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1.
Ascorbic acid and hemoglobins have been linked to nitric oxide metabolism in plants. It has been hypothesized that ascorbic acid directly reduces plant hemoglobin in support of NO scavenging, producing nitrate and monodehydroascorbate. In this scenario, monodehydroascorbate reductase uses NADH to reduce monodehydroascorbate back to ascorbate to sustain the cycle. To test this hypothesis, rates of rice nonsymbiotic hemoglobin reduction by ascorbate were measured directly, in the presence and absence of purified rice monodehydroascorbate reductase and NADH. Solution NO scavenging was also measured methodically in the presence and absence of rice nonsymbiotic hemoglobin and monodehydroascorbate reductase, under hypoxic and normoxic conditions, in an effort to gauge the likelihood of these proteins affecting NO metabolism in plant tissues. Our results indicate that ascorbic acid slowly reduces rice nonsymbiotic hemoglobin at a rate identical to myoglobin reduction. The product of the reaction is monodehydroascorbate, which can be efficiently reduced back to ascorbate in the presence of monodehydroascorbate reductase and NADH. However, our NO scavenging results suggest that the direct reduction of plant hemoglobin by ascorbic acid is unlikely to serve as a significant factor in NO metabolism, even in the presence of monodehydroascorbate reductase. Finally, the possibility that the direct reaction of nitrite/nitrous acid and ascorbic acid produces NO was measured at various pH values mimicking hypoxic plant cells. Our results suggest that this reaction is a likely source of NO as the plant cell pH drops below 7, and as nitrite concentrations rise to mM levels during hypoxia. 相似文献
2.
Transgenic alfalfa (Medicago sativa L.) root cultures expressing sense and antisense barley (Hordeum vulgare L.) hemoglobin were examined for their ability to metabolize NO. Extracts from lines overexpressing hemoglobin had approximately twice the NO conversion rate of either control or antisense lines under normoxic conditions. Only the control line showed a significant increase in the rate of NO degradation when placed under anaerobic conditions. The decline in NO was dependent on the presence of reduced pyridine nucleotide, with the NADH-dependent rate being about 2.5 times faster than the NADPH-dependent rate. Most of the activity was found in the cytosolic fraction of the extracts, while only small amounts were found in the cell wall, mitochondria, and 105,000-g membrane fraction. The NADH-dependent NO conversion exhibited a broad pH optimum in the range 7–8 and a strong affinity to NADH and NADPH (K
m 3 M for both). It was sensitive to diphenylene iodonium, an inhibitor of flavoproteins. The activity was strongly reduced by applying antibodies raised against recombinant barley hemoglobin. Extracts of Escherichia coli overexpressing barley hemoglobin showed a 4-fold higher rate of NO metabolism as compared to non-transformed cells. The NADH/NAD and NADPH/NADP ratios were higher in lines underexpressing hemoglobin, indicating that the presence of hemoglobin has an effect on these ratios. They were increased under hypoxia and antimycin A treatment. Alfalfa root extracts exhibited methemoglobin reductase activity, using either cytochrome c or recombinant barley hemoglobin as substrates. There was a correspondence between NO degradation and nitrate formation. The activity was eluted from a Superose 12 column as a single peak with molecular weight of 35±4 kDa, which corresponds to the size of the hemoglobin dimer. The results are consistent with an NO dioxygenase-like activity, with hemoglobin acting in concert with a flavoprotein, to metabolize NO to nitrate utilizing NADH as the electron donor.Abbreviation
Hb
Hemoglobin 相似文献
3.
In the course of nitric oxide (NO) scavenging, hemoglobin (Hb) turnover is linked to antioxidant metabolism and affects the
cellular redox level. The influence of Hb presence on the ascorbate-glutathione cycle enzymes and the levels of H2O2 and ascorbate was investigated in alfalfa root cultures transformed to over-express (Hb+) or down-regulate (Hb–) class-1
Hb. Hb+ lines had substantially increased ascorbate levels as well as elevated monodehydroascorbate reductase and ascorbate
peroxidase activities. Hb– lines showed significant increases in dehydroascorbate reductase and glutathione reductase activities.
