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Peroxidases glutathione

Glutathione hydrogen-peroxidase oxidoreductase (EC 1.11.1.9) is a selenoprotein enzyme that catalyses the reduction of a large number of hydroperoxides ranging from H202 to a spectrum of organic hydroperoxides (ROOH). [Pg.194]

H202 + 2GSH - GSSG + 2H20 ROOH + 2GSH - GSSG + ROH + H20 [Pg.194]

Although methods have been devised for the measurement of GSH utilization by the enzyme, and of H202 consumption, these are difficult and have now largely been replaced by an assay based on that of Paglia and Valentine (1967) in which the product GSSG is used to drive the oxidation of NADPH+H+ catalysed by glutathione reductase  [Pg.195]

The oxidation of NADPH + H+ is measured spectrophotometrically and, under appropriate conditions, may be used to measure the activity of glutathione peroxidase. The procedure which follows is that described by Flohe and Gunzler (1984). [Pg.195]

Reagents 0.1 M potassium phosphate buffer, pH 7.0, containing 0.1 mM EDTA. [Pg.195]

Before glutathione peroxidase was known to be a selenoprotein , glutathione peroxidase had been characterized kinetically and mechanistically and had even been isolated in crystalline form . The function of this enzyme is to catalyze the decomposition of peroxides (H2O2 and a variety of organic peroxides) which can damage red blood cell membranes and other tissues which function in aerobic surroundings (Eq. 1) .  [Pg.12]

Glutathione peroxidase has a molecular weight between 76,000 and 92,000 daltons and contains four identical 19-23,(X)0 dalton subunits , each of which contains a single selenocysteine residue . Purified forms of the enzyme have been obtained from the red blood cells of cattle , sheep and humans as well as from rat liver and bovine lens . An amino acid composition of homogeneous rat liver glutathione peroxidase has been determined and an X-ray diffi-action study at 2.8 A resolution has been published . There is some discrepancy between these two studies since the amino acid analysis indicates two cysteine residues per subunit which were not detected by the X-ray study. This point will have to be clarified. The X-ray study has shown that the active selenocysteines are found in flat depressions on the surface of the molecule which exists in long a-helices. [Pg.12]

Debate still exists concerning the form of the selenocysteine residues in the reduced from of the enzyme (SeH ). It is not clear whether there is a selenium valency change upon reaction or if, during the reaction with peroxide substrate, the selenium in the enzyme is converted to oxygen-containing derivatives (e.g. selenenic acids, Enz-RSeOH). Direct experimental evidence concerning this oxidation step is needed. [Pg.12]

The active site of GPx-ase contains a selenol group (SeH) which is oxidized to Se(=0)H with formation of one equivalent of water in the first step of the enzymatic cycle (equation 17b). Two equivalents of glutathione then react with [Pg.40]

GSHPx from several tissues of a number of different species has been purified and the relative molecular mass was found to be in the range of 76000-lOOOOOdaltons [9]. The enzyme consists of four subunits which are apparently identical, with molecular weights ranging from 18 000 to 24 000 daltons, and there are 4 g-atoms of selenium per mole of enzyme. The enzyme contains [Pg.117]

The question of the biosynthesis of GSHPx has been the subject of much research and it is now known with certainty that the formation of the seleno-cysteinyl residue depends on the existence of a gene that specifies a unique UGA codon that codes specifically for selenocysteine the complimentary tRNA binds serine to which is then added the selenyl moiety to form selenocysteine which is added to the nascent protein by the normal translational process [13], This mechanism has also been demonstrated for the biosynthesis of other seleno-enzymes in several bacterial species [14-16]. [Pg.118]

The catalytic mechanism of GSHPx action is very complex and is even now only partially understood. The original 1975 proposal of Ganther[17] is shown in Fig. 4. This mechanism has however been challenged [18] and it is clear that the actual mechanism is very much more complex than that proposed by Ganther[17]. The specificity with respect to substrate is absolute with respect to GSH and even very similar analogues of GSH cannot support the enzymic activity. With respect to the substrate toward which the enzyme catalysis is [Pg.118]

Primary targets for attack by oxygen-derived free radical species are the polyunsaturated fatty-acid (PUFA) moieties of membrane phospholipids. Attack on low-density lipoprotein PUFA (LDL PUFA) must also be considered and is of primary importance in the consideration of the aetiology of atherosclerosis. The mechanism of all such peroxidation processes is likely to be the same and the inhibitory effect of antioxidants toward PUFA can be considered to be [Pg.119]


