Differential Effects of Monovalent and Bivalent Antisera on the Interaction of Follicle-Stimulating Hormone with Its Receptor*

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Abstract
Polyclonal antisera to human FSH (hFSH) and its .alpha.- and .beta.-subunits were used as probes of the interaction between hFSH and the FSH receptor from bovine testis. Preincubation of [125I]iodo-hFSH with antisera to the subunits of hFSH induced an augmentation in binding of radioiodinated hFSH to membrane receptors. If the antisera were made monovalent by papain digestion, all binding augmentation previously seen with bivalent antisera was eliminated. Furthermore, whereas bivalent antiserum to intact hFSH had no effect on [125I]iodo-hFSH binding to receptor, papain-generated monovalent antisera to hFSH strongly inhibited [125I]iodo-hFSH binding. Formation of [125I]iodo-hFSH-receptor complex reduces the ability of bivalent antibodies to FSH or its subunits to interact with the complex, as determined by immunoprecipitation studies. Each FSH subunit evidently interacts with the membrane receptor. A comparison of bivalent and monovalent antisera is necessary to determine if a particular antibody effects binding of hormone to receptor.