Sedimentation

Ultracentrifugation involves sedimentation at high rotation speeds. This technique is routinely used for separating macromolecules and determining their molecular weights and for the analysis of mixtures of proteins [1]. In this chapter, we present models for sedimentation velocity and equilibrium experiments and discuss several application to protein biochemistry.

In ultracentrifugation, a homogeneous solution of macromolecules is placed into a sector-shaped cell like that shown in Figure 10.1. This cell is placed in a rotor that spins about the rotation axis at angular velocity &>. Centrifugal, buoyant, and frictional forces act upon the macromolecules in the cell. The interplay between these forces govern the displacement of the macromolecules during the ultracentrifugation [1],

In this chapter, we discuss of two types of ultracentrifuge experiments and applications of their use. Sedimentation velocity experiments can be used to obtain the sedimentation coefficient of a macromolecule, which depends on the molecular weight and the frictional coefficient. Sedimentation equilibrium experiments are used to obtain weight average molecular weights.

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