The regulation of amino acid incorporation into thyroid protein: Evidence that thyroxine and iodide inhibit protein synthesis at a ribosomal site

Abstract

1. The regulation of protein synthesis in the rat-thyroid gland was studied utilizing both a tissue slice system and a cell-free amino acid incorporating system. 2. Thyroid tissue slices and thyroid cell-free amino acid incorporating systems obtained from iodine-deficient rats both had an increased ability to incorporate [ 14C]valine into protein compared to similar systems obtained from control rats. 3. The addition of low concentrations of thyroxine and iodide to the incubation medium reduced the increased incorporation observed in iodine-deficient rat thyroid glands to levels near those of controls in both experimental systems. 4. It was observed that the increased ability for [ 14C]valine incorporation in iodine-deficient rat-thyroid glands and the inhibitory action of thyroxine and iodide were associated with the microsomal fraction. 5. The action of thyroxine and iodide is discussed in terms of the regulation of protein synthesis. It is suggested that thyroxine and iodide act as ribosomal inhibitors of protein synthesis in the rat-thyroid gland.