Separation by Adsorption—Affinity Techniques

Abstract

Affinity chromatography, developed during the 1960s and 1970s, referred originally to the use of an immobilized natural ligand, which specifically interacts with the desired protein. The ligand is immobilized on suitable particles which can be packed into a column. Then a sample containing the protein is passed into the column, and the specific interaction holds back the desired protein, while others pass through (Figure 7.1). “Affinity” techniques in general make use of a biospecific interaction that results in a change in properties of the protein such that it can be separated from other proteins. Not only can it apply to column chromatography, but also to precipitation, electrophoresis, liquid-phase partitioning, and other separation methods. It should be noted that many workers have used the words “affinity chromatography” to describe processes that do not involve biospecific interactions. “Affinity” is then being used in its more general sense of “attraction”; so we have affinity chromatography on adsorbents such as dyes, immobilized metals, and mixedfunction ligands, which do not necessarily interact at natural ligands’ binding sites. Used in this way, the word “affinity” becomes a tautology, since the word “chromatography” is sufficient to imply that an attraction is occurring.