Electron transport chain of Saccharomyces cerevisiae mitochondria is inhibited by H2O2 at succinate-cytochrome c oxidoreductase level without lipid peroxidation involvement

The deleterious effects of H₂O₂ on the electron transport chain of yeast mitochondria and on mitochondrial lipid peroxidation were evaluated. Exposure to H₂O₂ resulted in inhibition of the oxygen consumption in the uncoupled and phosphorylating states to 69% and 65%, respectively. The effect of H₂O₂ on the respiratory rate was associated with an inhibition of succinate-ubiquinone and succinate-DCIP oxidoreductase activities. Inhibitory effect of H₂O₂ on respiratory complexes was almost completely recovered by β-mercaptoethanol treatment. H₂O₂ treatment resulted in full resistance to Q_O site inhibitor myxothiazol and thus it is suggested that the quinol oxidase site (Q_O) of complex III is the target for H₂O₂. H₂O₂ did not modify basal levels of lipid peroxidation in yeast mitochondria. However, H₂O₂ addition to rat brain and liver mitochondria induced an increase in lipid peroxidation. These results are discussed in terms of the known physiological differences between mammalian and yeast mitochondria.     

Aging, cytochrome oxidase activity, and hydrogen peroxide release by mitochondria

The objective of this study was to explore the possible cause(s) underlying the previously observed, age-related increase in the rate of mitochondrial H₂O₂ release in the housefly. The hypothesis that an imbalance between different respiratory complexes may be a causal factor was tested. Cytochrome c oxidase activity was found to sharply decline in the latter part of the life span of the flies. Effects of different substrates and respiratory inhibitors were determined in order to ascertain if a decrease in cytochrome c oxidase activity could be responsible for the increased H₂O₂ release. H₂O₂ was measured spectrofluorometrically using horseradish peroxidase and p-hydrophenylacetate as an indicator. Neither NADH-linked substrates nor succinate caused a stimulation of H₂O₂ production. H₂O₂ release by mitochondria, inhibited with rotenone and antimycin A, was greatly increased upon supplementation with -glycerophosphate; however, the further addition of KCN or myxothiazol, to such preparations, caused a depression of H₂O₂ generation. In contrast, relatively low concentrations of KCN or myxothiazol were found to stimulate H₂O₂ release in insect mitochondria supplemented with -glycerophosphate and exposed to rotenone, but not antimycin A. Results are interpreted to suggest that partial inhibition of cytochrome c oxidase activity can lead to the stimulation of mictochondrial H₂O₂ production in the housefly at site(s) other than NADH dehydrogenase and ubisemiquinone/ cytochrome b region; a possible source may be glycerophosphate dehydrogenase.     

Ca2+参与H2O2促进盐碱混合胁迫下燕麦种子的萌发和成苗

盐碱胁迫是制约作物高产优质的重要因素,Ca²⁺和H₂O₂作为信号分子参与作物逆境响应调节。为了解Ca²⁺是否参与H₂O₂对盐碱胁迫下植物种子萌发和成苗的调控,以燕麦（Avena nude）为试验材料,采用隶属函数分析方法,研究了胞外游离Ca²⁺螯合剂EGTA、质膜Ca²⁺通道阻断剂LaCl₃和液泡膜Ca²⁺释放抑制剂钌红（RR）与H₂O₂共处理对盐碱混合（NaCl：Na₂SO₄：NaHCO₃：Na₂CO₃=12：8：9：1）胁迫下种子萌发和成苗的影响。结果表明,25~200 mmol·L^-1盐碱混合胁迫显著抑制燕麦的种子萌发和成苗,抑制程度随浓度提高而增强;0.001~2 mmol·L^-1 H₂O₂能够促进燕麦种子的萌发和成苗,且0.5 mmol·L^-1 H₂O₂可以显著缓解75 mmol·L^-1盐碱混合胁迫对燕麦种子萌发和成苗的抑制作用;而EGTA、LaCl₃和RR均能消减H₂O₂对盐碱混合胁迫下燕麦种子萌发和成苗的促进作用。表明Ca²⁺参与H₂O₂促进盐碱混合胁迫下燕麦种子萌发和成苗的信号转导过程。     

