[2] Measurement of Changes of Hydrodynamic Properties by Sedimentation

This chapter discusses measurement of changes of hydrodynamic properties by sedimentation. To define accurately the conformational change in question, and to differentiate between local and global structural change, the overall picture of the macromolecule should be examined. One approach which may be used to obtain such information is to study the hydrodynamic properties of the macromolecule by sedimentation, specifically difference sedimentation velocity, l This technique monitors only those changes that perturb the hydrodynamic properties of the macromolecule; thus localized perturbations which do not affect the size and shape of the macromolecule may not be detected. Conventional sedimentation studies yield information about the size and shape of macromolecules. Frequently, the sedimentation coefficient of a macromolecule changes little as a result of the perturbation, so that the effect cannot be described quantitatively using conventional sedimentation. Sedimentation coefficients may be measured with a precision of greater than ±1% and accuracy of about 1%. 2 Hence, to measure small changes in the hydrodynamic properties of macromolecules, the difference sedimentation technique is essential.