Previous studies on the biosynthesis of sheep thyroglobulin in vitro have shown that the formation of this iodoprotein (19S) is preceded by the appearance of two other components having a slower sedimentation rate (3-8S and 12S). While the 12S protein was interpreted as an intermediate in the synthesis of thyroglobulin, the nature of the 3-8S component still remained unclear. Studies recently carried out in our laboratory have shown a clearcut precursor-product relationship between a slow sedimenting component (6S) and 19S thyroglobulin during the synthesis of this iodoprotein followed in vivo. The present experiments have definitely clarified the nature of the slow-sedimenting component labeled in vivo with radioactive aminoacids. Only about 25% of the total radioactivity present in the so-called 3-8S component is related to thyroglobulin. This fraction has been isolated and some of its physico-chemical properties have been determined: it has a sedimentation constant of about 6S and a molecular weight of about 165000 and probably represents one quarter of the thyroglobulin molecule.
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Con il contributo del Ministero per i Beni e le Attività Culturali