The Action of Hydrogen Peroxide on the Formation of Thiobarbituric Acid-Reactive Material From Microsomes, Liposomes Or From Dna Damaged By Bleomycin Or Phenanthroline. Artefacts in the Thiobarbituric Acid Test

Incubation of rat-liver microsomes, previously azide-treated to inhibit catalase, with H₂O₂ caused a loss of cytochrome P-450 but not of cytochrome b₅. This loss of P-450 was not prevented by scavengers of hydroxyl radical, chain-breaking antioxidants or metal ion-chelating agents. Application of the thiobarbituric acid (TBA) assay to the reaction mixture suggested that H₂O₂ induces lipid peroxidation, but this was found to be due largely or completely to an effect of H²O₂ on the TBA assay. By contrast, addition of ascorbic acid and Fe(III) to the microsomes led to lipid peroxidation and P-450 degradation: both processes were inhibited by chelating agents and chain-breaking antioxidants, but not by hydroxyl radical scavengers. H₂O₂ inhibited ascorbate/Fe (III)-induced microsomal lipid peroxidation, but part of this effect was due to an action of H₂O₂ in the TBA test itself. H₂O₂ also decreased the colour measured after carrying out the TBA test upon authentic malondialdehyde, tetraethoxypropane, a DNA-Cu²⁺/o-phenanthroline system in the presence of a reducing agent, ox-brain phospholipid liposomes in the presence of Fe(III) and ascorbate, or a bleomycin-iron ion/DNA/ascorbate system. Caution must be used in interpreting the results of TBA tests upon systems containing H₂O₂.     

Mechanisms of Saccharomyces Cerevisiae PMA1 H+-ATPase inactivation by Fe2+, H2O2 and Fenton reagents

Although considerably more oxidation-resistant than other P-type ATPases, the yeast PMA1 H⁺-ATPase of Saccharomyces cerevisiae SY4 secretory vesicles was inactivated by H₂O₂, Fe²⁺, Fe- and Cu-Fenton reagents. Inactivation by Fe²⁺ required the presence of oxygen and hence involved auto-oxidation of Fe²⁺ to Fe³⁺. The highest Fe^2- (100 μM) and H₂O₂ (100 mM) concentrations used produced about the same effect. Inactivation by the Fenton reagent depended more on Fe²⁺ content than on H₂O₂ concentration, occurred only when Fe²⁺ was added to the vesicles first and was only slightly reduced by scavengers (mannitol, Tris, NaN₃, DMSO) and by chelators (EDTA, EGTA, DTPA, BPDs, bipyridine, 1, 10-phenanthroline). Inactivation by Fe- and Cu- Fenton reagent was the same; the identical inactivation pattern found for both reagents under anaerobic conditions showed that both reagents act via OH^·. The lipid peroxidation blocker BHT prevented Fenton-induced rise in lipid peroxidation in both whole cells and in isolated membrane lipids but did not protect the H⁺-ATPase in secretory vesicles against inactivation. ATP partially protected the enzyme against peroxide and the Fenton reagent in a way resembling the protection it afforded against SH-specific agents. The results indicate that Fe²⁺ and the Fenton reagent act via metal-catalyzed oxidation at specific metal-binding sites, very probably SH-containing amino acid residues. Deferrioxamine, which prevents the redox cycling of Fe²⁺, blocked H⁺-ATPase inactivation by Fe²⁺ and the Fenton reagent but not that caused by H₂O₂, which therefore seems to involve a direct non-radical attack. Fe-Fenton reagent caused fragmentation of the H⁺-ATPase molecule, which, in Western blots, did not give rise to defined fragments bands but merely to smears.     

Does hydrogen peroxide exist “free” in biological systems?

