Abstract
Summary1. Beef thyroid tissue slices were incubated in the presence of 100 microcuries UL-C14-tyrosine with 3 variations: a) no additions, b) propylthiouracil addition, c) non-radioactive thyronine. 2. Following digestion, analysis proceeded through counter current, paper and thin layer chromatography. The results for each of the experimental designs were the same. 3. Of the 3 major areas of radioactivity seen after counter current, only one could be further subdivided by the systems usually used for separation of iodotyro-sines, and iodothyronines, and this yielded at least 7 peaks in the systems used. 4. No evidence was found for in vitro formation of thyroxine or any of its precursors using tyro-sine as the labeled substrate.Since this work was completed, Nunez. Mauchamp, Macchia and Roche (Biochim. Biophys. Acta, 1965, vl07, 247) have also reported that they were unable to demonstrate incorporation of tritiated tyrosine into the iodotyrosines of thyroglobulin formed by sheep thyroid slices. Since the ...
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