The observed changes in ascorbate and ascorbate-glutathione cycle enzymes were pronounced both at high (40 kPa) and low (3 kPa)
O2 pressures. Hb– lines had significantly reduced levels of the NO- and H2O2-sensitive enzyme, aconitase, as compared to Hb+ lines. This reduced activity was likely due the higher levels of NO in Hb–
lines, as treatment of plant extracts with the NO-donor DEANO also affected aconitase activity. The H2O2 levels were not significantly different amongst the lines and showed no variation with change in oxygen partial pressure.
In conclusion, the expression of class-1 Hb improves the antioxidant status through increased ascorbate levels and increased
activity of enzymes involved in H2O2 removal. 相似文献
4.
Monodehydroascorbate reductase (MDHAR; EC 1.6.5.4) catalyses the reduction of the monodehydroascorbate (MDHA) radical to ascorbate,
using NADH or NADPH as an electron donor, and is believed to be involved in maintaining the reactive oxygen scavenging capability
of plant cells. This key enzyme in the ascorbate-glutathione cycle has been studied here in the moss Physcomitrella patens, which is tolerant to a range of abiotic stresses and is increasingly used as a model plant. In the present study, three
cDNAs encoding different MDHAR isoforms of 47 kDa were identified in P. patens, and found to exhibit enzymic characteristics similar to MDHARs in vascular plants despite low-sequence identity and a distant
evolutionary relationship between the species. The three cDNAs for the P. patens MDHAR enzymes were expressed in Escherichia coli and the active enzymes were purified and characterized. Each recombinant protein displayed an absorbance spectrum typical
of flavoenzymes and contained a single non-covalently bound FAD coenzyme molecule. The K
m and k
cat values for the heterologously expressed PpMDHAR enzymes ranged from 8 to 18 μM and 120–130 s−1, respectively, using NADH as the electron donor. The K
m values were at least an order of magnitude higher for NADPH. The K
m values for the MDHA radical were ∼0.5–1.0 μM for each of the purified enzymes, and further kinetic analyses indicated that
PpMDHARs follow a ‘ping–pong’ kinetic mechanism. In contrast to previously published data, site-directed mutagenesis indicated
that the conserved cysteine residue is not directly involved in the reduction of MDHA. 相似文献
5.
Mitochondria isolated from the roots of barley (Hordeum vulgare L.) and rice (Oryza sativa L.) seedlings were capable of oxidizing external NADH and NADPH anaerobically in the presence of nitrite. The reaction was
linked to ATP synthesis and nitric oxide (NO) was a measurable product. The rates of NADH and NADPH oxidation were in the
range of 12–16 nmol min−1 mg−1 protein for both species. The anaerobic ATP synthesis rate was 7–9 nmol min−1 mg−1 protein for barley and 15–17 nmol min−1 mg−1 protein for rice. The rates are of the same order of magnitude as glycolytic ATP production during anoxia and about 3–5%
of the aerobic mitochondrial ATP synthesis rate. NADH/NADPH oxidation and ATP synthesis were sensitive to the mitochondrial
inhibitors myxothiazol, oligomycin, diphenyleneiodonium and insensitive to rotenone and antimycin A. The uncoupler FCCP completely
eliminated ATP production. Succinate was also capable of driving ATP synthesis. We conclude that plant mitochondria, under
anaerobic conditions, have a capacity to use nitrite as an electron acceptor to oxidize cytosolic NADH/NADPH and generate
ATP. 相似文献
6.
This study investigated the regulation of ascorbate and glutathione metabolism by nitric oxide in Agropyron cristatum leaves under water stress. The activities of ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate
reductase (MDHAR), dehydroascorbate reductase (DHAR), L-galactono-1,4-lactone dehydrogenase (GalLDH) and γ-glutamylcysteine
synthetase (γ-ECS), and the contents of NO, reduced ascorbic acid (AsA), reduced glutathione (GSH), total ascorbate and total
glutathione increased under water stress. These increases were suppressed by pretreatments with NO synthesis inhibitors N
G-nitro-L-arginine methyl ester (L-NAME) and 4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO). However,
application of L-NAME and cPTIO to plants sufficiently supplied with water did not affect the activities of above mentioned
enzymes and the contents of NO and above mentioned antioxidants. Pretreatments with L-NAME and cPTIO increased the malondialdehyde
(MDA) content and electrolyte leakage of plants under water stress. Our results suggested that water stress-induced NO is
a signal that leads to the upregulation of ascorbate and glutathione metabolism and has important role for acquisition of
water stress tolerance. 相似文献
7.