Hydrogen peroxide (H₂O₂) can diffuse far from the site of production to intracellular locations where biological effects may be greater. The diffusion range is extended by H₂O₂ carriers formed spontaneously by hydrogen bonding with monomeric and polymeric compounds, including amino and dicarboxylic acids, peptides, proteins, nucleic acid bases, and nucleosides. Hydrogen peroxide adducts (HPAs) are readily synthesized, e.g., crystalline histidine (His)-H₂O₂ adducts. An equilibrium exists between an adduct-forming compound and H₂O₂. The detection and relative stabilities of HPAs are measured by the degree of decomposition of H₂O₂ as influenced by test compounds in buffered solution competing with glucose or fructose for H₂O₂. The HPAs delay decomposition of H₂O₂ up to several hundredfold. The overall charge on an HPA, i.e., its ability to penetrate cell membranes, influences the cytotoxic and clastogenic effects of H₂O₂. Growth inhibition of Salmonella typhimurium LT₂ by H₂O₂ is enhanced by neutral HPAs but decreased by anionic HPAs. Addition of catalase 1, 10, or 30 min after inoculation of S. typhimurium LT₂ reduces or nearly eliminates partial growth inhibition by H₂O₂, but a neutral HPA, expecially his-H₂O₂, transported H₂O₂ into the cells within 1 min, and in about 10 min completely inhibited growth. The stability of HPAs decreases with increasing pH or increasing temperature, while added Fe(II) in the presence and absence of EDTA accelerates H₂O₂ and HPA decomposition. Calculations indicate H₂O₂ hydrogen bonds with nucleic acid-base pairs with no apparent bond strain and energy stabilization comparable to normal hydrogen bonding.     

Scavenging of Hypochlorous Acid and the Myoglobin-Derived Oxidants By of Cardioprotective Agent Mercaptopropionylglycine

Mercaptopropionylglycine (MPG) has a marked cardioprotective action in several model systems of ischaemia-reoxygenation injury. Suggested mechanisms of action include scavenging of hydroxyl radical and the hypochlorous acid and reacting with an oxidant formed by reaction of myoglobin with H₂O₂, thereby slowing lipid peroxidation stimulated by myoglobin-H₂O₂ mixtures. This oxidant seems not to be singlet O₂ or hydroxyl radical. Studies in vitro show that scavenging of hypochlorous acid is a feasible mechanism of cardioprotective action for MPG in vivo in ischaemia/reperfusion systems to which neutrophil-mediated injury contributes. However, the poor ability of MPG to inhibit lipid peroxidation stimulated by myoglobin/H₂O₂ mixtures and its ability to increase iron ion release from myoglobin in the presence of a large excess of H₂O₂, suggests that MPG is unlikely to protect the myocardium by interfering with oxidants produced by the myoglobin-H₂O₂ system.     

Oxidant-mediated AA release from astrocytes involves cPLA(2) and iPLA(2)

Excessive generation of reactive oxygen species (ROS) in the central nervous system (CNS) is a leading cause of neuronal injury. Despite yet unknown mechanisms, oxidant compounds such as H₂O₂ have been shown to stimulate the release of arachidonic acid (AA) in a number of cell systems. In this study, H₂O₂ and menadione, a compound known to release H₂O₂ intracellularly, were used to examine the phospholipases A₂ (PLA₂) responsible for AA release from primary murine astrocytes. Both H₂O₂ and menadione dose-dependently stimulated AA release, and the release mediated by H₂O₂ was completely inhibited by catalase. H₂O₂ also stimulated phosphorylation of extracellular signal-regulated kinases (ERK1/2) and cytosolic phospholipase A₂ (cPLA₂). However, complete inhibition of cPLA₂ phosphorylation by U0126, an inhibitor for mitogen-activated protein kinase kinase (MEK) and GF109203x, a nonselective PKC inhibitor preferring the conventional and novel isoforms, only reduced H₂O₂-stimulated AA release by 50%. MAFP, a selective, active, site-directed, irreversible inhibitor of both cPLA₂ and the Ca²⁺-independent iPLA₂, nearly completely inhibited H₂O₂-mediated AA release; but, HELSS, a potent irreversible inhibitor of iPLA₂, only inhibited H₂O₂-mediated AA release by 40%. Along with the observation that H₂O₂-mediated AA release was only partially inhibited upon chelating intracellular Ca²⁺ by BAPTA, these results indicate the involvement of both cPLA₂ and iPLA₂ in H₂O₂-mediated AA release in murine astrocytes.     

