Monoiodotyrosine formation during thyroglobulin processing in golgi vesicles

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Abstract
A golgi‐enriched subfraction was obtained from porcine throid glands by differential centrifugation. When incubated in a suitable medium, these vesicles were able to concentrate iodide from the medium and bind it to protein. The iodination process was inhibited by methylmercapto‐imidazole and was increased by the addition of an H2O2 generating system to the medium. Analysis of the protein content of the vesicles revealed the presence of 18 and 12–13 S thyroglobulin molecules, lacking mannose residues, and containing only monoiodotyrosine.It is concluded that in vitro, iodination can begin before exocytosis, in the smooth‐surfaced vesicles derived from the golgi apparatus, as soon as N‐acetylglucosamine is incorporated onto the pre‐thyroglobulin molecule.