THE SIGNIFICANCE OF IODINE IN THE AGGREGATION OF SUBUNITS INTO THYROGLOBULIN AND IN THE FORMATION OF 27S IODOPROTEIN

Abstract

ABSTRACT The significance of stable iodine in the formation of thyroglobulin (TG) with particular reference to the aggregation of subunits into TG and the formation of 27S iodoprotein has been investigated in guinea-pigs and rabbits. An increase in the content of iodine in the diet or its parenteral application to normally fed animals results in considerable quantitative and qualitative changes in the soluble thyroid proteins as revealed by analytical ultra-centrifugation and sucrose density gradient centrifugation. Although some differences in the protein patterns between guinea-pigs and rabbits normally exist, the changes induced by single and repeated doses of stable iodine (5–100 μg/day) were characterized by: (a) decrease of light proteins, particularly the 12S protein fraction in the guinea-pig; (b) a marked increase of TG and (c) the appearance of a quantity of 27S iodoprotein. These changes in composition of the thyroid soluble proteins are accompanied by changes in the radioiodine distribution among the protein fractions. The results obtained suggest that the process of thyroid protein polymerization and the process of their iodination are not independent of each other. The level of the supply of the thyroid gland with iodine under normal iodine metabolic conditions considerably influences both the aggregation of subunits into TG and the formation of 27S iodoprotein. It is likely that 27S iodoprotein is formed when larger quantities of normally iodinated TG are synthesized and stored in the gland.