Oxidant-Induced Activation of Protein Kinase C in Uc11mg Cells

Free radical formation and subsequent lipid peroxidation may participate in the pathogenesis of tissue injury, including the brain injury induced by hypoxia or trauma and cardiac injury arising from ischemia and reperfusion. However, the exact cellular mechanisms by which the initial oxidative insult leads to the ultimate tissue damage are not known. A number of reports have indicated that protein kinase C (PKC) may be activated following oxidative stress and that this enzyme may play an important role in the steps leading to cellular damage. In this work, we have examined in a cell model whether PKC is activated following oxidative exposure. UC11MG cells, a human astrocytoma cell line, were treated with H₂O₂. Incubation with 0.5 mM H₂O₂ increased malondialdehyde levels by as early as 15 minutes. To assess the effects of H₂O₂ treatment on PKC activation, we measured phosphorylation of an endogenous PKC substrate, the MARCKS (myristoylated alanine-rich C kinase substrate) protein. Treatment of cells with 0.2-1.0 mM H₂O₂ resulted in a rapid increase in MARCKS phosphorylation. Phosphorylation was stimulated approximately 2.5-fold following treatment with 0.5 mM H₂O₂ for ten minutes. Treatment with phorbol 12-myristate 13-acetate, a PKC activator, increased MARCKS phosphorylation approximately 4-fold. The H₂O₂-induced MARCKS phosphorylation was inhibited by the addition of the kinase inhibitors H-7 and staurosporine. Furthermore, specific down-regulation of PKC by phorbol ester also inhibited H₂O₂-induced MARCKS phosphorylation. These results indicate that PKC is rapidly activated in cells following an oxidative exposure and that this cell system may be a good model to further investigate the role of PKC in regulating oxidative damage in the cell.     

The Effect of Hydrogen Peroxide on β-Adrenoceptor Function in the Heart

A membrane preparation of calf heart left ventricle has been used to study the effect of radical stress on the β-adrenoceptor complex. To this end the membranes were incubated for 30 minutes with several concentrations of hydrogen peroxide. This resulted in a dose dependent peroxidation of the membrane lipids. Preincubation with hydrogen peroxide in the concentration range 10^--⁷-^-10^--³M caused an increase in specific (—)-[¹²⁵I]-Iodocyanopindolol binding. possihly due to a decrease in membrane fluidity as a result of lipid peroxidation, thus making the receptor protein more accessible. Higher concentrations H₂O₂ reduced the specific (—)-[¹²⁵I]-lodocyanopindolol binding, which is most likely the effect of deterioration of the receptor protein by the more pronounced radical stress induced by these higher concentrations. Also adenylate cyclase activity was affected by radical stress. Basal cyclic-AMP production and cyclic-AMP production induced by NaF (10^--² M) or guanylylimidodiphosphate (10^--⁴ M), was suppressed after pretreatment with concentrations of H₂O₂ above 10^--⁴ M. This indicates a higher sensitivity of the adenylate cyclase toward radical stress when compared to the receptor protein. Our results show that radical stress can perturb β-adrenoceptor function considerably in the heart.     

Hydrogen Peroxide and the Proliferation of Bhk-21 Cells

Intracellular levels of H2O2 in BHK-21 cells are not static but decline progressively with cell growth. Exposure of cells to inhibitors of catalase, or glutathione peroxidase, not only diminishes this decline but also depresses rates of cell proliferation, suggesting important growth regulatory roles for those antioxidant enzymes. Other agents which also diminish the growth-associated decline in intracellular levels of H₂O₂, such as the superoxide dismutase mimic, copper II—(3,5-diisopropylsalicylate)₂, or docosahexaenoic acid, also reduced cell proliferation. In contrast, proliferation can be stimulated by the addition of 1 μM exogenous H₂O₂ to the culture medium. Under these conditions, however, intracellular levels of H₂O₂ are unaffected, whereas there is a reduction in intracellular levels of glutathione. It is argued that critical balances between intracellular levels of both H₂O₂ and glutathione are of significance in relation both to growth stimulation and inhibition. In addition growth stimulatory concentrations of H₂O₂, whilst initially leading to increased intracellular levels of lipid peroxidation breakdown products, appear to “trigger” their metabolism, possibly through aldehyde dehydrogenase, whose activity is also stimulated by H₂O₂     

Influence of chelators and iron ions on the production and degradation of H2O2 by beta-amyloid-copper complexes

