Quantifying the concentration dependence of sedimentation coefficients for globular macromolecules: a continuing...

Area of Science:

• Biophysical Chemistry
• Macromolecular Science
• Analytical Ultracentrifugation

Background:

• Sedimentation velocity experiments are crucial for characterizing macromolecular behavior.
• Accurate determination of the sedimentation coefficient (s) dependence on concentration (c) is vital for understanding molecular interactions and properties.
• Theoretical models for radial dilution effects in sedimentation velocity experiments have historically faced limitations due to experimental precision.

Purpose of the Study:

• To evaluate the feasibility of directly incorporating radial dilution effects into sedimentation coefficient calculations.
• To identify the simplest, most accurate method for quantifying linear s-c dependence in dilute systems using current analytical ultracentrifuge technology.
• To propose improvements for optical systems to enhance precision in sedimentation velocity experiments.

Main Methods:

• Retrospective analysis of theoretical models for radial dilution in sedimentation velocity experiments.
• Evaluation of precision requirements for concentration distributions in analytical ultracentrifugation.
• Assessment of standard c(s), g*(s), and G(s) analysis methods for determining average sedimentation coefficients.

Main Results:

• Early theoretical models require concentration distribution precision exceeding that of current analytical ultracentrifuge optical systems.
• For dilute systems, the simplest approach involves using an average sedimentation coefficient ($$) corresponding to the mean plateau concentration ($$) after radial dilution.
• The relationship between this average parameter and current descriptions of concentration dependence for sedimentation and translational diffusion coefficients was examined.

Conclusions:

• Directly incorporating radial dilution effects into sedimentation coefficient calculations is currently limited by experimental precision.
• The use of average sedimentation coefficients provides a practical method for analyzing dilute systems with existing technology.
• Significant improvements in analytical ultracentrifuge optical systems are necessary for more precise measurements and advanced theoretical modeling.