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7852512 
Journal Article 
Follitropin binding to receptors in testis. Modulation by monovalent salts and divalent cations 
Andersen, TT; Reichert, LE 
1982 
Yes 
Journal of Biological Chemistry
ISSN: 0021-9258
EISSN: 1083-351X 
257 
19 
11551-11557 
English 
6288691 
The effects of monovalent salts and divalents metal ions on the interactions of radioiodinated human follitropin (125I-hFSH) with membrane-bound, detergent-solubilized, or buffer-soluble receptors from calf testis were studied. Binding of 125I-hFSH to the membrane-bound receptor was stimulated 2- to 3-fold by Mn2+, Mg2+, or Ca2+ (each at 2-5 mM), but was inhibited by Co2+ or Ni2+. Neither of these ions was capable of causing dissociation of preformed hormone receptor complexes. Addition of 10 mM EDTA resulted in a rapid, reversible dissociation of 125I-hFSH from each class of the receptor. Binding of FSH to detergent-solubilized or buffer-soluble receptor in the absence of divalent ions was negligible and was maximal at approximately 5 mM Mn2+, or Ca2+, with a midpoint of 0.8 mM. Various monovalent salts either inhibited or stimulated specific binding of FSH to the three classes of receptor. Inhibition of halides increased with ionic radius, in the order F-<Cl-<I-. Among the alkali ions, Na+ was more inhibitory than Li+ or K+ at 0.1 M. Acetate (0.1 M) was noninhibitory, while NO3- or HCO3- was a potent inhibitor. Stimulation of 125I-hFSH binding was seen at 0.1 M NH4+ ion. The effects of the various monovalent salts were primarily on receptor affinity, with the rate of dissociation being affected more than the rate of association. These effects, which are discussed in terms of their relationship to the B coefficient of viscosity, were reversible and nonspecific binding was largely unaffected. The similarity of effects of these salts or cations on the interaction of FSH with receptors in testis membranes, after detergent solubilization, and with FSH binding components soluble in the absence of detergent support the notion that the latter preparations are suitable models for the study of the receptor once removed from its membrane. The results also indicate that a detailed understanding of the effects of common inorganic ions on the interaction of FSH with receptor is essential to proper evaluation of in vitro binding studies. 
Animals; Calcium/pharmacology; Cations, Divalent; Follicle Stimulating Hormone/metabolism; Kinetics; Magnesium/pharmacology; Manganese/pharmacology; Receptors, Cell Surface/drug effects/metabolism; Receptors, FSH; Testis/metabolism