Comparison of hydrophobic-interaction and reversed-phase chromatography of proteins.

The variable hydrophobic nature of proteins allows their separation through differential hydrophobic surface interactions. From these observations two modes of protein chromatography have been developed, hydrophobic-interaction chromatography (HIC) and reversed-phase chromatography (RPC). Selectivity of the HIC column can be easily manipulated by changing mobile phase variables. Protein retention was increased by decreasing the pH from neutrality or by using a salt with a greater "salting-out" ability. In addition, selectivity can be altered through chemical modification of the matrix surface. Protein retention and resolution decreased concomitantly with matrix ligand density. There were several major differences in HIC and RPC selectivity. Hydrophilic proteins such as cytochrome c and myoglobin were weakly retained on the HIC column but strongly retained on the RPC column. In contrast, a hydrophobic protein such as beta-glucosidase was strongly retained on the HIC column and only weakly retained on the RPC column. Other proteins were retained equally by RPC and HIC columns. Load capacity on the HIC column was determined by plotting resolution as a function of protein load. Resolution decreased significantly after 7.5 mg of total protein had been loaded onto the column per cm3 of column material. Samples of lactic dehydrogenase and alpha-chymotrypsin ranging in size from 10-200 micrograms were recovered from an HIC column with greater than 86% enzymatic activity in all cases. The recovery of enzymatic activity of alpha-chymotrypsin ranged from 55-91%, while none of the activity of beta-glucosidase was recovered from the RPC column.