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At least 1,621 records · Page 90Linked to original sources
PubMed1985

Glutathione peroxidase and reductase activities in the aging mouse.

Previous results from this laboratory demonstrated that glutathione concentrations decrease in aging mouse tissues. In this investigation glutathione (GSH) peroxidase and glutathione (GSSG) reductase activities were measured in tissues of standardized aging mice. Methods were validated for the quantitative determination of both enzymes in liver, kidney and heart tissues. GSH peroxidase activities were 27-53% lower in liver, kidney and heart of very old (36 months) mice compared to mature (10 months) mice (P less than 0.01). The same aging decreases were found with either hydrogen peroxide or cumene hydroperoxide as substrate. In a similar way GSSG reductase activities in liver and kidney were 25-28% lower in the old versus mature mice (P less than 0.01), but heart levels were unchanged. Further the lower GSSG reductase levels were unaffected by FAD supplementation in vitro. The changes in specific activity for both enzymes were not due to changes in organ weights and total protein contents, which were constant from 10 to 36 months of age. These decreases in GSH peroxidase and GSSG reductase do not account for the lower GSH levels in aging. Of special importance, however, is that these decreases indicate that detoxification via glutathione peroxidase and glutathione reductase could be impaired in senescence.

Aging↗
PubMed1989

Concerted loss of cyclooxygenase and peroxidase activities from prostaglandin H synthase upon proteolytic attack.

Prostaglandin H synthase has two distinct enzymatic activities: a cyclooxygenase that forms PGG2 from arachidonate and a peroxidase that can reduce hydroperoxides, such as PGG2, to the corresponding alcohols. The relative sensitivities of the two synthase activities to proteolytic attack have been examined, using trypsin, chymotrypsin, and proteinase K, all known to attack the native apoprotein in the arg 253 region. The relation between the specific activity of the synthase and the loss of the two activities and the cleavage of the synthase subunit during trypsin digestion was also examined. The cyclooxygenase and peroxidase activities declined in concert throughout room temperature digestions with each of the three proteases. There was no indication of a selective loss of either activity in any of the digestions. In separate digestions with the same preparation of synthase, 3.3% (w/w) proteinase K resulted in more extensive loss of activity (90% decrease after 90 min) than did 3% (w/w) trypsin (70% decrease after 120 min) or 5% (w/w) chymotrypsin (60% decrease after 135 min). In tryptic digestions of synthase preparations with cyclooxygenase specific activity between 16 and 125 k units/mg protein, the fractional loss of cyclooxygenase activity was, within experimental error, the same as that of peroxidase activity. The extent of cleavage of the 70 kDa synthase subunit was greater than the loss of enzymatic activity, with the discrepancy being larger for synthase preparations with lower specific activity. The presence of a variable amount of catalytically-inactive, protease-sensitive, synthase protein could account for the difference between surviving activity and intact subunit in six out of the seven synthase preparations examined. Thus, it is likely that the cyclooxygenase and peroxidase activities are destroyed together during proteolytic attack on the arg 253 region of the native synthase apoprotein.

Animals↗
PubMed1991

Glutathione peroxidase deficiency and childhood seizures.

4 children with intractable seizures, repeated infections, and intolerance to anticonvulsants had evidence of glutathione peroxidase deficiency. 2 had low intracellular enzyme activity but normal blood selenium and high plasma glutathione peroxidase concentrations. The other 2 had low intracellular glutathione peroxidase activity with low circulating glutathione peroxidase and selenium concentrations. The clinical state of the children improved after discontinuation of anticonvulsant medication and selenium substitution.

Anticonvulsants↗
PubMed1984

Interaction of gold(I) with the active site of selenium-glutathione peroxidase.

