Ascorbate peroxidase: A novel antioxidant enzyme in insects

Ascorbate peroxidase (APOX) activity, which catalyzes the oxidation of ascorbic acid with the concurrent reduction of hydrogen peroxide (H₂O₂), was found in larvae of Helicoverpa zea. Since insects apparently lack a Se-dependent glutathione peroxidase and since catalase has a low affinity for H₂O₂, this enzyme may be important in removing H₂O₂ in insects. We partially purified the APOX activity 58x from the whole body homogenates and investigated its activity with model lipid peroxides, electron donors, and known inhibitors of plant APOX. The H. zea APOX has activity with model lipid peroxides. This, along with the APOX activity found in fat body tissues, suggests that ascorbate peroxidase may be important in removing lipid peroxides in insects. The H. zea APOX has broader specificity for electron donors than the plant APOX with activity using cysteine, NADPH, glutathione, and cytochrome C as electron donors (22–93% of activity with ascorbate). The H. zea APOX is also resistant to many of the known inhibitors of plant APOX, suggesting that the enzyme has a different active site and may not be a heme-peroxidase. © 1997 Wiley-Liss, Inc.     

Joint effects of dimethoate and heavy metals on metabolic responses in a grasshopper (Chorthippus brunneus) from a heavy metals pollution gradient

We studied how an exposure to an additional stressing factor-dimethoate, might affect detoxifying ability of grasshoppers collected at 5 meadow sites located along a heavy metal pollution gradient. Activities of esterases and enzymes linked with glutathione (GSH) metabolism were assayed 24 h after topical treatment with 0.32 microg dimethoate per insect. Inhibition of acetylcholinesterase (AChE) reaches nearly 50% of the value stated in untreated insects, without significant site-dependent differences. The pesticide also caused a significant decrease in activities of glutathione peroxidase (GPx) followed by a decrease in GSH levels in grasshoppers from all assayed groups, demonstrating high sensitivity of glutathione-dependent metabolism to the additional stressing factor. In the case of glutathione reductase (GR) and carboxylesterases (CarE) the fall of activity was shown especially in insects from less polluted meadows and the reference site. Glutathione reductase (GR) activity in individuals treated with dimethoate did not decrease only in insects from the most contaminated site I. This might suggest the trade-off mechanisms adapting grasshoppers to life in seriously polluted environments.     

Bioaccumulation of Cry1Ab Protein from an Herbivore Reduces Anti-Oxidant Enzyme Activities in Two Spider Species

Cry proteins are expressed in rice lines for lepidopteran pest control. These proteins can be transferred from transgenic rice plants to non-target arthropods, including planthoppers and then to a predatory spider. Movement of Cry proteins through food webs may reduce fitness of non-target arthropods, although recent publications indicated no serious changes in non-target populations. Nonetheless, Cry protein intoxication influences gene expression in Cry-sensitive insects. We posed the hypothesis that Cry protein intoxication influences enzyme activities in spiders acting in tri-trophic food webs. Here we report on the outcomes of experiments designed to test our hypothesis with two spider species. We demonstrated that the movement of CryAb protein from Drosophila culture medium into fruit flies maintained on the CryAb containing medium and from the flies to the spiders Ummeliata insecticeps and Pardosa pseudoannulata. We also show that the activities of three key metabolic enzymes, acetylcholine esterase (AchE), glutathione peroxidase (GSH-Px), and superoxide dismutase (SOD) were significantly influenced in the spiders after feeding on Cry1Ab-containing fruit flies. We infer from these data that Cry proteins originating in transgenic crops impacts non-target arthropods at the physiological and biochemical levels, which may be one mechanism of Cry protein-related reductions in fitness of non-target beneficial predators.     

A novel selenocystine-beta-cyclodextrin conjugate that acts as a glutathione peroxidase mimic

A novel artificial glutathione peroxidase mimic consisting of a selenocystine-di-beta-cyclodextrin conjugate (selenium-bridged-6, 6'-amino-selenocystine-6,6'-deoxy-di-beta-cyclodextrin), in which selenocystine is bound to the primary side of beta-cyclodextrin through the two amino nitrogen groups of selenocystine, was synthesized. The glutathione peroxidase activities of the mimic-catalyzed reduction of H(2)O(2), tert-butylhydroperoxide, and cumene hydroperoxide by glutathione are 4.1, 2.11, and 5.82 units/micromol, respectively. The first activity was 82 and 4.2 times as much as that of selenocysteine and ebselen, respectively. Studies on the effect of substrate binding on the glutathione peroxidase activity suggest that it is important to consider substrate binding in designing glutathione peroxidase mimics. The detailed steady-state kinetic studies showed that the mimic-catalyzed reduction of H(2)O(2) by glutathione followed a ping-pong mechanism, which was similar to that of the native glutathione peroxidase.     