β-Amyloid peptide (Aβ) 1–42, involved in the pathogenesis of Alzheimer’s disease, binds copper ions to form Aβ · Cu_n complexes that are able to generate H₂O₂ in the presence of a reductant and O₂. The production of H₂O₂ can be stopped with chelators. More reactive than H₂O₂ itself, hydroxyl radicals HO (generated when a reduced redox active metal complex interacts with H₂O₂) are also probably involved in the oxidative stress that creates brain damage during the disease. We report in the present work a method to monitor the effect of chelating agents on the production of hydrogen peroxide by metallo-amyloid peptides. The addition of H₂O₂ associated to a pre-incubation step between ascorbate and Aβ · Cu_n allows to study the formation of H₂O₂ but also, at the same time, its transformation by the copper complexes. Aβ · Cu_n peptides produce but do not efficiently degrade H₂O₂. The reported analytic method, associated to precipitation experiments of copper-containing amyloid peptides, allows to study the inhibition of H₂O₂ production by chelators. The action of a ligand such as EDTA is probably due to the removal of the copper ions from Aβ · Cu_n, whereas bidentate ligands such as 8-hydroxyquinolines probably act via the formation of ternary complexes with Aβ · Cu_n. The redox activity of these bidentate ligands can be modulated by the incorporation or the modification of substituents on the quinoline heterocycle.     

The Generation of Ferryl or Hydroxyl Radicals During Interaction of Haemproteins with Hydrogen Peroxide

The oxidation of 2-keto-4-thiomethyl butyric acid (KTBA) and methionine to ethylene has been used to evaluate generation of ferryl species or hydroxyl radicals by H₂O₂-_-activated haemproteins or free ferric ions. Hydrogen peroxide was generated by a glucose oxidase-glucose system at a rate of 1 μM/min. Free ferric in the presence of H₂O₂ oxidizes KTBA, and this was highly inhibited by hydroxyl radical scavengers, caeruloplasmin, superoxide dismutase (SOD) and EDTA. However, when metmyoglobin, methaemoglobin (MtHb) or horseradish peroxidase (HRP) were tested in the same model system, hydroxyl radical scavengers suppressed partially KTBA oxidation and caeruloplasmin, SOD and EDTA failed to inhibit the reaction. Cytochrome-c was found to be a weak promoter of KTBA oxidation in the presence of H₂O₂. Methionine was oxidized to ethylene by an active system which generates hydroxyl radicals, but not by H₂O₂-_-activated metmyoglobin. Ferric ions chelated to membranes or ADP in the presence of H₂O₂ generated enzymatically, initiated membranal lipid peroxidation only in the presence of ascorbic acid, and this was inhibited by EDTA. In contrast, metmyoglobin and methaemoglobin activated by H₂O₂ generated by the same system, initiated membranal lipid peroxidation and this was not inhibited by EDTA. It is concluded that ferryl and not HO. is the main oxidant in systems containing myoglobin and haemoglobin activated by low concentrations of H₂O₂.     

黑腹果蝇white基因在H2O2影响下卷翅形成中的作用及机理

卷翅是果蝇遗传学上最常用的标记之一,但卷翅形成的具体机制还不清楚.过去的研究发现,理化刺激影响果蝇卷翅的形成.我们最近研究发现,H₂O₂处理不仅会影响果蝇的羽化率,还会使其出现卷翅现象.本研究通过改变H₂O₂浓度、果蝇培养温度和H₂O₂处理时间,探讨影响黑腹果蝇卷翅形成的具体因素,并对其超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和谷胱甘肽过氧化物酶(GSH-PX)活力进行检测,探讨H₂O₂对果蝇抗氧化能力的影响.结果表明: 果蝇的羽化率与H₂O₂浓度成反比.温度、H₂O₂浓度和H₂O₂处理时间的改变均会影响果蝇翅的卷曲程度和卷翅果蝇所占的比例.其中white基因突变果蝇对这3种条件反应最明显,mini-white(white基因回复突变)果蝇却可以拯救该表型,它的反应与野生型OR相似.H₂O₂对含Cy基因的果蝇卷翅的形成也有一定的影响,可以加大果蝇翅的卷曲程度.对SOD、CAT和GSH-PX活力检测发现,H₂O₂处理会使果蝇的抗氧化能力降低.实时荧光定量PCR检测发现,H₂O₂处理会导致果蝇基因表达量发生改变.黑腹果蝇卷翅形成是一个十分复杂的过程,H₂O₂可能作为某种信号分子或是间接影响某种因子参与黑腹果蝇的卷翅形成过程.该卷翅形成过程可能与Cy基因导致的果蝇卷翅过程是同一个信号途径,两者也可能是通过不同的模式进行调控的.     

