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1.
《Free radical research》2013,47(1):499-508
The hydrogen peroxide dependent oxidation of the epinephrinecopper complex to adrenochrome is mediated by free copper ions. The oxidation is enhanced by chloride ions and by the presence of serum albumin. The reaction is not inhibited by SOD or by hydroxyl radical scavengers.

The 2:1 epinephrine or dopamine:Cu(II) complexes are able to bind to DNA and to catalyze its oxidative destruction in the presence of hydrogen peroxide. The DNA-epinephrine-Cu(II) terenary complex has characteristic spectral properties. It has the capacity to catalyze the reduction of oxygen or H2O2 and it preserves the capacity over a wide range of comp1ex:DNA ratios. The rate of DNA cleavage is proportional to the rate of epinephrine oxidation and the rate determining step of the reaction Seems to be the reduction of free Cu(II) ions. The ability to form redox active stable DNA ternary complexes, suggests that under specific physiological conditions, when “free” copper ions are available. catecholamina may induce oxidative degradation of DNA and other biological macromolecules.  相似文献   

2.
The inactivation of the water-soluble form of bovine adrenal dopamine β-monooxygenase by H2O2 and by ascorbate was studied. Inactivation by H2O2 was slow for the copper-free apoenzyme, but addition of copper gave a rapid inactivation. The results presented indicate that the enzyme-bound copper during this inactivation catalyzes partial destruction of its own binding site. The reaction orders for the inactivation by H2O2 seem to be 1.0 with respect to the enzyme and in the range 0.6 to 0.8 with respect to H2O2. The rate of inactivation obtained in the presence of ascorbate increases with addition of copper and is faster than that obtained by similar concentrations of H2O2. The data could not, however, be used to decide whether the inactivation by ascorbate was catalyzed by the enzymebound copper. The inactivation reaction in the presence of ascorbate seems to be of first order with respect to ascorbate at ascorbate concentrations less than 40 μm and decreases toward zero as the ascorbate concentration is increased. Experiments with the Cu(I)-chelator, bathocuproine disulfonate, revealed that inactivation led to weaker binding of copper to the protein, and this effect was more pronounced with H2O2 than with ascorbate.  相似文献   

3.
A novel bacterial species identified as Exiguobacterium sp. RD3 degraded the diazo dye reactive yellow 84A (50 mg l−1) within 48 h at static condition, at 30°C and pH 7. Lower salinity conditions were found to be favorable for growth and decolorization. Enzymatic activities of an H2O2 independent oxidase along with laccase and an azoreductase suggest their prominent role during the decolorization of reactive yellow 84A. Presence of an H2O2 independent oxidase in Exiguobacterium sp. RD3 was confirmed and hydrogen peroxide produced was detected by a coupled iodometric assay. Azoreductase activity was prominent in presence of cofactors NADH and NADP in mineral salt medium. Considerable depletion of COD of the dye solution during degradation of dye was indicative of conversion of complex dye into simple oxidizable products. Products of degradation were analyzed by HPLC, FTIR and GCMS. A possible product of the degradation was identified by GCMS. Degradation of dye resulted with significant reduction of phytotoxicity, confirming the environmentally safe nature of the degradation metabolites.  相似文献   

4.
Described are further studies directed towards elucidating the mechanism of the nitric oxide reduction of the copper(II) model system, Cu(dmp)2(2+) (I, dmp=2,9-dimethyl-1,10-phenanthroline). The reaction of I with NO in methanol results in the formation of Cu(dmp)2+ (II) and methyl nitrite (CH3ONO), with a second order rate constant kNO=38.1 M-1 s-1 (298K). The activation parameters for this reaction in buffered aqueous medium were measured to be DeltaH(double dagger)=41.6 kJ/mol and DeltaS(double dagger)=-82.7 kJ/mol deg. The addition of azide ion (N3-) as a competing nucleophile results in a marked acceleration in the rate of the copper(II) reduction. Analysis of the kinetics for the NO reduction of the bulkier Cu(dpp)(2)2+ (IV, dpp=2,9-diphenyl-1,10-phenanthroline) and the stronger oxidant, Cu(NO2-dmp)2(2+) (V, NO2-dmp=5-nitro-2,9-dimethyl-1,10-phenanthroline), gave the second order rate constants kNO=21.2 and 29.3 M-1 s-1, respectively. These results argue against an outer sphere electron transfer pathway and support a mechanism where the first step involves the formation of a copper-nitrosyl (Cu(II)-NO or Cu(I)-NO+) adduct. This would be followed by the nucleophilic attack on the bound NO and the labilization of RONO to form the nitrite products and the cuprous complex.  相似文献   

