Cd（Ⅱ）与HSA或BSA的结合平衡研究

用平衡透析法详细研究了生理pH(7.43)条件下Cd(Ⅱ)与HSA或BSA的结合平衡.通过非线性最小二乘法拟合Bjerrum方程,首次报道了Cd(Ⅱ)-HSA和Cd(Ⅱ)-BSA体系的逐级稳定常数值,其K_1～K_3的数量级均为10~4;Hill系数和自由能偶合定量分析表明Cd(Ⅱ)与HSA或BSA的结合均产生在类似体系中少见的强的正协同效应,且Cd(Ⅱ)与HSA结合产生的正协同效应大于BSA;Scatchard图分析表明,Cd(Ⅱ)在HSA和BSA中均有3个强结合部位.通过Cd(Ⅱ)与Cu(Ⅱ),Zn(Ⅱ)或Ca(Ⅱ)等竞争结合HSA或BSA的结果,进一步讨论了Cd(Ⅱ)在HSA或BSA中强结合部位的可能位置和(或)配体.

Study on the Binding Equilibrium between Cd(II) and HSA or BSA

The binding of Cd( II) to human serum albumin (HSA) or bovine serum albumin (BSA) has been studied by equilibrium dialysis at physiological pH (7.43). The successive stability constants for the Cd( II ) - HSA and Cd ( II ) - BSA systems are determined for the first time by non - linear least - square method fitting Bjerrum formula, the order of magnitude of the K1 ~ K3 in both systems is found to be 104. The analyses of Hill coefficients and free energy coupling indicate that the strong positive cooperative effect exists in both Cd( II ) - HSA and Cd( II ) - BSA systems, and the positive cooperative effect in Cd( II ) - HSA system is much stronger than that in Cd( II) - BSA system. The Scatchard analysis indicates that there are three strong binding sites for Cd(II) in both HSA and BSA. The probable locations and (or) coordinated atoms of the sites are also suggested based on the results of Cd( II) competing with Cu( II ), Zn( II ) or Ca( II ) to bind to HSA or BSA.