摘要
在ｐＨ６．３０、３７℃条件下，采用离心超过滤技术测定了１１种稀土离子（Ⅲ）与牛血清白蛋白（Ｂ８Ａ）的专一性结合常数Ｋ＿ｓ和非专一性结合常数Ｋ＿（ｎｓ）观察到Ｋ＿ｓ随稀土系列原子序数（Ｚ＿（ＲＥ））的变化有明显的＂四分组效应＂和＂钆断现象＂，而Ｋ＿（ｎｓ）～Ｚ＿（ＲＥ）类似于一元羧酸－稀土配合物稳定常数的变化规律。求出Ｔｂ（Ⅲ）－ＢＳＡ结合反应的热力学函数分别为ΔＨ＿ｓ＝４４．５±０．８ｋＪ／ｍｏｌ，ΔＳ＿ｓ＝２４３．２±２．４Ｊｍｏｌ·Ｋ，ΔＨ＿（ｎｓ）＝１９．９±１．１ＫＪ／ｍｏｌ，ΔＳ＿（ｎｓ）＝１４１．４±３．２Ｊ／ｍｏｌ·Ｋ。根据不同ｐＨ下测得的Ｔｂ（Ⅲ）与ＢｓＡ结合的Ｋ＿ｓ和Ｋ＿（ｎｓ）拟合出ＢＳＡ分子中参与稀土配位的基团的质子解离常数ｐＫ＝４．６０，进而确定出这些基团主要为天冬氨酸和谷氨酸残基侧链中的β、γ－ＣＯＯ￣－。
The binding constants of 11 Lanthanide ions(Ⅲ)to bovine serum albu-min(BSA)were determined at 37℃ in 50mmol/L,pH6.30 hexamethylenetetramine buffer by the Centrifugal Ultrafiltration method.It was found that the dependence of the high affinity binding constants(K_s)on the atomic number of Lanthanide ions(Z_(RE))exhibits"tetrad effect"and "gadolinium break" ,across the series. However,the variation of non-specific binding constant(K_(ns))with Z_(RE) was following the pattern of the acetie-lanthanide ions complexes. The thermodynamie funetions are determined as follows:ΔH_s=44.5±0.8KJ/mol,ΔS_s=243.2±2.4J/mol·K;ΔH_(ns)=19.9±1.1kJ/mol,ΔS_(ns)=141.4±3.2J/mol·K. In addition,on the basis of overall pK of 4.6 was estimated for describing the ionization of the side chains which functions as the metal ligands ,implying that the metal ligands are carboxyl group of aspartic and /or glutamic acid residues.
出处
《北京大学学报（自然科学版）》
CSCD
北大核心
1994年第4期383-387,共5页
Acta Scientiarum Naturalium Universitatis Pekinensis
关键词
稀土离子
牛
血清白蛋白
结合常数
rare earths
bovine serum albumin
binding reaction
thermodynamics
