Thermodynamic study of the effects of ethanol on the interaction of ochratoxin A with human serum albumin

Ethanol effect on the interaction of ochratoxin A (OTA) with human serum albumin (HSA) was investigated by using fluorescence spectroscopy and Raman spectroscopy. The Raman results showed that after the binding of OTA, the microenvironment of tryptophan residue on HSA became less hydrophobic. The fluorescence quenching observations revealed that the binding constant for the binding of OTA to HSA decreased as ethanol concentration increased. The thermodynamic studies showed that the binding process of OTA to HSA switched from being entropy-driven to enthalpy-driven in the presence of increasing concentrations (0.7-24.7%, vol/vol) of ethanol. Enthalpy-entropy compensation effect for the binding of OTA to HSA in the presence of different ethanol concentrations had been found. Based on the thermodynamic analyses, we concluded that the ethanol-induced variation of the shape of binding site of OTA on HSA and the solvent reorganization surrounding the OTA-HSA complex are the two dominant effects.