Allowance for boundary sharpening in the determination of diffusion coefficients by sedimentation velocity: a historical perspective
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This review summarizes endeavors undertaken in the middle of last century to employ the Lamm equation for quantitative analysis of boundary spreading in sedimentation velocity experiments on globular proteins, thereby illustrating the ingenuity required to achieve that goal in an era when an approximate analytical solution of that nonlinear differential equation of second order provided the only means for its application. Application of procedures based on that approximate solution to simulated sedimentation velocity distributions has revealed a slight disparity (about 3%) between returned and input values of the diffusion coefficient—a discrepancy comparable with that of estimates obtained by current simulative analyses based on numerical solution of the Lamm equation. Although the massive technological developments in the gathering and treatment of sedimentation velocity data over the past three to four decades have changed dramatically the manner in which boundary spreading is analyzed, they have not led to any significant improvement in the accuracy of the diffusion coefficient thereby deduced.
KeywordsAnalytical centrifugation Sedimentation velocity Sedimentation coefficient Concentration dependence Boundary spreading Diffusion coefficient
We thank Dr. Peter Schuck for helpful advice on the use of his SEDFIT program for the simulation of sedimentation velocity distributions. The financial support of this investigation by the Science and Technology Facilities Council (UK) through an award to DJS is also gratefully acknowledged, as is the travel and accommodation support provided to DJW by the University of Nottingham over many years for this collaborative project.
Compliance with ethical standards
Conflict of interest
Donald J. Winzor declares that he has no conflicts of interest. David J. Scott declares that he has no conflicts of interest.
This article does not contain any studies with human participants or animals performed by any of the authors.
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