Phylogenetic distribution of glutathione peroxidase.

1. The enzyme glutathione peroxidase (E.C.1.11.1.9), known to be a selenoprotein from mammalian sources, was detected in the following vertebrates: fish, frog, salamander, and turtle. 2. Among invertebrates, the enzyme was detected in crayfish and snail but not in insects or earthworm. 3. No plant tissues or microorganisms showed any evidence of the enzyme activity. 4. The presence of the enzyme activity in so many animal groups implies the widespread occurrence of genetic information for the specific assimilation of the selenium atom.     

A direct test of the effects of changing atmospheric pressure on the mating behavior of Drosophila melanogaster

Changes in weather can be catastrophic for small insects. As such, it would be highly adaptive for insects to be able to sense when a weather front is approaching and respond appropriately. While correlative and anecdotal evidence exists that flies behaviorally respond to changes in barometric pressure, which indicate variation in weather, a direct test has yet to be performed. Here, we subject multiple strains of Drosophila melanogaster to changes in barometric pressure within a hypobaric chamber and measure male courtship and female receptivity. Since this species has a long copulation duration, copulating when adverse weather is approaching could subject both males and females to potentially lethal conditions. As predicted, some flies reduced their mating activity when exposed to a change in pressure that indicated imminent adverse weather. Surprisingly, however, some flies instead increased their mating activity; the behavioral response depended upon the strain’s native population location and intra-population variation, demonstrating that there is genetic variation for the behavioral response. This indicates that flies are able to anticipate weather patterns and change their behavior depending on the barometric pressure they experience, but that the form of behavioral response varies both within and between populations.     

A novel strategy of oxygen restriction by some diazotrophic enteric bacteria

Protection of nitrogenase against oxygen inactivation in diazotrophs involves numerous strategies. Glutathione is known to play an important role in scavenging oxyradicals in many living systems. The involvement of glutathione (reduced) (GSH), glutathione peroxidase (GPX) and glutathione reductase (GR) in the protection of nitrogenase in free living diazotrophs is reported here for the first time. Reduced glutathione content and the activity of glutathione peroxidase and glutathione reductase increased with increase in oxygen concentration under nitrogen fixing conditions but decreased under anaerobic and nitrogenase repressed conditions. This correlation is used to postulate a protecting role for GSH-GPX-GR system against oxygen inactivation of nitrogenase.     

Catalytic function of Drosophila melanogaster glutathione S-transferase DmGSTS1-1 (GST-2) in conjugation of lipid peroxidation end products.

Drosophila melanogaster glutathione S-transferase DmGSTS1-1 (earlier designated as GST-2) is related to sigma class GSTs and was previously described as an indirect flight muscle-associated protein with no known catalytic properties. We now report that DmGSTS1-1 isolated from Drosophila or expressed in Escherichia coli is essentially inactive toward the commonly used synthetic substrate 1-chloro-2,4-dinitrobenzene (CDNB), but has relatively high glutathione-conjugating activity for 4-hydroxynonenal (4-HNE), an electrophilic aldehyde derived from lipid peroxidation. 4-HNE is thought to have signaling functions and, at higher concentrations, has been shown to be cytotoxic and involved in the etiology of various degenerative diseases. Drosophila strains carrying P-element insertions in the GstS1 gene have a reduced capacity for glutathione conjugation of 4-HNE. In flies with both, one, or none of the GstS1 alleles disrupted by P-element insertion, there is a linear correlation between DmGSTS1-1 protein content and 4-HNE-conjugating activity. This correlation indicates that in adult Drosophila 70 +/- 6% of the capacity to conjugate 4-HNE is attributable to DmGSTS1-1. The high abundance of DmGSTS1-1 (approximately 2% of the soluble protein in adult flies) and its previously reported localization in tissues that are either highly aerobic (indirect flight muscle) or especially sensitive to oxidative damage (neuronal tissue) suggest that the enzyme may have a protective role against deleterious effects of oxidative stress. Such function in insects would be analogous to that carried out in mammals by specialized alpha class glutathione S-transferases (e.g. GSTA4-4). The independent emergence of 4-HNE-conjugating activity in more than one branch of the glutathione S-transferase superfamily suggests that 4-HNE catabolism may be essential for aerobic life.     