5.
The interaction of a series of mixed ligand complexes of the type [Ru(NH3)4(diimine)]Cl2, where diimine=2,2-bipyridine (bipy), 1,10-phenanthroline (phen), 5,6-dimethyl-1,10-phenanthroline (5,6-dmp), 4,7-dimethyl-1,10-phenanthroline (4,7-dmp), 2,9-dimethyl-1,10-phenanthroline (2,9-dmp), 3,4,7,8-tetra-methyl-1,10-phenanthroline (Me4phen), with calf thymus DNA has been studied using absorption, emission and circular dichroic spectral measurements and viscometry and electrochemical techniques. On interaction with DNA the complexes show hypochromism and red-shift in their MLCT band suggesting that the complexes bind to DNA. The magnitude of the binding constant (Kb) obtained from absorption spectral titration varies depending upon the nature of the diimine ligand: Me4phen > 5,6-dmp > 4,7-dmp > phen suggesting the use of diimine ‘face’ of the octahedral complexes in binding to DNA. The interaction of phen complex possibly involves phen ring partially inserted into the DNA base pairs. In contrast, the methyl-substituted phen complexes would involve hydrophobic interaction of the phen ring in the grooves of DNA, which is supported by hydrogen bonding interactions of the ammonia ligands with the intrastrand nucleobases. Also the shape and size of the phen ligand as modified by the methyl substituents determine the DNA binding site sizes (0.12-0.45 base pairs). The relative emission intensities (I/I0) of the DNA-bound complexes parallel the variation in Kb values. Almost all the metal complexes exhibit induced CD bands on binding to B DNA, with the 4,7-dmp and Me4phen complexes inducing certain structural modifications on the biopolymer. DNA melting curves obtained in the presence of metal complexes reveal a monophasic melting of the DNA strands, the Me4phen complex exhibiting a slightly enhanced tendency to stabilize the double-stranded DNA. There were slight to appreciable changes in the relative viscosities of DNA, which are consistent with enhanced hydrophobic interaction of the methyl-substituted phen rings. Upon interaction with CT DNA, the Me4phen, 4,7-dmp and 5,6-dmp complexes, in contrast to bipy, phen and 2,9-dmp complexes, show a decrease in anodic peak current in their cyclic voltammograms suggesting that they exhibit enhanced DNA binding. DNA cleavage experiments show that all the complexes induce cleavage of pBR322 plasmid DNA, the Me4phen and 5,6-dmp complexes being remarkably more efficient than other complexes.  相似文献   

6.
A novel effect of the inhibition of the decomposition of amino acids to carbonates on addition of imidazole (HIm) to a reacting system containing equimolar amounts of copper and zinc metal powders, an amino acid [glycine (Hgly), aspartic acid (H2Asp) or glycylglycine (H2gg)] (1:1:2) and excess hydrogen peroxide (H2O2) resulting in formation of a mixed metal mixed ligand peroxo complex compound was observed, because in the absence of imidazole the corresponding reaction system yields only a mixed metal peroxo carbonate. For the resulting complex compounds, the homogeneity, i.e. [Cu(Zn)(O2 2–)(Gly)2(HIm)(H2O)], [Cu(Zn)(O2 2–)(Asp)(HIm)(H2O)2] or [Cu(Zn)2(O2 2–)2(gg)(HIm)(H2O)4], molecular formula, presence of peroxo group and coordination environment were established by combined physicochemical evidence from elemental and thermogravimetric analysis in air and argon atmospheres, electron spin resonance and electronic and IR spectral data. It is noteworthy to mention that the corresponding carboxylic acids of the above-mentioned amino acids, i.e. acetic and succinic acids, either do not decompose to carbonates in the absence of imidazole or form novel homogeneous peroxo mixed metal mixed ligand complex compounds as described above in the presence of imidazole. This suggests an important and significant mutual influence (in vitro) of biologically active chromophores like peroxo ions, imidazole and amino groups in the above-mentioned chemical reactions containing bioactive metals such as copper and zinc.  相似文献   

