Some Properties of the Soluble Iodoproteins from Normal and Certain Abnormal Thyroid Glands

Abstract

Some of the physicochemical properties of thyroglobulin obtained from normal and diseased thyroid glands have been studied. Properties of the soluble component from gland homogenates have been compared with those obtained after purification of thyroglobulin by chromatographic fractionation on Sephadex G-200. Purified thyroglobulins from both normal and diseased glands precipitated sharply between 1.57 and 1.75M phosphate buffer (equimolar KH2PO4 and K2HPO4). On the other hand, the salting-out curves of the soluble supernatants were incomplete in this concentration zone, and a significant fraction of the protein remained soluble even in 2.45 molar phosphate buffer. By starch gel electro-phoresis this soluble protein was found to be predominantly albumin. Similar abnormal salting-out curves could be obtained by using artificial mixtures of purified thyroglobulin and albumin. The salting-out of labeled thyroglobulin was not altered by admixture of albumin. The electophoretic mobility of the thyroglobulin was the same in all cases. Analytical ultracentrifugal examination of the soluble supernatants done in some cases showed that the major component sedimented between 17S and 19S. Measurement of the iodination of the thyroglobulins by Edelhoch''s spectrophotometric technique performed in some cases revealed an appreciable reduction in the diiodotyrosine and thyroxine contents. Thus, the degree of iodination of thyroglobulin seems to have little if any influence on its solubility and electrophoretic mobility.