Ion-Exchange Chromatography

Abstract

Proteins contain charged groups on their surfaces, which enhance their interactions with solvent water and hence their solubility. At physiological pH, some of these charged groups are cationic (positively charged, e.g., Lysine), whereas others are anionic (negatively charged, e.g., Aspartate). Since proteins differ from each other in their amino acid sequence, the net charge possessed by a protein at physiological pH is determined ultimately by the balance between these charges (i.e., negatively charged proteins possess more negatively charged groups than positively charged groups). This also underlies the different pIs of proteins (see Chapter 23). Ion-exchange chromatography (1) separates proteins first on the basis of their charge type (cationic or anionic) and, second, on the basis of relative charge strength (e.g., strongly anionic from weakly anionic).