The interaction between zinc ion and human serum albumin (HSA) was investigated by nano-Watt- scale isothermal titration calorimetry (ITC). From the analysis of the ITC data, the binding characteristics and thermodynamic properties of the system were obtained and the binding mechanism was discussed. It was found that the experimental data fit well with the Langmuir’s binding theory and the system behaved as a system with two classes of binding sites (high-affinity and low-affinity binding site). The binding number of high-affinity binding site (N1) is 1.40 and the binding constant (K1) is 2.72×105 L/mol. For the low-affinity binding site, the binding number (N2) is 1.55 and the binding constant (K2) is 3.78×103 L/mol. Moreover, it was indicated by the thermodynamic analysis that the binding processes of both types of binding sites were exothermic and spontaneous. The high-affinity binding was an enthalpy-entropy synergically driven process and the electrostatic interaction was the main force, while the low-affinity binding was an enthalpy-driven process and this process was mainly driven by the van der Waals forces.

Ming Guo, Huidong Li, Yan Zhang, Shuang Shao, Min Guo and Xiaomeng Wang