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1.
Copper Fenton systems (Cu(II)/H 2O 2 and Cu(II)/Asc) inactivated the lipoamide reductase and enhanced the diaphorase activity of pig-heart lipoamide dehydrogenase (LADH). Cupric ions alone were less effective. As a result of Cu(II)/H 2O 2 treatment, the number of titrated thiols in LADH decreased from 6 to 1 per subunit. NADH and ADP (not NAD + or ATP) enhanced LADH inactivation by Cu(II). NADH also enhanced the effect of Cu(II)/H 2O 2. Dihydrolipoamide, dihydrolipoic acid, Captopril, acetylcysteine, EDTA, DETAPAC, histidine, bathocuproine, GSSG and trypanothione prevented LADH inactivation. 100 μM GSH, DL-dithiothreitol, N-(2-mercaptopropionylglicine) and penicillamine protected LADH against Cu(II)/Asc and Cu(II), whereas 1.0 mm GSH and DL-dithiothreitol also protected LADH against Cu(II)/H 2O 2. Allopurinol provided partial protection against Cu(II)/H 2O 2. EthanoI, mannitol, Na benzoate and superoxide dismutase failed to prevent LADH inactivation by Cu(II)/H 2O 2 or Cu(II). Catalase (native or denaturated) and bovine serum albumin protected LADH but that protection should be due to Cu binding. LADH inhibited deoxyribose oxidation and benzoate hydroxylation by Cu(II)/H 2O 2. It is concluded that site-specifically generated HO, radicals were responsible for LADH inactivation by Cu(II) Fenton systems. The latter effect is discussed in the context of ischemia-reoxygenation myocardial injury. 相似文献
2.
Although thiourea has been used widely to study the role of hydroxyl radicals in metal-mediated biological damage, it is not a specific hydroxyl radical scavenger and may also exert antioxidant effects unrelated to hydroxyl radical scavenging. Thus, we investigated the effects of thiourea on copper-induced oxidative damage to bovine serum albumin (1 mg/ml) in three different copper-containing systems: Cu(II)/ascorbate, Cu(II)/H 2O 2, and Cu(II)/H 2O 2/ascorbate [Cu(II), 0.1 mM; ascorbate, 1 mM; H 2O 2, 1 mM]. Oxidative damage to albumin was measured as protein carbonyl formation. Thiourea (0.1–10 mM) provided marked and dose-dependent protection against protein oxidation in all three copper-containing systems. In contrast, only minor protection was observed with dimethyl sulfoxide and mannitol, even at concentrations as high as 100 mM. Strong protection was also observed with dimethylthiourea, but not with urea or dimethylurea. Thiourea also significantly inhibited copper-catalyzed oxidation of ascorbate, and competed effectively with histidine and 1,10-phenanthroline for binding of cuprous, but not cupric, copper, as demonstrated by both UV-visible and low temperature electron spin resonance measurements. We conclude that the protection by thiourea against copper-mediated protein oxidation is not through scavenging of hydroxyl radicals, but rather through the chelation of cuprous copper and the formation of a redox-inactive thiourea-copper complex. 相似文献
3.
Incubation of rat-liver microsomes, previously azide-treated to inhibit catalase, with H 2O 2 caused a loss of cytochrome P-450 but not of cytochrome b 5. 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 H 2O 2 induces lipid peroxidation, but this was found to be due largely or completely to an effect of H 2O 2 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. H 2O 2 inhibited ascorbate/Fe (III)-induced microsomal lipid peroxidation, but part of this effect was due to an action of H 2O 2 in the TBA test itself. H 2O 2 also decreased the colour measured after carrying out the TBA test upon authentic malondialdehyde, tetraethoxypropane, a DNA-Cu 2+/ 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 H 2O 2. 相似文献
4.
