Numerical study of the Johnston-Ogston effect in two-component systems

Area of Science:

• Biophysical Chemistry
• Analytical Ultracentrifugation
• Sedimentation Velocity Analysis

Background:

• The Johnston-Ogston effect describes complex sedimentation behavior in analytical ultracentrifugation due to interactions between components.
• Accurate interpretation of sedimentation velocity requires understanding how component interactions influence concentration profiles.
• Existing models may not fully capture dynamic changes throughout centrifugation.

Purpose of the Study:

• To numerically solve the Lamm equation for systems exhibiting the Johnston-Ogston effect.
• To demonstrate the relationship between concentration gradient maxima movement and sedimentation velocities.
• To generalize the Johnston-Ogston analysis for broader applicability in centrifugation studies.

Main Methods:

• Numerical solutions of the Lamm equation were employed.
• Analysis focused on systems with distinct and mixed plateaus of slow and fast sedimenting components.
• The study considered radial field and sector-shaped cell conditions.

Main Results:

• The movement of concentration gradient curve maxima directly reflects the sedimentation velocity of individual components.
• Solutions show distinct plateau behaviors for slow and fast components.
• A generalized Johnston-Ogston analysis was developed.

Conclusions:

• The movement of concentration gradient maxima provides a reliable indicator of sedimentation velocity, even with the Johnston-Ogston effect.
• The generalized analysis is valid for all centrifugation times under specified conditions.
• This work enhances the quantitative interpretation of sedimentation velocity experiments.