Gold(I) thioglucose in the presence of excess glutathione (GSH) leads to strong and reversible inhibition of selenium-glutathione peroxidase (EC 1.11.1.9) around neutral pH. Binding at equilibrium and competition studies demonstrated that the most reduced form of the active site selenocysteine is the only binding site for gold(I). Steady-state kinetics that gold(I) forms a dead-end complex with glutathione peroxidase in competition with the reduction of hydroperoxide. The apparent Ki is 2.3 microM at pH 7.6, 37 degrees C and 1 mM GSH. Theoretical models of inhibition were assessed by the use of linear least-squares fitting to a generalized integrated rate equation. The results are consistent with trapping of gold(I) at the active site in the form of a mixed bidentate selenolato -thiolate complex involving GSH and the active site selenocysteine. The kinetics of inhibition imply that the resting form of glutathione peroxidase in the presence of excess GSH is also within the enzyme cycle. This rules out the existence of selenium(+IV) species in the redox cycle of the active site when t- butylhydroperoxide is used as a substrate. Electronic properties of selenium and gold as well as a large relief of inhibition by selenocysteine suggest that a very stable interaction should be obtained between Se(-II) and gold(I) through covalent bonding. These results suggest that glutathione peroxidase could be a target of gold drugs used in the treatment of rheumatoid arthritis.

Animals↗
PubMed1994

Tandem lignin peroxidase genes of the fungus Trametes versicolor.

A DNA fragment containing two lignin peroxidase genes (LPG I and LPG II) has been isolated from a genomic library of the white-rot fungus Trametes versicolor. The genes are separated by 2.2 kbp and have the same direction of transcription. Conserved elements preceding the translation start have been identified. In addition to the TATA box, a stretch of 11 identical nucleotides is found 23-24 bp downstream of the TATA box. The putative mature peroxidases encoded by LPG I and LPG II are 87% identical in amino acid sequence. Both are preceded by two basic residues, also observed in lignin peroxidases from Phanerochaete chrysosporium. Strong evidence suggests that LPG I encodes a quantitatively dominant lignin peroxidase isozyme (TvLP12), whereas the product of LPF II has not been identified so far.

Amino Acid Sequence↗
PubMed1982

Purification of horse eosinophil peroxidase.

Eosinophil peroxidase (donor: hydrogen-peroxidase oxidoreductase, EC 1.11.1.7) was isolated in a highly purified form (415/280 nm ratio, 1.05) from horse peripheral blood eosinophil. Eosinophil peroxidase was extracted from intact eosinophils (98-100% purity) or isolated eosinophil granules with 0.05 M acetate buffer (pH 4.7)/0.18 M NaCl and purified by chromatography on Sephadex G-200 and carboxymethylcellulose. Final elution was with 0.05 M acetate buffer (pH 4.7)/ 1 M NaCl. Horse eosinophil peroxidase is a strongly basic protein with bacterial properties when combined with H2O2 and iodide, bromide or, to a lesser degree, chloride.

Animals↗
PubMed1991

1H-NMR characterization of cucumber peroxidases.

Two peroxidase isoenzymes from Cucumber seedlings, one acidic (pI = 4) and one basic (pI = 9), were characterized by 1H-NMR spectroscopy. The NMR spectra were obtained in the native (ferric high-spin) and cyanide ligated (ferric low-spin) forms of both isoenzymes. The NMR spectral comparison of paramagnetically shifted resonances with those of the well characterized horseradish peroxidase C, HRP(C), isoenzyme indicates that both cucumber peroxidases have a protohemin IX prosthetic group with proximal histidine coordinated to the heme iron. The downfield heme 1H-NMR shift pattern is distinct for each isoenzyme, and this reflects presumably dissimilar heme active site environments. The basic isoenzyme shows less asymmetry in heme 1H-NMR signals as compared to the acidic isoenzyme or HRP(C) isoenzyme. It was also found that the acidic cucumber peroxidase exists predominantly as a monomeric species in solution with 30 kDa molecular mass as opposed to its earlier characterization as a 60 kDa dimeric protein.

Binding Sites↗
PubMed1995

Identification of the site of non-enzymatic glycation of glutathione peroxidase: rationalization of the glycation-related catalytic alterations on the basis of three-dimensional protein structure.

