Section on Physical Biochemistry, Laboratory of Biochemistry and Genetics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, U.S. Department of Health and Human Services, Bethesda, Maryland 20892, USA.
J Phys Chem B. 2010 Aug 26;114(33):10876-80. doi: 10.1021/jp104342f.
Quantitative analysis of the composition dependence of the concentration gradient of each species of macromolecule within a solution mixture at sedimentation equilibrium permits the quantitative characterization of self- and heterointeractions between sedimenting solutes. Sedimentation equilibrium experiments were conducted on solutions containing a trace concentration of FITC-labeled BSA in varying concentrations of Ficoll 70 and on solutions containing a trace concentration of FITC-labeled Ficoll 70 in varying concentrations of BSA. The equilibrium gradient of each solute component in each mixture was measured independently. Analysis of the resulting gradients resulted in evaluation of the dependence of the activity coefficient of Ficoll upon the concentrations of Ficoll and BSA at concentrations of up to 100 g/L and the dependence of the activity coefficient of BSA upon the concentrations of Ficoll and BSA at concentrations of up to 100 g/L. The activity coefficients of both species increase significantly with increasing Ficoll and BSA concentration and do not vary with temperature, to within the precision of measurement, over the temperature range of 5-37 degrees C, indicating that the dominant interaction between Ficoll molecules and between BSA and Ficoll molecules is repulsive and probably due to steric volume exclusion. The measured dependences may be accounted for quantitatively by a simple model in which BSA and Ficoll 70 are represented by equivalent rigid particles.
在沉降平衡中，对溶液混合物中每种大分子物质浓度梯度的组成依赖性进行定量分析，可定量描述沉降溶质之间的自相互作用和异相互作用。在含有痕量浓度 FITC 标记 BSA 的溶液中，进行了不同浓度 Ficoll 70 的沉降平衡实验，以及在含有痕量浓度 FITC 标记 Ficoll 70 的溶液中，进行了不同浓度 BSA 的沉降平衡实验。分别独立测量了每种混合物中每种溶质成分的平衡梯度。对所得梯度的分析导致了对 Ficoll 活度系数随 Ficoll 和 BSA 浓度的依赖性的评估，其浓度高达 100 g/L，以及 BSA 活度系数随 Ficoll 和 BSA 浓度的依赖性的评估，其浓度高达 100 g/L。两种物质的活度系数都随着 Ficoll 和 BSA 浓度的增加而显著增加，并且在 5-37°C 的温度范围内，不随温度变化，在测量精度范围内，这表明 Ficoll 分子之间以及 BSA 和 Ficoll 分子之间的主要相互作用是排斥的，可能是由于空间位阻排斥。可以通过一个简单的模型对测量的依赖性进行定量解释，其中 BSA 和 Ficoll 70 用等效刚性粒子表示。
