A polyclonal antibody to a synthetic peptide derived from the rat follicle-stimulating hormone receptor reveals the recombinant receptor as a 74-kilodalton protein.

We have prepared a polyclonal antibody (AntiF) against a synthetic peptide comprising residues 19-29 of the rat FSH receptor. The specificity of this antibody was documented using human embryonic kidney (293) cells and stable transfectants of 293 cells expressing the recombinant LH/CG and FSH receptors. The data presented show that AntiF inhibits the binding of FSH, but not that of LH/CG, to their cognate receptors. AntiF also recognizes a specific protein(s) representing the FSH receptor in Western blots or by immunoprecipitation of cells transfected with the FSH receptor. This protein(s) is not present in untransfected 293 cells or in 293 cells permanently transfected with the LH/CG receptor. Finally, addition of the 19-29 peptide prevents immunoprecipitation of the FSH receptor by AntiF, whereas an unrelated peptide corresponding to residues 637-647 has no effect. In Western blots of 293 cells transfected with the FSH receptor, AntiF reveals the recombinant receptor as a heterogenous glycoprotein with a molecular mass of 58,000-83,000 daltons (in the absence of thiol-reducing agents) or 69,000-81,000 (in the presence of thiol reducing agents). Pulse-chase experiments with metabolically labeled cells show that the mature FSH receptor is a 74-kilodalton protein derived from 67- and 72-kilodalton precursors.