Dihydrolipoamide dehydrogenase (LADH) lipoamide reductase activity decreased whereas enzyme diaphorase activity increased after LADH treatment with myeloperoxidase (MPO) dependent systems (MPO/H 2O 2/halide, MPO/NADH/halide and MPO/H 2O 2/nitrite systems. LADH inactivation was a function of the composition of the inactivating system and the incubation time. Chloride, iodide, bromide, and the thiocyanate anions were effective complements of the MPO/H 2O 2 system. NaOCl inactivated LADH, thus supporting hypochlorous acid (HOCl) as putative agent of the MPO/H 2O 2/NaCl system. NaOCl and the MPO/H 2O 2/NaCl system oxidized LADH thiols and NaOCl also oxidized LADH methionine and tyrosine residues. LADH inactivation by the MPO/ NADH/halide systems was prevented by catalase and enhanced by superoxide dismutase, in close agreement with H 2O 2 production by the LADH/NADH system. Similar effects were obtained with lactoperoxidase and horseradish peroxidase suplemented systems. L-cysteine, N-acetylcysteine, penicillamine, N-(2-mercaptopropionylglycine), Captopril and taurine protected LADH against MPO systems and NaOCl. The effect of the MPO/H 2O 2/NaNO 2 system was prevented by MPO inhibitors (sodium azide, isoniazid, salicylhydroxamic acid) and also by L-cysteine, L-methionine, L-tryptophan, L-tyrosine, L-histidine and reduced glutathione. The summarized observations support the hypothesis that peroxidase-generated “reactive species” oxidize essential thiol groups at LADH catalytic site. 相似文献
5.
Dihydrolipoamide dehydrogenase (LADH) from Trypanosoma cruzi was inactivated by treatment with myeloperoxidase (MPO)-dependent systems. With MPO/H 2O 2/NaCl, LADH lipoamide reductase and diaphorase activities significantly decreased as a function of incubation time. Iodide, bromide, thiocyanide and chloride effectively supplemented the MPO/H 2O 2 system, KI and NaCl being the most and the least effective supplements, respectively. LADH inactivation by MPO/H 2O 2/NaCl and by NaOCl was similarly prevented by thiol compounds such as GSH, L-cysteine, N-acetylcysteine, penicillamine and N-(2-mercaptopropionyl-glycine) in agreement with the role of HOCl in LADH inactivation by MPO/H 2O 2/NaCl. LADH was also inactivated by MPO/NADH/halide, MPO/H 2O 2/NaNO 2 and MPO/NADH/NaNO 2 systems. Catalase prevented the action of the NADH-dependent systems, thus supporting H 2O 2 production by NADH-supplemented LADH. MPO inhibitors (4-aminobenzoic acid hydrazide, and isoniazid), GSH, L-cysteine, L-methionine and L-tryptophan prevented LADH inactivation by MPO/H 2O 2/NaNO 2. Other MPO systems inactivating LADH were (a) MPO/H 2O 2/chlorpromazine; (b) MPO/H 2O 2/monophenolic systems, including L-tyrosine, serotonin and acetaminophen and (c) MPO/H 2O 2/di- and polyphenolic systems, including norepinephrine, catechol, nordihydroguaiaretic acid, caffeic acid, quercetin and catechin. Comparison of the above effects and those previously reported with pig myocardial LADH indicates that both enzymes were similarly affected by the MPO-dependent systems, allowance being made for T. cruzi LADH diaphorase inactivation and the greater sensitivity of its LADH lipoamide reductase activity towards the MPO/H 2O 2/NaCl system and NaOCl. 相似文献
6.
Iron ions in the two iron centers of beef heart mito-chondrial F, ATPase, which we have been recently characterized ( FEBS Letters 1996, 379, 231-235), exhibit different redox properties. In fact, the ATP-dependent site is able to maintain iron in the redox state of Fe(II) even in the absence of reducing agents, whereas in the nucleotide-independent site iron is oxidized to Fe(III) upon removal of the reductant. Fe(III) ions in the two sites display different reactivity towards H 2O 2, because only Fe(III) bound in the nucleotide-independent site rapidly reacts with H 2O 2 thus mediating a 30% enzyme inactivation. Thermophilic bacterium PS3 bears one Fe(III) binding site, which takes up Fe(III) either in the absence or presence of nucleotides and is unable to maintain iron in the redox state of Fe(II) in the absence of ascorbate. Fe(III) bound in thermophilic F 1ATPase in a molar ratio 1:1 rapidly reacts with H 2O 2 mediating a 30% enzyme inactivation. These results support the presence in mitochon-drial and thermophilic F 1ATPase of a conserved site involved in iron binding and in oxidative inactivation, in which iron exhibits similar redox properties. On the other hand, at variance with thermophilic F 1ATPase, the mitochondrial enzyme has the possibility of maintaining one equivalent of Fe(II) in its peculiar ATP-dependent site, besides one equivalent of Fe(III) in the conserved nucleotide-independent site. In this case mitochondrial F, ATPase undergoes a higher inactivation (75%) upon exposure to H 2O 2. Under all conditions the inactivation is significantly prevented by PBN and DMSO but not by Cu, Zn superoxide dis-mutase, thus suggesting the formation of OH radicals as mediators of the oxidative damage. No dityrosines, carbonyls or oxidized thiols are formed. In addition, in any cases no protein fragmentation or aggregation is observed upon the treatment with H 2O 2. 相似文献
7.
