Simultaneous thyrotropin stimulation of thyroid protein synthesis and degradation determined by leucine pool sampling in nascent peptides.

TSH stimulated protein synthesis in calf thyroid slices, but this effect was masked by the simultaneous stimulation of thyroglobulin hydrolysis. These simultaneous effects on both synthesis and degradation were separated by determining the specific activity of amino acids serving as precursors for protein synthesis. Precursor pool specific activity was determined in thyroid nascent peptides which had been purified by epichlorohydrin triethanolamine cellulose chromatography from thyroid polysomes. TSH had no effect on the crude incorporation of [3H]leucine into thyroid protein, even though specific activity of the precursor pool [3H]leucine was diluted. As a consequence, TSH actually stimulated thyroid protein synthesis 2.6-fold. The proportion of nascent peptides immunoprecipitable by antithyroglobulin serum was unchanged by TSH, indicating a general stimulation of protein synthesis.