Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

Spinach chloroplasts exposed to iodide can be washed free of the bulk of the iodide. In the presence of lactoperoxidase and H2O2, iodide can be introduced into chloroplasts in high amounts and in non diffusible forms. The resultant particles, which have been named iodochloroplasts, extrude their iodide upon stimulation by light. The form and the amount of extruded iodide bears a definite relationship to the amount of incident light. A flash of marginally effective light is additive to the next such flash even after a lapse of 10 min of darkness. These and other properties of iodochloroplasts may make them of great use in the study of intermediate reactions of photosynthesis.
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PMID:Iodination of chloroplasts. I. Properties of iodinated chloroplasts. 94 60

Circulating enzymes may be inactivated in the plasma and the inactive breakdown products may be hydrolyzed in the lumen of the small intestine. Evidence for this mechanism was based upon previous studies with 125I-labeled lactate dehydrogenase-5, and here similar studies with radioiodinated lactate dehydrogenase-1 are reported, to determine whether this isoenzyme is similarly catabolized. The pure rabbit enzyme was labeled with 125I by use of lactoperoxidase and hydrogen peroxide (the labeled enzyme had 80-85% of the original catalytic activity). After its intravenous injection into rabbits, plasma enzyme activity and radioactivity disappeared during the first 4 h at similar fast rates, apparently because of distribution of the injected enzyme throughout the extracellular fluid. During a second phase (30-h), catalytic activity disappeared significantly faster than radioactivity, suggesting inactivation of the enzyme in either the plasma or a compartment in close proximity to it, or both. Enzyme activity then remained constant while plasma radioactivity continued to decrease at a slower, exponential rate, apparently owing to removal of breakdown products. In no case did tissue radioactivity, studied 6 h after injection, approach that of plasma. We therefore conclude that removal of the enzyme protein or its breakdown products is a passive process. Appreciable radioactivity was detected in the intestinal contents, a finding which suggests that removal via the small intestine is an important route for the removal of inactivated enzyme products from the circulation. Less than 3% of the injected radioactivity appeared in the feces during the first three days; urinary excretion accounted for about 67% during the same period, about 60% of which consisted of radio-iodinated amino-acids, the remainder of iodide. Free mono- and di-iodotyrosines were among the products excreted. These appear to originate from absorption of the products of further breakdown of the enzyme molecule in the intestine.
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PMID:Catabolism of plasma enzymes, as studied with 125I-labeled lactate dehydrogenase-1 in the rabbit. 94 35

An 8-year-old boy with goiter and bilateral nerve deafness had a 46% discharge of radioiodine after thiocyanate administration. He was clinically euthyroid. Although the serum total T4 was low (2.4 mug/100 ml) and TSH was significantly high (181 muU/ml), the serum total T3 was normal (152 ng/100ml). It was considered that the increased release of TSH by the feedback mechanism in response to the low T4 resulted in a quite normal level of serum T3. The thyroid gland demonstrated a low stable iodine content, an increase in MIT/DIT ration and a decrease in iodothyronine. The thyroglobulin behaved normally in Sephadex G-200 chromatography and immunoreaction. Thyroid tissue exhibited increased peroxidase activity as measured by I3 formation. Increased peroxidase activity may be related to the observed increase in serum level of TSH.
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PMID:Increased peroxidase activity in Pendred's syndrome with hypothyroidism. 95 8

Two established techniques for analysis of plasma membranes, namely, lactoperoxidase catalyzed surface radioiodination of intact cells and bulk membrane isolation following disruption of cells by shear forces, were applied in studies of membrane proteins of continuously cultured cells of the monoclonal T lymphoma line WEHI-22. It was found that macromolecular 125I-iodide incorporated into plasma membrane proteins of intact cells was at least as good a marker for the plasma as was the commonly used enzyme 5'-nucleotidase. T lymphoma plasma membrane proteins were complex when analysed by polyacrylamide gel electrophoresis in sodium dodecylsulphate-containing buffers and more than thirty distinct components were resolved. More than fifteen of the components observed on a mass basis were also labelled with 125I-iodide. Certain bands, however, exhibited a degree of label disproportionate to their staining properties with Coomassie Blue. This was interpreted in terms of their accessibility to the solvent in the intact cells.
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PMID:Plasma membrane of a murine T cell lymphoma: surface labelling, membrane isolation, separation of membrane proteins and distribution of surface label amongst these proteins. 108 76

