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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

Aurothioglucose (ATG), an inhibitor of selenium-dependent glutathione peroxidase activity, at a concentration of 100 microM, strongly increases lipid peroxidation of rat liver microsomes exposed to either ferrous ion (10 microM) or the combination of ferric ion (10 microM) and ascorbic acid (500 microM), in the presence of reduced glutathione (GSH, 800 microM). This effect was not achieved using heat-inactivated microsomes and was dependent on the presence of GSH. ATG did not affect the lag period associated with ascorbic acid/ferric ion-induced microsomal lipid peroxidation (previously attributed to an undefined GSH-dependent microsomal agent), but did increase the rate of peroxidation subsequent to the lag period. The potent GSH-dependent inhibition of microsomal lipid peroxidation by cytosol (10% of total volume) was completely reversed by ATG (100 microM). ATG similarly reversed an inhibition of phosphatidylcholine hydroperoxide-dependent liposomal peroxidation that has been attributed to phospholipid hydroperoxide glutathione peroxidase (PHGPX), an enzyme distinct from the classical glutathione that cannot utilize intact phospholipids. ATG inhibited, in addition to the classical selenium-dependent glutathione peroxidase, both cytosolic and microsomal (basal and N-ethyl maleimide-stimulated) glutathione S-transferase activities with greater than 80% inhibition achieved at 100 microM ATG. ATG, at concentrations up to 250 microM, did not inhibit PHGPX activity measured by the coupled-enzyme method in the presence of Triton X-100 (0.1%).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effects of aurothioglucose on iron-induced rat liver microsomal lipid peroxidation. 314 31

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

The reduction of membrane-bound hydroperoxides is a major factor acting against lipid peroxidation in living systems. This paper presents the characterization of the previously described 'peroxidation-inhibiting protein' as a 'phospholipid hydroperoxide glutathione peroxidase'. The enzyme is a monomer of 23 kDa (SDS-polyacrylamide gel electrophoresis). It contains one gatom Se/22 000 g protein. Se is in the selenol form, as indicated by the inactivation experiments in the presence of iodoacetate under reducing conditions. The glutathione peroxidase activity is essentially the same on different phospholipids enzymatically hydroperoxidized by the use of soybean lipoxidase (EC 1.13.11.12) in the presence of deoxycholate. The kinetic data are compatible with a tert-uni ping-pong mechanism, as in the case of the 'classical' glutathione peroxidase (EC 1.11.1.9). The second-order rate constants (K1) for the reaction of the enzyme with the hydroperoxide substrates indicate that, while H2O2 is reduced faster by the glutathione peroxidase, linoleic acid hydroperoxide is reduced faster by the present enzyme. Moreover, the phospholipid hydroperoxides are reduced only by the latter. The dramatic stimulation exerted by Triton X-100 on the reduction of the phospholipid hydroperoxides suggests that this enzyme has an 'interfacial' character. The similarity of amino acid composition, Se content and kinetic mechanism, relative to the difference in substrate specificity, indicates that the two enzymes 'classical' glutathione peroxidase and phospholipid hydroperoxide glutathione peroxidase are in some way related. The latter is apparently specialized for lipophylic, interfacial substrates.
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PMID:The selenoenzyme phospholipid hydroperoxide glutathione peroxidase. 397 21

We studied enzyme kinetics parameters of plasma glutathione peroxidase (GSHPx-P) and the major cellular enzyme, GSHPx-1, for the substrates, H2O2, linoleic acid hydroperoxide (LinOOH), and glutathione (GSH). The major objectives were to determine whether the relatively slow GSHPx-P enzyme had a lower reactivity with hydroperoxides or with GSH and to identify favored hydroperoxide substrates. The rate constants describing the reactivity of human GSHPx-P and human GSHPx-1 with LinOOH and H2O2 are in the same range; GSHPx-P is more reactive with LinOOH and GSHPx-1 is more reactive with H2O2. GSHPx-P also has a low level of reducing activity toward cholesterol 7 alpha-OOH and no detectable activity with the 5 alpha-OOH isomer in contrast to phospholipid hydroperoxide glutathione peroxidase (PHGPx) which readily reduced both isomers. GSHPx-P catalytic activity toward phospholipid hydroperoxides is demonstrable in the absence of detergents, enhanced at low concentrations by deoxycholate, and strongly inhibited by Triton X-100 and incorporation into liposomes. These properties are the opposite of PHGPx. These results suggest that GSHPx-P largely lacks the membrane interfacial properties of PHGPx. GSHPx-P exhibits a smaller GSH rate constant than GSHPx-1. This property partially explains the slower turnover of GSHPx-P with several hydroperoxide substrates; the low reactivity with GSH is not consistent with efficient GSHPx function in the bulk plasma volume. GSHPx-P kinetic properties suggest that it would function best as a free fatty acid hydroperoxidase in GSH-rich microenvironments. Minimally, the secretion of reduced enzyme would permit it to scavenge free fatty acid hydroperoxides.
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PMID:Reactivity of plasma glutathione peroxidase with hydroperoxide substrates and glutathione. 823 61

