SELECTIVE DISPLACEMENT CHROMATOGRAPHY OF PROTEINS

In contrast to high molecular weight polyelectrolyte displacers, the e fficacy of low molecular weight displacers are dependent on both mobil e phase salt and displacer concentration. This sensitivity to the oper ating conditions opens up the possibility of carrying out selective di splacement where the product(s) of interest can be selectively displac ed while the low affinity impurities can be desorbed in the induced sa lt gradient ahead of the displacement train, a nd the high affinity im purities either retained or desorbed in the displacer zone. This type of displacement combines the operational advantages of step gradient a nd the high resolution inherent in a true displacement process, in a s ingle operation. Theoretical expressions are presented for establishin g selective displacement operating conditions (initial salt concentrat ion, displacer concentration) based on the Steric Mass Action paramete rs of the displacer and the linear Steric Mass Action parameters of th e feed proteins. Experimental results are presented to elucidate the c oncept of selective displacement in both cation and anion exchange sys tems. A mixture of alpha-lactalbumin and beta-lactoglobulin A and B ha s been used for anion-exchange systems; a four-protein mixture consist ing of ribonuclease B, bovine and horse heart cytochrome c, and lysozy me has been employed in cation exchange systems. This article also dem onstrates that on-line monitoring can be readily employed for the sele ctive displacement process, thus facilitating the scale-up and control of the process. This work sets the stage for the development of robus t large scale high resolution separations using selective displacement chromatography. (C) 1997 John Wiley & Sons, Inc.