Schuck Peter
Division of Bioengineering and Physical Science, ORS, OD, National Institutes of Health, Building 13, Rm. 3N17, 13 South Drive, Bethesda, MD 20892-5766, USA.
Biophys Chem. 2004 Mar 1;108(1-3):201-14. doi: 10.1016/j.bpc.2003.10.017.
The effects of solvent compressibility on the sedimentation behavior of macromolecules as observed in analytical ultracentrifugation are examined. Expressions for the density and pressure distributions in the solution column are derived and combined with the finite element solution of the Lamm equation in inhomogeneous media to predict the macromolecular concentration distributions under different conditions. Independently, analytical expressions are derived for the sedimentation of non-diffusing particles in the limit of low compressibility. Both models are quantitatively consistent and predict solvent compressibility to result in a reduction of the sedimentation rate along the solution column and a continuous accumulation of solutes in the plateau region. For both organic and aqueous solvents, the calculated deviations from the sedimentation in incompressible media can be very large and substantially above the measurement error. Assuming conventional configurations used for sedimentation velocity experiments in analytical ultracentrifugation, neglect of the compressibility of water leads to systematic errors underestimating sedimentation coefficients by approximately 1% at a rotor speeds of 45000 rpm, but increasing to 2-5% with increasing rotor speeds and decreasing macromolecular size. The proposed finite element solution of the Lamm equation can be used to take solvent compressibility quantitatively into account in direct boundary models for discrete species, sedimentation coefficient distributions or molar mass distributions. Using the analytical expressions for the sedimentation of non-diffusing particles, the ls-g*(s) distribution of apparent sedimentation coefficients is extended to the analysis of sedimentation in compressible solvents. The consideration of solvent compressibility is highly relevant not only when using organic solvents, but also in aqueous solvents when precise sedimentation coefficients are needed, for example, for hydrodynamic modeling.
研究了在分析超速离心中观察到的溶剂压缩性对大分子沉降行为的影响。推导了溶液柱中密度和压力分布的表达式，并与非均匀介质中Lamm方程的有限元解相结合，以预测不同条件下的大分子浓度分布。另外，还推导了低压缩性极限下非扩散颗粒沉降的解析表达式。两种模型在定量上是一致的，并且预测溶剂压缩性会导致沿溶液柱的沉降速率降低以及溶质在平台区域持续积累。对于有机溶剂和水性溶剂，计算得出的与不可压缩介质中沉降的偏差可能非常大，且大大高于测量误差。假设在分析超速离心中用于沉降速度实验的常规配置，忽略水的压缩性会导致系统误差，在45000 rpm的转子速度下，沉降系数被低估约1%，但随着转子速度的增加和大分子尺寸的减小，误差会增加到2 - 5%。所提出的Lamm方程的有限元解可用于在离散物种、沉降系数分布或摩尔质量分布的直接边界模型中定量考虑溶剂压缩性。利用非扩散颗粒沉降的解析表达式，将表观沉降系数的ls - g*(s)分布扩展到可压缩溶剂中沉降的分析。考虑溶剂压缩性不仅在使用有机溶剂时高度相关，而且在需要精确沉降系数的水性溶剂中也很重要，例如用于流体动力学建模。
