The PFBMI has a ProteomeLab XL-I (Beckman-Coulter) analytical ultracentrifuge with a dual UV/visible and interference detection system. The hydrodynamic behavior of a macromolecule and its sedimentation coefficient are determined by different parameters: volume, shape, density and mass. Analytical ultracentrifugation allows a direct measurement of the mass and sedimentation coefficient of macromolecules in solution. In the case of oligomeric assemblies and non-covalent complexes, it allows to determine the number of chains involved in the native architecture of a macromolecule or the stoichiometry of a complex, as well as their equilibrium constant. Informations about the conformation of macromolecules or the homogeneity of samples can also be obtained.