Analytical ultracentrifugation is a classical technique of physical
biochemistry, but it is still rapidly developing and regaining
popularity, in particular, for the study of protein interactions in
solution. Key features of this technique, including experiments
covering a large concentration range at once and the characterization
of protein complexes without their removal from the bath
of building blocks, make it a highly useful tool for the study of
high- and low-affinity interactions as well as self-association and
heteroassociation processes. In the present work, we have exploited
the fact that the hydrodynamic separation of protein
complexes in sedimentation velocity can be combined with
another dimension of separation based on absorbance spectral
properties of the sedimenting species, an approach pioneered by
Steinberg and Schachman (21).