Journal of Biochemistry Advance Access originally published online on December 12, 2008
Journal of Biochemistry 2009 145(3):309-314; doi:10.1093/jb/mvn170
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Study on the Binding of Fluoride, Bromide and Iodide to Ovalbumin by Using Ion-Selective Electrodes
1College of Chemistry and Environmental Science, Henan Normal University, Xinxiang, Henan 453007, PR China
*To whom the correspondence should be addressed. Tel: +86-373-3325249, Fax: +86-373-3326335, E-mail: yanlu2001{at}sohu.com
Received November 7, 2008; Accepted December 29, 2008
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Abstract |
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The interactions of F–, Br– and I– with ovalbumin (OVA) were studied in acetate buffers of pH 5.68, at 288.15 K, 298.15 K and 308.15 K, using ion-selective electrodes. The data for the ion-protein systems were treated according to the Klotz equation, and the number of binding sites and the binding constants were determined. It is shown that the binding sites of F– on OVA molecule are more than those of Br– and I–, and that the binding sites of F–, Br– and I– on OVA molecule decreases with increasing temperature. At the same time, our studies indicate that the binding constants for the interactions of F–, Br– and I– with OVA show a same trend: They decrease as temperature increases. These were reasonably interpreted with the structural and thermodynamic factors. The thermodynamic functions (
G
, H, S) at different temperatures were calculated with thermodynamic equations, and the enthalpy change for the interactions were also determined by isothermal titration calorimetry (ITC) at 298.15 K, which indicate that the interactions of F–, Br– and I– with OVA are mainly electrostatic interaction. Simultaneously, there are also partial desolvation of solutes and solvent reorganization effect.
Key Words: binding, halide ion, interaction, ion-selective electrode, ovalbumin
Abbreviations: OVA, ovalbumin; BSA, bovine serum albumin; ITC, isothermal titration calorimetry