AFFINITY-BASED REVERSED MICELLAR PROTEIN EXTRACTION .2. EFFECT OF COSURFACTANT TAIL LENGTH

The selectivity of protein extraction by reversed micellar solutions c an be improved by the addition of affinity cosurfactants bearing ligan ds which bind strongly to the target protein. The interactions between cosurfactant and protein, as well as the interfacial activity of both the free cosurfactant and the protein-cosurfactant complex, were acco unted for in a model of the affinity-partitioning process. The aqueous phase dissociation constant was used to describe the protein-ligand i nteractions. The interfacial partition coefficient for several cosurfa ctant families varied with tail length according to the well-establish ed hydrophobic effect. Control studies with alkylated chymotrypsin sho wed that when longer hydrophobic tails are irreversibly attached to th e protein, the protein partitions more strongly to the reversed micell ar phase. In contrast, for reversible protein-cosurfactant binding, th e model predicts a maximum in protein uptake when the cosurfactant tai l length is varied; the decrease at longer tail lengths is due to the lowered aqueous phase concentration of affinity cosurfactant, resultin g in the formation of fewer protein-cosurfactant complexes. This behav ior was confirmed experimentally. (C) 1993 John Wiley & Sons, Inc.