ION-EXCHANGE CHROMATOGRAPHY
Ion-exchange chromatography is logistically similar to Affinity chromatography. Both use a column resin that binds the proteins interest. With this technique, however, the interaction is less specific and is based on the net charge. An ion-exchange resin has a ligand with a positive or a negative charge. A ligand with a negative charge is called a cation exchanger, and a positively charged one is called anion exchanger. The column is initially equilibrated with a buffer of suitable pH and ionic strength. The exchange resin is bound to counterions. A cation-exchange resin is usually bound to Na+ or K+ ions, and an anion exchanger is usually bound to Cl- ions. A mixture of proteins is loaded on the column and allowed to flow through it. Proteins that have a net charge opposite to that of the exchanger stick to the column, exchanging plates with the bound counterions. Proteins that have no net charge or have the same charge as the exchanger elute.
|