Binding Equilibrium Study Between Co(Ⅱ), La(Ⅲ) And HSA Or BSA

The binding of Co(ll)and La(Lll) to human serum albumin (HSA) or bovine serum albumin(BSA) and the compection with Cu(ll), Zn(ll) or C~ll) have been studied by equilibrium dialysis at physiological pH(7.43) and pH(6.30), respectively. The Scatchard analysis indicates that there are three strong binding sites, 12 and 15 weak binding sites of Co( II) in HSA and BSA, respectively; and there are 2 strong binding sites, S and 6 weak binding sites of La(Ill) in HSA and BSA ,respectively. The successive stability constants of Co( II) -lISA , Co( II) -BSA , La(llI)-HSA and L.a(III)-BSA are obtained by non-linear least-square method fitting Bjemim formula. The order of magnitude of k1is found to be 1O~. The successive stability constants of Co( Ii) -HSA and La(IIl)-HSA are greater than that of Co( II) -BSA and L.a(llI)-BSA The results of the compectition between Co( II) and Cu( II), Zn( II) or Ca( II )indicate that one of the strong binding sites of Co( II) in HSA or BSA is most probably located at the tripeptide segment of N-terminal sequence of HSA and BSA taking octahedral configuration. Another binding site is located inside of the protein. The coordinated atoms are two or three Nitrogen atoms of imidazole and one or two oxygen atoms of carboxyl, that take tetrahedral configuration. The last one is coordinated with almost all oxygen atoms. Judged from the compectidon between La(llI) and Cu( II), Zn( II) or Cd( II), One of the strong binding sites of La(IIJ) in HSA or BSA is most probably coordinated with almost all oxygen atoms. The analyses of Hill plots and free energy coupling show that the binding of Co( II) to HSA and BSA results some positive cooperative effect (Co( II )-HSA system, h,.~=2.7:Co( 11 )-BSA, h,,~=1 .4), and the former is greater than the latter. In La(llI)-HSA and La(llI)BSA systems, there are some negative cooperative effect (La(llI)-HSA system, h=O.83 and...