Concentration of Extracts

Abstract

In a typical purification starting from 1 kg of tissue, the volume of the initial homogenate might be 2 L and the final product of the procedure might be 2 mL of pure protein solution; that is, a volume decrease of 1000-fold is required. This emphasizes the fact that water is a major contaminant during protein purification, and at several steps during the procedure, the need will arise for concentration of the active extract or fraction. Concentration may occur as a concomitant of a step in purification (e.g., fractional precipitation [see Chapter 13] or ion-exchange chromatography [see Chapter 14]); in the latter case, protein from a dilute solution may be absorbed onto the resin and subsequently eluted in a smaller volume by application of a salt gradient. In general, however, one or more steps specifically aimed at concentration of the protein solution will need to be done.