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Query: UNIPROT:P36969 (phospholipid hydroperoxide glutathione peroxidase)
 344 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Lipid hydroperoxides (LOOHs) in various lipid assemblies are shown to be efficiently reduced and deactivated by phospholipid hydroperoxide glutathione peroxidase (PHGPX), the second selenoperoxidase to be identified and characterized. Coupled spectrophotometric analyses in the presence of NADPH, glutathione (GSH), glutathione reductase and Triton X-100 indicated that photochemically generated LOOHs in small unilamellar liposomes are substrates for PHGPX, but not for the classical glutathione peroxidase (GPX). PHGPX was found to be reactive with cholesterol hydroperoxides as well as phospholipid hydroperoxides. Kinetic iodometric analyses during GSH/PHGPX treatment of photoperoxidized liposomes indicated a rapid decay of total LOOH to a residual level of 35-40%; addition of Triton X-100 allowed the reaction to go to completion. The non-reactive LOOHs in intact liposomes were shown to be inaccessible groups on the inner membrane face. In the presence of iron and ascorbate, photoperoxidized liposomes underwent a burst of thiobarbituric acid-detectable lipid peroxidation which could be inhibited by prior GSH/PHGPX treatment, but not by GSH/GPX treatment. Additional experiments indicated that hydroperoxides of phosphatidylcholine, cholesterol and cholesteryl esters in low-density lipoprotein are also good substrates for PHGPX. An important role of PHGPX in cellular detoxification of a wide variety of LOOHs in membranes and internalized lipoproteins is suggested from these findings.
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PMID:Enzymatic reduction of phospholipid and cholesterol hydroperoxides in artificial bilayers and lipoproteins. 238 98

The 15,000xg supernatant of sonicated rat PMN contains 5-lipoxygenase that converts arachidonic acid to 5-hydroperoxyeicosatetraenoic acid (5-HPETE) and leukotriene A4 and an HPETE peroxidase that catalyzes reduction of the 5-HPETE. The specificity of this HPETE peroxidase for peroxides, reducing agents, and inhibitors has been characterized to distinguish this enzyme from other peroxidase activities. In addition to 5-HPETE, the HPETE peroxidase will catalyze reduction of 15-hydroperoxyeicosatetraenoic acid, 13-hydroperoxyoctadecadienoic acid, and 15-hydroperoxy-8,11,13-eicosatrienoic acid, but not cumene or t-butylhydroperoxides. The HPETE peroxidase accepted 5 of 11 thiols tested as reducing agents. However, glutathione is greater than 15 times more effective than any other thiol tested. Other reducing agents, ascorbate, NADH, NADPH, phenol, p-cresol, and homovanillic acid, were not accepted by HPETE peroxidase. This enzyme is not inhibited by 10 mM KCN, 2 mM aspirin, 2 mM salicylic acid, or 0.5 mM indomethacin. When 5-[14C]HPETE is generated from [14C]arachidonic acid in the presence of unlabeled 5-HPETE and the HPETE peroxidase, the 5-[14C]HETE produced is of much lower specific activity than the [14C]arachidonic acid. This indicates that the 5-[14C]HPETE leaves the active site of 5-lipoxygenase and mixes with the unlabeled 5-HPETE in solution prior to reduction and is a kinetic demonstration that 5-lipoxygenase has no peroxidase activity. Specificity for peroxides, reducing agents, and inhibitors differentiates HPETE peroxidase from glutathione peroxidase, phospholipid-hydroperoxide glutathione peroxidase, a 12-HPETE peroxidase, and heme peroxidases. The HPETE peroxidase could be a glutathione S-transferase selective for fatty acid hydroperoxides.
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PMID:Specificity of an HPETE peroxidase from rat PMN. 285 18

The present review deals with the chemical properties of selenium in relation to its antioxidant properties and its reactivity in biological systems. The interaction of selenite with thiols and glutathione and the reactivity of selenocompounds with hydroperoxides are described. After a short survey on distribution, metabolism and organification of selenium, the role of this element as a component of the two seleno-dependent glutathione peroxidases is described. The main features of glutathione peroxidase and phospholipid hydroperoxide glutathione peroxidase are also reviewed. Both enzymes reduce different hydroperoxides to the corresponding alcohols and the major difference is the reduction of lipid hydroperoxides in membrane matrix catalyzed only by the phospholipid hydroperoxide glutathione peroxidase. However, in spite of the different specificity for the peroxidic substrates, the kinetic mechanism of both glutathione peroxidase and phospholipid hydroperoxide glutathione peroxidase seems identical and proceeds through a tert-uni ping pong mechanism. In the reaction cycle, indeed, as supported by the kinetic data, the oxidation of the ionized selenol by the hydroperoxide yields a selenenic acid that in turn is reduced back by two reactions with reduced glutathione. Special emphasis has been given to the role of selenium-dependent glutathione peroxidases in the prevention of membrane lipid peroxidation. While glutathione peroxidase is able to reduce hydrogen peroxide and other hydroperoxides possibly present in the soluble compartment of the cell, this enzyme fails to inhibit microsomal lipid peroxidation induced by NADPH or ascorbate and iron complexes. On the other hand, phospholipid hydroperoxide glutathione peroxidase, by reducing the phospholipid hydroperoxides in the membranes, actively prevents lipid peroxidation, provided a normal content of vitamin E is present in the membranes. In fact, by preventing the free radical generation from lipid hydroperoxides, phospholipid hydroperoxide glutathione peroxidase decreases the vitamin E requirement necessary to inhibit lipid peroxidation. Finally, the possible regulatory role of the selenoperoxidases on the arachidonic acid cascade enzymes (cyclooxygenase and lipoxygenase) is discussed.
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PMID:The role of selenium peroxidases in the protection against oxidative damage of membranes. 331 19