The lactoperoxidase-catalyzed iodination technique was utilized to incorporate radioactive iodine into membrane proteins which lie on the outer surface of the myelin sheath. An intact, myelinated nerve bundle, the dorsal column of the cat spinal cord, was employed. The enzymatically iodinated proteins were identified by polyacrylamide gel electrophoresis, and the specific radioactivity was determined. Results indicated that several high molecular weight proteins were predominantly labeled by the nonpenetrating lactopreoxidase. Proteolipid protein was also labeled, although to a lesser extent; basic protein was not labeled under these conditions. The data suggest that several high molecular weight proteins are exposed on the outer surface of the myelin sheath. Proteolipid protein is at least partially exposed on the outer surface, although it could be present at both membrane surfaces. Evidence is presented which suggests that the basic protein is located at the inner surface of the membrane, corresponding to the major dense line of myelin.
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PMID:Topographical arrangement of membrane proteins in the intact myelin sheath. Lactoperoxidase incorproation of iodine into myelin surface proteins. 111 91

Myeloperoxidase, H2O2, and a halide constitute a potent antimicrobial system. A cytotoxic effect of this system on a line of mouse ascitic lymphoma cells (LSTRA) is demonstrated here using four different assay systems: 51Cr release, trypan blue exclusion, inhibition of glucose C-1 oxidation, and loss of oncogenicity for mice. Deletion of each component of the system, preheating the peroxidase, or addition of azide, cyanide, or catalase abolished the cytotoxicity. Myeloperoxidase was effective with either chloride or iodide as the halide, while lastoperoxidase was effective with iodide but not chloride. The iodinated thyroid hormones, triiodothyronine and thyroxine, could substitute for the halide, and H2O2 could be replaced by a peroxide-generating enzyme system such as glucose and glucose oxidase or by H2O2 producing bacteria such as pneumococci or streptococci. The possibility is raised that the peroxidases of inflammatory cells and certain biologic fluids may affect tumor initiation or growth in vivo.
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PMID:Peroxidase-H2O2-halide system: Cytotoxic effect on mammalian tumor cells. 112 Jan 84

Free diiosotyrosine exerts two opposite effects on the reactions catalyzed by thyroid peroxidase, thyroglobulin iodination and thyroid hormone formation. 1. Inhibition of thyroglobulin iodination catalyzed by thyroid peroxidase was observed when free diiodotyrosine concentration was higher than 5 muM. This inhibition was competitive, suggesting that free diiodotyrosine interacts with the substrate site(s) of thyroid peroxidase. Free diiodotyrosine also competively inhibited iodide peroxidation to I2. 2. Free diiodotyrosine, when incubated with thyroid peroxidase in the absence of iodide was recovered unmodified; in the presence of iodide an exchange reaction was observed between the iodine atoms present in the diiodotyrosine molecule and iodide present in the medium. Using 14C-labelled diiodotyrosine, 14C-labelled non-iodinated products were also observed, showing that deiodination occurred as a minor degradation pathway. However, no monoiodo[14C]tyrosine or E114C]tyrosine were observed. Exchange reaction between free diiototyrosine and iodide is therefore direct and does not imply deiodination-iodination intermediary steps. Thyroglobulin inhibits diiodotyrosine-iodide exchange and vice versa, again suggesting competition for both reactions. These results support, by a different experimental approach, the two-site model for peroxidase previously described by us in this journal. 3. Free diiodotyrosine when present at a very low concentration, 0.05 muM, exerts a stimulatory effect on throid hormones synthesis. The relationship between diiodotyrosine concentration and thyroid hormone synthesis give an S-shaped curve, suggesting that free diiodotyrosine acts as a regulatory ligand for thyroid peroxidase. Evidence is also presented that free diiodotyrosine is not incorporated into thyroid hormones. Therefore, thyroid peroxidase catalyzes only intra-molecular coupling between iodotyrosine hormonogenic residues. 4. Finally, although no direct proof exists that these free diiodotyrosine effects upon thyroglobulin iodination and thyroid hormone synthesis are physiologically significant, such a possibility deserves further investigation.
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PMID:Free diiodotyrosine effects on protein iodination and thyroid hormone synthesis catalyzed by thyroid peroxidase. 114 35

