Thyroid albumin. I. Isolation and purification

Amino Acid Composition of Proteins Extracted from Endemic Goiter Glands

Proteins were isolated and characterized in thyroid tissue of six patients from Brazil with endemic goiter. Biochemical studies of these thyroidal proteins included gel filtration, electrophoresis, and amino acid analysis. In addition to thyroglobulin, two of the most abundant proteins found in all goiters studied had molecular weights of 68 and 14 kDa. One protein was identified as albumin based on its immunoreactivity with antibodies to serum albumin. The other protein was identified as a hemoglobin subunit using reverse-phase high-performance liquid chromatography (H PLC). Identification was confirmed by partial N-terminal amino acid sequencing that showed several nonconservative differences in thyroid albumin when compared to human serum albumin (HSA). Biochemical findings were correlated with iodine and hormone contents in serum and thyroglobulin from these patients. Based on these findings, we suggest that hemoglobin and albumin are taken up from the blood by the hyperplastic thyroid tissue. Albumin would be processed by the thyroid follicular cell, becoming iodinated and released into the circulation.

Biochemical and immunohistochemical characterization of proteins in Hürthle cell carcinoma

The present study reports the biochemical and immunohistochemical findings in the cytosol of a Hürthle cell carcinoma as compared with that of normal thyroid tissue. Sephadex G-200 chromatography of the extract derived from a Hürthle cell carcinoma and from normal thyroid tissue revealed three identical pools. Pool I consisted mainly of thyroglobulin (Tg), pool II corresponded to albumin, while pool III contained unidentified low molecular weight fragments which could not be studied further. Hürthle cell carcinoma, pool I, had a Tg content of 12.9 micrograms Tg/mg equivalent tissue and a 127I content of 5,6 mole/mole of Tg. Its sialic acid content was undetectable, however. In pool I of the normal thyroid gland, the respective values were 62.8 micrograms Tg/mg equivalent tissue, 21.3 +/mole 127I/mole Tg, and 15.4 mole sialic acid/mole Tg. The albumin contained in both pools II was shown to be ioidinated at the following levels: 0.025 mole 127I/mole albumin in Hürthle tumor pool II vs 1.28 mole 127I/mole albumin in normal thyroid pool II. Immunohistochemical studies confirmed the presence of Tg and albumin in the malignant Hürthle cells and acini and colloid. Thus, Hürthle cell carcinoma contained Tg and albumin. The Tg content was five times less compared with control tissue. Both proteins (Tg and albumin) were poorly iodinated in Hürthle carcinoma tissue, and the iodination of albumina seemed to be more severely impaired. The site of synthesis of both proteins could not be derived from the present studies.

Biosynthesis of thyroid hormone: basic and clinical aspects

Thyroid hormone formation requires the coincident presence of peroxidase, H2O2, iodide, and acceptor protein at one anatomic locus in the cell. The peroxidase enzyme appears to be a protoporphyrin lX containing heme protein, with binding sites for both iodide and tyrosine. It is probable that both iodide and tyrosine are oxidized to free radical forms which unite to form iodotyrosine. The peroxidase is also involved through an uncertain mechanism in iodotyrosine coupling and probably in oxidation of sulfhydryl bonds in thyroglobulin. H2O2 may be supplied by microsomal NADPH-cytochrome c reductase or NADH-cytochrome b5 reductase. Other possible intracellular H2OI generating systems include monoamine oxidase and xanthine oxidase. The usual acceptor for iodide is thyroglobulin, which is currently believed to be iodinated within apical secretory vesicles at the cell border just prior to liberation into the colloid, or possibly after liberation into the colloid. Other soluble an insoluble proteins are also iodinated within the gland. The peroxidase is present in numerous cellular structures, but iodination activity occurs primarily, if not only, at the apical cell border. The controls of iodination are imperfectly known. Thyrotrophin modulation of iodide uptake, H2O2 generation, thyroglobulin synthesis, and peroxidase enzyme level obviously are the main regulations. Many of these actions are thought to involve mediation of adenyl cyclase and subsequent activation of intracellular phosphokinases. Antithyroid drugs of the thiocarbamide group are competitive inhibitors of iodination under some circumstances, but if much iodide is present, they react with the oxidized iodine intermediate and are irreversibly inactivated themselves. Clinical problems involving defective peroxidase function are among the most frequent hereditary defects of thyroid hormone formation. Recognized abnormalities include deficient peroxidase, abnormality in binding of the peroxidase apoprotein to its prosthetic group, and other less well-identified abnormalities in peroxidase structure and function. Peroxidase is typically elevated in thyroid tissue from patients with hyperthyroidism sometimes deficient in cold thyroid nodules, and frequently diminished in tissue from patients with Hashimoto's thyroiditis.

Familial goitre with partial iodine organification defect, lack of thyroglobulin, and high levels of thyroid peroxidase

