离子选择电极法研究钙调素与重金属铅的结合平衡

Study on the Binding Equilibrium of Calmodulin-Pb^(2+) by Pb^(2+) Ion-selective Electrode

用Pb2+选择电极法首次测定了CaM与Pb2+的结合常数,结果说明:Pb2+在CaM中约有10个结合位点,与文献报道的一致。其中包括4个强结合位点,结合常数在107量级,对应于Pb2+在CaM中的4个主结合位点;而其余的位点则结合常数较低,对应于Pb2+在CaM中的约6个辅助结合位点。逐级结合常数分别为:K1=2.62×107,K2=3.75×107,K3=1.03×107,K4=1.85×107,K5=2.53×106,K6=8.07×105,K7=3.36×105,K8=2.76×105,K9=2.22×105,K10=3.96×104。由于Pb2+与CaM的4个主结合位点的稳定常数比相应Ca2+的强几十到几百倍,因此Pb2+对Ca2+与CaM的竞争结合作用能够调节CaM的功能。

This paper reports the measurement of the successive binding constants of Pb^2＋ to arabidopsis CaM（ isoform Ⅱ） by using Pb^2＋-ion selective electrode（Pb-ISE） combined with the Excel calculation program. The Scatchard plot of Pb^2＋-CaM shows that there are about 4 stronger binding sites and about 6 weak binding sites of Pb^2＋ in CaM. This is in agreement with the literature reports. The successive binding constants for the Pb^2＋ -CaM system are ： K1 = 2. 62×10^7, K2 = 3.75×10^7, K3 = 1.03×10^7, K4 = 1.85×10^7, K5 = 2.53×10^6, K6 = 8.07×10^5, K7 = 3.36×10^5, K8 = 2.76×10^5, K9 = 2.22×10^5 , and K10 = 3.96×10^4. The data show that the stronger binding constants for Pb^2＋ to CaM are higher 1 -2 order than those of Ca^2＋ to CaM（ gerenally, 10^6 to 10^5 orders）. This result is benefit to the further quantitative understanding of Pb^2＋- Ca^2＋ antagonism in CaM as well as its influence on CaM＇s function.