The effects of Triton X-100, deoxycholate, and fatty acids were studied on the two steps of the ping-pong reaction catalyzed by Se-dependent glutathione peroxidases. The study was carried out by analyzing the single progression curves where the specific glutathione oxidation was monitored using glutathione reductase and NADPH. While the "classic" glutathione peroxidase was inhibited only by Triton, the newly discovered "phospholipid hydroperoxide glutathione peroxidase" was inhibited by deoxycholate and by unsaturated fatty acids. The kinetic analysis showed that in the case of glutathione peroxidase only the interaction of the lipophilic peroxidic substrate was hampered by Triton, indicating that the enzyme is not active at the interface. Phospholipid hydroperoxide glutathione peroxidase activity measured with linoleic acid hydroperoxide as substrate, on the other hand, was not stimulated by the Triton concentrations which have been shown to stimulate the activity on phospholipid hydroperoxides. Furthermore a slight inhibition was apparent at high Triton concentrations and the effect could be attributed to a surface dilution of the substrate. Deoxycholate and unsaturated fatty acids were not inhibitory on glutathione peroxidase but inhibited both steps of the peroxidic reaction of phospholipid hydroperoxide glutathione peroxidase, in the presence of either amphiphilic or hydrophilic substrates. This inhibition pattern suggests an interaction of anionic detergents with the active site of this enzyme. These results are in agreement with the different roles played by these peroxidases in the control of lipid peroxide concentrations in the cells. While glutathione peroxidase reduces the peroxides in the water phase (mainly hydrogen peroxide), the new peroxidase reduces the amphyphilic peroxides, possibly at the water-lipid interface.
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PMID:Different effects of Triton X-100, deoxycholate, and fatty acids on the kinetics of glutathione peroxidase and phospholipid hydroperoxide glutathione peroxidase. 380 Mar 87

1. Ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one) is a non-toxic seleno-organic drug with antiinflammatory, antiatherosclerotic and cytoprotective properties. 2. Ebselen and some of its metabolites are effective reductants of hydroperoxides including those arising in biomembranes and lipoproteins. 3. By reactions with hydroperoxides and thiols several interconversion cycles are formed which include ebselen metabolites with varying oxidation number of the selenium. 4. In the presence of thiols ebselen mimics the catalytic activities of phospholipid hydroperoxide glutathione peroxidase. 5. Ebselen inhibits at low concentrations a number of enzymes involved in inflammation such as lipoxygenases, NO synthases, NADPH, oxidase, protein kinase C and H+/K(+)-ATPase. The inhibitions are manifested on the cellular level and may contribute to the antiinflammatory potential of ebselen.
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PMID:Molecular actions of ebselen--an antiinflammatory antioxidant. 759 Jan 3

Evidence that rat liver microsomal glutathione transferase is responsible for the glutathione-dependent inhibition of lipid peroxidation in liver microsomes has been obtained. Activation of the microsomal glutathione transferase in microsomes by cystamine renders this organelle even more resistant to lipid peroxidation in the presence of glutathione compared with untreated microsomes. Upon examining the effect of seven glutathione analogues on lipid peroxidation, it was found that only those that serve as good substrates for the microsomal glutathione transferase (Glutaryl-L-Cys-Gly and alpha-L-Glu-L-Cys-Gly) can inhibit lipid peroxidation. The lack of inhibition by the other five analogues (alpha-D-Glu-L-Cys-Gly, gamma-D-Glu-L-Cys-Gly, beta-L-Asp-L-Cys-Gly, alpha-L-Asp-L-Cys-Gly and alpha-D-Asp-L-Cys-Gly) shows the specificity of the protection and rules out any non-enzymic component. Inhibitors of selenium-dependent glutathione peroxidase (mercaptosuccinate at 50 microM) and phospholipid hydroperoxide glutathione peroxidase (iodoacetate, 1 mM + glutathione, 0.5 mM) do not inhibit the glutathione-dependent protection of rat liver microsomes against lipid peroxidation. Purified microsomal glutathione transferase, NADPH-cytochrome P450 reductase and cytochrome P450 were reconstituted in microsomal phospholipid vesicles by cholate dialysis. The resulting membranes contained functional enzymes and did display enzymic lipid peroxidation induced by 75 microM NADPH and 10 microM Fe-EDTA (2:1). This model system was used to investigate whether microsomal glutathione transferase could inhibit lipid peroxidation in a glutathione-dependent manner. The results show that 5 mM glutathione did inhibit lipid peroxidation when functional microsomal glutathione transferase was included. This was not the case when the enzyme had been pre-inactivated with diethylpyrocarbonate. Furthermore, the protective effect of glutathione could be partly reversed by an inhibitor (100 microM bromosulphophtalein) of the enzyme. Apparently, rat liver microsomal glutathione transferase has the capacity to inhibit lipid peroxidation in a reconstituted system.
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PMID:Evidence that rat liver microsomal glutathione transferase is responsible for glutathione-dependent protection against lipid peroxidation. 848 4

