Thermodynamics of binding of cadmium to bovine serum albumin

Abstract

The binding isotherm of Cd 2+ ion to bovine serum albumin (BSA) has been investigated by microcalorimetry at 310.15 K and pH 7.0. The thermodynamic parameters of the binding reaction have been determined, and the stoichiometry of the complex is 2:1, indicating that there exist two identical binding sites of BSA with Cd 2+ ion. The value of Δ r H m Θ is −28.4±1.7 kJ mol −1 , the free energy of binding Δ r G m Θ is −25.2 kJ mol −1 , and the entropy of binding Δ r S m Θ is −10.3 J mol −1 K −1 . The negative Δ r H m Θ and Δ r S m Θ values are observed for the binding reaction of Cd 2+ ion and BSA, suggesting that the binding reaction is mainly enthalpy-driven and the entropy is unfavorable for it.