Salt-Stable Hydrophobic Versus Salt-Reversible Electrostatic Effects in Adsorptive Protein Binding
It appearsthat “structure forming” electrolytes, through a “salting out” effect, enhance hydrophobic “bonding”, i.e., the inter- and intra-molecular association of hydrophobic groups (1–3). Binding of many proteins to immobilized hydrophobic ligands indeed has been found to be stable in, and even stabilized by, high concentrations (1–3 M) of NaC1 (4–7). On the other hand, it has been stated, or implied (8,9) that hydrophobic bonding of certain proteins to agarose substituted with amines carrying hydrophobic groups, is reversed by the mere addition of NaCl. A hydrophobic group on the adsorbent apparently was required for binding and the salt concentration needed for reversal increased with increasing hydrophobicity of the ligand. Also, a “chaotropic” salt, such as KCNS was more effective in reversing the binding than a structure forming one such as Na2SO4 (9). These observations were taken as evidence for the hydrophobic nature of the binding. However, reversibility of hydrophobic bonding by the mere addition of NaCl would be contradictory to the observed stability of this mode of binding in the presence of the salt. This might indicate that actually another hydrophobic effect, such as hydrophobic shielding of the positive charges on the agarose-bound amino group (which retains its basic properties, ref.l0) was involved. It also has been postulated (11) that hydrogen bonding and/or preferential binding of anions may be enhanced through polarization of water around a hydrophobic group, which is assumed to occur with the hydrogens oriented outward.
KeywordsHydrophobic Group Hydrophobic Effect Substrate Analog Hydrophobic Bonding Immobilize Ligand
Unable to display preview. Download preview PDF.
- 1.VON HIPPEL, P.H., SCHLEICH, T. In “Structure and Stability of Biological Macromolecules” (Eds. S.N. Timasheff, G.D. Fasman,)Vol. 2, Marcel Dekker, New York, 1969, p. 417.Google Scholar
- 2.JENCKS, W.P. “Catalysis in Chemistry and Enzymology” McGraw-Hill, New York, 1969.Google Scholar
- 3.DANDLIKER, W.B., DE SAUSSURE, V.A. In “The Chemistry of Bio-Surfaces”, Vol. 1 (Ed. M.L. Hair) Marcel Dekker, New York, 1971, p.l.Google Scholar
- 11.LEWIN, S. “Displacement of Water and Its Control of Biochemical Reactions”, Academic Press, London, 1974.Google Scholar
- 12.McCLURE, W.O., EDELMAN, G.M. Biochemistry 5: 1908, 1966.Google Scholar
- 15.HOFSTEE, B.H.J. In “Polymer Grafts in Biochemistry” (Ed. H.F. Hixson), Marcel Dekker, (in the press).Google Scholar
- 17.TANFORD, C. “The Hydrophobic Effect: Formation of Micelles and Biological Membranes” John Wiley, Sons, New York, 1973.Google Scholar
- 18.PETERSON, E.A., SOBER, E.A. In “The Plasma Proteins” (Ed. F.W. Putnam) Vol. 1, Academic Press, New York, 1966, p. 105.Google Scholar
- 20.HOFSTEE, B.H.J. In “Methods of Protein Separation” (Ed. N. Catsimpoolas) Vol. 2, Plenum Press, New York, (in the (press).Google Scholar