Gonadotropin receptor binding regulators in serum. Characterization and separation of follitropin binding inhibitor and lutropin binding stimulator.

Subfractions of human serum capable of inhibiting specific binding of radioiodinated human follitropin and stimulating specific binding of radioiodinated human lutropin to testicular receptors were prepared by molecular sieving techniques, separated by ion exchange chromatography, and further purified by reversed phase high pressure liquid chromatography. Although purified approximately 2000-fold, the exact chemical nature of the follicle-stimulating hormone binding inhibitor is as yet uncertain. However, a variety of analytical procedures indicated it to be separate and distinct from the lutropin binding stimulator, to have a molecular weight of about 700, and to contain a peptide component. Available evidence suggests that the serum factor responsible for luteinizing hormone binding stimulation may be calcium.