Samhan-Arias AK Duarte RO Martín-Romero FJ Moura JJ Gutiérrez-Merino C 《Archives of biochemistry and biophysics》2008,469(2):243-254
Synaptic plasma membranes (SPMV) decrease the steady state ascorbate free radical (AFR) concentration of 1 mM ascorbate in phosphate/EDTA buffer (pH 7), due to AFR recycling by redox coupling between ascorbate and the ubiquinone content of these membranes. In the presence of NADH, but not NADPH, SPMV catalyse a rapid recycling of AFR which further lower the AFR concentration below 0.05 μM. These results correlate with the nearly 10-fold higher NADH oxidase over NADPH oxidase activity of SPMV. SPMV has NADH-dependent coenzyme Q reductase activity. In the presence of ascorbate the stimulation of the NADH oxidase activity of SPMV by coenzyme Q1 and cytochrome c can be accounted for by the increase of the AFR concentration generated by the redox pairs ascorbate/coenzyme Q1 and ascorbate/cytochrome c. The NADH:AFR reductase activity makes a major contribution to the NADH oxidase activity of SPMV and decreases the steady-state AFR concentration well below the micromolar concentration range. 相似文献
8.
Yayoi Aki Masako Nagai Yukifumi Nagai Kiyohiro Imai Michihiko Aki Akira Sato Minoru Kubo Shigenori Nagatomo Teizo Kitagawa 《Journal of biological inorganic chemistry》2010,15(2):147-158
Among the four types of hemoglobin (Hb) M with a substitution of a tyrosine (Tyr) for either the proximal (F8) or distal (E7)
histidine in the α or β subunits, only Hb M Saskatoon (βE7Tyr) assumes a hexacoordinate structure and its abnormal subunits
can be reduced readily by methemoglobin (metHb) reductase. This is distinct from the other three M Hbs. To gain new insight
into the cause of the difference, we examined the ionization states of E7 and F8 Tyrs by UV resonance Raman (RR) spectroscopy
and Fe–O(Tyr) bonding by visible RR spectroscopy. Hb M Iwate (αF8Tyr), Hb M Boston (αE7Tyr), and Hb M Hyde Park (βF8Tyr) exhibited
two extra UV RR bands at 1,603 cm−1 (Y8a′) and 1,167 cm−1 (Y9a′) arising from deprotonated (ionized) Tyr, but Hb M Saskatoon displayed the UV RR bands of protonated (unionized) Tyr
at 1,620 and 1,175 cm−1 in addition to those of deprotonated Tyr. Evidence for the bonding of both ionization states of Tyr to the heme in Hb M Saskatoon
was provided by visible RR spectroscopy. These results indicate that βE7Tyr of Hb M Saskatoon is in equilibrium between protonated
and deprotonated forms, which is responsible for facile reducibility. Comparison of the UV RR spectral features of metHb M
with that of metHb A has revealed that metHb M Saskatoon and metHb M Hyde Park are in the R (relaxed) structure, similar to
that of metHb A, whereas metHb M Iwate, metHb M Boston and metHb M Milwaukee are in the T (tense) quaternary structure. 相似文献
9.
Drought Influences the Activity of Enzymes of the Chloroplast Hydrogen Peroxide Scavenging System 总被引:12,自引:2,他引:10
Smirnoff, N. and Colomb?, S. V. 1988. Drought influences theactivity of enzymes of the chloroplast hydrogen peroxide scavengingsystem.J. exp. Bot. 39: 10971108. The effect of drought on the activity of ascorbate peroxidase(AP), glutathione reductase (GR) and monodehydroascorbate reductase(MDAR) in leaves of barley (Hordeum vulgare) and tef {Eragrostistef) was studied. These enzymes are components of the chloroplasthydrogen peroxide scavenging system. Severe leaf water deficit(<30 M Pa) resulted in increased activity (leaf dryweight basis) of GR and MDAR in barley and of AP and MDAR intef. The specific activity of all the scavenging enzymes wasgreater in droughted plants. The activities (dry weight basis)of two control enzymes, malate dehydrogenase (barley)and phosphoenolpyruvate carboxylase (tef), not directly involvedin the scavenging system, were not affected by drought. These data suggest that drought may cause an increase in thecapacity of the hydrogen peroxide scavenging system and thatit may, therefore, increase the rate of hydrogen peroxide formationin chloroplasts. Key words: Water stress, hydrogen peroxide, enzyme activity 相似文献
10.
