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

We have examined the ability of nonionic detergents to solubilize thyroid peroxidase from a porcine thyroid particulate fraction, as measured by the release of peroxidase activity into the supernatant fraction after centrifugation at 105,000 X g for 1 hour and the retardation of the supernatant peroxidase of Sepharose 6B. The parameters of peroxidase solubilization by Triton X-100 have been investigated in detail. Under optimum conditions, 60 to 95% of the thryoid peroxidase and about 50% of the total protein is released into the 105,000 X g, 1-hour supernatant. Under the optimum conditions established with Triton X-100, a series of Brij detergents of different chemical structure were equally effective in releasing peroxidase and protein. The protein patterns of the supernatants obtained with these detergents were similar on sodium dodecyl sulfate-polyacrylamide electrophoresis gels, suggesting that the detergents studied release similar membrane proteins. The Triton X-100 and Brij 58 supernatants were chromatographed separately on Sepharose 6B equilibrated with 0.1% Triton X-100 or Brij 58, respectively. In both cases, 75 to 80% of the peroxidase activity was retarded, thereby indicating that the nonionic detergents effect solubilization of the peroxidase rather than dispersal of nonsedimentable membrane fragments. These studies report the first successful solubilization of thyroid peroxidase by nonionic detergents. Together with previous evidence from our laboratory, these experiments indicate that thyroid peroxidase is an integral membrane protein.
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PMID:Solubilization of thyroid peroxidase by nonionic detergents. 0 49

We have investigated the interaction between concanavalin A-agarose (Con A-agarose) and thyroid peroxidase, an integral membrane protein found in the 105,000 X g, 1-h particulate fraction of thyroid tissue. An intact form of porcine thyroid peroxidase was obtained by solubilization with the nonionic detergent Triton X-100 and two fragmented, hydrophilic forms of the enzyme were prepared by trypsin treatment of the membrane. The three types of thyroid peroxidase bind to Con A-agarose and can be eluted with alpha-methyl-D-mannoside. The alpha-methyl-D-mannoside eluate of the most purified thyroid peroxidase preparation has been analyzed by polyacrylamide gel electrophoresis. Peroxidase activity corresponds with a glycoprotein band. The binding of thyroid peroxidase to Con A-agarose can be inhibited by sugars in the following order: alpha-methyl-D-mannoside greater than D-mannose greater than alpha-methyl-D-glucoside greater than D-glucose greater than D-galactose. This order of specificity is typical of Con A-sugar interactions. Furthermore, inactivation of the carbohydrate binding site of Con A by demetallization greatly reduces the extent of thyroid peroxidase binding. Reactivation of the carbohydrate binding site by the addition of Ca2+ and Mn2+ to demetallized Con A-agarose restores thyroid peroxidase binding. These and other experiments suggest that htyroid peroxidase is, like several other peroxidases, a glycoprotein. In addition, the interaction between thyroid peroxidase and Con A-agarose may provide a new purification tool for thyroid peroxidase.
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PMID:Interaction of thyroid peroxidase with concanavalin A covalently coupled to agarose. 1 48

Trypsin-solubilized peroxidase activity from beef subcellular particles was resolved by DEAE-cellulose chromatography into 5 fractions, which contained enzymatically active components that ranged in molecular size from 73,000 to 340,000 daltons. The most active fraction (mol wt, 92,000 by gel filtration) was further purified (59,000-fold overall) by chromatography on hydroxylapatite. This highly purified peroxidase preparation had an absorbance purity ratio (A410:A280) of 0.55 and oxidized iodide (I3-formation) and guaiacol at rates of 300 and 460 micronmol/min/mg, respectively, which were about 3 and 1 1/2 times, respectively, greater than any previously described preparations. The enzyme was contaminated with an inactive protein of equal size. The highly purified peroxidase preparation lost its activity within a few days even when stored at -15 C with iodide. Two of the other DEAE-cellulose fractions contained peroxidase components with estimated sizes (gel filtration) of 73,000, 96,000, and 98,000, which were further purified purified (1,600 and 15,600 fold) on hydroxylapatite. They were 1/4 to 1/40 as active as the highly purified preparation and also became increasingly labile on purification. The remaining two DEAE-cellulose fractions were heterogeneous mixtures of stable peroxidase components whose average molecular sizes (gel filtration) were 220,000, 300,000, and 340,000 daltons, and which were not amenable to further purification on hydroxylapatite. The ratio of guaiacol to iodide activity decreased from 3.0 in the particles to about 1.5 in the highly purified preparations. The turnover numbers of the purest peroxidase component (mol wt. 92,000) for iodide and guaiacol were very similar to those of highly purifed, commericial lacto- and horseradish peroxidases. The pH maxima for iodide oxidation were 7.4, 6.0, and 4.5 for thyroid, lacto-, and horseradish peroxidases, respectively, whereas guaiacol oxidation peaked at pH 7.0-7.8 for all three enzymes. On the basis of these results and the dissimilar molecular sizes reported for trypsin-solubilized thyroid peroxidase by several other investigators, it was concluded that the molecular size is primarily determined by the conditions of proteolysis.
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PMID:Purification of bovine thyroid peroxidase. 1 22

