Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.11.1.7 (peroxidase)
 65,474 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Ultrastructural localization of endogenous thyroid peroxidase under benign pathological conditions such as toxic diffuse goiter, non-toxic multinodular goiter, and adenoma, and in normal tissue was studied. Peroxidase activity was visualized by a cytochemical reaction for electron microscopy. In toxic diffuse goiters and most non-toxic multinodular goiters, reaction product for peroxidase was observed not only in the cytoplasm but also at the external surface of microvilli of follicular cells. In normal thyroid tissues and adenomas, peroxidase was visualized only in the cytoplasm. Peroxidase activity at the external surface of microvilli of the follicular cells was found in the tissues obtained from the goiters which showed "hot" radioiodine scintigram. These findings suggest that follicles with peroxidase activity at the external surface of microvilli in non-toxic multinodular goiter are "autonomous follicles" and that peroxidase at the external surface of microvilli plays some role in active iodine uptake.
 ...
PMID:Ultrastructural localization of endogenous peroxidase activity in benign thyroid diseases. 363 Jun 96

The interaction between thyroid microsomal autoantibodies and thyroid microsomal antigen/thyroid peroxidase (TPO) has been studied using both intact antigen preparations and their water-soluble trypsin fragments. In an analysis of sera from 30 patients with Graves' or Hashimoto's diseases, microsomal antibodies showed similar reactivity towards trypsin fragments (with TPO activity) and intact detergent (sodium deoxycholate, DOC)-solubilized human microsomal antigen preparations (r = 0.96). This raised the possibility that both the peroxidase-active site and the major autoantigenic site(s) of microsomal antigen were present on the same trypsin fragments. Studies with porcine TPO showed that only a few sera contained microsomal antibodies which cross-reacted strongly with the porcine preparations. Further analysis was carried out by immunoprecipitation of 125I-labelled microsomal antigen followed by SDS-PAGE and autoradiography. These studies suggest that intact human microsomal antigen (a single-chain protein with Mr = 110,000) contains an intrachain loop of amino acids formed by a disulphide bridge. Trypsin treatment cleaves the antigen close to its transmembrane section and releases a water-soluble fragment (Mr = 100,000), containing the intact disulphide-linked loop of amino acids. Further trypsin action causes cleavage of the peptide bonds within the loop in some preparations. Consequently, three major water-soluble trypsin fragments (Mr = 100,000, 73,000 and 68,000) are formed all of which contain an intact disulphide bridge and have microsomal antibody binding activities. The integrity of the disulphide bridge in intact antigen/TPO preparations and their trypsin fragments is essential for autoantibody binding activity.
 ...
PMID:Structure-activity analysis of microsomal antigen/thyroid peroxidase. 366 90

Peroxidase activity in thyroid tissue from 25 patients with Graves' disease was measured by Mini assay method (J. Biochem. 98, 637-647, 1985) employing guaiacol or iodide as a second substrate. The mean values of protein-based specific activity were 0.496 guaiacol unit/mg protein and 0.187 iodide unit/mg protein, reaching 16 fold and 28 fold those of normal thyroids, respectively. The mean value of ratio of iodide unit to guaiacol unit in each thyroid, 0.68, was also much higher than that of normal human thyroid, 0.16. No significant difference in peroxidase activity was observed between patients treated with methylmercaptoimidazole and those with propylthiouracil, but the activities of those groups were significantly higher than those of patients treated with potassium iodide, suggesting that inorganic iodine therapy plays some role in suppressing the synthesis of thyroid peroxidase in vivo.
 ...
PMID:[Peroxidase activity of thyroid tissue in toxic diffuse goiter. Difference among thyroids administered antithyroid drugs and potassium iodide]. 375 18

