首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
Sea urchins have elaborated multiple defenses to assure monospermic fertilization. In this work, we have concentrated on a study of the mechanism(s) by which hydrogen peroxide (H2O2) prevents polyspermy in Arbacia punctulata. We found that it is not H2O2 but probably hypochlorous acid/hypochlorite (HOCl/OCl?) derived from H2O2 that is toxic to the supernumerary sperm. The spermicidal activity of H2O2 is potentiated by at least one order of magnitude by cupric ions (Cu2+). This increased toxicity is not due to the formation of hydroxyl radicals (·OH) because ·OH scavengers did not counteract the activity of Cu2+. More-over, substitution of Cu2+ by ferrous ions (Fe2+), which are known to cause formation of ·OH from H2O2, had no effect on fertilization even at 102?103 times higher concentrations. In contrast, 3-amino-1,2,4-triazole (AT), an HOCl/OCl? scavenger, totally reversed the toxic effects of Cu2+. Furthermore, we found that HOCl/OCl? is generated in solutions of H2O2 and Cu2+ in the presence of 0.5 M NaCl and that its accumulation is abolished by AT. Thus it is possible that the antifertility properties of copper are due to its ability to mediate formation of HOCl/OCl?. HOCl/OCl? generated by Cu2+ from H2O2 and Cl?, a low concentration of exogenously added HOCl/OCl?, or increased concentrations of H2O2 has similar inhibitory effects on the fertilization process in sea urchins. Therefore, we suggest that polyspermy is prevented by the action of a myeloperoxidase that affects the formation of HOCl/OCl? from the Cl? present in sea water through reaction with H2O2 generated by the newly fertilized egg.  相似文献   

2.
Ethylene from 2-keto-4-thiomethyl butyric acid: the Haber-Weiss reaction   总被引:4,自引:0,他引:4  
2-Keto-4-thiomethyl butyric acid is cooxidized, with production of ethylene, by the xanthine oxidase reaction. Ethylene production was inhibited by either superoxide dismutase or catalase indicating an essential role for both O2? and H2O2. Ethylene production was dependent upon iron complexes, while a variety of other metals were found ineffective. At pH 7.8 ethylenediaminetetraacetate-iron was much more effective in facilitating ethylene production, in the xanthine oxidase system, than was diethylenetriaminepentaacetate-iron; yet these two chelates were equally effective in ethylene production dependent upon the Fenton reaction. pH was an important variable in determining the activity of iron chelates in facilitating ethylene production in the xanthine oxidase system. The effectiveness of hydroxyl radical scavengers, in preventing ethylene production, was directly related to their abilities to scavenge OH · and this was the case in the presence of any of the several chelating agents tested. The proximal oxidant, responsible for ethylene production, thus appears to be OH ·, rather than some metal-oxy complex.  相似文献   

3.
The occurrence of the Haber-Weiss reaction and other interactions between free radicals has been investigated in the effects of mixtures of free radicals on the permeability of resealed erythrocyte ghosts and on the activity of membrane-bound glyceraldehyde-3-phosphate dehydrogenase. The following mixtures were found to induce damage greater than that which could be accounted for by the independent actions of the constituent free radicals: (i) · OH + H2O2, and (ii) · OH + H2O2 + O2?. In contrast, the following mixtures were found to induce less damage than that predicted on the basis of independent actions of constituent free radicals: (i) H2O2 + O2?, and (ii) oxidizing radicals ( · OH, H2O2) + reducing radicals (e?, H · ). These results suggest a Haber-Weiss-like interaction between H2O2 and O2?and an interaction between H2O2 and · OH to produce a species more potent than either in causing increased permeability. The decrease in damage observed in the simultaneous presence of oxidizing and reducing radicals suggests an antagonistic effect by which each tends to moderate damage by the other. Inactivation of glyceraldehyde-3-phosphate dehydrogenase was found to be more sensitive to radiation than permeability by an order of magnitude, while permeability was more sensitive to the enhancement of damage by oxygen. Comparison of the effectiveness of free radical scavengers in inhibiting the increase in permeability caused by free radicals showed the following order of effectiveness, expressed in terms of percentage protection: formate (90%) > nitrogen (65%) > catalase (60%) > dismutase (32%), and with respect to enzymatic inactivation, nitrogen (100%) > formate (77%) > dismutase (48%) > catalase (44%). The relative rates observed anaerobically and aerobically in the presence and absence of the above scavengers suggest that (at least in the case of radiation damage to the membranes of erythrocyte ghost cells) the “oxygen effect” is due to the interaction of oxygen with e? and H., producing O2? which aggravates damage under conditions which allow consequent Haber-Weiss-like reactions. The further increase in damage when oxygen concentration is raised yet higher is due to the interaction of oxygen with the sites of initial damage.  相似文献   