The effects of methyl jasmonate (MJ) and salicylic acid (SA) on changes of the activities of major antioxidant enzymes, superoxide anion accumulation (O2
−), ascorbate, total glutathione (TG), malondialdehyde (MDA) content and ginsenoside accumulation were investigated in ginseng roots (Panax ginseng L.) in 4 l (working volume) air lift bioreactors. Single treatment of 200 μM MJ and SA to P. ginseng roots enhanced ginsenoside accumulation compared to the control and harvested 3, 5, 7 and 9 days after treatment. MJ and SA treatment induced an oxidative stress in P. ginseng roots, as shown by an increase in lipid peroxidation due to rise in O2
− accumulation. Activity of superoxide dismutase (SOD) was inhibited in MJ-treated roots, while the activities of monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), SOD, guaiacol peroxidase (G-POD), glutathione peroxidase (GPx) and glutathione reductase (GR) were induced in SA-treated roots. A strong decrease in the activity of catalase (CAT) was obtained in both MJ- and SA-treated roots. Activities of ascorbate peroxidase (APX) and glutathione S transferase (GST) were higher in MJ than SA while the contents of reduced ascorbate (ASC), redox state (ASC/(ASC+DHA)) and TG were higher in SA- than MJ-treated roots while oxidized ascorbate (DHA) decreased in both cases. The result of these analyses suggests that roots are better protected against the O2
− stress, thus mitigating MJ and SA stress. The information obtained in this work is useful for efficient large-scale production of ginsenoside by plant-root cultures. 相似文献
11.
D. Camejo M. C. Martí E. Olmos W. Torres F. Sevilla A. Jiménez 《Biologia Plantarum》2012,56(3):537-544
Alfalfa (Medicago sativa L.) roots were treated with 50 and 100 μg cm−3 of oligogalacturonide (OGA) solutions with a degree of polymerization between 7 and 15. Changes in the activities of superoxide
dismutase (SOD), catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR) and
dehydroascorbate reductase (DHAR) as well as ascorbate (ASC) content were determined in crude extract of alfalfa roots after
30, 60 and 120 min of treatment. An increase in the SOD activity was observed in roots treated with 50 and 100 μg cm−3 OGA, which could be related to its O2
·− scavenging function. As concern H2O2 scavenging, CAT activity was increased in the first 30 min by both OGA concentrations, while POX was a key enzyme at higher
OGA concentration and treatment duration. ASC content firstly increased upon exposure to high OGA concentration, and then
decreased after longer treatment while low OGA concentration had no effect on ASC content. 相似文献
12.
Consuelo Gómez-Díaz Juan Carlos Rodríguez-Aguilera María P. Barroso José M. Villalba Francisco Navarro Frederick L. Crane Plácido Navas 《Journal of bioenergetics and biomembranes》1997,29(3):251-257
Plasma membranes isolated from K562 cells contain an NADH-ascorbate free radical reductase activity and intact cells show the capacity to reduce the rate of chemical oxidation of ascorbate leading to its stabilization at the extracellular space. Both activities are stimulated by CoQ10 and inhibited by capsaicin and dicumarol. A 34-kDa protein (p34) isolated from pig liver plasma membrane, displaying NADH-CoQ10 reductase activity and its internal sequence being identical to cytochrome b
5 reductase, increases the NADH-ascorbate free radical reductase activity of K562 cells plasma membranes. Also, the incorporation of this protein into K562 cells by p34-reconstituted liposomes also increased the stabilization of ascorbate by these cells. TPA-induced differentiation of K562 cells increases ascorbate stabilization by whole cells and both NADH-ascorbate free radical reductase and CoQ10 content in isolated plasma membranes. We show here the role of CoQ10 and its NADH-dependent reductase in both plasma membrane NADH-ascorbate free radical reductase and ascorbate stabilization by K562 cells. These data support the idea that besides intracellular cytochrome b
5-dependent ascorbate regeneration, the extracellular stabilization of ascorbate is mediated by CoQ10 and its NADH-dependent reductase. 相似文献
13.
