Thyroid Proteins in Sporadic Nontoxic Goiter

Abstract

In 9 cases of sporadic goiter, a study was made of the soluble proteins of thyroid glands obtained at operation. All the patients were euthyroid. A tracer dose of radioiodine I¹³¹ was given before the operation. Similar investigations were performed on histologically “normal” tissue (from 5 patients, thyroidectomized because of localized carcinoma of the thyroid). In both normal and goitrous tissues, thyroglobulin was the only iodoprotein present. In the goitrous glands, the general characteristics of this protein were normal, but its iodinated amino acids content was altered: an average MI¹³¹T/DI¹³¹T ratio of 2.58 was observed (below 1 in normal tissue), together with a very low content of iodothyronines. These observations seem to indicate that the iodination of MIT into DIT and the synthesis of the iodothyronines are decreased. These facts suggest that hormone synthesis is less active. Nevertheless, the thyroid secretion—as shown by the level of protein-bound iodine—still appears to be sufficient, owing to the presence of glandular hyperplasia. All the goitrous glands contained another protein which appeared to be iodine-free and which was called prethyroglobulin because of its electrophoretic properties. No prethyroglobulin was detectable in normal thyroid specimens.