A single photon counting procedure for measuring lipid hydroperoxides in human plasma or LDL-VLDL, escaping from extraction and chromatography, is described. This appears to be a relevant procedure because the recovery of phospholipid hydroperoxides from plasma is a critical point which, in our hands, was limited and poorly reproducible. The sample is added to a reaction mixture containing luminol, hemin, and Triton X-100 in an alkaline buffer, the photon emission is recorded, and the data are processed using the monoexponential decay of the photon emission rate. The measurement is applied to (a) plasma passed through a "desalting" cartridge to eliminate the small water-soluble antioxidants which inhibit the chemiluminescent process or (b) apo-B-containing lipoproteins (LDL-VLDL) isolated by heparin-Sepharose affinity chromatography. The content of lipid hydroperoxides is calculated using an internal calibration with palmitoyllinoleoylphosphatidylcholine hydroperoxide. This procedure, based on a single photon counting technology, was adopted to produce reliable results using samples from which inhibitors of the photon emission process have not been completely eliminated. The specificity of the signal for lipid hydroperoxides was validated by its complete disappearance following incubation of the sample with glutathione and phospholipid-hydroperoxide glutathione peroxidase (EC 1.11.1.12), the sole enzyme specific for all classes of lipid hydroperoxides in lipoproteins. The interassay variability was < 10%. The results indicated that the concentration of lipid hydroperoxides in the plasma of 20 healthy subjects was 353 +/- 78 nM. In different subjects, LDL-VLDL accounted for 40-80% of the lipid hydroperoxides in plasma.
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PMID:Direct measurement by single photon counting of lipid hydroperoxides in human plasma and lipoproteins. 860 Aug 17

Sperm capacitation is a maturation process, occurring in the female reproductive tract, that produces fertilization-competent spermatozoa. Protein tyrosine phosphorylation represents an important event in capacitation. The present study demonstrates the capacitation-dependent tyrosine-phosphorylation of phospholipid hydroperoxide glutathione peroxidase (PHGPx), the disulfide cross-linked, major structural protein of the sperm mitochondrial capsule. Immunofluorescence microscopy using an antiphosphotyrosine monoclonal antibody (anti-pY20) demonstrated the presence of capacitation-associated tyrosine phosphorylated proteins in the flagellum of hamster spermatozoa. Among the tyrosine-phosphorylated polypeptides (M(r) 19,000- 99,000), a 19-kDa polypeptide was the only one that can be solubilized completely by Triton X-100-dithiothreitol (DTT). The 19-kDa polypeptide was purified by anion-exchange chromatography and by immunoaffinity chromatography. Proteomic identification of the 19-kDa polypeptide by nano-electrospray tandem mass spectrometry yielded six peptides that matched the National Center for Biotechnology Information (NCBI) database sequences of bovine PHGPx. Indirect immunofluorescence localized PHGPx to the midpiece of the flagellum and the immunoblot analysis demonstrated its DTT-dependent release from purified flagella. DTT extracts of noncapacitated spermatozoa exhibited a charge train of four major PHGPx isoforms (pIs 7.5- 9.0) by two-dimensional PAGE, whereas capacitated spermatozoa revealed the generation of new acidic PHGPx isoforms with isoelectric points ranging between pH 6.0-7.0 and 4.0-5.0, indicating that it is posttranslationally modified during capacitation. These data suggest that the tyrosine-phosphorylation of PHGPx may represent an important event in the signaling pathway(s) associated with capacitation and could potentially affect mitochondrial function.
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PMID:Tyrosine phosphorylation generates multiple isoforms of the mitochondrial capsule protein, phospholipid hydroperoxide glutathione peroxidase (PHGPx), during hamster sperm capacitation. 1538 12