Isolation and characterization of gonadotropin inhibitor from porcine folliculkar fluid

Abstract

A gonadotropin receptor–binding inhibitor has been isolated in a highly purified state. It has been shown to inhibit the binding of labeled hFSH and hCG. The amount of protein required to inhibit 50% of the binding of labeled hFSH and hCG decreases progressively as purification proceeds. Both FSH and hCG binding inhibitory activities reside in the same molecule, which has a molecular weight of approximately 30,000. The binding of the labeled gonadotropin inhibitor to gonadotropins has also been demonstrated. Kinetic analysis shows that the mode of inhibition exerted by the gonadotropin receptor–binding inhibitor is competitive in nature. The inhibitor does not form any association complexes, nor does it possess intrinsic proteolytic activity. In addition to inhibiting the receptor binding of gonadotropins, the inhibitor also suppresses the biological response elicited by gonadotropins, as evidenced by decreased progesterone production in vitro. However, it does not inhibit dbcAMP stimulated progesterone production, indicating that its site of action is proximal to cAMP formation. A possible physiological role of this inhibitor as an autocrine regulator has been suggested.