Sedimentation equilibrium in the analytical ultracentrifuge

Abstract For many years analytical ultracentrifugation was the major source of information on the heterogeneity and molecular size of macromolecules. In the field of protein chemistry the question of solute heterogeneity is now usually addressed by gel electrophoretic and gel chromatographic techniques, and the molecular weight is either calculated from the amino acid sequence or obtained by mass spectrometry. Because such molecular weight values refer only to the covalently linked polypeptide chain(s), they provide no information about the macro molecular state of the functional protein or enzyme. In its simplest application molecular weight measurement by analytical ultracentrifugation is therefore used to characterize quaternary structure, which affords an example of a self-association equilibrium that has gone to completion.