AUC can be applied to a wide range of biological systems. An analytical ultracentrifuge identifies the solution properties of macromolecules (including their interactions), facilitates solution structural determinations of large proteins using constrained modelling, and complements new NMR and crystal structure determinations. We possess two Beckman-Coulter XL-I machines equipped with four-hole and eight-hole rotors and six-sector equilibrium cells and two-sector velocity cells. One machine is equipped with fluorescent optics. Samples are observed using absorbance, interference and/or fluorescent optics. Two types of experiments are performed:
(1) In sedimentation equilibrium experiments at low rotor speeds, diffusion opposes the process of sedimentation. When the two opposing forces reach equilibrium, the sample distribution is exponential in appearance, and molecular weights are obtained. Equilibria can be studied to yield dissociation Kd values.
(2) In sedimentation velocity experiments, if the sample is subjected to a high speed centrifugal field, relatively rapid sedimentation towards the bottom of the cell occurs. The sedimentation coefficient (s20,w) provides structural data for comparison with crystallography, scattering and NMR. Information on sample composition and the species present is obtained from size distribution functions.