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用定电位、定pH滴定法研究了Cd~(2+)离子与牛血清白蛋白(BSA)的结合。在滴定过程中溶液的pH用基本上不与金属离子络合的硼酸—硼酸钠—甘油缓冲溶液维持。在所研究的自由Cd~(2+)浓度(6×10~(-7)—1×10~(-3)M)和BSA浓度(3×10~(-6)—6×10~(-5)M)范围内,当pH=6.94±0.02、μ～0.5及t=25℃时,Cd~(2+)与BSA只生成MpHqA型的单核络合物。每个BSA分子结合的Cd~(2+)离子的平均数Z_B(b)与自由Cd~(2+)离子浓度b的关系可以经验地表示为Z_B(b)=4.6748+0.2978lnb+1.4050×10~4b-7.2592×10~6b~2。BSA对Cd~(2+)离子大致有两类结合部位,它们与Cd~(2+)离子结合的本征平衡常数分别为4.67×10~5和3.58×10~3。
The binding of Cd 2+ ions to bovine serum albumin (BSA) was studied by potentiometric titration and pH titration. The pH of the solution during the titration is maintained with a sodium borate-glycerol buffer solution that does not substantially complex with the metal ions. In this study, free Cd 2+ concentration (6 × 10 -7 -1 × 10 -3 M) and BSA concentration (3 × 10 -6 -6 × 10 ~ (-1) -5) M), only mononuclear complex of MpHqA was formed between Cd 2+ and BSA at pH = 6.94 ± 0.02, μ ~ 0.5 and t = 25 ℃. The relationship between the average number of Cd 2+ ions bound to each BSA molecule Z_B (b) and the free Cd 2+ ion concentration b can be empirically expressed as Z_B (b) = 4.6748 + 0.2978lnb + 1.4050 × 10 ~ 4b-7.2592 × 10 ~ 6b ~ 2. BSA possesses two types of binding sites for Cd 2+ ions. The intrinsic equilibrium constants of BSA binding to Cd 2+ ions are 4.67 × 10 -5 and 3.58 × 10 -3, respectively.