1. 1. The mechanism of the photooxidation of ascorbate and of Mn2+ by isolated chloroplasts was reinvestigated. 2. 2. Our results suggest that ascorbate or Mn2+ oxidation is the result of the Photosystem I-mediated production of the radical superoxide, and that neither ascorbate nor Mn2+ compete with water as electron donors to Photosystem II nor affect the rate of electron transport through the two photosystems: The radical superoxide is formed as a result of the autooxidation of the reduced forms of low potential electron acceptors, such as methylviologen, diquat, napthaquinone, or ferredoxin. 3. 3. In the absence of ascorbate or Mn2+ the superoxide formed dismutases either spontaneously or enzymatically producing O2 and H2O2. In the presence of ascorbate or Mn2+, however, the superoxide is reduced to H2O2 with no formation of O2. Consequently, in the absence of reducing compounds, in the reaction H2O to low potential acceptor one O2 (net) is taken up per four electrons transported where as in the presence of ascorbate, Mn2+ or other suitable reductants up to three molecules O2 can be taken up per four electrons transported. 4. 4. This interpretation is supported by the following observations: (a) in a chloroplast-free model system containing NADPH and ferredoxin-NADP reductase, methylviologen can be reduced to a free radical which is autooxidizable in the presence of O2; the addition of ascorbate or Mn2+ to this system results in a two fold stimulation of O2 uptake, with no stimulation of NADPH oxidation. The stimulation of O2 uptake is inhibited by the enzyme superoxide dismutase; (b) the stimulation of light-dependent O2 uptake in the system H2O → methylviologen in chloroplasts is likewise inhibited by the enzyme superoxide dismutase. 5. 5. In Class II chloroplasts in the system H2O → NADP upon the addition of ascorbate or Mn2+ an apparent inhibition of O2 evolution is observed. This is explained by the interaction of these reductants with the superoxide formed by the autooxidation of ferredoxin, a reaction which proceeds simultaneously with the photoreduction of NADP. Such an effect usually does not occur in Class I chloroplasts in which the enzyme superoxide dismutase is presumably more active than in Class II chloroplasts. 6. 6. It is proposed that since in the Photosystem I-mediated reaction from reduced 2,4-dichlorophenolindophenol to such low potential electron acceptor as methylviologen, superoxide is formed and results in the oxidation of the ascorbate present in the system, the ratio ATP/2e in this system (when the rate of electron flow is based on the rate of O2 uptake) should be revised in the upward direction.
Abbreviations: DCMU, 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea; HEPES, hydroxyethyl-piperazineethanesulfonic acid; MES, (N-morpholino)ethanesulfonic acid; DCIP, 2,4-dichlorophenol-indophenol 相似文献
8.
The toxicity of H 2O 2 in Escherichia coli wild type and superoxide dismutase mutants was investigated under different experimental conditions. Cells were either grown aerobically, and then treated in M9 salts or K medium, or grown anoxically, and then treated in K medium. Results have demonstrated that the wild type and superoxide dismutase mutants display a markedly different sensitivity to both modes of lethality produced by H 2O 2 (i.e. mode one killing, which is produced by concentrations of H 2O 2 lower than 5 mM, and mode two killing which results from the insult generated by concentrations of H 2O 2 higher than 10 mM). Although the data obtained do not clarify the molecular basis of H 2O 2 toxicity and/or do not explain the specific function of superoxide ions in H 2O 2-induced bacterial inactivation, they certainly demonstrate that the latter species plays a key role in both modes of H 2O 2 lethality. A mechanism of H 2O 2 toxicity in E. coli is proposed, involving the action of a hypothetical enzyme which should work as an O 2-• generating system. This enzyme should be active at low concentrations of H 2O 2 (<5 mM) and high concentrations of the oxidant (>5 mM) should inactivate the same enzyme. Superoxide ions would then be produced and result in mode one lethality. The resistance at intermediate H 2O 2 concentrations may be dependent on the inactivation of such enzyme with no superoxide ions being produced at levels of H 2O 2 in the range 5–10 mM. Mode two killing could be produced by the hydroxyl radical in concert with superoxide ions, chemically produced via the reaction of high concentrations of H 2O 2 (>10 mM) with hydroxyl radicals. The rate of hydroxyl radical production may be increased by the higher availability of Fe 2+ since superoxide ions may also reduce trivalent iron to the divalent form. 相似文献
9.