7.
Hongli Wu  Marjorie F. Lou 《BBA》2010,1797(10):1705-2117
Glutaredoxin 2 (Grx2) belongs to the oxidoreductase family and is an isozyme of glutaredoxin 1 (Grx1) present in the mitochondria, however its function is not well understood. The purpose of this study is to evaluate the potential anti-apoptotic function of Grx2 by examining its ability to protect complex I in the mitochondrial electron transport system using human lens epithelial cells as a model. We found that cells treated with 200 μM hydrogen peroxide (H2O2) for 24 h exhibited decreased viability and became apoptotic with corresponding Bax up-regulation, Bcl-2 down-regulation, caspase 3 activation and mitochondrial cytochrome c leakage. Grx2 over-expression (OE) could protect cells against H2O2-induced damage while Grx2 knockdown (KD) showed the opposite effect. Under the same conditions, H2O2 treatment caused 50% inactivation of complex I activity in control cells (vector only), 75% in Grx2 KD cells but only 20% in Grx2 OE cells. Furthermore, the inactivated complex I in the H2O2-treated cells could be protected mostly by importing the purified nascent Grx2 protein, but not the Grx2 protein mutated at the active site with C70S, or C73S, or with C70S plus C73S. Immunoprecipitation study also revealed that Grx2 co-precipitated with complex I, but not complex II, in the mitochondrial lysate. Thus, the mechanism of Grx2 protection against H2O2-induced apoptosis is likely associated with its ability to preserve complex I.  相似文献   

8.
Complex I (NADH-ubiquinone reductase) and Complex III (ubiquinol-cytochrome c reductase) supplemented with NADH generated O2? at maximum rates of 9.8 and 6.5 nmol/min/mg of protein, respectively, while, in the presence of superoxide dismutase, the same systems generated H2O2 at maximum rates of 5.1 and 4.2 nmol/min/mg of protein, respectively. H2O2 was essentially produced by disproportionation of O2?, which constitutes the precursor of H2O2. The effectiveness of the generation of oxygen intermediates by Complex I in the absence of other specific electron acceptors was 0.95 mol of O2? and 0.63 mol of H2O2/mol of NADH. A reduced form of ubiquinone appeared to be responsible for the reduction of O2 to O2?, since (a) ubiquinone constituted the sole common major component of Complexes I and III, (b) H2O2 generation by Complex I was inhibited by rotenone, and (c) supplementation of Complex I with exogenous ubiquinones increased the rate of H2O2 generation. The efficiency of added quinones as peroxide generators decreased in the order Q1 > Q0 > Q2 > Q6 = Q10, in agreement with the quinone capacity of acting as electron acceptor for Complex I. In the supplemented systems, the exogenous quinone was reduced by Complex I and oxidized nonenzymatically by molecular oxygen. Additional evidence for the role of ubiquinone as peroxide generator is provided by the generation of O2? and H2O2 during autoxidation of quinols. In oxygenated buffers, ubiquinol (Q0H2), benzoquinol, duroquinol and menadiol generated O2? with k3 values of 0.1 to 1.4 m? · s?1 and H2O2 with k4 values of 0.009 to 4.3 m?1 · s?1.  相似文献   