Bovine erythrocyte glutathione peroxidase has been glycated in vitro by incubation in 0.05 M glucose at pH 7.4. Upon glycation the estimated KM for t-butylhydroperoxide reduction increased by approx. 3-fold in comparison to non-glycated glutathione peroxidase. The glycated protein fraction was stabilized by NaBH4 reduction and subjected to tryptic cleavage. Affinity chromatography of the tryptic digest on m-aminophenylboronate-Agarose resulted in the isolation of a single glycated peptide. The peptide was identified as T94-K117 by amino-acid composition comparison to the published amino-acid sequence for this enzyme. The glycation site has been identified as the epsilon-NH2 group of K110. Examination of the three-dimensional structure of bovine erythrocyte glutathione peroxidase indicates that K110 lies on the surface of the protein approximately 15 A away from the active site selenocysteine (SEC 45). Modeling studies indicate that K110 can communicate via H-bonded interactions with the alpha-helix containing the active site residues (SEC-45 and R50). The observed elevation of KM upon glycation of bovine glutathione peroxidase is discussed in terms of the disruption of the long range H-bonded interaction.

Animals↗
PubMed1992

Electron transfer in chromaffin-vesicle ghosts containing peroxidase.

In chromaffin vesicles, the enzyme dopamine beta-monooxygenase converts dopamine to norepinephrine. It is believed that reducing equivalents for this reaction are supplied by intravesicular ascorbic acid and that the ascorbate is regenerated by importing electrons from the cytosol with cytochrome b-561 functioning as the transmembrane electron carrier. If this is true, then the ascorbate-regenerating system should be capable of providing reducing equivalents to any ascorbate-requiring enzyme, not just dopamine beta-monooxygenase. This may be tested using chromaffin-vesicle ghosts in which an exogenous enzyme, horseradish peroxidase, has been trapped. If ascorbate and peroxidase are trapped together within chromaffin-vesicle ghosts, cytochrome b-561 in the vesicle membrane is found in the reduced form. Subsequent addition of H2O2 causes the cytochrome to become partially oxidized. H2O2 does not cause this oxidation if either peroxidase or ascorbate are absent. This argues that the cytochrome is oxidized by semidehydroascorbate, the oxidation product of ascorbate, rather than by H2O2 or peroxidase directly. The semidehydroascorbate must be internal because the ascorbate from which it is formed is sequestered and inaccessible to external ascorbate oxidase. This shows that cytochrome b-561 can transfer electrons to semidehydroascorbate within the vesicles and that the semidehydroascorbate may be generated by any enzyme, not just dopamine beta-monooxygenase.

Adenosine Triphosphate↗
PubMed1995

Melatonin stimulates brain glutathione peroxidase activity.

Exogenously administered melatonin causes a 2-fold rise in glutathione peroxidase activity within 30 min in the brain of the rat. Furthermore, brain glutathione peroxidase activity is higher at night than during the day and is correlated with high night-time tissue melatonin levels. Glutathione peroxidase is thought to be the principal enzyme eliminating peroxides in the brain. This antioxidative enzyme reduces the formation of hydroxyl radicals formed via iron-catalyzed Fenton-type reactions from hydrogen peroxide by reducing this oxidant to water. Since the hydroxyl radical is the most noxious oxygen radical known, induction of brain glutathione peroxidase might be an important mechanism by which melatonin exerts its potent neuroprotective effects.

Animals↗
PubMed1985

Relation between thyroid peroxidase, H2O2 generating system and NADPH-dependent reductase activities in thyroid particulate fractions.

In thyroid gland, iodination takes place on the apical plasma membrane and requires the presence of the thyroid peroxidase and H2O2 generating system. H2O2 generation and NBT (nitro blue tetrazolium) reductase activity (both of which are NADPH-dependent) as well as peroxidase activity were compared for their respective orientations in membrane vesicles. The possible role of NADPH-NBT reductase activity in H2O2 generation was also examined. Results favor the conclusion that thyroid peroxidase is oriented towards the luminal side of the vesicles, whereas the NADPH site of NADPH oxidase-dependent H2O2 generation is located on the external side of the same or of different vesicles. Furthermore, it is shown that different NADPH-NBT reductase activities are present on both the outer and inner surfaces of the membrane vesicles, and that none of these activities is able to produce either H2O2 or O-2. The idea that a multi-component complex is involved in H2O2 generation is discussed, and a model is proposed which takes into account the possible spatial separation of the thyroid peroxidase site from the NADPH site of this H2O2 generation system on the apical membrane of the thyrocyte.