Trypanosoma cruzi trypanothione reductase (TR) was irreversibly inhibited by peroxidase/H 2O 2/phenothiazine (PTZ) systems. TR inactivation depended on (a) time of incubation with the phenothiazine system; (b) the peroxidase nature and (c) the PTZ structure and concentration. With the most effective systems, TR inactivation kinetics were biphasic, with a relatively fast initial phase during which about 75% of the enzyme activity was lost, followed by a slower phase leading to total enzyme inactivation. GSH prevented TR inactivation by the peroxidase/H 2O 2/PTZ +· systems. Production of PTZ +· cation radicals by PTZ peroxidation was essential for TR inactivation. Horseradish peroxidase, leukocyte myeloperoxidase (MPO) and the pseudo-peroxidase myoglobin (Mb) were effective catalysts of PTZ +· production. Promazine, thioridazine, chlorpromazine, propionylpromazine prochlorperazine, perphenazine and trimeprazine were effective constituents of the HRP/H 2O 2/PTZ system. The presence of substituents at the PTZ nucleus position 2 exerted significant influence on PTZ activity, as shown by the different effects of 2-trifluoromethyl and 2-H or 2-chlorophenothiazines. The PTZ +· cation radicals disproportionation regenerated the non-radical PTZ molecule and produced the PTZ sulfoxide that was inactive on TR. Thiol compounds including GSH interacted with PTZ +· cation radicals transferring an electron from the sulfide anion to the PTZ +·, thus nullifying the PTZ +· biological and chemical activities. 相似文献
10.
Although considerably more oxidation-resistant than other P-type ATPases, the yeast PMA1 H +-ATPase of Saccharomyces cerevisiae SY4 secretory vesicles was inactivated by H 2O 2, Fe 2+, Fe- and Cu-Fenton reagents. Inactivation by Fe 2+ required the presence of oxygen and hence involved auto-oxidation of Fe 2+ to Fe 3+. The highest Fe 2- (100 μM) and H 2O 2 (100 mM) concentrations used produced about the same effect. Inactivation by the Fenton reagent depended more on Fe 2+ content than on H 2O 2 concentration, occurred only when Fe 2+ was added to the vesicles first and was only slightly reduced by scavengers (mannitol, Tris, NaN 3, 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 Fe 2+ 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 Fe 2+, blocked H +-ATPase inactivation by Fe 2+ and the Fenton reagent but not that caused by H 2O 2, 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. 相似文献
11.
4-Hydrazinobenzoic acid, an ingredient of mushroom Agaricus bisporus, is carcinogenic to rodents. To clarify the mechanism of carcinogenesis, we investigated DNA damage by 4-hydrazinobenzoic acid using 32P-labeled DNA fragments obtained from the human p53 and p16 tumor suppressor genes. 4-Hydrazinobenzoic acid induced Cu(II)-dependent DNA damage especially piperidine-labile formation at thymine and cytosine residues. Typical hydroxyl radical scavengers showed no inhibitory effects on Cu(II)-mediated DNA damage by 4-hydrazinobenzoic acid. Bathocuproine and catalase inhibited the DNA damage, indicating the participation of Cu(I) and H 2O 2 in the DNA damage. These findings suggest that H 2O 2 generated by the autoxidation of 4-hydrazinobenzoic acid reacts with Cu(I) to form reactive oxygen species, capable of causing DNA damage. Interestingly, catalase did not completely inhibit DNA damage caused by a high concentration of 4-hydrazinobenzoic acid (over 50 μM) in the presence of Cu(II). 4-Hydrazinobenzoic acid induced piperidine-labile sites frequently at adenine and guanine residues in the presence of catalase. 4-Hydrazinobenzoic acid increased formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), a characteristic oxidative DNA lesion, in calf thymus DNA, whereas 4-hydrazinobenzoic acid did not increase the formation of 8-oxodG in the presence of catalase. ESR spin-trapping experiments showed that the phenyl radical was formed during the reaction of 4-hydrazinobenzoic acid in the presence of Cu(II) and catalase. Matrix-assisted laser desorption/ionization time-of-flight mass (MALDI-TOF/mass) spectrometry analysis showed that phenyl radical formed adduct with adenosine and guanosine. These results suggested that 4-hydrazinobenzoic acid induced DNA damage via not only H 2O 2 production but also phenyl radical production. This study suggests that both oxidative DNA damage and DNA adduct formation play important roles in the expression of carcinogenesis of 4-hydrazinobenzoic acid. 相似文献
12.