4.
Abstract

The O2-induced strand scission of 4′-DNA radicals is initiated by a reversible O2 addition reaction. The rate coefficient of the O2 release from the 4′-DNA peroxyl radical is 1.00 s?1 in single strands and 0.05 s?1 in double strands at 20°C. Because of this reversibility, an O2-dependent strand cleavage occurs only in the presence of H-donors which trap the 4′-DNA peroxyl radicals yielding DNA hydroperoxides. At very low H-donor concentrations the strand scission is the result of an O2-independent, spontaneous reaction even under aerobic conditions.  相似文献   

5.
A mixture of xanthine or hypoxanthine and xanthine oxidase generates the superoxide radical, O2?, and H2O2. In the presence of iron salts, O2? and H2O2 can interact to produce the hydroxyl radical, OH·. Superoxide-dependent formation of OH· can be measured by its ability to hydroxylate salicylate as followed by an improved colorimetric assay described in this paper. A more accurate analysis of OH· can be obtained using its ability to hydroxylate phenol, the hydroxylated products being separated and measured after derivatization using gas-liquid chromatography and electron-capture detection. The derivatization and separation techniques are described.  相似文献   

6.
The generation of active oxygen molecules, O2?, H2O2, and · OH, from the aqueous solution of aminosugars, such as d-glucosamine, was confirmed by their actual measurement. Both the C-2 amino and C-1 aldehyde groups in the aminosugar molecules were indispensable for the generation of active oxygen molecules. The introduction of a C-6 phosphate group to d-glucosamine or the simultaneous use of phosphate ion and d-glucosamine heightened the original activity of d-glucosamine to generate these oxygens, especially · OH. Cu2+, which promoted the DNA-breaking activity of aminosugar most at 1 mm, also promoted the generation of · OH most greatly at the same concentration, but neither O2? nor H2O2 was generated under the same conditions. Superoxide dismutase, catalase, and some radical scavengers inhibited the generation of these active oxygen molecules. Among the active oxygen molecules, only the amount of · OH generated was directly proportional to the DNA-breaking activity of the aminosugar.  相似文献   

7.
Many of the cytopathic effects of nitric oxide (NO·) are mediated by peroxynitrite (PN), a product of the reaction between NO· and superoxide radical (O·?2). In the present study, we investigated the role of PN, O·?2 and hydroxyl radical (OH·) as mediators of epithelial hyperpermeability induced by the NO· donor, S-nitroso-N-acetylpenicillamine (SNAP), and the PN generator, 3-morpholinosydnonimine (SIN-1). Caco-2BBe enterocytic monolayers were grown on permeable supports in bicameral chambers. Epithelial permeability, measured as the apical-to-basolateral flux of fluorescein disulfonic acid, increased after 24 h of incubation with 5.0 mM SNAP or SIN-1. Addition of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, an NO· scavenger, or Tiron, an O·?2 scavenger, reduced the increase in permeability induced by both donor compounds. The SNAP-induced increase in permeability was prevented by allopurinol, an inhibitor of xanthine oxidase (a source of endogenous O·?2). Diethyldithiocarbamate, a superoxide dismutase inhibitor, and pyrogallol, an O·?2 generator, potentiated the increase in permeability induced by SNAP. Addition of the PN scavengers deferoxamine, urate, or glutathione, or the OH· scavenger mannitol, attenuated the increase in permeability induced by both SNAP and SIN-1. Both donor compounds decreased intracellular levels of glutathione and protein-bound sulfhydryl groups, suggesting the generation of a potent oxidant. These results support a role for PN, and possibly OH·, in the pathogenesis of NO· donor-induced intestinal epithelial hyperpermeability.  相似文献   

