Effects of pH and NaCl concentration on binding of covalently-linked insulin dimers to liver plasma membranes.

The effects of NaCl concentration and pH on binding to purified rat liver plasma membranes were compared for labelled insulin and two covalently-linked insulin dimers. Specific binding of both dimers and insulin increased as NaCl concentration increased from 0 to 1M in 0.05M Tris/HCl buffer. The initial rise in binding was much greater for dimers than for insulin. Specific binding of dimers was sensitive to pH changes in 0.029M barbital sodium acetate buffer, but this effect was more marked with insulin, which reached a sharp binding peak at pH 7.7 to 8.0. Both total and non-specific dimer binding were approximately 2-fold greater at pH 5.0 than at pH 8.0. Specific-binding fraction determinations of both dimers relative to insulin have been shown to be critically dependent on the experimental conditions of Na+/Cl- ion concentration and pH. These observations allow a better understanding of the nature of ligand-receptor interaction.