Antioxidant defences of the apoplast 总被引:1,自引:0,他引:1
Summary The apoplast of barley and oat leaves contained superoxide dismutase (SOD), catalase, ascorbate peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase, and glutathione reductase activities. The activities of these enzymes in the apoplastic extracts were greatly modified 24 h after inoculation with the biotrophic fungal pathogenBlumeria graminis. The quantum efficiency of photosystem II, which is related to photosynthetic electron transport flux, was comparable in inoculated and healthy leaves during this period. Apoplastic soluble acid invertase activity was also modified in inoculated leaves. Inoculation-dependent increases in apoplastic SOD activity were observed in all lines. Major bands of SOD activity, observed in apoplastic protein extracts by activity staining of gels following isoelectric focusing, were similar to those observed in whole leaves but two additional minor bands were found in the apoplastic fraction. The apoplastic extracts contained substantial amounts of dehydroascorbate (DHA) but little or no glutathione (GSH). Biotic stress decreased apoplastic ascorbate and DHA but increased apoplastic GSH in resistant lines. The antioxidant cycle enzymes may function to remove apoplastic H2O2 with ascorbate and GSH derived from the cytoplasm. DHA and oxidized glutathione may be reduced in the apoplast or returned to the cytosol for rereduction.Abbreviations AA
reduced ascorbate
- APX
ascorbate peroxidase
- DHA
dehydroascorbate (oxidised ascorbate)
- DHAR
dehydroascorbate reductase
- G6PDH
glucose-6-phosphate dehydrogenase
- GSH
reduced glutathione
- GSSG
glutathione disulphide
- GR
glutathione reductase
- MDHA
monodehydroascorbate
- MDHAR
monodehydroascorbate reductase
- SOD
superoxide dismutase 相似文献
14.
Drought Induces Oxidative Stress and Enhances the Activities of Antioxidant Enzymes in Growing Rice Seedlings 总被引:7,自引:0,他引:7
When rice seedlings grown for 10 and 20 days were subjected to in vitro drought stress of −0.5 and −2.0 MPa for 24 h, an increase in the concentration of superoxide anion (O2.−), increased level of lipid peroxidation and a decrease in the concentration of total soluble protein and thiols was observed
in stressed seedlings compared to controls. The concentration of H2O2 as well as ascorbic acid declined with imposition of drought stress, however glutathione (GSH) concentration declined only
under severe drought stress. The activities of total superoxide dismutases (SODs) as well as ascorbate peroxidase (APX) showed
consistent increases with increasing levels of drought stress, however catalase activity declined. Mild drought stressed plants
had higher guaiacol peroxidase (GPX) and chloroplastic ascorbate peroxidase (c-APX) activity than control grown plants but
the activity declined at the higher level of drought stress. The activities of enzymes involved in regeneration of ascorbate
i.e. monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) were higher
in drought stressed plants compared to controls. Results suggest that drought stress induces oxidative stress in rice plants
and that besides SOD, the enzymes of ascorbate-glutathione cycle, which have not been studied in detail earlier under stressful
conditions, appear to function as important component of antioxidative defense system under drought stress. 相似文献
15.
Evidence for two different nitrate-reducing activities at the plasma membrane in roots ofZea mays L.
Ario de Marco Chen Jia Elke Fischer-Schliebs Zeno Varanini Ulrich Lüttge 《Planta》1994,194(4):557-564
Plasma-membrane (PM) vesicles isolated from 6-d-old corn roots by sucrose gradient centrifugation or two-phase partitioning showed an NADH-dependent nitrate reductase (NR) activity averaging at 40 nmol per milligram PM protein per hour. This membrane-associated NR activity could not be removed from two-phase-partitioned PM vesicles by salt washing, osmotic shock treatment, sonication, or freeze-thawing to reverse vesicle sidedness. Therefore, it could not be attributed to contamination of membrane vesicles by the soluble, cytosolic NR. Plasma-membrane vesicles reduced NO
3
-
in the presence of the electron donors NADH or NADPH at an activity ratio of 2.2. The NADH- and NADPH-dependent NR activities of outside-out oriented PM vesicles differed in their sensitivity toward the detergent Brij 58, leading to a latency of 65% or 29% using NADH or NADPH as electron donor, respectively. The activities of NO
3
-
reduction in the presence of saturating concentrations of NADH and NADPH were additive. Furthermore, both activities were characterized by a different pH dependence with a pH optimum of 7.5 for the NADH-dependent activity and of 6.8 for the NADPH-dependent activity. The membrane-associated NAD(P)H-dependent NR activities responded to different nitrogen nutrition of plants in a manner different from the soluble forms of the enzyme. The data confirm the existence of a corn PM NR and suggest that there may be two different NO
3
-
-reducing enzymes located at the PM of corn roots.Abbreviations PM
Plasma membrane
- NR
nitrate reductase
This research was supported by grants from the National Research Council of Italy (bilateral project between Italy and Germany to Z.V. and U.L.), by the Ministero dell' Università e Ricera Scientifice e Tecnologica (MURST 40%) and by the Deutsche Forschungsgemeinschaft. 相似文献
16.
