CORRELATION OF B COEFFICIENT OF VISCOSITY FOR MONO-VALENT SALTS WITH EFFECTS ON BINDING OF HUMAN FOLLITROPIN TO RECEPTOR

Various monovalent salts inhibit the binding of radioiodinated human follitropin ([125I]hFSH) to receptors present in calf testis. The effects were examined of salts on the affinity constant (Ka) and number of binding sites (R0) in the FSH-calf testis receptor system. A constant amount of [125I]hFSH and increasing amounts of unlabeled hFSH were allowed to bind to a constant amount of receptor in the absence or presence (0.10 M) of halides, nitrates or acetates of the alkali ions at 20.0.degree. C. There was an appreciable variation of the affinity constant depending on the salt being used, but there was no change in receptor number (R0). Within an alkali cation series (e.g., NaCH3CO2, NaF, NaCl, NaBr, NaNO3, NaI or a similar K series) the affinity decreased with decreasing B coefficient of viscosity. Within a halide series (e.g., LiCl, NaCl, KCl, RbCl or the similar bromide series) the minimum value of the affinity constant occurred with the Na+ salt. The special inhibitory potency of Na+ may suggest that it has a unique interaction with calf testis FSH receptor or with FSH. The studies indicate a correlation between the B coefficient of viscosity and the ability of salts to inhibit binding of [125I]hFSH to receptor.