Characterization and properties of thyroid iodoproteins from severely iodine-deficient rats.

Abstract

The iodoproteins from goitrous rat thyroid glands (300–800 mg), obtained by prolonged (20 months) and severe iodine deficiency, were isolated and characterized. The animals were given a low iodine diet (2 μg 1/100 g diet) containing 125I for 81 days (approach to equilibrium) and then they were pulse—labeled with 131I and 3H—leucine 2 hr prior to sacrifice. Thyroglobulinlike iodoproteins represented only 5% of the total protein in the crude soluble extract with 19 S comprising 90% and 27 S 10%. There was almost no iodine in 19 S while 27 S contained 0.12% iodine. Therefore a large proportion of the iodine stored in the soluble iodoproteins was due to the iodine in the 27 S protein. The turnover of iodine in 27 S, however, was much slower than in 19 S. In these severely iodine deficient animals the distribution of soluble thyroid iodoproteins was not significantly different from that observed in normal glands; the low iodine content, however, affects the stability of thyroglobulin. The iodinefree 19 S was m...