Study On The Interaction Between Heavy Metal Ions And Bovine Serum Albumin

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 K_s 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.