An in vitro method employing an iodide-specific electrode for monitoring lactoperoxidase-catalyzed iodination is described. The method utilized lactoperoxidase, potassium iodide, and a glucose--glucose oxidase system for the generation of hydrogen peroxide and l-tyrosine. As iodination of l-tyrosine proceeded, the free iodide concentration in solution decreased and was monitored by an iodide-specific electrode. The iodide electrode was reliable when compared to a 131I-method for measuring free iodide changes in solution. Increasing concentrations of resorcinol, a well-known inhibitor of thyroid peroxidase-catalyzed iodination, in the reaction mixture resulted in graded inhibition of the initial rate of lactoperoxidase-catalyzed l-tyrosine iodination. This in vitro system can be used to assess inhibitory activity of various antithyroid substances.
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PMID:Use of an iodide-specific electrode to study lactoperoxidase-catalyzed iodination of l-tyrosine. 4 87

Viable leucocytes obtained fresh from normal human subjects were shown to be able to catalyse the in vitro iodination of bovine serum albumin (BSA) in a H2O2-generating system. The rate and degree of iodination were greatly improved by sonication of the cells. A balanced salt solution was a more favourable medium than phosphate buffer for the myeloperoxidase (MPO)-catalysed iodination of whole cells and sonicated cells. Reactions known to be catalysed by other peroxidases (e.g. thyroid peroxidase (TPO) and lactoperoxidase), such as inorganic iodide exchange for organic iodine in di-iodotyrosine (DIT) and the de-iodination of thyroxine (T4), were also catalysed by the sonicated leucocyte suspension in the system used. The non-steroidal anti-inflammatory drugs indomethacin, flufenamic acid and naproxen were far less effective inhibitors of MPO-catalysed BSA iodination of sonicated leucocytes at concentrations expected in blood with therapeutic dose levels than was observed earlier with TPO-catalysed in vitro iodination of BSA. The antithyroid drug methylmercapto-imidazole (MMI) inhibited in vitro MPO-catalysed 131I delabelling of 131I-DIT at all concentrations between 10(-7) and 10(-2)M, whereas 131I-T4 delabelling was markedly stimulated at the same drug concentrations. On the other hand, 125I incorporation into 131I-DIT was not affected by increased concentrations of MMI up to 10(-5)M. At higher drug concentrations the drug caused inhibition of MPO-catalysed exchange of inorganic iodide for organic iodine in DIT.
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PMID:The influence of non-steroidal anti-inflammatory and antithyroid agents on myeloperoxidase-catalysed activities of human leucocytes. 8 4

Clinical and laboratory evaluations are reported on two patients with congenital goiter and hypothyroidism due to iodide organification defect. In one patient, a 31-year-old white male with severe mental retardation, administration of perchlorate caused discharge of 69% of the radioiodine accumulated in the thyroid gland. Thyroid tissue had negligible peroxidase activity in the tyrosine-iodinase, triliodide, and guaiacol assays. Preincubation of subcellular fractions with hematin restored activity. The restored enzyme was labile to high concentrations of H2O2 (5.6times 10-4 h2o2 produced inhibition in the triiodide assay). Heating of the enzyme for 5 min at 46 degrees C produced 50% inactivation, while higher temperatures were required to half-inactivate normal peroxidases. This case represents a second example of the "peroxidase apoenzyme-prosthetic group defect" causing congenital goiter. The second patient, an example of the "deficient peroxidase defect," was a 10-yr-old girl with 35% discharge of thyroidal radioiodine by perchlorate. Peroxidase activity in the goiter tissue was quantitatively decreased (10%-20% of normal values) but kinetically normal with respect to apparent Km for H2O2. Hematin had little effect on the enzyme. Peroxidase activity had abnormal subcellular distribution, since pellets sedimenting between 39,000 and 105,000 g contained most of the activity. Normal thyroglobulin was observed in the thyroid gland of the patient. Two distinct defects of the peroxidase system can produce congenital goiter by limiting organification of iodide.
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PMID:Differentiation of two abnormalities in thyroid peroxidase causing organification defect and goitrous hypothyroidism. 16 74

