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Salt-Stable Hydrophobic Versus Salt-Reversible Electrostatic Effects in Adsorptive Protein Binding

  • B. H. J. Hofstee

Abstract

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.

Keywords

Hydrophobic Group Hydrophobic Effect Substrate Analog Hydrophobic Bonding Immobilize Ligand 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer Science+Business Media New York 1978

Authors and Affiliations

  • B. H. J. Hofstee
    • 1
  1. 1.Biochemistry DivisionPalo Alto Medical Research FoundationPalo AltoUSA

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