Heme catalases are considered to degrade two molecules of H 2O 2 to two molecules of H 2O and one molecule of O 2 employing the catalatic cycle. We here studied the catalytic behaviour of bovine liver catalase at low fluxes of H 2O 2 (relative to catalase concentration), adjusted by H 2O 2-generating systems. At a ratio of a H 2O 2 flux (given in μM/min - 1) to catalase concentration (given in μM) of 10 min - 1 and above, H 2O 2 degradation occurred via the catalatic cycle. At lower ratios, however, H 2O 2 degradation proceeded with increasingly diminished production of O 2. At a ratio of 1 min - 1, O 2 formation could no longer be observed, although the enzyme still degraded H 2O 2. These results strongly suggest that at low physiological H 2O 2 fluxes H 2O 2 is preferentially metabolised reductively to H 2O, without release of O 2. The pathways involved in the reductive metabolism of H 2O 2 are presumably those previously reported as inactivation and reactivation pathways. They start from compound I and are operative at low and high H 2O 2 fluxes but kinetically outcompete the reaction of compound I with H 2O 2 at low H 2O 2 production rates. In the absence of NADPH, the reducing equivalents for the reductive metabolism of H 2O 2 are most likely provided by the protein moiety of the enzyme. In the presence of NADPH, they are at least in part provided by the coenzyme. 相似文献
13.
Alcohol dehydrogenase (ADH) was used as a marker molecule to clarify the mechanism of gastric mucosal damage as a side effect of using piroxicam. Piroxicam inactivated ADH during interaction of ADH with horseradish peroxidase and H 2O 2 (HRP-H 2O 2). The ADH was more easily inactivated under aerobic than anaerobic conditions, indicating participation by oxygen. Superoxide dismutase, but not hydroxyl radical scavengers, inhibited inactivation of ADH, indicating participation by superoxide. Sulfhydryl (SH) groups in ADH were lost during incubation of piroxicam with HRP-H 2O 2. Adding reduced glutathione (GSH) efficiently blocked ADH inactivation. Other SH enzymes, including creatine kinase and glyceraldehyde-3-phosphate dehydrogenase, were also inactivated by piroxicam with HRP-H 2O 2. Thus SH groups in the enzymes seem vulnerable to piroxicam activated by HRP-H 2O 2. Spectral change in piroxicam was caused by HRP-H 2O 2. ESR signals of glutathionyl radicals occurred during incubation of piroxicam with HRP-H 2O 2 in the presence of GSH. Under anaerobic conditions, glutathionyl radical formation increased. Thus piroxicam free radicals interact with GSH to produce glutathionyl radicals. Piroxicam peroxyl radicals or superoxide, or both, seem to inactivate ADH. Superoxide may be produced through interaction of peroxyl radicals with H 2O 2. Thus superoxide dismutase may inhibit inactivation of ADH through reducing piroxicam peroxyl radicals or blocking interaction of SH groups with O 2-, or both. Other oxicam derivatives, including isoxicam, tenoxicam and meloxicam, induced ADH inactivation in the presence of HRP-H 2O 2. 相似文献
14.
Ceruloplasmin (CP) is a blue copper glycoprotein with multiple physiological functions including ferroxidase and oxidase activities. CP is also an important serum oxygen free radical (OFR) scavenger and antioxidant, exerting cardioprotective and antifibrillatory actions. Although it has been reported that CP activities can be inhibited by OFR, the intimate mechanism of this inactivation is still not clear. Exposure of bovine CP to H 2O 2 induced inactivation of the protein as well as structural alterations as indicated by loss of protein bands by SDS-PAGE. Both phenomena were H 2O 2 concentration and time dependent. HPLC gel filtration and capillary electrophoresis analysis of CP treated with H 2O 2 revealed an aggregation of the protein. Quantification of dityrosine formation by fluorescence indicated the involvement of dityrosine bridging, which could be responsible for aggregation of CP under oxidative attack. Oxidative damage to CP under H 2O 2 treatment was completely prevented by pyruvate, suggesting that the association of CP with antioxidants could extend the range of the protective action of this protein. 相似文献
15.
