DIFFUSION STUDIES OF BOVINE SERUM-ALBUMIN BY QUASI-ELASTIC LIGHT-SCATTERING
DIFFUSION STUDIES OF BOVINE SERUM-ALBUMIN BY QUASI-ELASTIC LIGHT-SCATTERING
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DOI：
10.1021/bi00713a024
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发表时间：
1974-01-01
期刊：
影响因子：
2.9
通讯作者：
FLYGARE, WH
中科院分区：
文献类型：
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作者：
RAJ, T;FLYGARE, WH
T. Rajt和WH Flygare* 摘要：在pH值为7.0至2.0的范围内，测量牛血清白蛋白（BSA）的平移扩散系数D，作为离子强度和BSA浓度的独立函数。在相对高的离子强度下，扩散系数在相对低的浓度下与BSA浓度无关，并且当pH值降低到等电位以下时，分子似乎膨胀（较小的扩散常数）。牛血清白蛋白（BSA）* 1在其等电点（pH=<$5）和附近作为紧凑分子存在。尽管该分子在pH 4.5-10.5范围内的构型或构象没有变化，但所有过去的研究表明，BSA溶液在pH 4.5-2.0范围内的某些理化性质发生了非常显著的变化，尽管是可逆的。沉积常数（哈灵顿等人，1956年; Kronman和Foster，1957年; Charlwood和Ens，1957年）、平移扩散系数（香槟，1957年）、比粘度（Yang和Foster，1954年; Tanford等，1955）、比旋光度（Yang和Foster，1954; Sogami和Foster，1968）和低角X射线散射研究（Luzzatti等，1961）都表明BSA分子在低pH下膨胀。这种膨胀是可逆的，本质上显然是静电的，因为它高度依赖于BSA溶液的离子强度;随着离子强度的降低，膨胀增加。然而，由于随着pH降低，旋转弛豫时间ph减小，排除了形状没有变化的分子的总体溶胀（Weber，1952; Weber和Young，1964;哈灵顿等人，1956年）。Foster（1960）提出了一个模型，该模型解释了上述变化，其中蛋白质由柔性肽链段连接的球状部分组成。当pH值大于等于5时，紧密分子从pH值5到约3.5发生转化和膨胀，在较低pH值时，分子进一步膨胀。
T. Rajt and WH Flygare* abstract: The translational diffusion coefficient, D, of bo-vine serum albumin (BSA) is measured in a pH range from 7.0 to 2.0 as independent functions of ionic strength and BSA con-centration. At relatively high ionic strength the diffusion coefficients are BSA concentration independent at relatively low concentrations and the molecule appearsto expand (smaller diffusion constant) as the pH is lowered below the isoelectric. Bovine serum albumin (BSA)* 1 exists as a compact molecule at and near its isoelectric point (pH=¿ 5). Although the molecule shows no change in configuration or conformation in the pH range 4.5-10.5, all past studies reveal that BSA solutions change very markedly, though reversibly, certain of their phys-icochemical properties over the pH range 4.5-2.0. The sedi-mentation constant (Harrington et al., 1956; Kronman and Foster, 1957; Charlwood and Ens, 1957), translational diffu-sion coefficient (Champagne, 1957), specific viscosity (Yang and Foster, 1954; Tanford et al., 1955), specific optical rota-tion (Yang and Foster, 1954; Sogami and Foster, 1968), and low-angle X-ray scatteringstudies (Luzzatti et al., 1961) all suggest expansion of the BSA molecule at low pH. This expan-sion is reversible and apparently electrostatic in nature, as it is highly dependent on the ionic strength of the BSA solution; the expansion increases as the ionic strength is lowered. However, an overall swelling of the molecule with no change in shape is ruled outbecause of the decrease in the rotational relaxation time, ph, as the pH is lowered (Weber, 1952; Weber and Young, 1964; Harrington et al., 1956). A model has been pro-posed by Foster (1960) which accounts for the above changes where the protein is composed of globularparts linked by flexi-ble peptide chain segments. The compact molecule (at and above pH 5) undergoes a transformation and expansion from pH 5 to about 3.5 and at lower pH the molecule expands fur-ther.