The role of H2O2 as a mediator of UVB-induced apoptosis in keratinocytes

Apoptosis is an active form of cell death that is initiated by a variety of stimuli, including reactive oxygen species (ROS) and ultraviolet (UV) radiation. Previously, it has been reported that UVB-irradiation of keratinocytes leads to intracellular generation of hydrogen peroxide (H₂O₂) and that antioxidants can inhibit ROS-induced apoptosis. Although both UVB-irradiation and H₂O₂-incubation led to increased intracellular H₂O₂ levels, the antioxidants catalase and glutathione monoester (GME), inhibited apoptosis only when induced by H₂O₂, not by UVB. Furthermore, extracellular signal-regulated kinase (ERK), a prominent member of the mitogen-activated protein kinase (MAPK) family, was found to be activated by treatment with both UVB and H₂O₂. Inhibition of ERK phosphorylation by pre-treatment with PD98059 resulted in enhanced apoptosis after H₂O₂-exposure. However, no significant difference of apoptosis was observed between cells with and without inhibitor pre-treatment upon UVB-irradiation. DNA damage in the form of cyclobutane pyrimidine dimers was observed after exposure to UVB, but no photoproducts were found in H₂O₂-treated cells. These results suggest a ROS-independent pathway of UVB-induced apoptosis. Although UVB-irradiation causes moderate increase in H₂O₂, the generation of H₂O₂ does not contribute to the induction of apoptosis. Moreover, activation of ERK only blocks H₂O₂-dependent apoptosis but has no impact on UVB-induced apoptosis.     

Oxidative modification of human low-density lipoprotein by horseradish peroxidase in the absence of hydrogen peroxide

Heme-peroxidases, such as horseradish peroxidase (HRP), are among the most popular catalysts of low density lipoprotein (LDL) peroxidation. In this model system, a suitable oxidant such as H₂O₂ is required to generate the hypervalent iron species able to initiate the peroxidative chain. However, we observed that traces of hydroperoxides present in a fresh solution of linoleic acid can promote lipid peroxidation and apo B oxidation, substituting H₂O₂.

Spectral analysis of HRP showed that an hypervalent iron is generated in the presence of H₂O₂ and peroxidizing linoleic acid. Accordingly, careful reduction of the traces of linoleic acid lipid hydroperoxide prevented formation of the ferryl species in HRP and lipid peroxidation. However, when LDL was oxidized in the presence of HRP, the ferryl form of HRP was not detectable, suggesting a Fenton-like reaction as an alternative mechanism. This was supported by the observation that carbon monoxide, a ligand for the ferrous HRP, completely inhibited peroxidation of LDL.

These results are in agreement with previous studies showing that myoglobin ferryl species is not produced in the presence of phospholipid hydroperoxides, and emphasize the relevance of a Fenton-like chemistry in peroxidation of LDL and indirectly, the role of pre-existing lipid hydroperoxides.     

Inactivation of Yeast Glutathione Reductase by Fenton Systems: Effect of Metal Chelators, Catecholamines and Thiol Compounds

Oxygen radical generating systems, namely, Cu(II)/ H₂O₂, Cu(II)/ascorbate, Cu(II)/NAD(P)H, Cu(II)/ H₂O₂/catecholamine and Cu(II)/H₂O₂/SH-compounds irreversibly inhibited yeast glutathione reductase (GR) but Cu(II)/H₂O₂ enhanced the enzyme diaphorase activity. The time course of GR inactivation by Cu(II)/H₂O₂ depended on Cu(II) and H₂O₂ concentrations and was relatively slow, as compared with the effect of Cu(II)/ascorbate. The fluorescence of the enzyme Tyr and Trp residues was modified as a result of oxidative damage. Copper chelators, catalase, bovine serum albumin and HO^˙ scavengers prevented GR inactivation by Cu(II)/H₂O₂ and related systems. Cysteine, N-acetylcysteine, N-(2-dimercaptopropi-onylglycine and penicillamine enhanced the effect of Cu(II)/H₂O₂ in a concentration- and time-dependent manner. GSH, Captopril, dihydrolipoic acid and dithiotreitol also enhanced the Cu(II)/H₂O₂ effect, their actions involving the simultaneous operation of pro-oxidant and antioxidant reactions. GSSG and try-panothione disulfide effectively protected GR against Cu(II)/H₂O₂ inactivation. Thiol compounds prevented GR inactivation by the radical cation ABTS*⁺. GR inactivation by the systems assayed correlated with their capability for HO* radical generation. The role of amino acid residues at GR active site as targets for oxygen radicals is discussed.     

