Receptor heterogeneity in the human thyroid: differences between thyrotrophin binding sites in membrane and nuclear fractions.

Binding of 125I-labelled bovine TSH to crude membrane fractions of human thyroid tissue was a saturable, hormonally specific process which yielded non-linear Scatchard plots with limiting affinities of approximately 10(9) and 10(7) l/mol. Binding activity in membranes was soluble in Triton X-100, was inhibited specifically by immunoglobulins from patients with Graves's disease, and was increased by the beta-blocking drug, propranolol. In contrast, purified nuclear preparations showed a predominance of lower affinity binding, and their binding activity was insoluble in Triton and insensitive to immunoglobulins from patients with Grave's disease and to propranolol. Tryptic digestion liberated only low affinity binding activity from membranes or nuclei. It was concluded that human thyroid tissue contains independent classes of TSH-binding sites, which differ in their chemical, immunological and hormone-binding properties.