Surfactant-mediated protein hydrophobic-interaction chromatography

Three proteins have been subjected to hydrophobic-interaction chromatography in the presence of submicellar concentrations of the surfactant (3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulfonate (CHAPS). At several concentrations of CHAPS below the critical micelle concentration, CHAPS increased the retention of lysozyme and pancreatic trypsin inhibitor, but decreased that of ribonuclease A. The dependence of retention on CHAPS concentration was substantially different for the three proteins, i.e., the surfactant showed selectivity in its interactions with the proteins. In the solvents that were used for chromatography the surface tension decreases monotonically with increasing CHAPS concentration. Since different proteins may either be eluted or retained by the addition of CHAPS, our findings are inconsistent with the idea that retention is a simple function of surface tension. It also appears unlikely that the selectivity we have observed can be accounted for by a formulation of retention as a function of surface tension. As an alternative interpretation, we present a scheme of multiple equilibria and their kinetic components as a basis for formulating the dependence of retention on surfactant concentration.