Senescence is a developmentally regulated and highly ordered sequence of events. Senescence leads to abscission of plant organs
and eventually leads to death of a plant or part of it. Present study revealed that Phalaenopsis flower undergo senescence due to over activation of O2
·−generating xanthine oxidase (XO), which consequently increases the concentrations of O2
·− leading to enhanced oxidative damage and disturbed cellular redox environment as indicated by increased lipid peroxidation
and DHA/AsA + DHA ratio, respectively. While activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), and non-specific
peroxidase (POD) were enhanced in sepals and petals of old flower, activities of catalase (CAT) and glutathione reductase
(GR) were decreased. Exogenous application of nitric oxide (NO) retarded H2O2-induced senescence of Phalaenopsis flower by downregulating activity of XO and concentrations of O2
·−, H2O2 and malondialdehyde (MDA, an index of lipid peroxidation). Exogenous application of NO also downregulated SOD activity and
upregulated antioxidant enzymes involved in the detoxification of H2O2 (CAT and APX), and in the regulation of redox couples viz, monodehydroascorbate reductase (MDHAR) and GR, together with the
modulation in non-protein thiol status and DHA/AsA + DHA ratio. 相似文献
17.
Placido Navas Iris Sun Frederick L. Crane Dorothy M. Morré D. James Morré 《Journal of bioenergetics and biomembranes》2010,42(2):181-187
Golgi apparatus from rat liver contain an ascorbate free radical oxidoreducatse that oxidizes NADH at neutral pH with monodehydroascorbate
as acceptor to generate a membrane potential. At pH 5.0, the reverse reaction occurs from NAD+. The electron spin resonance signal of the ascorbate-free radical and its disappearance upon the addition of NADH (pH 7)
or NAD+ (pH 5.0) confirms monodehydroascorbate involvement. Location of monodehydroascorbate both external to and within Golgi apparatus
compartments is suggested from energization provided by inward or outward flux of electrons across the Golgi apparatus membranes.
The isolated membranes are sealed, oriented cytoplasmic side out and impermeable to NAD+ and ascorbate. NAD+ derived through the action of Golgi apparatus β-NADP phosphohydrolase is simultaneously reduced to NADH with monodehydroascorbate
present. The response of the NADH- (NAD+-) ascorbate free radical oxidoreductase system to pH in Golgi apparatus provides a simple regulatory mechanism to control
vesicle acidification. 相似文献
18.
Glutathione reductase fromSaccharomyces cerevisiae undergoes redox interconversionin situ andin vivo
José Peinado Javier Florindo J. López-Barea 《Molecular and cellular biochemistry》1992,110(2):135-143
Redox interconversion of glutathione reductase was studiedin situ withS. cerevisiae. The enzyme was more sensitive to redox inactivation in 24 hour-starved cells than in freshly-grown ones. While 5 μM NADPH
or 100 μM NADH caused 50% inactivation in normal cells in 30 min, 0.75 μM NADPH or 50 μM NADH promoted a similar effect in
starved cells. GSSG reactivated the enzyme previously inactivated by NADPH, ascertaining that the enzyme was subjected to
redox interconversion. Low EDTA concentrations fully protected the enzyme from NADPH inactivation, thus confirming the participation
of metals in such a process. Extensive inactivation was obtained in permeabilized cells incubated with glucose-6-phosphate
or 6-phosphogluconate, in agreement with the very high specific activities of the corresponding dehydrogenases. Some inactivation
was also observed with malate, L-lactate, gluconate or isocitrate in the presence of low NADP+ concentrations.