Animals↗
PubMed1985

Inhibition of the effects of 12-O-tetradecanoylphorbol-13-acetate on mouse epidermal glutathione peroxidase and ornithine decarboxylase activities by glutathione level-raising agents and selenium-containing compounds.

The present study was undertaken to determine the effect of 12-O-tetradecanoylphorbol-13-acetate (TPA), a potent tumor promoter known to inhibit superoxide dismutase (SOD) (superoxide: superoxide oxidoreductase, EC 1.15.1.1) and catalase (CAT) (H2O2: H2O2 oxidoreductase, EC 1.11.1.6) activities, on mouse epidermal glutathione (GSH) peroxidase (glutathione: H2O2 oxidoreductase, EC 1.11.1.9) activity in vivo and in vitro. TPA led to a rapid and transient increase in GSH peroxidase specific activity within 30 min followed by a decrease from 1 to 12 h. Incubation of isolated epidermal cells with GSH level-raising agents and/or selenium-containing compounds increased remarkably basal GSH peroxidase activity, and thus, abolished totally the prolonged inhibitory effects of TPA on this enzyme. The inhibitory effects of 0.2 mM cysteine (Cys) or 0.5 mM GSH and 2.5 microM Na2 SeO3 or 50 microM selenocystamine on TPA-decreased GSH peroxidase activity were additive, in relation with their additive inhibitory effects on TPA-induced ornithine decarboxylase (ODC) (L-ornithine carboxylase, EC 4.1.1.17) activity. These data support the hypothesis that the stimulators of the GSH-dependent antioxidant protective system of the epidermal cells may inhibit the oxidative challenge linked to skin tumor promotion by TPA.

Animals↗
PubMed1992

Peroxidase oxidizes N-nitrosomethylaniline to ultimate carcinogens(s) binding to DNA and transfer RNA in vitro.

Carcinogenic N-nitrosomethylaniline is oxidized in vitro by horseradish peroxidase in the presence of H2O2 to ultimate carcinogens, which bind to DNA and transfer RNA (tRNA). tRNA is more accessible for modification by the activated carcinogen studied. The modification of nucleic acid by N-nitrosomethylaniline metabolite(s) formed by peroxidase is inhibited by some compounds of physiological importance (ascorbate, glutathine) and by radical trapping agents (nitrosobenzene, methyl viologen). 32P-postlabeling assay of DNA and tRNA modified by N-nitrosomethylaniline activated by peroxidase shows covalent adduct formation with nucleic acids. The role of peroxidases in the activation of N-nitrosamines leading to organ and/or cell specificity of these carcinogens is discussed.

Autoradiography↗
PubMed1996

Expression of heat shock proteins, glutathione peroxidase and catalase in childhood acute lymphoblastic leukemia and nephroblastoma.

In this study we analyzed the mRNA expression of the heat shock proteins 27 and 70, and the expression of the radical scavenging enzymes catalase and glutathione peroxidase (GPX) in childhood acute lymphoblastic leukemia (ALL, n = 54) and in nephroblastoma (n = 34). We found a significant positive correlation between both heat shock proteins and also between glutathione peroxidase and both heat shock proteins in ALL and nephroblastoma. There was also a significant correlation between catalase and glutathione peroxidase detectable. Furthermore, we investigated whether the expression of the heat shock proteins and the antioxidant enzymes glutathione peroxidase and catalase have implications in the clinical outcome in ALL. However, we found no significant correlation between the expression of these proteins and relapse rate, the relapse free intervals or the overall survival.