From a sibship of three sisters having congenital goitre and normal hearing, two had impairment of organification of iodine. S1 (4 years old) had goitre since birth, euthyroidism, and a negative perchlorate test. S2 (15 years old) and S3 (13 years old) were hypothyroid, and had radioiodide discharge after potassium perchlorate administration of 19.8% and 26.1%, respectively. Thyroid tissue was obtained at thyroidectomy. Peroxidase activity, in the thyroidal subcellular particles, was found to be qualitatively normal, but quantitatively increased. In the triiodide assay, the activity was: S1 6912 u, S2 2590 u, and S3 3844 u (normal values 900-1700 u). In the tyrosine-iodinase assay, the activities, expressed as nmoles of iodide incorporation per gram of tissue, were S1 1046, S2 471 (normal values 220-410). The activity of the thyroidal NADPH-cytochrome c reductase, an enzyme possibly involved in hydrogen peroxide generation, was: S1 0.084, S2 0.047, and S3 0.005 (normal values 0.018 muEq/min/mg). No thyroglobulin was detected by analytical ultracentrifugation, polyacrylamide gel electrophoresis, or double immunodiffusion in agar of the supernatant fractions. In patient S2, whose gland was labelled in vivo with 125I, 60% of the total radioactivity of the gland (pooled nodular and paranodular specimens) was in a particulate iodoprotein that was solublilized by trypsin, deoxycholate or digitonin. In the soluble fraction there were two iodoproteins: iodalbumin, and a second iodoprotein similar to the solubilized particulate iodoprotein. It is postulated that absence of the normal thyroidal receptor protein might be in some cases a cause of iodine organification defect.

Transport of thyroglobulin and peroxidase in the thyroid follicle cell

The purpose of this study was to explore the nature of the protein(s) in the exocytotic vesicles in the thyroid follicle cells and to ascertain whether or not thyroglobulin and peroxidase are transported by the same vesicles through the apical region of the cells to the follicle lumen. The study was performed on rats pretreated with thyroxine for 2 days in order to inhibit endocytosis. A fraction of exocytotic vesicles was isolated by centrifugation in continuous and discontinuous sucrose density gradients. The protein content of the vesicles were analysed by electrophoresis in continuous polyacrylamide gradient gels. The vesicles contained (uniodinated) thyroglobulin, 12-S protein and thyralbumin. Parallel histochemical studies in the electron microscope. These observations have important bearings on the mechanisms for thyroglobulin iodination, since it has been demonstrated that iodination does not occur in the exocytotic vesicles but in connection with the opening of the vesicles at the apical cell surface.

Studies on mono- and diiodohistidine. II. Congenital goitrous hypothyroidism with thyroglobulin defect and iodohistidine-rich iodoalbumin production

Butanol-insoluble iodinated compounds in the urine of patients with congenital goiters have been generally regarded as iodopeptides. Monoiodohistidine (MIH) and diiodohistidine (DIH) were identified from the urine of four patients with congenital goitrous hypothyroidism. From radioiodine studies, 40-70% of the urinary radioactivity was in the iodide-free fraction from which about 40% was identified as MIH and DIH by crystallizations to a constant specific activity. Iodotyrosines were simultaneously identified in the urine. However the presence of an iodotyrosine-deiodinase activity was demonstrated in the two removed goiters with a normal K(m) for MIT. In vivo iodotyrosine deiodination was normal for hypothyroid subjects. No thyroglobulin was identified in the thyroids from these patients. The major iodoprotein was iodoalbumin which, after in vivo labeling, contained 84-89% of the total soluble protein radioactivity. The thyroxine content of the goiter iodoalbumins and other iodoproteins was extremely low. Iodohistidines were identified in comparable proportions in the iodoalbumin and in the other iodoproteins isolated from each goiter. The average iodohistidine content of these proteins as crystallizable MIH and DIH was in the individual cases 15 and 4% of the in vivo incorporated radioiodine. DIH was identified in all iodoprotein fractions. The mean DIH/MIH ratios from the individual cases were 1.16 and 0.35. The corresponding DIT/MIT ratios were 3.19 and 1.45, respectively. The major consequence of this thyroglobulin defect is the iodination of inappropriate proteins (mainly albumin) resulting in low yields of thyroxine and high yields of iodohistidines. Iodohistidines from the goiter iodoproteins were not deiodinated and, at least for MIH, were quantitatively excreted in the urine of these patients. From the MIH iodoalbumin content and the MIH urinary excretion, goiter iodoalbumin turnover estimates were made and, although elevated, could not maintain a normal thyroxine secretion. The urinary excretion of iodohistidines easily demonstrated by column chromatography is offered as a test for detecting this variety of congenital goiter.

Studies on mono- and diiodohistidine. I. The identification of iodohistidines from thyroidal iodoproteins and their peripheral metabolism in the normal man and rat

The problem as to whether iodohistidines are normally biosynthetized in thyroglobulin and thyralbumin has been examined both in man and the rat. Evidence has been obtained for the first time that diiodohistidine (DIH) is present in both species in these two iodoproteins. The biosynthesis of monoiodohistidine (MIH) in the thyroglobulin of the normal rat has been confirmed and extended to rat thyralbumin and to human thyroid iodoproteins. THE IODOHISTIDINE IDENTIFICATION IS BASED ON FIVE ORIGINAL METHODS INCLUDING: (a) the preparation of stable and radioiodine-labeled iodohistidines; (b) the protection of the labile iodohistidines during the iodoprotein enzymatic hydrolysis; (c) the isolation of iodohistidines by ion-exchange resin chromatography; (d) their separation from each other and from iodinated cationic butanol-insoluble compounds by Sephadex G-10 chromatography; and (e) their purification by successive crystallizations to a constant specific activity. Iodohistidine levels (in percent of protein radioactivity from iodide given in vivo) were found comparable in man and the rat. However, the values (mean +/-SE) for thyroglobulin (MIH, 0.61+/-0.10%; DIH, 0.050+/-0.015%) and for thyralbumin (MIH, 2.61+/-0.57%; DIH, 0.28+/-0.09%) differ significantly (P < 0.05). Iodohistidines are stable during in vitro exposure to iodotyrosine dehalogenase preparations. In contrast to iodotyrosines the iodohistidines when given in vivo to man either orally or intravenously were in large part recovered in 24-h urines.