Bulk Purification by Fractional precipitation

Abstract

The solubility of a particular protein in aqueous solution depends on the solvent composition and on the pH; hence, variation in these parameters provides a way of purifying proteins by fractional precipitation. The factors that dictate solubility are complex, because the surface of a protein is itself complex, containing ionized residues, polar regions, and hydrophobic patches, all of which will interact with the solvent in ways that are not completely understood. Hence, it is not possible to elaborate a theoretical approach to fractional precipitation (1); rather, the methods are used in an essentially empirical fashion. The most widely used procedures are precipitation by the addition of salt (salting out) and by the addition of organic solvents; these are the focus of this chapter (see Note 1).