Characterization of the hydroperoxide-reducing activity of human plasma

A peroxidase was identified in human plasma using a novel peroxidase assay. In this assay both the substrate 5-phenyl-4-pentenyl hydroperoxide (PPHP) and its reduction product, 5-phenyl-4-pentenyl alcohol (PPA) are quantitated by HPLC. Substrate specificity studies indicated that the peroxidase requires glutathione as reducing substrate. No reduction was detected using the classical heme peroxidase reducing substrates, phenol and hydroquinone. Peroxidase activity was not due to glutathione transferases. Failure to saturate the peroxidase activity with reduced glutathione and inhibition by Cd+2 indicated that it is probably selenium dependent. The enzyme appears to be different from erythrocyte glutathione peroxidase based on kinetic and immunological experiments. The apparent Km values for PPHP are 25 microM for erythrocyte peroxidase and 54 microM for plasma peroxidase at 0.5 mM reduced glutathione. Anti-peroxidase prepared against bovine erythrocyte glutathione peroxidase partially inhibited human erythrocyte peroxidase but did not inhibit human plasma peroxidase.     

A comparative study on the hydroperoxide and thiol specificity of the glutathione peroxidase family and selenoprotein P

Glutathione peroxidase catalyzes the reduction of hydrogen peroxide and organic hydroperoxide by glutathione and functions in the protection of cells against oxidative damage. Glutathione peroxidase exists in several forms that differ in their primary structure and localization. We have also shown that selenoprotein P exhibits a glutathione peroxidase-like activity (Saito, Y., Hayashi, T., Tanaka, A., Watanabe, Y., Suzuki, M., Saito, E., and Takahashi, K. (1999) J. Biol. Chem. 274, 2866-2871). To understand the physiological significance of the diversity among these enzymes, a comparative study on the peroxide substrate specificity of three types of ubiquitous glutathione peroxidase (cellular glutathione peroxidase, phospholipid hydroperoxide glutathione peroxidase, and extracellular glutathione peroxidase) and of selenoprotein P purified from human origins was done. The specific activities and kinetic parameters against two hydroperoxides (hydrogen peroxide and phosphatidylcholine hydroperoxide) were determined. We next examined the thiol specificity and found that thioredoxin is the preferred electron donor for selenoprotein P. These four enzymes exhibit different peroxide and thiol specificities and collaborate to protect biological molecules from oxidative stress both inside and outside the cells.     

Deficient metabolic utilization of hydrogen peroxide in Trypanosoma cruzi.

The glutathione peroxidase-glutathione reductase system, an alternative pathway for metabolic utilization of H2O2 [Chance, Sies & Boveris (1979) Physiol. Rev. 59, 527-605], was investigated in Trypanosoma cruzi, an organism lacking catalase and deficient in peroxidase [Boveris & Stoppani (1977) Experientia 33, 1306-1308]. The presence of glutathione (4.9 +/- 0.7 nmol of reduced glutathione/10(8) cells) and NADPH-dependent glutathione reductase (5.3 +/- 0.4 munit/10(8) cells) was demonstrated in the cytosolic fraction of the parasite, but with H2O2 as substrate glutathione peroxidase activity could not be demonstrated in the same extracts. With t-butyl hydroperoxide or cumene hydroperoxide as substrate, a very low NADPH-dependent glutathione peroxidase activity was detected (equivalent to 0.3-0.5 munit of peroxidase/10(8) cells, or about 10% of glutathione reductase activity). Blank reactions of the glutathione peroxidase assay (non-enzymic oxidation of glutathione by hydroperoxides and enzymic oxidation of NADPH) hampered accurate measurement of peroxidase activity. The presence of superoxide dismutase and ascorbate peroxidase activity in, as well as the absence of catalase from, epimastigote extracts was confirmed. Ascorbate peroxidase activity was cyanide-sensitive and heat-labile, but no activity could be demonstrated with diaminobenzidine, pyrogallol or guaiacol as electron donor. The summarized results support the view that T. cruzi epimastigotes lack an adequate enzyme defence against H2O2 and H2O2-related free radicals.     

Antioxidant enzymatic systems in pigment tissue of amphibia

Superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase activities in pigmented and unpigmented liver tissues of frog and albino rat, respectively, were studied. Our results show that pigmented tissue is lacking in manganese superoxide dismutase activity and that the main enzymatic activity utilized in the cytosol by pigmented cells to reduce the hydrogen peroxide to water is represented by catalase; on the contrary, for the same reaction, the cells of albino rat liver primarily utilize the glutathione peroxidase activity. Both a low glutathione peroxidase activity and a low glutathione reductase activity were found in pigmented tissue of frog liver when compared with unpigmented tissue of rat liver. In light of our results, we also report a hypothetical interrelationship between melanin and reduced glutathione: We believe that in pigmented cells the melanin could act as a reducing physiological agent replacing the glutathione in the reduction of hydrogen peroxide. This reducing action of melanin could cause a diminished need for GSH and therefore could provoke the low glutathione peroxidase and reductase activities in pigmented tissue.     

