镉(Ⅱ)与牛血清白蛋白的相互作用及pH、钙(Ⅱ)、锌(Ⅱ)和表面活性剂的影响

本文用恢复电位法、荧光分光光度法及粘度法研究了镉(Ⅱ)与牛血清白蛋白(BSA)的配位平衡和pH的影响。结果表明BSA有两类镉结合部位(2个强结合和10个弱结合部位)。Cd—BSA配位反应受pH影响,在近中性pH范围Cd(Ⅱ)与BSA结合未接近饱和时,以CURFIT程序对结合曲线拟合发现,每摩尔BSA平均结合Cd(Ⅱ)摩尔数的对数值与游离镉浓度的对数间成线性关系,进一步用Marguardt法处理得到Cd(Ⅱ)与BSA结合平衡方程式:N=K[Cd²⁺]^m,K和m均为pH函数。构象研究表明H⁺和Cd(Ⅱ)的结合都能引起BSA构象改变。用凝胶色谱法测定了Zn(Ⅱ)、Ca(Ⅱ)、吐温—80和十二烷基硫酸钠(SDS)对Cd—BSA结合的影响。Z_n(Ⅱ)可以竞争Cd(Ⅱ)在BSA上结合部位使Cd(Ⅱ)活动化。SDS能够有效抑制Cd(Ⅱ)与BSA结合,这种作用可能与SDS引起BSA构象改变有关。

INTERACTION BETWEEN CADMIUM (II) AND BOVINE SERUM ALBUMIN AND INFLUENCES OF pH, CALCIUM(II),ZINC(II) AND SURFACTANTS

The binding of cadmium ion to BSA and the pH effect Were studied by means of potential-restoration,fluorescence and viscosity studies. The results show that there may be two kinds of binding sites to cadmium (two strong and ten weak) .The binding of cadmium is significantly affected by variation of pH.In nearly neutral media,if Cd binding is not saturated,there is linear relation between the logarithm of number of moles of Cd bound per mole of BSA and the logarithm of free Cd ion concentration. Further treatment gives an equation N=K[Cd²⁺]^m,with which the Cd -binding equilibrium may be estimated.In this equation,K and m are all functions of pH.The experimental results give information of the conforma-tional changes induced by the binding of proton or Cd(II). By means of gel chromatographic studies,the influences of Zn(II),Ca(II),Tween-80 and SDS were studied.The effective competition of Zn (II) may mobilize the BSA bound Cd(II).SDS inhibits the Cd-BSA binding.These actions may be relevant with conformation conversion.