Properties of thyrotropin receptor on cloned hybrid human thyroid cells

Purification of the thyrotropin (TSH) binding sites from cloned human thyroid cells (GEJ) was performed after biosynthetic labelling of the cells, affinity chromatography on a human TSH-sepharose column and polyacrylamide gel electrophoresis in sodium dodecyl sulphate (PAGE-SDS). The relative molecular mass (Mr) of the GEJ cell TSH receptor (TSH-R) was approximately 48,000. This was confirmed by cross-linking [125I]TSH to GEJ binding sites with two homobifunctional agents: dimethyl suberimidate and disuccinimidyl suberate. Moreover, the absence of a dithiothreitol effect demonstrated that the TSH binding site on GEJ cells is formed by a single chain lacking disulphide bonds.