Enzymes often need for their activity the presence of a non-protein portion, which may be closely combined with the protein, in which case it is called a prosthetic group, or more loosely associated, in which case it is a coenzyme. Certain metals may be combined with the enzyme such as copper in ascorbic oxidase and selenium in glutathione peroxidase. Often the presence of other metals in solution, such as magnesium, are necessary for the action of particular enzymes. [Pg.159]

Fig. 7. The glutathione peroxidase (a selenium enzyme) system where GSH = A -(A -L-7-giutamyi -L-cysteinyi )giycine and G—S—S—G, the disulfide. Fig. 7. The glutathione peroxidase (a selenium enzyme) system where GSH = A -(A -L-7-giutamyi -L-cysteinyi )giycine and G—S—S—G, the disulfide.
In 1956 selenium was identified (123) as an essential micronutrient iu nutrition. In conjunction with vitamin E, selenium is effective iu the prevention of muscular dystrophy iu animals. Sodium selenite is adrninistered to prevent exudative diathesis iu chicks, a condition iu which fluid leaks out of the tissues white muscle disease iu sheep and infertility iu ewes (see Eeed ADDITIVES). Selenium lessens the iacidence of pneumonia iu lambs and of premature, weak, and stillborn calves controls hepatosis dietetica iu pigs and decreases muscular inflammation iu horses. White muscle disease, widespread iu sheep and cattle of the selenium-deficient areas of New Zealand and the United States, is insignificant iu high selenium soil areas. The supplementation of animal feeds with selenium was approved by the U.S. EDA iu 1974 (see Eeed additives). Much of selenium s metaboHc activity results from its involvement iu the selenoproteia enzyme, glutathione peroxidase. [Pg.337]

Glutathione peroxidase [9013-66-5] oxidizes glutathione, and helps to remove inorganic and organic hydroperoxides (221] It exhibits antiinflammatory activity in experimental uveitis of rats (234). [Pg.312]

The increased concentrations of K, Ca, Fe, Br, Se and Rb in infarction and scar areas are observed for patient with the recent infarction. For the patients with old infarction the levels of these elements are decreased in the same areas. This reflects the intensity of metabolic processes in the pathological area of myocardium. Additionally, the elevated levels of Se was find out in myocardium of right ventricle in both patients, that may be caused by the increasing the activity of the glutathione peroxidase enzyme. [Pg.353]

Two classes of antioxidants are known the low-molecular weight compounds (tocopherols, ascorbate, -carotene, glutathione, uric acid and etc.) and the proteins (albumin, transferrin, caeruloplasmin, ferritin, etc.) including antioxidant enzymes (e.g. superoxide dismutase, catalase, glutathione peroxidase). [Pg.354]

Organoselenium compounds in particular, once ingested, are slowly released over prolonged periods and result in foul-smelling breath and perspiration. The element is also highly toxic towards grazing sheep, cattle and other animals, and, at concentrations above about 5 ppm, causes severe disorders. Despite this, Se was found (in 1957) to play an essential dietary role in animals and also in humans — it is required in the formation of the enzyme glutathione peroxidase which is involved in fat metabolism. It has also been found that the Incidence of kwashiorkor (severe protein malnutrition) in children is associated with inadequate uptake of Se, and it may well be involved in protection... [Pg.759]

Polidoro G, Dillio C, Arduini A, et al. 1982. Glutathione peroxidase and glutathione S-transferase activities in human fetal tissues. Inability of acidic forms of glutathione S-transferase to catalyze the reduction of organic hydroperoxides. Biochem Int 4 637-645. [Pg.226]

THE PENTOSE PHOSPHATE PATHWAY GLUTATHIONE PEROXIDASE PROTECT ERYTHROCYTES AGAINST HEMOLYSIS... [Pg.166]

Figure 20-3. Role of the pentose phosphate pathway in the glutathione peroxidase reaction of erythrocytes. (G-S-S-G, oxidized glutathione G-SH, reduced glutathione Se, selenium cofactor.)... Figure 20-3. Role of the pentose phosphate pathway in the glutathione peroxidase reaction of erythrocytes. (G-S-S-G, oxidized glutathione G-SH, reduced glutathione Se, selenium cofactor.)...
In erythrocytes, the pathway has a major function in preventing hemolysis by providing NADPH to maintain glutathione in the reduced state as the substrate for glutathione peroxidase. [Pg.172]