报道了干旱胁迫下外源24-表油菜素内酯(EBR)对辣椒幼苗叶片H 2O 2和MDA含量,抗氧化酶活性,以及耐旱相关基因表达的影响。结果表明,0.1 μmol·L -1 EBR处理诱导了辣椒幼苗叶片H 2O 2含量的增加,并提高了SOD、APX、CAT、DHAR、MDAR和GR活性;干旱胁迫下,EBR处理显著诱导了辣椒叶片抗氧化酶活性的增加,并抑制了H 2O 2和MDA含量的上升;EBR处理也促进了cAPX和MDAR等抗氧化酶基因的表达,以及WRKY3、WRKY6和MYB等转录因子的表达。由此认为,适宜浓度的外源EBR可能是通过信号分子H 2O 2调控辣椒叶片中WRKY和MYB等转录因子的表达以调控相关耐旱基因表达,增强细胞的抗氧化酶活性,减轻干旱造成的膜质过氧化伤害,从而增强了辣椒幼苗的耐旱性。 相似文献
16.
采用水培方法,研究高浓度镉(0.1 mmol·L -1 Cd 2+)、锌(0.15 mmol·L -1 Zn 2+)及其复合作用(0.1 mmol·L -1 Cd 2++0.15 mmol·L -1Zn 2+)对烟草种子的萌发率、幼苗叶片活性氧(ROS)水平、抗氧化物浓度、抗氧化酶活性及膜脂过氧化程度的影响.结果表明: 单因子条件下,与对照相比,高浓度镉、锌处理烟草种子萌发率降低;叶片超氧自由基(O 2-· )产生速率与过氧化氢(H 2O 2)含量升高;过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX)、脱氢抗化血酸还原酶(DHAR)、单脱氢抗坏血酸还原酶(MDAR)和谷胱甘肽还原酶(GR)活性升高;谷胱甘肽(GSH)含量及其与氧化型谷胱甘肽比值(GSH/GSSG)下降;丙二醛(MDA)含量升高.与镉、锌单因子处理相比,镉、锌复合处理的烟草种子萌发率显著升高;O 2-· 产生速率、H 2O 2和MDA含量降低;CAT、APX、MDAR活性在处理末期升高.镉、锌胁迫对烟草可造成生理水平上的损伤,且毒性效应随着处理时间的延长而增强.镉、锌复合作用可缓解镉、锌单因子胁迫对烟草幼苗的毒害. 相似文献
17.
The role of histidine on DNA breakage induced by hydrogen peroxide (H 2O 2) and ferric ions or by H 2O 2 and cupric ions was studied on purified DNA. L-histidine slightly reduced DNA breakage by H 2O 2 and Fe 3+ but greatly inhibited DNA breakage by H 2O 2 and Cu 2+. However, only when histidine was present, the addition of EDTA to H 2O 2 and Fe 3+ exhibited a bimodal dose response curve depending on the chelator metal ratio. The enhancing effect of histidine on the rate of DNA degradation by H 2O 2 was maximal at a chelator metal ratio between 0.2 and 0.5, and was specific for iron. When D-histidine replaced L-histidine, the same pattern of EDTA dose response curve was observed. Superoxide dismutase greatly inhibited the rate of DNA degradation induced by H 2O 2, Fe 3+, EDTA and L-histidine involving the superoxide radical.
These studies suggest that the enhancing effect of histidine on the rate of DNA degradation by H 2O 2 and Fe 3+ is mediated by an oxidant which could be a ferrous-dioxygen-ferric chelate complex or a chelate-ferryl ion. 相似文献
18.
