Chapter 10 - Ultracentrifugation of Macromolecules

Abstract

This chapter discusses the ultracentrifugation of macromolecules. Two types of ultracentrifuge experiments: sedimentation velocity experiments, sedimentation equilibrium experiments, and applications of their use have been presented in the chapter. Ultracentrifugation involves sedimentation at high rotation speeds. This technique is used for separating macromolecules and determining their molecular weights and for the analysis of mixtures of proteins. Sedimentation velocity experiments are 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. The chapter presents models for sedimentation velocity and equilibrium experiments and discusses several applications to protein biochemistry. In ultracentrifugation, a homogeneous solution of macromolecules is placed into a sector-shaped cell. 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 governs the displacement of the macromolecules during the ultracentrifugation.