TABLE OF CONTENTS Although the expressions for sedimentation equilibrium were derived initially from the viewpoint of a balance between centrifugal and diffusional fluxes, [1] current theory stems from a realization by Goldberg [2] that solute distribution is amenable to rigorous thermodynamic description. This development led to analysis of the concentration dependence of apparent molecular weight for a single, nonassociating solute in terms of its true molar mass (the value extrapolated to zero solute concentration) and an activity coefficient that quantified the concentration dependence. [3] [6] The exact nature of that empirically defined activity coefficient has been recognized only recently. [7]
The next theoretical breakthrough was the demonstration that the sedimentation equilibrium procedure had the potential to accurately define the thermodynamic activity of a solute in incompressible solutions. [8] [11] This potential was strengthened further by the realization that statistical mechanics provided a means of interpreting the experimentally derived thermodynamic activities and activity coefficients. [10] , [12] [15]
Originally, the characterization of protein self-association by direct analysis of the experimental concentration distribution entailed, for ideal systems, evaluation of the equilibrium concentration of monomers throughout the distribution, and hence deduction of the equilibrium constant(s) by combining that quantity with the total concentration at each radial distance. [9] , [15] , [16] Despite its simplicity, this procedure has usually been overlooked in favour of an alternative direct analysis that is based on a nonlinear least-squares minimization procedure to obtain the...
