Study on the Interaction between Heavy Metal Ions and Bovine Serum Albumin
|Course||Biochemistry and Molecular Biology|
|Keywords||Bovine serum albumin mercury lead fluorescence spectra equilibrium dialysis conformation binding sites coordination analysis|
The interaction of bovine serum albumin（BSA） to Hg2+ or Pb2+ has been studied by fluorescence spectra and equilibrium dialysis. The results have indicated that tryptophan and tyrosine, which are located in BSA, have a max fluorescence emission peak at 345nm with an excitation wavelength of 296nm. It is show that Hg2+, Pb2+ or Cu2+ has a powerful ability to quench the BSA fluorescence with a mechanism of a static process rather than a dynamic one under the conditions pH4.40, 5.20, 6.37 and 7.43. The binding contant Ks can be obteined Lineweaver-Burk equation. The change of the binding contents in different pH condition can be discovered.The effects of some metal ions coming from Zn2+, Mg2+, Ca2+ and Cu2+ on the binding properties were discussed. The binding constants between Hg2+ and serum albumin decreased in various degrees in presence of Zn2+ and Ca2+, but increased in presence of Cu2+ except for Mg2+. The binding constants betweem Pb2+ and BSA decreased in various degrees in presence of Zn2+ and Ca2+, but increased in presence of Cu2+ and Mg2+. With changing of the Cu2+ concent, the conformation transition of BSA can effect the binding of Hg2+ and Pb2+.The binding of BSA with Hg2+ at physiological pH（7.43） and with Pb2+ at similar physiological pH（6.37） has been studied by the method of equilibrium dialysis. The results from Scatchard plot show that there are two strong binding sites and eight weak binding sites of Hg2+ in BSA, and the binding constants are 1.26×105 and 5.12×103 L.mol-1 respectivily. There are two strong binding sites and sixteen weak binding sites of Pb2+ in BSA, and the binding constants each are 8.89×104 and 2.9×103 L.mol-1. The successive stability constants which are reported first time are obtained by the methods of non-linear least-squares fitting Bjerrum formula. For both Hg2+-BSA and Pb2+-BSA systems, the order of magnitude of K1 is found to be 105. The analyses of Hill coefficients show that the weak negative cooperative effects are found in both Hg2+-BSA and Pb2+-BSA systems.