The thyrotropin (TSH) receptor belongs to a subfamily of G protein-coupled receptors, which
also includes luteinizing hormone and follicle-stimulating hormone receptors. The TSH
receptor (TSHR) differs from the latter by the presence of an additional specific segment in
the C-terminal part of its ectodomain. We show here that this insertion is excised in the
majority of receptor molecules. Preparation of specific monoclonal antibodies to this region,
microsequencing, enzyme-linked immunosorbent assay, and immunoblot studies have …