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)

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.
 ...
PMID:Biosynthesis of thyroid hormone: basic and clinical aspects. 6 47

We report a relatively simple and convenient method for iodinating human alpha-fetoprotein and for purifying the 125I-labeled material. The label is incorporated into human alpha-fetoprotein enzymatically by use of lactoperoxidase. Before each assay the labeled material is purified over two successive short columns: Sepharcryl S-200 Superfine and cellulose. This procedure removes both free iodine and "damaged" fetoprotein. With the purified material we developed a sensitive and reliable radioimmunoassay for alpha-fetoprotein in serum and amniotic fluid.
 ...
PMID:Radioimmunoassay of alpha-fetoprotein, with special reference to iodination and purification techniques. 7 75

T lymphoblasts of specificity Lewis anti-DA, Lewis anti-BN, BN anti-DA and L.BN anti-DA were purified on Ficoll-Paque from mixed leucocyte cultures on day 5. Blasts were radiolabelled with iodine-125 by the lactoperoxidase method and lysed by the aid of Nonidet P40. Idiotypic molecules were puried from the lysates by the use of anti-idiotypic antiserum of specificity anti-(Lewis anti-DA) and Staphylococcus aureus bearing protein-A. In this way, molecules with a molecular weight of 150,000 and 75,000 daltons could be isolated from Lewis anti-DA and L.BN anti-DA T lymphoblasts but no significant radioactivity was brought down by the same procedure from Lewis Lewis anti-BN or BN anti-DA T lymphoblasts. No additional molecules were detected on the lower molecular weight regions where light chains of Ig type as well as conventional products of the MHC genes would appear. The 150,000 dalton molecules are composed of two single polypeptide chains with a molecular weight of around 75,000 daltons. These data are in complete agreement with earlier results on antigen-binding, idiotypic receptors obtained from normal rat T lymphocytes.
 ...
PMID:Partial characterization of cell surface idiotypes on alloantigen-activated T lymphoblasts. 8 24

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.
 ...
PMID:The influence of non-steroidal anti-inflammatory and antithyroid agents on myeloperoxidase-catalysed activities of human leucocytes. 8 4

The rates of oxidation of several goitrogens by lactoperoxidase and the rates of inactivation of lactoperoxidase by the same goitrogens have been measured. The influence of iodide on both reactions has also been evaluated. It has been shown by us that iodide acts catalytically in regulating lactoperoxidase activity at pH 8.8. The rate data have been analyzed by a computer program which solves the differential equations for the above mentioned reactions. From this computer analysis we have been able to obtain binding constants of the goitrogens and inactivation rate constants of lactoperoxidase. Iodide was shown to inhibit goitrogenic activity either by increasing the rate of drug oxidation or by reducing the rate of enzyme inactivation, or both, depending on the particular drug. Iodide had little or no effect on the goitrogen-binding constants. We have also shown that the relative rates of enzyme inactivation can be correlated with the potency of the goitrogen as an antithyroid drug.
 ...
PMID:The effects of thioureylene compounds (goitrogens) on lactoperoxidase activity. 9 9

At sub-bactericidal concentrations of hydrogen peroxide, Mycobacterium tuberculosis was killed by hydrogen peroxide/peroxidase/halide microbicidal systems. The halide cofactor could be either iodide or, with much lower efficiency, chloride. Omission of any one of the reactants eliminated the tuberculocidal effect. Differences in susceptibility between different strains of M. tuberculosis did not correlate with virulence differences. The observations are discussed in the context of host defence mechanisms against tuberculosis.
 ...
PMID:Virulence of Mycobacterium tuberculosis and susceptibility to peroxidative killing systems. 9 84

The principle amatoxin, alpha-amanitin, is found to be extremely sensitive toward lactoperoxidase catalyzed degradation, rather than iodination, of the indole nucleus. Extensive attenuation of inhibitor potency against eukaryotic DNA-dependent RNA polymerase II accompanies the treatment of alpha-amanitin with lactoperoxidase, iodide and hydrogen peroxide.
 ...
PMID:alpha-Amanitin: inactivation by bovine lactoperoxidase. 10 6

A simplified solid-state enzymatic iodination procedure for routine labeling of unstable pure protein or complex amino acid-containing molecules is presented. The procedure was designed using agarose-bound lactoperoxidase to iodinate human IgG with iodine-125. This method consistently resulted in a labeling efficiency greater than 90% with high stability and undetectable gross structural alterations of the substrate as evaluated by immunodiffusion and electrophoresis. The technique presented is simple, efficient, and may be employed to yield a sterile, pyrogen-free labeled species.
 ...
PMID:Radioiodination of biologically active compounds: a simplified solid-state enzymatic procedure. 11 67

The iodide-peroxidase activity of the thyroid gland remains, in hypophysectomized Rats maintained on a low iodine diet, below normal value. This result suggests that the early increase of peroxidase activity observed in control Rats maintained on a low iodine diet is TSH dependent.
 ...
PMID:[Development of thyroid peroxidase activity during the early stage of iodine deficiency in the hypophysectomized rat]. 11 12

NIL 8 hamster fibroblast cells were labeled by lactoperoxidase-catalyzed iodination. Their membranes were fractionated by sedimentation-rate and isopycnic zonal centrifugation. All the iodinated proteins except the very prominently labeled high molecular weight protein (greater than 200,000 daltons) were located in a fraction identified enzymically and compositionally as plasma membrane. The high molecular weight protein that was previously shown to be sensitive to virus transformation (Hynes, 1973) is concentrated in a very high density particle (rho equals 1.253-1.259) which contains mainly carbohydrate and protein and very low levels of lipid. 5'-nucleotidase was the only enzyme reproducibly demonstrated in this fraction, and electron micrographs revealed a predominantly amorphous morphology together with a few membraneous structures. The iodine label in this fraction was very sensitive to trypsinization prior to homogenization. All the available evidence indicates that this fraction is derived from the surface coat. Mitochondria, nuclei, and soluble protein were labeled to an insignificant extent. The presence of the iodinated surface proteins associated with the endoplasmic reticulum fraction is discussed in the light of these results.
 ...
PMID:The location of proteins labeled by the 125I-lactoperoxidase system in the NIL 8 hamster fibroblast. 12 85


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