9.
《Free radical research》2013,47(1):479-488
Washed or growing E. coli cells are killed by epinephrine, norepinephrine or dopamine in the presence of non lethal concentrations of Cu(II). Killing is enhanced by anoxia and by sublethal Concentrations of H2O1. The rate of killing is proportional to the rate of catecholamine oxidation. The copper epinephrine complex binds to E. coli cells, induces membrane damage and depletion of the cellular ATP pool. The cells may be partially protected by SOD or catalase but not by OH radical scavengers. Addition of H2O2 to cells which were sensitized by preincubation with the epinephrine-copper complex, causes rapid killing and DNA degradation. Sensitized cells are not protected by BSA.  相似文献   

10.
Summary.  In cell suspension cultures of Nicotiana tabacum L. cv. Bright Yellow 2 (BY-2) a rapid and concentration-dependent accumulation of H2O2 is induced by excess concentrations of copper (up to 100 μM). This specific and early response towards copper stress was shown to be extracellular. Addition of 300 U of catalase per ml decreased the level of H2O2. Superoxide dismutase (5 U/ml) induced an increase in H2O2 production by 22.2%. This indicates that at least part of the H2O2 is produced by dismutation of superoxide. Pretreatment of the cell cultures with the NAD(P)H oxidase inhibitors diphenylene iodonium (2 and 10 μM) and quinacrine (1 and 5 mM) prevented the generation of H2O2 under copper stress for 90%. The influence of the pH on the H2O2 production revealed the possible involvement of cell-wall-dependent peroxidases in the generation of reactive oxygen species after copper stress. Received May 20, 2002; accepted July 26, 2002; published online May 21, 2003 RID="*" ID="*" Correspondence and reprints: Plant Physiology, Department of Biology, University of Antwerp (RUCA), Groenenborgerlaan 171, 2020 Antwerp, Belgium.  相似文献   

11.
Particulate methane monooxygenase (pMMO), a copper-containing membrane protein, catalyzes methane hydroxylation under aerobic conditions. We found that the activity of pMMO was increased by catalase, implying that hydrogen peroxide (H2O2) is generated by pMMO with duroquinol, an electron donor for pMMO, and that the generated H2O2 inhibits pMMO activity. In addition, reversible inhibition of pMMO with H2O2 was observed upon treatment of pMMO with H2O2 followed by the addition of catalase, and H2O2 formation by pMMO with duroquinol was detected using a fluorescence probe. The redox behavior of type 2 copper in pMMO measured by the electron paramagnetic resonance revealed that H2O2 re-oxidizes the type 2 copper in pMMO reduced with duroquinol.  相似文献   

12.
Metals can potentially play a role in the non-enzymatic processes involved in wood biodegradation. Dihydroxybenzenes reduce Cu(II)–Cu(I), which then react with H2O2 driving a Fenton reaction. In this work the degradation of veratryl alcohol (VA), the simplest non-phenolic lignin model compound, via a cuprous Fenton reaction mediated by 1,2-dihydroxybenzene (catechol, CAT) was studied. A factorial experimental design was performed to assess the impact of several experimental variables including, pH, and CAT, CuCl2 and H2O2 concentrations on VA degradation. Optimized conditions were determined using a response surface modeling methodology (RSM). The greatest amount of VA degradation occurred at a CAT:CuCl2:H2O2 ratio of 0.287:0.313:4.062, a pH of 3.6. A time-course measurement for VA degradation was performed under these experimental conditions and after an 8 h reaction period, 31% of the VA was degraded. Under the same experimental conditions, VA degradation by an iron CAT-driven Fenton reaction was more effective than the copper CAT-driven Fenton reaction. In a similar experiment, carboxymethyl cellulose (CMC) depolymerization was also determined. Only the iron CAT-driven Fenton reaction was found to depolymerize CMC. We suggest that the greater redox potential of the Fe(III)CAT complex compared to the Cu(II)CAT complex would dictate that under most environmental conditions, degradation of VA would occur by the iron complex only. This research has important implications for the mechanisms of brown rot fungal degradation in wood because it eliminates a pathway that had previously been proposed as a mechanism explaining free radical generation in the oxidative depolymerization of cellulose in the cell wall.  相似文献   

