Spectroscopic study on binding of gentisic acid to bovine serum albumin

• Determination of Stern–Volmer and binding constant of BSA and gentisic acid (GA).
• Determination of thermodynamic parameters of the binding of BSA with GA.
• Study of the secondary structure alteration of BSA in the presence of GA.

The interaction of (gentisic acid) GA with (bovine serum albumin) BSA has been studied by different spectroscopic techniques. GA is a monoanionic specie at the working pH of 7.4, it was determined by combining UV–Vis absorption spectroscopy and theoretical calculations. A set of fluorescence quenching experiments at different temperatures was carried out employing the native fluorescence of BSA. A Stern–Volmer constant (KSV) of (2.07 ± 0.12) × 104 mol−1 L and a binding constant (Ka) of (8.47 ± 4.39) × 103 were determined at 310 K. The static quenching caused by the BSA–GA complex formation seems to play a significant role in the overall quenching process. A single binding site on BSA for GA was observed. ΔH = −55.6 ± 0.2 kJ mol−1 and ΔS = −104.3 ± 0.6 J mol−1 K−1 were determined in a set of experiments on the dependence of Ka with the temperature. The binding process is, therefore, spontaneous and enthalpy-driven. Van der Waals forces and hydrogen bonds could also play the major role in the binding mode. The secondary structure changes of BSA in the absence and presence of GA were studied by FTIR and UV–Vis absorption spectroscopy.

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