8.
A reaction of the superoxide radical with tetrapyrroles   总被引:1,自引:0,他引:1  
Bilirubin and biliverdin were bleached during exposure to the aerobic xanthine oxidase reaction. Enzymic scavenging of O2?, by Superoxide dismutase, inhibited, whereas enzymic scavenging of H2O2, by catalase, did not. Increasing the rate of production of O2? without increasing the turnover rate of xanthine oxidase, by increasing pO2, accelerated the bleaching of the biliverdin. Moreover, a scavenger of OH·, such as benzoate, or an inactivating chelating agent for iron, such as diethylenetriamine pentaacetate or desferrioxamine mesylate, did not inhibit. It follows that O2? can directly attack these tetrapyrroles. Kinetic competition between Superoxide dismutase and bilirubin yielded a value for kbilirubin, O2? = 2.3 × 104 M?1s?1 at pH 8.3 and at 23 °C. A similar experiment for biliverdin yielded a value for kbilirubin, O2? = 7 × 104 M?1s?1.  相似文献   

9.
Transient spectra and kinetic data of Tiron (1,2-dihydroxybenzene-3,5-disulphonic acid) are reported, obtained after pulse-radiolytic oxidation by hydroxyl radicals (°OH), superoxide anions (O2?) or a combination of both oxygen radicals. The rate constant with °OH radicals was determined at 1.0·109 M?1·s?1. Contrary to a previous report (Greenstock, C.L. and Miller, R.W. (1975) Biochim. Biophys. Acta 396, 11–16), the rate constant with O2? of 1.0·107 M?1·s?1 is lower by one order of magnitude; also the semiquinone absorbs at 300 nm rather than at 400 nm. The ratio of the rate constants with °OH and O2? of 100 again demonstrates that any oxidation reaction by the latter radical is unspecific due to the more efficient reaction of °OH radicals, leading to the same products with catechol compounds.  相似文献   

10.
The interaction of chartreusin with covalently closed circular PM2 phage DNA was studied. The antibiotic caused a single strand scission in the presence of reducing agents, such as dithiothreitol, ascorbic acid or NaBH4. The degree of DNA breakage was dependent upon the drug concentration. The DNA-cleaving activity was enhanced by ferrous ion; but was completely blocked by catalase and partially by superoxide dismutase. The results suggest that reduction, chelate formation and auto-oxidation of the antibiotic, presumably the 5,12-dione moiety, produce free radicals, including O2? and ?OH, which are capable of inducing DNA strand scission.  相似文献   

11.
Understanding spatio-temporal patterns of grassland evapotranspiration (ET) and water use efficiency (WUE) in arid areas is important for livestock production and ecological conservation. Xinjiang, China, was used as an example in the Biome-BGC model to explore spatio-temporal patterns of grassland ET and WUE from 1979 to 2012 in arid areas. The ET ranked from high to low as follows: among seasons, summer (142.4 mm), spring (49.7 mm), autumn (45.9 mm) and winter (7.7 mm); among regions, the Tianshan Mountains (357.9 mm), northern Xinjiang (221.3 mm) and southern Xinjiang (183.2 mm); among grassland types, mid-mountain meadow (387.7 mm), swamp meadow (358.3 mm), typical grassland (343.9 mm), desert grassland (236.2 mm), alpine meadow (229.7 mm), and saline meadow (154.7 mm). The WUE ranked from high to low as follows: among seasons, summer (0.60 g C kg H2O?1), autumn (0.48 g C kg H2O?1) and spring (0.43 g C kg H2O?1); among regions, northern Xinjiang (0.73 g C kg H2O?1), the Tianshan Mountains (0.69 g C kg H2O?1) and southern Xinjiang (0.26 g C kg H2O?1); among grassland types, mid-mountain meadow (0.86 g C kg H2O?1), typical grassland (0.84 g C kg H2O?1), swamp meadow (0.77 g C kg H2O?1), saline meadow (0.52 g C kg H2O?1), alpine grassland (0.37 g C kg H2O?1) and desert grassland (0.34 g C kg H2O?1). In Xinjiang grasslands, the spatio-temporal ET patterns were more strongly influenced by precipitation than by temperature, whereas most high WUE values occurred when precipitation and temperature were relatively conducive to grass growth.  相似文献   

12.
The Oxygen activating mechanism of Fusarium lipoxygenase, a heme-containing dioxygenase, was studied. The enzyme did not require any cofactors, such as H2O2, however, both superoxide dismutase and catalase inhibited linoleate peroxidation by Fusarium lipoxygenase. A low concentration of H2O2 caused a distinct acceleration in enzymatic peroxidation. These results indicate that both O2? and H2O2 are produced as essential intermediates of oxygen activation during formation of linoleate hydroperoxides by Fusarium lipoxygenase. This peroxidation reaction was also prevented by scavengers of singlet oxygen (1O2), but not by scavengers of hydroxy 1 radical (OH). Generation of O2? in the enzyme reaction was detected by its ability to oxidize epinephrine to adrenochrome. Moreover, the rate of peroxide formation was greater in the D2O than in the H2O buffer system. These results suggest that the Haber–Weiss reaction (O2?+H2O2→OH?+OH·+1O2) is taking part in linoleate peroxidation by Fusarium lipoxygenase, and the 1O2 evolved could be responsible for the peroxidation of linoleate. H2O2 produced endogenously in the enzyme reaction might act as an activating factor for the enzyme. This possible mechanism of oxygen activation can explain the absence of a need for exogenous cofactors with Fusarium lipoxygenase in contrast to an other heme-containing dioxygenase, tryptophan pyrrolase, which requires an exogenous activating factor, such as H2O2.  相似文献   

