Iodide peroxidase catalyzes

In vitro, iodide peroxidase catalyzes the reaction 2H+-]- 2I - - H2O2 —> I2 4- 2H2O. However, in vivo... 

This enzyme [EC 1.11.1.8], also known as iodotyrosine deiodase, iodinase, and thyroid peroxidase, catalyzes the reaction of iodide with hydrogen peroxide to produce iodine and two water. The cofactor for this enzyme is heme. M. Morrison (1970) Meth. Enzymol. 17A, 653 and 658. 

Conventional ISEs have been used as detectors for immunoassays. Antibody-binding measurements can be made with hapten-selective electrodes such as the trimethylphenylammonium ion electrode. Enzyme immunoassays, in which the enzyme label catalyzes the production of a product that is detected by an ISE, take advantage of the amplification effect of enzyme catalysis in order to reach lower detection limits. Systems for hepatitis B surface antigen and estradiol use horseradish peroxidase as the enzyme label and an iodide electrode as the detector. The horseradish peroxidase catalyzes the oxidation of p-fluoroanadine with the fluoride detected by the ISE. Biotin and cyclic have been determined... 

Coupling Reaction and Storage as Colloid. Iodide peroxidase or a coupling enzyme catalyzes the coupling reaction at the cell-colloid interface by intramolecular coupling of two iodotyrosyl residues with formation of an iodothyronyl residue. Coupling of DIT residues is favored thus, formation of T4... 

The oxidation of intracellular iodide is catalyzed by thyroid peroxidase (located at the apical border of the thyroid acinar cell) in what may be a two-electron oxidation step forming 1 (iodinium ion), lodinium ion may react with a tyrosine residue in the protein thyroglobulin to form a tyrosine quinoid and then a 3 -monoiodotyrosine (MIT) residue. It has been suggested that a second iodide is added to the ring by similar mechanisms to form a 3,5-diiodotyrosine (DIT) residue. Because iodide is added to these organic compounds, iodination is also referred to as the organification of iodide. ... 

In vitro models ofTPO activity and which use thiourey-lene compounds, as well as iodine (Taurog, 1996) and H2O2, and similar models of lactoperoxidase activity (Edelhoch et al., 1979) demonstrate that other substrates are often oxidized in preference to iodide. The peroxidase catalyzes the formation of disulfide compounds. These are subsequently oxidized and excreted, but only in the presence of iodine. Absolute iodine deficiency or relative deficiency in the presence of high concentrations of thioureylene compounds results in recovery of the thioureylene from the disulfide and irreversible inhibition of peroxidase (Taurog, 1996). In the sow and cow experiments inactivation of thioureylenes by TPO at the expense of iodide oxidation, and therefore storage of elemental-iodine in the thyroid, resulted in increased iodine (and presumably iodide) concentrations in urine and feces, respectively. 

R.Z. Harris, S.L. Newmyer, and P.R. Ortiz de Montellano, Horseradish-peroxidase-catalyzed two-electron oxidations. Oxidation of iodide, thioanisoles, and phenols at distinct sites, J. Biol. Chem. 268 1637 (1993). 

The enzymes involved in tyrosine iodination remain unknown. It has been proposed that in addition to the iodide peroxidase, a specific tyrosine iodinase is also required. Whether this iodinase catalyzes the iodination of both mono- and diiodotyrosine remains to be established. 

Other solutions to dealing with interferences in the detection of H O have included the use of a copperfll) diethyldithiocarbamate precolumn to oxidize the sample before it reaches the immobilized enzyme, as well as the use of a palladium/gold sputtered electrode which catalyzes the oxidation of hydrogen peroxide In addition, peroxidase has been used to catalyze the reaction between hydrogen peroxide and iodide ferrocyanide and organo-fluorine compounds Am-... 

Another important example of catalytic oxidation of inorganic compounds by peroxidases is the catalysis of iodide oxidation by TPO. TPO is involved in the biosynthesis of thyroid hormone and catalyzes the reactions of iodination and coupling in the thyroid gland. Magnusson et al. [215] considered two possible pathways of iodination the formation of enzyme-bound hypoiodite and the formation of free hypoiodide (Reactions (17) and (18)) ... 

The concentration of Li+ in the thyroid is three to four times that in serum [179]. It is thought that Li+ may be concentrated in the thyroid gland by a mechanism similar to the incorporation of iodide, I-, resulting in competition between Li+ and I the levels of intracellular 1 decrease when those of Li+ increase, and vice versa [182]. Li+ inhibits both the ability of the gland to accumulate 1 and the release of iodine from the gland. In vitro, Li+ has no effect on thyroid peroxidase, the enzyme that catalyzes the incorporation of I" into tyrosyl residues leading to thyroidal hormone synthesis, but does increase the activity of iodotyrosine-deio-dinase, which catalyzes the reductive deiodination of iodotyrosyls, thus maintaining the levels of intracellular I [182]. The increase in iodoty-rosine-deiodinase activity is probably a response to the Li+-induced decrease in the concentration of thyroidal I". Li+ has no effect on the conversion of thyroxine to triiodothyronine. The overall effect of this competition between Li+ and 1 is, therefore, reduced levels of thyroid hormone in the presence of Li+. 

Thioamides are reducing agents. They inhibit thyroid hormone synthesis by inhibiting the peroxidase enzymatic system, which catalyzes oxidation of iodide ions and iodine that are consumed in food, which is necessary for iodination of tyrosine derivatives. Thus they reduce the concentration of free iodine necessary to react with tyrosine derivatives, and they can also block oxidative addition reactions of mono- and diiodtyrosines, which form L-thyroxine and L-triiodothyronin. 

Interestingly, unlike the heme-containing peroxidases myeloperoxidase and chloroperoxidase, the vanadium enzyme does not catalyze the direct disproportionation of H2O2 in the absence of bromide or iodide... 

Several authors investigated ion selective electrodes incorporating GOD coupled with oxidative reactions catalyzed by horseradish peroxidase (HRP). Thus, glucose has been determined by measuring iodide concentration at an iodide sensitive electrode (Nagy at al., 1973) according to ... 

Oxidation and Iodination. The oxidation of iodide to its active form and the iodination of tyrosine are catalyzed by thyroid peroxidase, a heme-containing enzyme that utilizes hydrogen peroxide (HjOj) as the oxidant. The peroxidase is membrane-bound and concentrated at the apical surface of the thyroid cells. The reaction forms mono- and diiodotyrosyl residues in thyroglobulin just prior to its extracellular storage in the lumen of the thyroid follicle. is formed near its site of utilization and is stimulated by a rise in cytosolic Cd . ... 

Thyroid peroxidase, TPO, is a large heme-containing glycoprotein that plays a key role in the biosynthesis of thyroid hormones. It catalyzes iodide oxidation, iodina-tion of tyrosine residues and coupling of iodotyrosines to generate the iodothyronines T3 and T4. 

Virion A, Michot JL, Deme D, et al. NADPH oxidation catalyzed by the peroxidase/H202 system. Iodide-mediated oxidation of NADPH to iodinated NADP. Eur J Biochem 1985 148 239-248. 

Thyroid peroxidase thyroid peroxidase (TPO) is a membrane bounding protein catalyzing iodide oxidation and iodination of tyrosine residues to generate T3 and T4. This enzyme is encoded by a gene consists of 17 exons. 

An iodide-selective electrode can be used to measure glucose concentration. The measurement is based on reactions catalyzed by glucose oxidase (GOx) (reaction [III]) and peroxidase (POx) (reaction [IV]) ... 

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