The biosynthesis of thyroglobulin has been studied after incubation of rat thyroid hemilobes in the presence of radioactive carbohydrates and/or aminoacids. The incorporation of an aminoacid such as 3H-leucine and of a carbohydrate such as 3H-mannose follows a very similar pattern: a 3-8 S protein component becomes labeled at early times of incubation whereas a component having approximately the sedimentation rateof thyroglobulin (17 S) becomes labeled at later times. A sugar such as galactose (labeled with 3H or 14C) is incorporated directly into the 17-19 S component. Furthermore, the 3H-leucine and 3H-mannose labeled 3-8 S component is immunochemically related to thyroglobulin, whereas no 3H-galactose radioactivity immunologically related to thyroglobulin can be traced in the same zone of the gradient. The results indicate that mannose is incorporated on the precursor subunits of thyroglobulin whereas galactose is incorporated only after polymerization of such subunits. The incorporation of mannose takes place at a time and site very similar to those where the aminoacids are incorporated, i.e. during the protein assembly on polyribosomes.
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Con il contributo del Ministero per i Beni e le Attività Culturali