary structure of HSA dose not show any change during the binding nickel ions process. However, the tertiary structure of the protein changes, which shows the existence of two natives like states

Binding properties and structural changes of human growth hormone upon interaction with cobalt ion

Binding properties and structural changes of human growth hormone (hGH) due to the interaction by cobalt ion (Co2+) were done at 27°C in NaCl solution, 50 mM, using different techniques of UV-Vis spectroscopy, circular dichroism (CD), isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC) techniques. There is a set of three identical and non-interacting binding sites for cobalt ions. The intrinsic association equilibrium constant and the molar enthalpy of binding obtained by ITC are 0.80 mM-1 and -16.70 kJ mol-1, respectively. The intrinsic association equilibrium constant obtained by a standard isothermal titration UV-Vis spectrophotometry method is also 0.79 mM-1, which is in good agreement with the value obtained from ITC. The Gibbs free energy and entropy changes due to the binding of cobalt ion on hGH are -16.67 kJ mol-1 and -0.1 J K-1 mol-1, respectively. Energetic domains analysis by DSC shows that phase transition of hGH in the presence of cobalt occurs at one main transition. Deconvolution of the main transition provides two sub-transitions with different values of the melting point and enthalpy of unfolding (33°C and 164 kJ mol-1 for the first and 49°C and 177 kJ mol-1 for the second, respectively). Interaction of cobalt ions with hGH prevents aggregation by an affect on the hydrophobicity of the protein macromolecule and provide useful information about its structure due to becoming reversible of protein thermal denaturation. © 2007 Springer Science+Business Media LLC