The inactivation of yeast glutathione reductase has also been studiedin vivo. The activity decreased to 75% after 2 hours of growth with glucono-δ-lactone as carbon source, while NADPH rose to 144%
and NADP+ fell to 86% of their initial values. Greater changes were observed in the presence of 1.5 μM rotenone: enzymatic activity
descended to 23% of the control value, while the NADH/NAD+ and NADPH/NADP+ ratios rose to 171% and 262% of their initial values, respectively. Such results indicate that the lowered redox potential
of the pyridine nucleotide pool existing when glucono-δ-lactone is oxidized promotesin vivo inactivation of glutathione reductase. 相似文献
19.
Fei Chen Fang Wang Hongyan Sun Yue Cai Weihua Mao Guoping Zhang Eva Vincze Feibo Wu 《Journal of Plant Growth Regulation》2010,29(4):394-408
A greenhouse hydroponic experiment was performed using Cd-sensitive (cv. Dong 17) and Cd-tolerant (Weisuobuzhi) barley seedlings
to evaluate how different genotypes responded to cadmium (Cd) toxicity in the presence of sodium nitroprusside (SNP), a nitric
oxide (NO) donor. Results showed that 5 μM Cd increased the accumulation of O2•−, H2O2, and malondialdehyde (MDA) but reduced plant height, chlorophyll content, net photosynthetic rate (P
n), and biomass, with a much more severe response in the Cd-sensitive genotype. Antioxidant enzyme activities increased significantly
under Cd stress in the roots of the tolerant genotype, whereas in leaves of the sensitive genotype, superoxide dismutase (SOD)
and ascorbate peroxide (APX), especially cytosol ascorbate peroxidase (cAPX), decreased after 5–15 days Cd exposure. Moreover,
Cd induces NO synthesis by stimulating nitrate reductase and nitric oxide synthetase-like enzymes in roots/leaves. A Cd-induced
NO transient increase in roots of the Cd-tolerant genotype might partly contribute to its Cd tolerance. Exogenous NO dramatically
alleviated Cd toxicity, markedly diminished Cd-induced reactive oxygen species (ROS) and MDA accumulation, ameliorated Cd-induced
damage to leaf/root ultrastructure, and increased chlorophyll content and P
n. External NO counteracted the pattern of alterations in certain antioxidant enzymes induced by Cd; for example, it significantly
elevated the depressed SOD, APX, and catalase (CAT) activities in the Cd-sensitive genotype after 10- and 15-day treatments.
Furthermore, NO significantly increased stromal APX and Mn-SOD activities in both genotypes and upregulated Cd-induced decrease
in cAPX activity and gene expression of root/leaf cAPX and leaf CAT1 in the Cd-sensitive genotype. These data suggest that under Cd stress, NO, as a potent antioxidant, protects barley seedlings
against oxidative damage by directly and indirectly scavenging ROS and helps to maintain stability and integrity of the subcellular
structure. 相似文献
20.
Oxidative stress responses were tested in the unicellular cyanobacterium Synechococcus PCC 7942 (R2). Cells were exposed to hydrogen peroxide, cumene hydroperoxide and high light intensities. Activities of ascorbate peroxidase and catalase were correlated with the extent and time-course of oxidative stresses. Ascorbate peroxidase was found to be the major enzyme involved in the removal of hydrogen peroxide under the tested oxidative stresses. Catalase activity was inhibited in cells treated with high H2O2 concentrations, and was not induced under photo-oxidative stress. Regeneration of ascorbate in peroxide-treated cells was found to involve mainly monodehydroascorbate reductase and to a lesser extent dehydroascorbate reductase. The induction of the antioxidative enzymes was dependent on light and was inhibited by chloramphenicol. Peroxide treatment was found to induce the synthesis of eight proteins, four of which were also induced by heat shock.Abbreviations ASC
ascorbate
- DHA
dehydroascorbate
- MDA
monodehydroascorbate
- GSH
reduced glutathione
- GSSG
oxidized glutathione
- ASC Per
ascorbate peroxidase
- DHA red.
dehydroascorbate reductase
- MDA red.
monodehydroascorbate reductase
- GSSG red.
glutathione reductase
- HSP
heat shock proteins
- PSP
peroxide shock proteins
- Cm
chloramphenicol 相似文献