Binding and Thermodynamic Parameters of Ovalbumin-oleic acid Conjugate

Abstract

The present study aims to investigate association constants, binding capacity and different thermodynamic parameters of ovalbumin-oleic acid (Oval/OA) conjugate at different temperatures using fluorescence method. Oval/OA conjugate was prepared in a phoshphate buffer solution at different temperatures. The conjugation process resulted in a change of the fluorescence emission intensity. The emission spectra of the conjugate were analyzed according to Scatchard plot to obtain the association constant (ka ) values and the number of binding sites at several temperatures in the range of 22-55 0C. From the Ka value, the free energy (∆G°) was calculated. The Van’t Hoff enthalpy (∆HVH) and entropy (∆S°) values associated with the conjugation were estimated using the Van’t Hoff equation. The results showed that the binding capacity and the association constant of Oval/OA conjugate were temperature dependent. Average number of binding sites of OA in Oval and Ka value at 22°C were about 2.0 and 1.8 ×103 M –1, respectively. On the other hand, at 55 °C average OA binding capacity of Oval and Ka value were about 3.0 and 0.73 x 103 M –1, respectively. The results also showed that the conjugation was enthalpically driven, accompanied by a negative contribution of entropy. Key words: ovalbumin-oleic acid conjugate, fluorescence method, association constants, binding capacity, thermodynamic parameters. Acknowledgement : Our special thanks to Hussein Al-Talaa for his grateful experimental help in this work