Adolescent↗
PubMed1984

Glucocorticoid effects on gastric peroxidase activity.

The peroxidase activity in rat gastric mucosa is inhibited after administration of glucocorticoids. The synthetic steroid dexamethasone is more potent than the naturally occurring steroids, such as cortisone or corticosterone. Almost complete inhibition of the enzyme occurs after 24 h with a single dose of 100 micrograms dexamethasone/120 g body weight. Other mitochondrial enzyme activities, like monoamine oxidase, succinic dehydrogenase and Mg2+-ATPase, remain unaltered under the same experimental condition. Submaxillary peroxidase and thyroid peroxidase activity are not inhibited by dexamethasone. Gastric peroxidase activity is increased 200-250% on the 6th day after adrenalectomy. This effect is blocked by the administration of dexamethasone. In fact, the enzyme becomes more sensitive to dexamethasone after adrenalectomy, since it is inhibited by more than 90% at the dose of 25 micrograms/120 g body weight. The inhibition by dexamethasone in normal animals is reversible. The enzyme is also inhibited after the administration of a single dose of ACTH. The apparent Km of the enzyme for H2O2 is not altered after dexamethasone treatment or after adrenalectomy. The increase in enzyme activity following adrenalectomy is not blocked by actinomycin D or by alpha-amanitin, but is prevented by puromycin or cycloheximide. After administration of dexamethasone, the iodide concentration process in the gastric mucosa is not affected, but the organification of iodide is significantly diminished.

Adrenalectomy↗
PubMed1985

Subcellular localization and modification with ageing of glutathione, glutathione peroxidase and glutathione reductase activities in human fibroblasts.

Differential centrifugation and isopycnic equilibration in density gradients were used to localize glutathione (GSH), glutathione peroxidase and glutathione reductase in the subcellular organelles of WI-38 fibroblasts. GSH was present in all the subcellular fractions, whereas the glutathione peroxidase and reductase activities were restrained to the cytoplasm and the mitochondrial fractions. After equilibration in density gradients, the results showed the presence of GSH, glutathione peroxidase and glutathione reductase in both the cytoplasm and mitochondria. GSH was also located in plasma membranes and probably in peroxisomes, endoplasmic reticulum and lysosomal membranes. Evolution of GSH in ageing fibroblasts showed a sudden increase of its concentration just before cell death. The glutathione peroxidase activity already decreases in the early passages, while the decrease of the glutathione reductase activity was constant and reached a drastic low level at the end of the culture. In conclusion, GSH is probably involved in the cell degeneration associated with ageing but because of its multiple functions and its ubiquitous localization, it is difficult to assert to which extent this metabolite is implicated in the ageing process.

Cell Line↗
PubMed1986

A comparative study on the peroxidase activity within the aqueous humor of the rabbit, guinea-pig and rat.

Aqueous humor of the rabbit, guinea-pig and rat has been examined to determine if non-specific peroxidase activity is present within this ocular fluid. Substantial peroxidase activity was found within the aqueous humor of the rat. In contrast, no peroxidase activity could be detected in the aqueous humor of the rabbit or guinea-pig. Partial purification by gel chromatography revealed that the peroxidase within the aqueous humor of the rat has a mol. wt of approx. 45,000.

Animals↗
PubMed1989

Selenium-independent glutathione peroxidase activity associated with glutathione S-transferase from the housefly, Musca domestica.

1. A glutathione S-transferase having Se-independent glutathione peroxidase activity was isolated from 100,000 g supernatant from housefly homogenate. 2. The specific activity of the partially purified Se-independent glutathione peroxidase was 1776 nmol NADPH oxidized/min/mg protein, representing an 87-fold purification. 3. The Mr of this enzyme was estimated to be 37,000 and 26,000 by gel filtration chromatography and gel electrophoresis, respectively. 4. Selenium-dependent glutathione peroxidase activity could not be detected in this same supernatant. 5. Se-independent glutathione peroxidase activity should be considered in future studies of the insect antioxidant defense system.

Animals↗