Air-driven ultracentrifuge for sedimentation equilibrium and binding studies

This chapter focuses on air-driven ultracentrifuge for sedimentation equilibrium and binding studies. The air-driven ultracentrifuge, capable of high angular velocities, provides a convenient laboratory instrument for such studies. In addition, analysis of sedimentation behavior in the air-driven ultracentrifuge of solubilized membrane proteins permits characterization of their molecular size and interactions in solution. The analytical techniques involved in these latter studies are based on the use of sedimentation equilibrium theory. The air-driven ultracentrifuge provides a simple and thermodynamically rigorous technique for the analysis of the molecular weights and interactions of membrane proteins in solution. Ligand-membrane complexes can be rapidly sedimented, allowing the concentration of free ligand in the supernatant and hence the binding constant for the interaction to be determined. Effects due to re-equilibration of the ligand with the acceptor during centrifugation are small, especially for the low-molecular-weight ligands. The analytical techniques also allow the interactions between proteins of comparable size to be characterized.