13.
The high‐capacity cathode material V2O5·n H2O has attracted considerable attention for metal ion batteries due to the multielectron redox reaction during electrochemical processes. It has an expanded layer structure, which can host large ions or multivalent ions. However, structural instability and poor electronic and ionic conductivities greatly handicap its application. Here, in cell tests, self‐assembly V2O5·n H2O nanoflakes shows excellent electrochemical performance with either monovalent or multivalent cation intercalation. They are directly grown on a 3D conductive stainless steel mesh substrate via a simple and green hydrothermal method. Well‐layered nanoflakes are obtained after heat treatment at 300 °C (V2O5·0.3H2O). Nanoflakes with ultrathin flower petals deliver a stable capacity of 250 mA h g?1 in a Li‐ion cell, 110 mA h g?1 in a Na‐ion cell, and 80 mA h g?1 in an Al‐ion cell in their respective potential ranges (2.0–4.0 V for Li and Na‐ion batteries and 0.1–2.5 V for Al‐ion battery) after 100 cycles.  相似文献   

14.
It is well known that the principal biomolecules involved in Alzheimer’s disease (AD) are acetylcholinesterase (AChE), acetylcholine (ACh) and the amyloid beta peptide of 42 amino acid residues (Aβ42). ACh plays an important role in human memory and learning, but it is susceptible to hydrolysis by AChE, while the aggregation of Aβ42 forms oligomers and fibrils, which form senile plaques in the brain. The Aβ42 oligomers are able to produce hydrogen peroxide (H2O2), which reacts with metals (Fe2+, Cu2+, Cr3+, Zn2+, and Cd2+) present at high concentrations in the brain of AD patients, generating the hydroxyl radical (·OH) via Fenton (FR) and Fenton-like (FLR) reactions. This mechanism generates high levels of free radicals and, hence, oxidative stress, which has been correlated with the generation and progression of AD. Therefore, we have studied in vitro how AChE catalytic activity and ACh levels are affected by the presence of metals (Fe3+, Cu2+, Cr3+, Zn2+, and Cd2+), H2O2 (without Aβ42), and · OH radicals produced from FR and FLR. The results showed that the H2O2 and the metals do not modify the AChE catalytic activity, but the ·OH radical causes a decrease in it. On the other hand, metals, H2O2 and ·OH radicals, increase the ACh hydrolysis. This finding suggests that when H2O2, the metals and the ·OH radicals are present, both, the AChE catalytic activity and ACh levels diminish. Furthermore, in the future it may be interesting to study whether these effects are observed when H2O2 is produced directly from Aβ42.  相似文献   

15.
Human copper-zinc superoxide dismutase undergoes inactivation when exposed to O2? and H2O2 generated during the oxidation of acetaldehyde by xanthine oxidase at pH 7.4 and 37° C. In contrast, human manganese superoxide dismutase is not inactivated under the same conditions. Catalase and Mn-superoxide dismutase protect CuZn superoxide dismutase from inactivation. Similar protection is observed with hydroxyl radical (OH.) scavengers, such as formate and mannitol. In contrast, other OH. scavengers such as ethanol and tert-butyl alcohol, have no protective action. The latter results indicate that “free OH.” is not responsible for the inactivation. Furthermore, H2O2 generated during the oxidation of glucose by glucose oxidase, i.e., without production of O2?, does not induce CuZn superoxide dismutase inactivation. A mechanism accounting for this O2?H2O2-dependent inactivation of CuZn superoxide dismutase is proposed.  相似文献   

