BINDING OF HORMONE TO TISSUE: THE FIRST STEP IN POLYPEPTIDE HORMONE ACTION

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Abstract
Thyroid slices showed persistent effects of thyroid-stimulating hormone (TSH) on glucose-1-C14 oxidation when sequentially exposed to TSH at 1[degree], washed thoroughly in hormone-free medium, and incubated at 37[degree] in the absence of hormone. Exposure of the tissue to anti-TSH serum or to trypsin reversed the persistent hormone effect without damaging the cells. Similarly, the persistent effect of insulin on glucose-l-Cl4 incorporation into rat diaphragms was reversed by antiinsulin serum. From these experiments it was concluded that the initial interaction of polypeptide hormones with target tissue is rapid firm binding to a superficial cell site, presumably on the external cell membrane, and that the equilibrium constant at 1[degree] for the interaction of TSH and sites on the thyroid is approximately 3 x 108.