Sedimentation Velocity Analysis in Accelerating Gradients

Zone sedimentation is extensively employed for the separation and analysis of macromolecules and macromolecular complexes, and to obtain stably sedimenting bands, preformed density gradients are usually used as supporting media. This chapter describes various gradients for better separation in which the viscosity decreases with increasing concentration. In these accelerating gradients, the combination of increasing centrifugal force and decreasing viscous drag allows a substantial increase in sedimentation velocity as a function of distance sedimented. Sucrose and glycerol are the solutes most commonly chosen for the construction of such gradients. The faster sedimenting particle is accelerated over the slower sedimenting one, leading to a separation greater than proportional to the difference in their sedimentation coefficients. The accelerating gradient is most useful in separating particles possessing closely similar sedimentation coefficients.