Glutathione peroxidase activities from rat liver

There are two enzymes in rat liver with glutathione peroxidase activity when cumene hydroperoxide is used as substrate. One is the selenium-requiring glutathione peroxidase (glutathione:hydrogen-peroxide oxidoreductase, EC 1.11.1.9) and the other appears to be independent of dietary selenium. Activities of the two enzymes vary greatly among tissues and among animals. The molecular weight of the enzyme with selenium-independent glutathione peroxidase activity was estimated by gel filtration to be 35 000, and the subunit molecular weight was estimated by dodecyl sulfate-polyacrylamide gel electrophoresis to be 17 000. Double reciprocal plots of enzyme activity as a function of substrate concentration produced intersecting lines which are suggestive of a sequential reaction mechanism. The Km for glutathione was 0.20 mM and the Km for cumene hydroperoxide was 0.57 mM. The enzyme was inhibited by N-ethylmaleimide, but not by iodoacetic acid. Inhibition by cyanide was competitive with respect to glutathione and the Ki for cyanide was 0.95 mM. This selenium-independent glutathione peroxidase also catalyzes the conjugation of glutathione to 1-chloro-2,4-dinitrobenzene. Along with other similarities to glutathione S-transferase, this suggests that the selenium-independent glutathione peroxidase and glutathione S-transferase activities in rat liver are of the same enzyme.     

Variations among cultured cells in glutathione peroxidase activity in response to selenite supplementation

The aim of this study was to devise conditions for manipulation of the activity of selenium-dependent glutathione peroxidase in cell lines by means of variation in culture medium contents of selenite and fetal calf serum. Nine different cell lines were studied. A low glutathione peroxidase activity was, in most cases, obtained by the use of a medium with a low (2%) serum content. Selenite induced in most of the cell lines an increase in glutathione peroxidase activity, with a plateau ranging from 10 nM to 300-1000 nM. Growth-retarding effects of selenite became apparent at 300-2000 nM, showing a large cell line variation. Supplementation with 50-100 nM selenite for 1 week should generally be suitable for maximal glutathione peroxidase induction. The selenium contents of serum batches were highly variable, pointing to the importance of using only one well-defined, preferably low-selenium, batch. The glutathione peroxidase activities varied considerably between cell lines and the selenite-induced increases ranged from negligible to more than 10-fold. The availability of cell lines with such variable responses should be valuable for experiments aimed at evaluating the importance of glutathione peroxidase and selenium compounds independently of glutathione peroxidase for the protection against oxidative insult.     

Mitochondrial production of pro-oxidants and cellular senescence.

Mitochondria are the major intracellular producers of O2- and H2O2. The level of oxidative stress in cells, as indicated by the in vivo exhalation of alkanes and the concentration of molecular products of oxy-radical reactions, increases during aging in mammals as well as insects. In this paper, we discuss the relationship between mitochondrial generation of O2- and H2O2, and the aging process. The rate of mitochondrial O2- and H2O2 generation increases with age in houseflies and the brain, heart and liver of rat. This rate has been found to correspond to the life expectancy of flies and to the maximum life span potential (MLSP) of six different mammalian species, namely, mouse, rat, guinea pig, rabbit, pig and cow. In contrast, the level of antioxidant defenses provided by activities of superoxide dismutase, catalase, glutathione peroxidase and glutathione concentration neither uniformly declines with age nor corresponds to variations in MLSP of different mammalian species. It is argued that the rate of mitochondrial O2- and H2O2 generation rather than the antioxidant level may act as a longevity determinant.     

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.     

