Figure 1. Basis of anion exchange chromatography. Proteins with differing charge are represented as blue circles. The positively-charged ion exchange group immobilized on the stationary phase is charged with  Cl^– counterions. (a) Protein with net negative charge exchanges with  Cl^– while that with a net positive charge simply passes through the stationary phase without binding. (b) Negatively-charged protein is held on the ion exchange group by electrostatic attraction. (c) The protein is eluted by exchange with  Cl^– ions provided by an NaCl gradient.

Figure 2. Purification of acetolactate decarboxylase (ALD) by anion exchange chromatography on a column of POROS PI perfusive packing. Proteins from Leuconostoc lactis NCW1 bound to the column at pH 7.0 were selectively eluted with an NaCl gradient (dashed line). Several peaks of protein were deteced by monitoring the absorbance at 280 nm (A₂₈₀). ALD activity (red triangles) is expressed as mol L^–1 min^–1 of the decarboxylation product, acetoin, determined spectrophotometrically at 525 nm. It was found to elute in a single peak that was pure by the criterion of SDS polyacrylamide gel electrophoresis.