13.
14.
Human myeloperoxidase (MPO) uses hydrogen peroxide generated by the oxidative burst of neutrophils to produce an array of antimicrobial oxidants. During this process MPO is irreversibly inactivated. This study focused on the unknown role of hydrogen peroxide in this process. When treated with low concentrations of H2O2 in the absence of reducing substrates, there was a rapid loss of up to 35% of its peroxidase activity. Inactivation is proposed to occur via oxidation reactions of Compound I with the prosthetic group or amino acid residues. At higher concentrations hydrogen peroxide acts as a suicide substrate with a rate constant of inactivation of 3.9 × 10−3 s−1. Treatment of MPO with high H2O2 concentrations resulted in complete inactivation, Compound III formation, destruction of the heme groups, release of their iron, and detachment of the small polypeptide chain of MPO. Ten of the protein’s methionine residues were oxidized and the thermal stability of the protein decreased. Inactivation by high concentrations of H2O2 is proposed to occur via the generation of reactive oxidants when H2O2 reacts with Compound III. These mechanisms of inactivation may occur inside neutrophil phagosomes when reducing substrates for MPO become limiting and could be exploited when designing pharmacological inhibitors.  相似文献   

15.
A new heptadentate compartmental ligand has been synthesized by condensation of 3-formylsalicylic acid and 1,5-diamino-3-thiapentane in methanol (H4La). This Schiff base contains an inner N2SO2 and an outer O2O2 site and gives, by reaction with copper(II), nickel(II) and uranyl(VI) diacetate, mononuclear, homo- and heterobinuclear complexes. In the mononuclear copper and nickel complexes, the metal ion is in the inner N2SO2 site, while it is in the outer O2O2 for uranyl; a solvent molecule fills the fifth equatorial coordination position in this last complex. The physico-chemical properties of the compounds are discusscd on the basis of infrared, electronic and magnetic data and by comparison with the analogous complexes with the ligand obtained by reaction of 3- formylsalicylic acid and diethylenetriamine (H4Lb). The mononuclear copper and the heterodinuclear copper-uranyl complexes show anomalously low magnetic moments.  相似文献   

16.
To determine the relationship between dietary selenium (Se) deficiency or excess and liver hydrogen peroxide (H2O2) metabolism in chickens, 1-day-old chickens received insufficient Se (0.028 mg Se per kg of diet) or excess Se (3.0 or 5.0 mg Se per kg of diet) in their diets for 8 weeks. Body and liver weight changes, alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities, H2O2 content, and activities and mRNA levels of enzymes associated with H2O2 metabolism (catalase (CAT) and superoxide dismutase (SOD) 1–3) were determined in the liver. This study showed that Se deficiency or excess Se intake elicited relative severe changes. Se deficiency decreased growth, while Se excess promoted growth in chickens. Both diets vastly altered the liver function, but no obvious histopathological changes were observed in the liver. Se deficiency significantly lowered SOD and CAT activities, and the H2O2 content in the liver and serum increased. Se excess (3.0 mg/kg) decreased SOD and CAT activities with changes in their mRNA levels, and the H2O2 content increased. The larger Se excess (5.0 mg/kg) showed more serious effects but was not fatal. These results indicated that the H2O2 metabolism played a destructive role in the changes in bird liver function induced by Se deficiency or excess.  相似文献   

17.
Abstract

The objectives of this study were to develop a robust protocol to measure the rate of hydrogen peroxide (H2O2) production in isolated perfused rat lungs, as an index of oxidative stress, and to determine the cellular sources of the measured H2O2 using the extracellular probe Amplex red (AR). AR was added to the recirculating perfusate in an isolated perfused rat lung. AR’s highly fluorescent oxidation product resorufin was measured in the perfusate. Experiments were carried out without and with rotenone (complex I inhibitor), thenoyltrifluoroacetone (complex II inhibitor), antimycin A (complex III inhibitor), potassium cyanide (complex IV inhibitor), or diohenylene iodonium (inhibitor of flavin-containing enzymes, e.g. NAD(P)H oxidase or NOX) added to the perfusate. We also evaluated the effect of acute changes in oxygen (O2) concentration of ventilation gas on lung rate of H2O2 release into the perfusate. Baseline lung rate of H2O2 release was 8.45?±?0.31 (SEM) nmol/min/g dry wt. Inhibiting mitochondrial complex II reduced this rate by 76%, and inhibiting flavin-containing enzymes reduced it by another 23%. Inhibiting complex I had a small (13%) effect on the rate, whereas inhibiting complex III had no effect. Inhibiting complex IV increased this rate by 310%. Increasing %O2 in the ventilation gas mixture from 15 to 95% had a small (27%) effect on this rate, and this O2-dependent increase was mostly nonmitochondrial. Results suggest complex II as a potentially important source and/or regulator of mitochondrial H2O2, and that most of acute hyperoxia-enhanced lung rate of H2O2 release is from nonmitochondrial rather than mitochondrial sources.  相似文献   