Glutathione metabolism in primate lenses: A phylogenetic study of glutathione synthesis and glutathione redox cycle enzyme activities

Lens wet weights, soluble protein, and activities of γ-glutiamylcysteine synthetase, glutathione synthetase, glutathione peroxidase, and glutathione reductase were determined in primate lenses. The primary sources of lenses were middle-aged adult animals. The Primates, from 23 genera, were categorized into six superfamilies: hominoids (five species), Old World monkeys (seven species), New World monkeys (five species), tarsiers (two species), lemurs (six species), and lorisids (three species). Significant differences between various groups or combinations of groups were noted for γ-glutamylcysteine synthetase, glutathione peroxidase, and glutathione reductase activities. Lenticular γ-glutamylcysteine synthetase activity was very low in the Old World simian lenses and highest in the prosimians. Glutathione peroxidase activity was extraordinarily high in lenses of Old World monkeys. Glutathione reductase activity was low in all the prosimians but tenfold higher in hominoid lenses with intermediate values in monkeys of both the Old World and New World. Glutathione synthetase activity was variable, and no clear pattern which might be useful for primate classification was noted. Lenticular activity ratios of glutathione synthetase:γ-glutamylcysteine synthetase were highest in the Old World simians and lowest in the prosimians. These data with emphasis upon Aotus and the tarsiers were examined with regard to phylogenetic relationships. © 1994 Wiley-Liss, Inc.     

Mechanisms for regulating oxygen toxicity in phytophagous insects

The antioxidant enzymatic defense of insects for the regulation of oxygen toxicity was investigated. Insect species examined were lepidopterous larvae of the cabbage looper (Trichoplusia ni), southern armyworm (Spodoptera eridania), and black swallowtail (Papilio polyxenes). These phytophagous species are subject to both endogenous and exogenous sources of oxidative stress from toxic oxygen radicals, hydrogen peroxide (H2O2) and lipid peroxides (LOOH). In general, the constitutive levels of the enzymes superoxide dismutase (SOD), catalase (CAT), glutathione transferase (GT), and its peroxidase activity (GTpx), and glutathione reductase (GR), correlate well with natural feeding habits of these insects and their relative susceptibility to prooxidant plant allelochemicals, quercetin (a flavonoid), and xanthotoxin (a photoactive furanocoumarin). Induction of SOD activity which rapidly destroys superoxide radicals, appears to be the main response to dietary prooxidant exposure. A unique observation includes high constitutive activity of CAT and a broader subcellular distribution in all three insects than observed in most mammalian species. These attributes of CAT appear to be important in the prevention of excessive accumulation of cytotoxic H2O2. Unlike mammalian species, insects possess very low levels of a GPOX-like activity toward H2O2. Irrefutable proof that this activity is due to a selenium-dependent GPOX found in mammals, is lacking at this time. However, the activity of selenium-independent GTpx is unusually high in insects, suggesting that GTpx and not GPOX plays a prominent role in scavenging deleterious LOOHs. The GSSG generated from the GPOX and GTpx reactions may be reduced to GSH by GR activity. A key role of SOD in protecting insects from prooxidant toxicity was evident when its inhibition resulted in enhanced toxicity towards prooxidants. The role of antioxidant compounds in protecting these insects from toxic forms of oxygen has not been explored in depth. A major finding, however, is that these insects are lutein accumulators. Lutein is a dihydroxy (diol) derivative of beta-carotene, and it is a good quencher of activated forms of oxygen and free radicals. Levels of lutein are highest in P. polyxenes which specializes in feeding on prooxidant-containing plants.     

Characterization of 12-L-hydroperoxyeicosa-5,8,10,14-tetraenoic acid peroxidase in platelets by monoclonal antibody against glutathione peroxidase

In the present investigation, 12-L-hydroxyeicosa-5,8,14-tetraenoic acid (12-HPETE) peroxidase in the platelet 12-lipoxygenase pathway was characterized by using a monoclonal antibody to erythrocyte glutathione peroxidase. Pure glutathione peroxidase was used for the immunization of mice. Monoclonal antibody directed against the erythrocyte glutathione peroxidase was obtained from hybridomas, following fusion of mouse NS-1 myeloma cells with spleen cells from a mouse immunized with the enzyme. The subclass of monoclonal antibody was immunoglobulin M with kappa-light chain. Enzyme activity assays using cumene hydroperoxide and [1-14C]12-HPETE as substrates were employed. The monoclonal antibody reacted with glutathione peroxidase in the cumene hydroperoxide assay. In order to see whether platelet 12-HPETE peroxidase reacts with the monoclonal antibody, platelet cytosol and glutathione peroxidase were incubated with the monoclonal antibody and the antibody was precipitated by goat anti-mouse immunoglobulin M. The activities of platelet 12-HPETE peroxidase and glutathione peroxidase remaining were then assayed by using [1-14C]12-HPETE as substrate. The ability of glutathione peroxidase to transform 12-HPETE to 12-HETE was removed by the monoclonal antibody; however, the activity of platelet cytosol was not removed by the antibody. The results indicated that the antigenic specificity of 12-HPETE peroxidase in the platelet 12-lipoxygenase pathway is different from that of erythrocyte glutathione peroxidase.