Abstract
When methylthiouracil (MTU) is injected chronically into hogs to block the iodination of thyroglobulin (TG), the iodine content decreased to essentially zero level after treatment with MTU for three or four weeks. One or two injections of thyroxine, given before killing the MTU-treated animals, caused a marked increase in the yield of noniodinated thyroglobulin. The treatment of animals with MTU also caused a significant decrease in the content of sialic acid residues of thyroglobulin. The sialic acid contents were as low as 0.8-0.9%(w/w%) in the poorly iodinated and non-iodinated thyroglobulins obtained from the MTU-treated animals, compared to a level of about 1.2%, as seen in normally iodinated thyroglobulin obtained from the untreated animals. This fact suggests that the differences (microheterogeneity) in the sialic acid content of the thyroglobulin preparations depend on a change in the regulating effect of thyrotrophin (TSH) action. The relathinship between the maturation of the thyroglobulin molecule and its sialic acid content is discussed.