Ascorbic acid (vitamin C) induced hydrogen peroxide (H 2O 2) formation was measured in household drinking water and metal supplemented Milli-Q water by using the FOX assay. Here we show that ascorbic acid readily induces H 2O 2 formation in Cu(II) supplemented Milli-Q water and poorly buffered household drinking water. In contrast to Cu(II), iron was not capable to support ascorbic acid induced H 2O 2 formation during acidic conditions (pH: 3.5-5). In 12 out of the 48 drinking water samples incubated with 2 mM ascorbic acid, the H 2O 2 concentration exceeded 400 μM. However, when trace amounts of Fe(III) (0.2 mg/l) was present during incubation, the ascorbic acid/Cu(II)-induced H 2O 2 accumulation was totally blocked. Of the other common divalent or trivalent metal ions tested, that are normally present in drinking water (calcium, magnesium, zinc, cobalt, manganese or aluminum), only calcium and magnesium displayed a modest inhibitory activity on the ascorbic acid/Cu(II)-induced H 2O 2 formation. Oxalic acid, one of the degradation products from ascorbic acid, was confirmed to actively participate in the iron induced degradation of H 2O 2. Ascorbic acid/Cu(II)-induced H 2O 2 formation during acidic conditions, as demonstrated here in poorly buffered drinking water, could be of importance in host defense against bacterial infections. In addition, our findings might explain the mechanism for the protective effect of iron against vitamin C induced cell toxicity. 相似文献
19.
Electron spin resonance spin trapping was utilized to investigate free radical generation from cobalt (Co) mediated reactions using 5,5-dimethyl-l-pyrroline (DMPO) as a spin trap. A mixture of Co with water in the presence of DMPO generated 5,5-dimethylpyrroline-(2)-oxy(1) DMPOX, indicating the production of strong oxidants. Addition of superoxide dismutase (SOD) to the mixture produced hydroxyl radical ( OH). Catalase eliminated the generation of this radical and metal chelators, such as desferoxamine, diethylenetriaminepentaacetic acid or 1,10-phenanthroline, decreased it. Addition of Fe(II) resulted in a several fold increase in the OH generation. UV and O 2 consumption measurements showed that the reaction of Co with water consumed molecular oxygen and generated Co(II). Since reaction of Co(II) with H 2O 2 did not generate any significant amount of OH radicals, a Co(I) mediated Fenton-like reaction [Co(I) + H 2O 2 → Co(II) + OH + OH −] seems responsible for OH generation. H 2O 2 is produced from O 2− via dismutation. O 2− is produced by one-electron reduction of molecular oxygen catalyzed by Co. Chelation of Co(II) by biological chelators, such as glutathione or β-ananyl-3-methyl-
-histidine alters, its oxidation–reduction potential and makes Co(II) capable of generating OH via a Co(II)-mediated Fenton-like reaction [Co(II) + H 2O 2 → Co(III) + OH + OH −]. Thus, the reaction of Co with water, especially in the presence of biological chelators, glutathione, glycylglycylhistidine and β-ananyl-3-methyl-
-histidine, is capable of generating a whole spectrum of reactive oxygen species, which may be responsible for Co-induced cell injury. 相似文献
20.
Thyroglobulin (Tg) was subjected to metal-catalyzed oxidation, and the oxidative degradation was analyzed by SDS-polyacrylamide gel electrophoresis under reducing conditions. In contrast to no effect of hydrogen peroxide (H 2O 2) alone on the Tg degradation, the inclusion of Cu 2+ (30 μM), in combination with 2 mM H 2O 2, caused a remarkable degradation of Tg, time- and concentration-dependent. The action of Cu 2+ was not mimicked by Fe 2+, suggesting that Tg may interact selectively with Cu 2+. A similar degradation of Tg was also observed with Cu 2+corbate system, and the concentration of Cu 2+ (5-10 μM), in combination with ascorbate, required for the effective degradation was smaller than that of Cu 2+ (10-30 μM) in combination with H 2O 2. In support of involvement of H 2O 2 in the Cu 2+ corbate action, catalase expressed a complete protection. However, hydroxyl radical scavengers such as dimethylsulfoxide or mannitol failed to prevent the oxidation of Tg whereas phenolic compounds, which can interact with Cu 2+, diminished the oxidative degradation, presumably consistent with the mechanism for Cu 2+-catalyzed oxidation of protein. Moreover, the amount of carbonyl groups in Tg was increased as the concentration (3-100 μM) of Cu 2+ was enhanced, while the formation of acid-soluble peptides was not remarkable in the presence of Cu 2+ up to 200 μM. In further studies, Tg pretreated with heat or trichloroacetic acid seemed to be somewhat resistant to Cu 2+-catalyzed oxidation, implying a possible involvement of protein conformation in the susceptibility to the oxidation. Based on these observations, it is proposed that Tg could be degraded non-enzymatically by Cu 2+-catalyzed oxidation. 相似文献
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