Affinity purification of proteins using expanded beds.
The use of expanded beds of affinity adsorbents for the purification of proteins from feedstocks containing whole or broken cells is described. It is demonstrated that such feedstocks can be applied to the bed without prior removal of particulate material by centrifugation or filtration thus showing considerable potential for this approach in simplifying downstream processing flow-sheets. A stable, expanded bed can be obtained using simple equipment adapted from that used for conventional packed bed adsorption and chromatography processes. Circulation and mixing of the adsorbent particles is minimal and liquid flow through the expanded bed shows characteristics similar to those of plug flow. Frontal analysis performed with the highly selective affinity system involving the adsorption of human polyclonal immunoglobulin G onto Protein A Sepharose Fast Flow indicate that the adsorption performance of the expanded bed is similar to that achieved when the same amount of adsorbent is used in a packed configuration at the same volumetric flow-rate. The adsorption performance of the expanded bed was not diminished when adsorption was carried out in the presence of intact yeast cells. Batch adsorption experiments also indicated that the adsorption characteristics of the affinity system were not greatly altered in the presence of cells in contrast to results from a less selective ion-exchange system. An expanded bed of Cibacron Blue Sepharose Fast Flow was used to purify phosphofructokinase from feedstock of disrupted yeast prepared by high pressure homogenisation without the need for prior removal of particulate material. The potential for the use of expanded beds in large scale purification systems is discussed.