Hydrogen Peroxide Modification of Human Oxyhemoglobin

The effect of H₂O₂ on the primary structure of OxyHb was studied. Upon treatment of Oxy Hb with H₂O₂ ([Heme]/[H₂O₂] =I), tryptophan and methionine residues of the /-chain were modified. Treatment of ApoHb with H₂O₂ resulted in the modification of histidine and methionine residues in both globin chains. Tryptophan residues were unaffected. Modification of methionine residues in both the β-chain of OxyHb and ApoHb probably results from the direct oxidation of mcthionine by H₂O₂. The modification of histidine residues in ApoHb may be mediated by a metal-catalyzed oxidation system comprised of H₂O₂ and histidine-bound iron. The H₂O₂-mediated modification of tryptophan in the OxyHb β-chain. however, requires the heme moiety.     

亚适宜温光盐环境下油菜素内酯对黄瓜幼苗抗氧化系统及光合作用的影响

研究了24 表油菜素内酯(EBR)对亚适宜温光盐环境下黄瓜幼苗抗氧化系统及光合作用的影响.结果表明: 与对照相比,亚适宜温光盐环境下黄瓜幼苗叶片H₂O₂含量增加,膜脂过氧化程度加剧,膜透性增强,净光合速率(P_n)、气孔导度(g_s)、胞间CO₂浓度(C_i)和蒸腾速率(T_r)分别显著下降39.3%、40.0%、21.2%和47.2%,幼苗干物质积累减少35.9%.外源喷施EBR可提高亚适宜温光盐环境下黄瓜幼苗的抗氧化酶活性,降低H₂O₂含量及膜透性,缓解亚适宜温光盐环境下P_n、g_s、T_r的下降幅度,幼苗干物质积累增加25.9%,生长加快．EBR可通过调节亚适宜温光盐环境下黄瓜幼苗抗氧化性,减少其膜脂过氧化程度,进而维持其较高的光合性能,有效促进了亚适宜温光盐环境下黄瓜幼苗的生长．     

Nitric oxide (as sodium nitroprusside) supplementation ameliorates Cd toxicity in hydroponically grown wheat roots

Cadmium (Cd) is a non-redox toxic heavy metal present in the environment and induces oxidative stress in plants. We investigated whether exogenous nitric oxide (NO) supplementation as sodium nitroprusside (SNP) has any ameliorating action against Cd-induced oxidative damage in plant roots and thus protective role against Cd toxicity. Cd treatment (50 or 250 μM) alone or in combination with 200 μM SNP was given to hydroponically grown wheat roots for a short time period of 24 h and then these were shifted to distilled water to observe changes in levels of oxidative markers (lipid peroxidation, H₂O₂ content and electrolyte leakage). Supplementation of Cd with SNP significantly reduced the Cd-induced lipid peroxidation, H₂O₂ content and electrolyte leakage in wheat roots. It indicated a reactive oxygen species (ROS) scavenging activity of NO. However, even upon removal of Cd-treatment solution, the levels of oxidative markers increased during 24 h recovery stage and later at 48 h these decreased. Cd treatment resulted in an upregulation of activities of antioxidant enzymes—superoxide dismutase (SOD, 1.15.1.1), guaiacol peroxidase (GPX, 1.11.1.7), catalase (CAT, 1.11.1.6), and glutathione reductase (GR, 1.6.4.2). SNP supply resulted in a reduction in Cd-induced increased activities of scavenging enzymes. The protective role of exogenous NO in decreasing Cd-induced oxidative damage was also evident from the histochemical localization of lipid peroxidation, plasma membrane integrity and superoxides. The study concludes that an exogenous supply of NO protects wheat roots from Cd-induced toxicity.