monoiodotyrosine and Thyroid-Diseases

Topics: Amino Acids; Animals; Autoradiography; Biological Evolution; Carbon Radioisotopes; Catecholamines; Dopa Decarboxylase; Fetus; Humans; Iodine; Iodine Radioisotopes; Iodoproteins; Melanins; Metamorphosis, Biological; Monoiodotyrosine; Neurotransmitter Agents; Sympathetic Nervous System; Thiourea; Thyroid Diseases; Thyroid Gland; Thyroxine; Tyrosine

Topics: Diiodotyrosine; Humans; Iodine; Isoenzymes; Liver; Monoiodotyrosine; NAD; NADP; Thyroid Diseases; Thyroid Gland

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.

Topics: Animals; Antithyroid Agents; Humans; Hydrogen Peroxide; Iodide Peroxidase; Iodides; Monoiodotyrosine; Oxidation-Reduction; Thyroid Diseases; Thyroid Gland; Thyroid Hormones; Tyrosine

In homogenate supernatants of kidneys of male rats the extent of deiodination of L-diiodotyrosine (L-DJT) and L-thyroxine (L-T4) was investigated in dependence on the thyroid function (hypo- and hyperthyroidized) and also in dependence on age. In rats hypothyroidized by loading with Methylthiouracil (MTU) or Methimazol (MMI) the deiodination for L-DJT and L-T4 was significantly reduced, in rats loaded with 40 mug T4 sc. for 10 days, the deiodination was significantly enhanced compared with untreated control animals. With advancing age (6 weeks, 3 or 12 month) the deiodination activity is highly significantly reduced. The results underline relations between thyroid gland function and deiodination activity in kidney.

Topics: Age Factors; Animals; Diiodotyrosine; Hyperthyroidism; Hypothyroidism; Iodine; Kidney; Male; Methimazole; Methylthiouracil; Monoiodotyrosine; Rats; Thyroid Diseases; Thyroid Hormones; Thyroxine; Triiodothyronine

Topics: Chemical Phenomena; Chemistry; Chromatography, Ion Exchange; Diiodotyrosine; Goiter; Graves Disease; Humans; Iodine; Iodine Isotopes; Methods; Monoiodotyrosine; Potassium Iodide; Spectrophotometry; Thyroglobulin; Thyroid Diseases; Thyroid Gland; Thyroid Neoplasms; Thyroiditis, Autoimmune; Thyroxine; Triiodothyronine

Topics: Age Factors; Female; Humans; Infant; Iodine; Male; Monoiodotyrosine; Pedigree; Sex Factors; Thyroid Diseases

Topics: Autopsy; Centrifugation, Density Gradient; Diiodotyrosine; Goiter; Humans; Hydrogen-Ion Concentration; Iodine; Iodoproteins; Monoiodotyrosine; Spectrophotometry; Thyroglobulin; Thyroid Diseases; Thyroxine; Tyrosine; Ultracentrifugation