The red cell contains a battery of cytosolic enzymes, such as superoxide dismutase, catalase, and glutathione peroxidase, to dispose of powerful oxidants generated during its metabolism. [Pg.624]

It participates in the decomposition of potentially toxic hydrogen peroxide in the reaction catalyzed by glutathione peroxidase (Ghapter 20). [Pg.629]

Figure 15.11 Possible scheme for the formation of free radicals from the metabolism of dopamine. Normally hydrogen peroxide formed from the deamination of DA is detoxified to H2O along with the production of oxidised glutathione (GSSG) from its reduced form (GSH), by glutathione peroxidase. This reaction is restricted in the brain, however, because of low levels of the peroxidase. By contrast the formation of the reactive OH-radical (toxification) is enhanced in the substantia nigra because of its high levels of active iron and the low concentration of transferin to bind it. This potential toxic process could be enhanced by extra DA formed from levodopa in the therapy of PD (see Olanow 1993 and Olanow et al. 1998)... Figure 15.11 Possible scheme for the formation of free radicals from the metabolism of dopamine. Normally hydrogen peroxide formed from the deamination of DA is detoxified to H2O along with the production of oxidised glutathione (GSSG) from its reduced form (GSH), by glutathione peroxidase. This reaction is restricted in the brain, however, because of low levels of the peroxidase. By contrast the formation of the reactive OH-radical (toxification) is enhanced in the substantia nigra because of its high levels of active iron and the low concentration of transferin to bind it. This potential toxic process could be enhanced by extra DA formed from levodopa in the therapy of PD (see Olanow 1993 and Olanow et al. 1998)...
Glutathione-peroxidase (GSH-Pxase) is an enzyme found in erythroqrtes and other tissues that has an essential selenocysteine residue involved in the catalytic decomposition of reactive oxygen species. In the erythrocyte, hydrogen peroxide is the principle reactive oxygen species available. [Pg.300]

Chaudiere, J. and Tappel, A.L. (1984) Interaction of gold(I) with the active site of selenium-glutathione peroxidase. Journal of Inorganic Biochemistry, 20, 313—325. [Pg.316]

Hu, M.-L., Dillard, C.J. and Tappel, A.L. (1988) Aurofhioglucose effect on sulfhydryls and glutathione-metabolizing enzymes in vivo inhibition of selenium-dependent glutathione peroxidase. Research Communications in Chemical Pathology and Pharmacology, 59,... [Pg.316]

Roberts, J. and Shaw, C.F. Ill (1998) Inhibition of erythrocyte selenium-glutathione peroxidase by auranofin analogs and metabolites. Biochemical Pharmacology, 55, 1291-1299. [Pg.317]

Roberts,J.(1993)Thekineticpropertiesof Au(I) drug binding to serum albumin and selenium-glutathione peroxidase and their significance for rheumatoid arthritis. Ph.D. thesis, University-Milwaukee. [Pg.317]


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A glutathione peroxidase

Active-site model Glutathione peroxidases

Antioxidant mechanisms glutathione peroxidase

Catalase and glutathione peroxidase

Drug Glutathione peroxidase

Erythrocytes pathway/glutathione peroxidase

Free radical glutathione peroxidase

Glutathion peroxidase

Glutathion peroxidase

Glutathione GSH peroxidase

Glutathione peroxidase (GSHPx

Glutathione peroxidase S-transferase

Glutathione peroxidase activation coefficient

Glutathione peroxidase activity

Glutathione peroxidase antioxidant defense

Glutathione peroxidase assay

Glutathione peroxidase decomposes superoxide

Glutathione peroxidase deficiency

Glutathione peroxidase exposure

Glutathione peroxidase heme-containing

Glutathione peroxidase hydroxide

Glutathione peroxidase reductase

Glutathione peroxidase riboflavin status

Glutathione peroxidase selenium

Glutathione peroxidase selenoprotein

Glutathione peroxidase system

Glutathione peroxidase, GPx

Glutathione peroxidase, action

Glutathione peroxidase, erythrocyte

Glutathione peroxidases , studied with

Glutathione peroxidases enzyme

Lipid hydroperoxide glutathione peroxidase

Oxidative glutathione peroxidases

Oxygen glutathione peroxidase

Peroxidases glutathione peroxidase

Phospholipid hydroperoxide glutathione peroxidase

Plasma glutathione peroxidase

Selenium-Dependent Glutathione Peroxidase

Selenium-independent glutathione peroxidase

Selenocysteine glutathione peroxidase

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