In the control animals of thyroid peroxidase is localized within the membrane of rough endoplasmic reticulum, perinuclear cisternae, microvilli, lamellar structures of the GOLGI apparatus and dispersed through the cytoplasm small vesicles. 3 weeks treatment of the animals with MTU leads to disappearance of the peroxidase activity from the follicular cells. However, a prolongation of MTU administration until the 6th month and latter causes a reappearance of the peroxidase activity within the same structures of the proliferating cells as in the control animals. In the epithelial cells of follicular and papillary carcinomas the reaction product is observed predominantly within the membrane of the rough endoplasmic reticulum, perinuclear space and outher membrane of the microvilli. The changes in the inhibitory effect of MTU on the peroxidase activity during thyroid carcinogenesis are discussed.
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PMID:Cytochemical localization of peroxidase activity in normal, proliferating and neoplastic thyroid tissues of rats. An ultrastructural study. 40 41

We have developed assays for thyroid peroxidase in crude thyroid tissue preparations, in which a linear relationship between activity and amount of tissue could be demonstrated. Linear assays were developed based on the following peroxidase catalyzed reactions in the presence of H2O2:(1) oxidation of I- to I(-3), (2) oxidation of guaiacol, and (3) iodination of human goiter thyroglobulin. To attain satisfactory linearity we found it necessary to solubilize the enzyme beforehand. This was accomplished by a brief treatment of the particulate fraction with trypsin and deoxycholate, followed by centrifugation at 40 000 X g and dialysis. Not only did this treatment facilitate the development of linear assays, but it also resulted in a substantial increase in enzyme activity compared with that in the untreated particulate fraction. The use of a Polytron homogenizer for the initial disruption of the tissue also proved helpful in developing these assay procedures. The three different assays were used to measure peroxidase activities in human thyroid adenomas and in normal tissue derived from adenomatous glands. T he adenomas generally displayed a higher level of peroxidase activity than normal tissue. The greatest difference was observed with the iodination assay and the smallest difference with the guaiacol assay.
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PMID:Improved assay procedures for thyroid peroxidase; application to normal and adenomatous human thyroid tissue. 62 Apr 58

bTSH augmented the fish thyroid peroxidase activity in a dose-response manner. Thyroxine could not modulate the effect of exogenous bTSH, but it decreased the peroxidase activity in a control system when administered alone. The data therefore suggest similar negative feedback control system for TSH-regulation as operative in the case of mammals.
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PMID:Bovine TSH-stimulation of fish thyroid peroxidase activity and role of thyroxine thereon. 62 Jul 27

Porcine thyroid peroxidase (Iodide: hydrogen-peroxide oxidoreductase, EC 1.11.1.8) was solubilized by proteolytic and non-proteolytic procedures. A kinetic and physical study was undertaken to ascertain the catalytic properties of the peroxidase prepared by the two purported solubilization procedures. Where possible, the properties of the two enzyme preparations were compared with the original microsomal preparation. The n-butanol-solubilized thyroid iodide peroxidase is not truly soluble, but exists as a large molecular weight lipoprotein aggregate. The trypsin-solubilized thyroid iodide peroxidase is truly soluble, active, and contains lipids. The microsomes, butanol-pseudosolubilized enzyme, and trypsin-solubilized enzyme have similar kinetic properties such as pH optima, Km for iodide and H2O2, sigmoid character of the saturation curves, substrate inhibition, and inhibition by 3,5-diiodotyrosine. Since the proteolytic solubilization procedure produced a soluble peroxidase with catalytic properties similar to the microsomal preparation, trypsin-solubilized peroxidase can be studied with reasonable assurance that its properties are essentially unaltered and are not artifacts of the solubilization procedure.
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PMID:The characterization of n-butanol-pseudosolubilized and trypsin-solubilized porcine thyroid iodide peroxidase. 71 42


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