Human haptoglobin (Hp) type 2-1 was modified with N-acetylimidazole, iodine or tetranitromethane (TNM), and the ability of the obtained derivatives to form with haemoglobin (Hb) complexes with peroxidase activity, was estimated. At low reagent to protein molar ratios, 11 tyrosine residues were nitrated, 12 acetylated and 13 iodinated. The biological activity of NO2-Hp and I-Hp amounted to 40% of the activity of native Hp whereas the activity of Ac-Hp only to 16%. The derivatives modified at high ratios of N-acetylimidazole or iodine lost the ability to bind with Hb. Deacylation. of tyrosines and partial liberation of acetylated xi-amino groups resulted in partial recovery of the activity. As demonstrated by polyacrylamide-gel electrophoresis, the modification of Hp with high excess of TNM or iodine induced polymer formation
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PMID:Effect of modification on physico-chemical and biological properties of haptoglobin. Acetylation, iodination and nitration. 115 43

A 37-yr-old woman with nontoxic goiter is presented. The thyroid 131I uptake at 3 and 24 hr were, respectively, 77.1% and 81.4% dose. Thiocyanate discharged 65.5% of the accumulated 131I in 30 min. In vitro organification of iodine in the thyroid homogenate from the patient was impaired and it was restored to normal by the addition of H2O2, glucose, and glucose oxidase system, FAD, or reduced cytochrome b5. Riboflavin, FMN, oxidized cytochrome b5, oxidized or reduced cytochrome c, NAD(H), and NADP(H) were ineffective in the reaction. The microsomal NADH-cytochrome b5 reductase activity was definitely low in the patient's thyroid. It was augmented to a normal level by incubation of the microsomes with FAD for 30 min or more. The activities of thyroid peroxidase, G6-PD, 6-PGD, catalase, protease, and NADPH-cytochrome c reductase were within normal limits. The major thyroid protein was normal thyroglobulin which could be readily iodinated in the presence of H2O2 and horse radish peroxidase. These findings suggest the correlation of an iodide organification defect with a cytochrome b5 reductase deficiency. Administration of high doses of FAD led to the restoration of thyroidal iodide organification mechanism associated with an increased thyroid hormone production and to a marked decrease of the goiter. Riboflavin was given without effect even at a high dosage level. Consequently, it seems likely that the deficient cytochrome b5 reductase activity in this patient is due to a defect in the biosynthesis of FAD, the coenzyme of the reductase, from riboflavin.
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PMID:Deficient cytochrome b5 reductase activity in nontoxic goiter with iodide organification defect. 116 26

Erythrocytes are hemolyzed by myeloperoxidase, an H2O2-generating system (glucose + glucose oxidase; hypoxanthine + xanthine oxidase) and an oxidizable cofactor (chloride, iodide, thyroxine, triiodothyronine). The combined effect of chloride and either iodide or the thyroid hormones is greater than additive. Myeloperoxidase can be replaced by lactoperoxidase in the iodide-, thyroxine and triiodothyronine-dependent, but not in the chloride-dependent, systems. Hemolysis is is inhibited by the peroxidase inhibitors, azide and cyanide, and by catalase and is stimulated by superoxide dismutase when the xanthine oxidase system is employed as the source of H2O2. Hemolysis by the iodide-dependent system is associated with the iodination of erythrocyte components.
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PMID:Hemolysis and iodination of erythrocyte components by a myeloperoxidase-mediated system. 117 52


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