As spermatozoa pass through the epididymis they complete a maturation process that enables these cells to participate in the process of fertilization. Epididymal maturation involves a complex cascade of changes involving the remodelling of the sperm surface, the induction of chromatin condensation, the acquisition of movement, and development of the potential for capacitation. In this review we shall consider how changes in the redox status of mammalian spermatozoa may contribute to the completion of these maturation events. Spermatozoa from all regions of the epididymis exhibit a spontaneous capacity for superoxide anion production which can be enhanced by exposure to NADPH, particularly in the caput region. It is hypothesized that this spontaneous free radical generating activity is mediated by a membrane-bound NADPH oxidase, the function of which is to generate the peroxides that are needed to serve as hydrogen acceptors for phospholipid hydroperoxide glutathione peroxidase in the induction of sperm chromatin condensation. As spermatozoa enter the cauda epididymidis they also express a capacity for hydrogen peroxide (H2O2) generation when released into simple, defined culture media. The onset of this activity is thought to be associated with the induction of sperm capacitation through stimulation of the tyrosine phosphorylation events involved in the attainment of a capacitated state. It is concluded that sperm maturation is a dynamic, redox regulated process, any imbalance in which could lead to the production of spermatozoa that are compromised in terms of their potential for fertilization and the integrity of their DNA.
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PMID:Maturation of redox regulatory mechanisms in the epididymis. 1064 71

We have previously reported that Saccharomyces cerevisiae has three glutathione peroxidase homologues (GPX1, GPX2, and GPX3) (Inoue, Y., Matsuda, T., Sugiyama, K., Izawa, S., and Kimura, A. (1999) J. Biol. Chem. 274, 27002-27009). Of these, the GPX2 gene product (Gpx2) shows the greatest similarity to phospholipid hydroperoxide glutathione peroxidase. Here we show that GPX2 encodes an atypical 2-Cys peroxiredoxin which uses thioredoxin as an electron donor. Gpx2 was essentially in a reduced form even in mutants defective in glutathione reductase or glutaredoxin under oxidative stressed conditions. On the other hand, Gpx2 was partially oxidized in a mutant defective in cytosolic thioredoxin (trx1Deltatrx2Delta) under non-stressed conditions and completely oxidized in tert-butyl hydroperoxide-treated cells of trx1Deltatrx2Delta and thioredoxin reductase-deficient mutant cells. Alanine scanning of cysteine residues of Gpx2 revealed that an intramolecular disulfide bond was formed between Cys37 and Cys83 in vivo. Gpx2 was purified to determine whether it functions as a peroxidase that uses thioredoxin as an electron donor in vitro. Gpx2 reduced H2O2 and tert-butyl hydroperoxide in the presence of thioredoxin, thioredoxin reductase, and NADPH (for H2O2, Km= 20 microm, kcat = 9.57 x 10(2) s(-1); for tert-butyl hydroperoxide, Km= 62.5 microm, kcat = 3.68 x 10(2) s(-1)); however, it showed remarkably less activity toward these peroxides in the presence of glutathione, glutathione reductase, and NADPH. The sensitivity of yeast cells to tert-butyl hydroperoxide was found to be exacerbated by the co-existence of Ca2+, a tendency that was most obvious in gpx2Delta cells. Although the redox state of Gpx2 was not affected by Ca2+, the Gpx2 level was markedly increased in the presence of both tert-butyl hydroperoxide and Ca2+. Gpx2 is likely to play an important role in the protection of cells from oxidative stress in the presence of Ca2+.
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PMID:GPX2, encoding a phospholipid hydroperoxide glutathione peroxidase homologue, codes for an atypical 2-Cys peroxiredoxin in Saccharomyces cerevisiae. 1625 Nov 89