Effect of Bacitracin and Polyamines on Follicle- Stimulating Hormone Binding to Membrane-Bound and Detergent-Solubilized Bovine Calf Testis Receptor*

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Abstract
We have examined the effects of bacitracin and several polyamines on the interaction of 125I-human FSH (125I-hFSH) with membrane-bound receptors (MR) or detergent-solubilized receptors (DSR) derived from bovine calf testes. Binding of 125I-hFSH to either calf testis MR or DSR was inhibited by bacitracin in a dose-related manner. Inhibition of 125I-hFSH binding to either MR or DSR was due to a decrease in the apparent affinity constant (Ka) of receptor for FSH. FSH binding inhibition by bacitracin was significantly greater with the MR (ED50 = 5.9 mM) than with the DSR (ED50 = 25 mM). Bacitracin was a more potent inhibitor of binding than the polyamines at equimolar concentrations in both MR and DSR systems. The inhibitor potency of the polyamines when using DSR was related to chain length and the number of amino groups present (spermine greater than spermidine greater than putrescine). Although it was not possible to ascertain the mechanism of binding inhibition, our results demonstrate a direct effect of bacitracin and polyamines on the interaction of FSH with testis receptors.

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