The coupling of iodotyrosine (coupling reaction) is one of the least studied in the formation of thyroid hormone, particularly in human thyroid diseases. This paper describes a method of measuring iodotyrosine coupling catalyzed by human thyroid peroxidase (TPO) in vitro. There were two important requirements to demonstrate the coupling reaction: 1) thyroglobulin with a low thyroid hormone content, and 2) partially purified TPO. Thyroglobulin with low thyroid hormone content was obtained from Grave's and follicular adenoma tissues after propylthiouracil (PTU) therapy and L-T4 therapy, respectively. TPO was prepared from Graves' thyroid by solubilizing the 100,000 X g pellet of thyroid homogenate with sodium deoxycholate and trypsin, followed by Sephacryl S-300 gel filtration. Before the coupling reaction, thyroglobulin was iodinated with chloramine-T and potassium iodide, followed by dialysis. The coupling reaction was carried out by incubating newly iodinated thyroglobulin with TPO, diiodotyrosine, a coupling stimulator, and a H2O2-generating system (glucose and glucose oxidase) for 20 min at 37 C. After thyroglobulin was digested with Pronase, the thyroid hormone content of the thyroid digest was measured by RIA. Coupling activity was measured by the amount of newly formed T3 (nanograms of T3 per mg thyroglobulin). The time course of coupling reaction showed a progressive increase in coupling activity up to 30 min, and the reaction was temperature and pH dependent, with a pH optimum of 7.0. Coupling activity in the presence of H2O2 and TPO was 43 +/- 5.0 ng T3/mg thyroglobulin (mean +/- SD of triplicate samples), and addition of diiodotyrosine to the H2O2-TPO system caused a nearly 3-fold increase in coupling activity. This method has potential utilization for measurement of peroxidase coupling activity, since there was a linear relationship between the measured coupling activity and the amount of added TPO when the TPO concentration was over 3 micrograms/300 microliter. Methimazole (MMI) and PTU had similar potencies in inhibiting the TPO-catalyzed coupling reaction, whereas MMI was distinctly more potent than PTU as an inhibitor of TPO-mediated iodination in vitro. The different potencies of MMI in the two reactions suggest that different inhibitory mechanisms may be involved in iodination and coupling. The reducing agent, sodium metabisulfite, was also found to be a more potent inhibitor of the TPO-mediated coupling reaction than of the TPO-mediated iodination reaction. The method of iodotyrosine coupling described here may be useful to investigate the coupling step of thyroid hormone formation in human thyroid diseases.
 ...
PMID:Coupling of iodotyrosine catalyzed by human thyroid peroxidase in vitro. 383 97

Primary cultures of ovine thyroid cells were induced to differentiate by addition of thyrotropin (TSH). This was demonstrated as an accumulation of 2 thyroid-specific proteins, thyroglobulin and thyroid peroxidase, using immunofluorescent staining methods and immunoprecipitation of biosynthetically labeled cultures. As an additional measure of differentiation, cells exhibited a morphological response to TSH and regained the ability to incorporate radioactive iodide. Epidermal growth factor (EGF) markedly inhibited differentiation when added together with TSH. Thyroglobulin synthesis was reduced to low levels and peroxidase synthesis was reduced to levels that were undetectable by the methods used. Morphological changes in response to TSH were also diminished by EGF. The antagonistic interaction between TSH and EGF in regulating differentiation in cultured thyroid cells may reflect the type of control that exists in vivo.
 ...
PMID:Epidermal growth factor inhibits thyrotropin-mediated synthesis of tissue-specific proteins in cultured ovine thyroid cells. 387 50

A monoclonal antibody (30.1.2) to hog thyroid peroxidase was produced, purified, and characterized. The IgG of 30.1.2 formed an immune complex with the peroxidase in a 1:2 or 1:1 molar ratio depending on the IgG to antigen ratio in the incubation mixture. Immune complex formation did not inhibit the peroxidase activity, which was actually activated 2-fold in the 1:1 complex. Studies of the binding of the conjugate of the IgG or its Fab' with horseradish peroxidase to untreated and acetone-treated thyroid microsomes showed that the IgG conjugate could bind to only a very small portion of the total binding sites (thyroid peroxidase) present in untreated microsomes even after prolonged incubation. The binding of the Fab' conjugate to untreated microsomes, on the other hand, increased as the incubation time was increased, reaching 40% of the total sites after 20 h of incubation. These findings indicated that thyroid peroxidase is localized on the inner surface of the microsomal membranes and that the Fab' conjugate, but not the IgG conjugate, can slowly penetrate through the membrane barrier to reach the peroxidase. Immunohistochemical experiments using the Fab' conjugate as a probe revealed that most thyroid peroxidase in the thyroid gland is located in the endoplasmic reticulum and perinuclear cisternae of the follicular cell, although a small amount could occasionally be detected in the apical membrane including microvilli. In contrast to previous reports, no thyroid peroxidase could be found in other cellular structures such as Golgi apparatus and apical vesicles by the immunohistochemical technique employed.
 ...
PMID:Characterization of a monoclonal antibody to hog thyroid peroxidase and its use for immunohistochemical localization of the peroxidase in the thyroid gland. 389 14

