The Omega Analysis and the Characterization of Solute Self-Association by Sedimentation Equilibrium

Abstract

For many years the analytical ultracentrifuge was considered to be the major source of information on the heterogeneity and molecular weight of macromolecules, a role that has now been taken over largely by gel electrophoretic and gel chromatographic techniques. The main use of analytical ultracentrifugation in protein chemistry is now the determination of equilibrium constants for macromolecular interactions. The traditional approach to ultracentrifuge analysis undoubtedly influenced initial attempts to employ the ultracentrifuge for characterizing solute self-association. Those analyses were based on the concentration-dependence of weight-average molecular weights derived from sedimentation equilibrium distributions (Adams and Williams, 1964; Roark and Yphantis, 1969; Hoagland and Teller, 1969). Although such practices still prevail (Bucci, 1986; Chatelier and Minton, 1987; Minton, 1990), more direct procedures have also been developed for analyzing the sedimentation equilibrium distribution, which is an experimental record of total solute concentration, c(r), as a function of radial distance, r.