18.
A new heptadentate compartmental ligand has been synthesized by condensation of 3-formylsalicylic acid and 1,5-diamino-3-thiapentane in methanol (H4La). This Schiff base contains an inner N2SO2 and an outer O2O2 site and gives, by reaction with copper(II), nickel(II) and uranyl(VI) diacetate, mononuclear, homo- and heterobinuclear complexes. In the mononuclear copper and nickel complexes, the metal ion is in the inner N2SO2 site, while it is in the outer O2O2 for uranyl; a solvent molecule fills the fifth equatorial coordination position in this last complex. The physico-chemical properties of the compounds are discusscd on the basis of infrared, electronic and magnetic data and by comparison with the analogous complexes with the ligand obtained by reaction of 3- formylsalicylic acid and diethylenetriamine (H4Lb). The mononuclear copper and the heterodinuclear copper-uranyl complexes show anomalously low magnetic moments.  相似文献   

19.
According to different studies, the interaction between amyloid β-peptide (Aβ) and copper ions could yield radical oxygen species production, in particular the highly toxic hydroxyl radical OH· that is suspected to contribute to Alzheimer’s disease pathogenesis. Despite intensive experimental and computational studies, the nature of the interaction between copper and Aβ peptide, as well as the redox reactivity of the system, are still matter of debate. It was proposed that in Cu(II) → Cu(I) reduction the complex Cu(II)–Aβ could follow a multi-step conformational change with redox active intermediates that may be responsible for OH· radical production from H2O2 through a Fenton-like process. The purpose of this work is to evaluate, using ab initio Density Functional Theory computations, the reactivity of different Cu(I)–Aβ coordination modes proposed in the literature, in terms of OH· production. For each coordination model, we considered the corresponding H2O2 adduct and performed a potential energy surface scan along the reaction coordinate of O–O bond dissociation of the peroxide, resulting in the production of OH· radical, obtaining reaction profiles for the evaluation of the energetic of the process. This procedure allowed us to confirm the hypothesis according to which the most populated Cu(I)–Aβ two-histidine coordination is not able to perform efficiently H2O2 reduction, while a less populated three-coordinated form would be responsible for the OH· production. We show that coordination modes featuring a third nitrogen containing electron-donor ligand (an imidazole ring of an histidine residue is slightly favored over the N-terminal amine group) are more active towards H2O2 reduction.  相似文献   

20.
Reactive oxygen species are byproducts of mitochondrial respiration and thus potential regulators of mitochondrial function. Pyruvate dehydrogenase kinase 2 (PDHK2) inhibits the pyruvate dehydrogenase complex, thereby regulating entry of carbohydrates into the tricarboxylic acid (TCA) cycle. Here we show that PDHK2 activity is inhibited by low levels of hydrogen peroxide (H2O2) generated by the respiratory chain. This occurs via reversible oxidation of cysteine residues 45 and 392 on PDHK2 and results in increased pyruvate dehydrogenase complex activity. H2O2 derives from superoxide (O2˙̄), and we show that conditions that inhibit PDHK2 also inactivate the TCA cycle enzyme, aconitase. These findings suggest that under conditions of high mitochondrial O2˙̄ production, such as may occur under nutrient excess and low ATP demand, the increase in O2˙̄ and H2O2 may provide feedback signals to modulate mitochondrial metabolism.  相似文献   

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