Concentration dependence of translational diffusion coefficients for globular proteins

Area of Science:

• Biophysical Chemistry
• Protein Dynamics
• Solution Behavior

Background:

• Sedimentation velocity experiments analyze protein diffusion.
• The translational diffusion coefficient (D) is often assumed to be concentration-independent.
• Current theories predict significant concentration dependence of D for proteins.

Purpose of the Study:

• To evaluate the concentration independence assumption for D in protein analysis.
• To assess the applicability of Fujita's Lamm equation approximation.
• To investigate diffusion of ovalbumin and bovine serum albumin.

Main Methods:

• Analysis of published traditional diffusion experiments.
• Examination of protein diffusion under constant temperature and solvent chemical potential.
• Comparison of experimental data with theoretical predictions.

Main Results:

• No significant concentration dependence of D was detected for ovalbumin and bovine serum albumin.
• Observed minor concentration dependence aligns with solution viscosity effects.
• Predicted variation in D below 10 mg mL(-1) falls within experimental uncertainty.

Conclusions:

• The assumption of concentration independence for D is reasonable for proteins at low concentrations.
• Fujita's approximate solution of the Lamm equation is suitable for analyzing boundary spreading in sedimentation velocity experiments.
• Findings support the use of simplified models in protein biophysical characterization.