DIRECT ANALYSIS OF SOLUTE SELF-ASSOCIATION BY SEDIMENTATION EQUILIBRIUM

An improved procedure is described for the characterization of solute self-association by sedimentation equilibrium. Whereas previous statis tical-mechanical approaches to allowance for the effects of thermodyna mic nonideality have entailed tedious iteration because of their speci fication of activity coefficients in terms of the equilibrium concentr ations of all species, such reliance upon knowledge of the solution co mposition is avoided by the adaptation of an alternative statistical-m echanical form ulation [ T. L. Hill and Y. D. Chen (1973) Biopolymers, Vol. 12, pp. 1285-1312] in which thermodynamic nonideality is express ed in terms of total solute concentration. The development of an analy sis in terms of a relationship with total solute concentration as the experimental variable allows this attribute of the Adams-Fujita approa ch to be retained without sacrifice of statistical-mechanical rigor. I fs use is illustrated by application to Rayleigh interferometric recor ds of sedimentation equilibrium distributions reflecting alpha-chymotr ypsin dimerization and lysozyme self-association. (C) 1996 John Wiley & Sons, Inc.