Conformational change of the thyroglobulin molecule induced by oxidation in vitro

Previous electron-microscopical studies from this laboratory have shown that the thyroglobulin molecule can occur in two different conformations, one ovoid and the other cylindrical. Ovoid molecules are characteristic of well-iodinated thyroglobulin whereas cylindrical molecules are found after low-iodine diet or blocking of iodination. The present study was performed in order to elucidate the possible relation between the molecule conformation and the peroxidase-catalyzed reactions that occur in the thyroid in connection with hormone synthesis. Cylindrical thyroglobulin molecules (from PTU-exposed thyroids) were incubated in different media and the proportion of cylindrical and ovoid molecules after incubation was estimated in electron micrographs. It was found that incubation with glucose-glucose oxidase caused an extensive conversion of cylindrical molecules into ovoid molecules. Peroxidase and/or iodide were not necessary for this change of conformation. It is suggested that this in vitro molecule transformation was the result of an oxidation reaction.