Abstract
The denaturation of bovine serum albumin (BSA) induced by guanidine chloride or urea at different pH values was studied by isothermal microcalorimetry measurements at 30°C. The simple bonding model, which was developed by Privalov, was employed to obtain the apparent bonding constant K, the apparent singular bonding Gibbs bonding energy ΔG and the total Gibbs energy ΔG(a) between the protein and denaturant, from analysis of the calorimetric data. Furthermore, linear extrapolation at the midpoint of transition was employed to determine the apparent denaturation enthalpy ΔH d. The results showed that for guanidine chloride, the bonding between BSA and guanidine chloride could proceed more easily in an alkaline condition, and the apparent denaturation enthalpy ΔH d of BSA due to guanidine chloride was 350 kJ·mol−1 at pH 6.97 and 7.05, while it was 275 kJ·mol−1 at pH 9.30, which indicated that BSA was more stabilized in a neutral condition. However, for urea, the bonding between BSA and urea could proceed more easily in an acidic condition, and the apparent denaturation enthalpy ΔHd of BSA due to urea was 295 kJ · mol−1 at pH 6.97, while it was 230 kJ · mol−1 at pH 7.05 and 9.30. The results indicate that the degree of expansion of BSA in the two denaturants is different.
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