Allowance for thermodynamic nonideality in the analysis of sedimentation equilibrium distributions reflecting complex formation between dissimilar reactants

Abstract

General quantitative expressions are developed to take rigorous statistical-mechanical account of the effects of thermodynamic nonideality in sedimentation equilibrium distributions reflecting interaction between dissimilar macromolecular reactants. These quantitative expressions form the basis of an analysis which yields global estimates of the equilibrium constant(s) and the corresponding reference thermodynamic activities of free reactants in several experiments. Simulated data for 1:1 complex formation between dissimilar reactants are used to illustrate the procedure, which is currently unable to take advantage of the third virial coefficient terms to nonideality because of the lack of expressions for the excluded-volume contribution of three-body clusters of dissimilar species. In the absence of experimental studies where chemical interaction is sufficiently weak to warrant the use of concentrations commensurate with significant thermodynamic nonideality effects, published data on lysozyme self-association have been analysed to demonstrate the experimental application of the global analysis.