Several fundamental properties of purified hog thyroid peroxidase (A413 nm/A280 nm = 0.55) were investigated in comparison with bovine lactoperoxidase. The Mr of thyroid peroxidase was 71,000. The prosthetic group of thyroid peroxidase was identified spectrophotometrically as protoheme IX after the enzyme was hydrolyzed with Pronase. Optical spectra of oxidized and reduced thyroid peroxidases and their complexes with azide and cyanide were very similar to lactoperoxidase, except that lactoperoxidase had two reduced forms with the Soret band either at 446 or 435 nm, and thyroid peroxidase lacked a reduced form having the 446-nm band. From comparison of their pyridine hemochrome spectra, epsilon mM at 413 nm of thyroid peroxidase was estimated to be 114, being the same as that of lactoperoxidase. The cyanide inhibition for the reaction of thyroid peroxidase was competitive with hydrogen peroxide and the inhibition constant was in rough accord with the dissociation constant of its cyanide complex measured from spectrophotometric titration. Azide inhibited the reaction with an inhibition constant which was about one one-thousandth of the dissociation constant for its spectrally discernible complex. The azide inhibition was not competitive with hydrogen peroxide and decreased as the reaction proceeded. Aminotriazole inhibited the reaction strongly, and the inhibition was augmented during the reaction. These inhibition patterns of azide and aminotriazole were more or less observed in the reaction of lactoperoxidase, but not in the case of horseradish peroxidase. Characteristics of animal peroxidases are discussed.
 ...
PMID:Characterization of hog thyroid peroxidase. 396 58

The present study was undertaken to investigate degradation of thyroxine (T4) mediated by thyroid peroxidase in man. A particulate fraction (1,000-100,000 x g) of normal human thyroid tissue was prepared and used as crude enzyme. 125I-T4 and unlabeled T4 were incubated with the particulate fraction in buffer containing glucose and glucose oxidase for generation of H2O2. After incubation, iodoamino acids were extracted with ethanol and the products of T4 degradation were analyzed by thin layer chromatography. In this system, T4 was degraded in time-, temperature- and pH-dependent manners, but not in the absence of the H2O2-generating system. The rate of degradation was related to concentration of the particulate fraction. The reaction was inhibited by methimazole, propylthiouracil and catalase. When [3',5'-125I] T4 was used as a tracer, major labeled products of T4 degradation were inorganic iodide and ethanol-unextracted fraction and no detectable labeled 3,5,3'-triiodothyronine (T3) or 3,3',5'-triiodothyronine (rT3) was generated. From a kinetic study by adding various doses of unlabeled T4, the apparent Km value for T4 was 30 microM and the Vmax value was 230 pmol/mg protein/min. When [3,5-125I] T4 was incubated with enzyme preparation, one third of degraded T4 was recovered as diiodotyrosine (DIT) and half of 125I-DIT was degraded in parallel incubation. No formation of radiolabeled DIT was observed in incubation with Na- 125I done in tandem. These findings suggest that thyroid hormones can be metabolized by peroxidase in human thyroid by pathways that include cleavage of ether linkage.
 ...
PMID:Peroxidatic degradation and ether link cleavage of thyroxine in a particulate fraction of human thyroid. 397 5

A rapid method was developed for purification of hog thyroid peroxidase by immunoaffinity chromatography on a column of Sepharose 4B coupled to a monoclonal antibody to the peroxidase. The purified enzyme had a specific activity of 194 units/mg and showed the same absorption spectrum in the Soret and visible regions as that of the enzyme purified after trypsin treatment. The ratio of A413 nm to A280 nm was 0.24, being much less than that for the trypsinized enzymes. Upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis, it gave a broad protein band in the 100,000-dalton region. It is concluded that the preparation purified in this study represents a native form of thyroid peroxidase.
 ...
PMID:Purification of thyroid peroxidase by monoclonal antibody-assisted immunoaffinity chromatography. 397 28

In thyroid gland, iodination takes place on the apical plasma membrane and requires the presence of the thyroid peroxidase and H2O2 generating system. H2O2 generation and NBT (nitro blue tetrazolium) reductase activity (both of which are NADPH-dependent) as well as peroxidase activity were compared for their respective orientations in membrane vesicles. The possible role of NADPH-NBT reductase activity in H2O2 generation was also examined. Results favor the conclusion that thyroid peroxidase is oriented towards the luminal side of the vesicles, whereas the NADPH site of NADPH oxidase-dependent H2O2 generation is located on the external side of the same or of different vesicles. Furthermore, it is shown that different NADPH-NBT reductase activities are present on both the outer and inner surfaces of the membrane vesicles, and that none of these activities is able to produce either H2O2 or O-2. The idea that a multi-component complex is involved in H2O2 generation is discussed, and a model is proposed which takes into account the possible spatial separation of the thyroid peroxidase site from the NADPH site of this H2O2 generation system on the apical membrane of the thyrocyte.
 ...
PMID:Relation between thyroid peroxidase, H2O2 generating system and NADPH-dependent reductase activities in thyroid particulate fractions. 401 97


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>