16.
Superoxide (O 2 ·? ) overproduction, by decreasing the nitric oxide (·NO) bioavailability, contributes to vascular complications in type 1 diabetes. In this disease, the vascular O 2 ·? can be produced by the NADPH oxidase (NOX), nitric oxide synthase (NOS), and xanthine oxidase (XO). This study aimed to determine the contribution of each enzymatic pathway in hyperglycemia-induced O 2 ·? overproduction, and the effects of an endurance training program and insulin therapy, associated or not, on the O 2 ·? production (amount and related enzymes) in diabetic rats. Forty male Wistar rats were divided into diabetic (D), diabetic treated with insulin (D-Ins), diabetic trained (D-Tr), or diabetic insulin-treated and trained (D-Ins + Tr) groups. An additional healthy group was used as control. Insulin therapy (Glargine Lantus, Sanofi) and endurance training (treadmill run: 60 min/day, 25 m/min, 5 days/week) started 1 week after diabetes induction by streptozotocin (45 mg/kg), and lasted for 8 weeks. At the end of the protocol, the O 2 ·? production in aorta rings was evaluated by histochemical analyses (DHE staining). Each production pathway was studied by inhibiting NOX (apocynin), NOS (L-Name), or XO (allopurinol) before DHE staining. Diabetic rats exhibited hyperglycemia-induced O 2 ·? overproduction, resulting from NOX, NOS, and XO activation. Insulin therapy and endurance training, associated or not, decreased efficiently and similarly the O 2 ·? overproduction. Insulin therapy reduced the hyperglycemia and decreased the three enzymatic pathways implicated in the O 2 ·? production. Endurance training decreased directly the NOS and XO activity. While both therapeutic strategies activated different pathways, their association did not reduce the O 2 ·? overproduction more significantly.  相似文献   

17.
There are five oxidation-reduction states of horseradish peroxidase which are interconvertible. These states are ferrous, ferric, Compound II (ferryl), Compound I (primary compound of peroxidase and H2O2), and Compound III (oxy-ferrous). The presence of heme-linked ionization groups was confirmed in the ferrous enzyme by spectrophotometric and pH stat titration experiments. The values of pK were 5.87 for isoenzyme A and 7.17 for isoenzymes (B + C). The proton was released when the ferrous enzyme was oxidized to the ferric enzyme while the uptake of the proton occurred when the ferrous enzyme reacted with oxygen to form Compound III. The results could be explained by assuming that the heme-linked ionization group is in the vicinity of the sixth ligand and forms a stable hydrogen bond with the ligand.The measurements of uptake and release of protons in various reactions also yielded the following stoichiometries: Ferric peroxidase + H2O2 → Compound I, Compound I + e? + H+ → Compound II, Compound II + e? + H+ → ferric peroxidase, Compound II + H2O2 → Compound III, Compound III + 3e? + 3H+ → ferric peroxidase.Based on the above stoichiometries and assuming the interaction between the sixth ligand and heme-linked ionization group of the protein, it was possible to picture simple models showing structural relations between five oxidation-reduction states of peroxidase. Tentative formulae are as follows: [Pr·Po·Fe-(II) $?PrH+·Po·Fe(II)] is for the ferrous enzyme, Pr·Po·Fe(III)OH2 for the ferric one, Pr·Po·Fe(IV)OH? for Compound II, Pr(OH?)·Po+·Fe(IV)OH? for Compound I, and PrH+·Po·Fe(III)O2? for Compound III, in which Pr stands for protein and Po for porphyrin. And by Fe(IV)OH?, for instance, is meant that OH? is coordinated at the sixth position of the heme iron and the formal oxidation state of the iron is four.  相似文献   

18.
The effect of lactic acid (lactate) on Fenton based hydroxyl radical (·OH) production was studied by spin trapping, ESR, and fluorescence methods using DMPO and coumarin-3-carboxylic acid (3-CCA) as the ·OH traps respectively. The ·OH adduct formation was inhibited by lactate up to 0.4mM (lactate/iron stoichiometry = 2) in both experiments, but markedly enhanced with increasing concentrations of lactate above this critical concentration. When the H2O2 dependence was examined, the DMPO-OH signal was increased linearly with H2O2 concentration up to 1 mM and then saturated in the absence of lactate. In the presence of lactate, however, the DMPO-OH signal was increased further with higher H2O2 concentration than 1 mM, and the saturation level was also increased dependent on lactate concentration. Spectroscopic studies revealed that lactate forms a stable colored complex with Fe3+ at lactate/Fe3+ stoichiometry of 2, and the complex formation was strictly related to the DMPO-OH formation. The complex formation did not promote the H2O2 mediated Fe3+ reduction. When the Fe3+-lactate (1:2) complex was reacted with H2O2, the initial rate of hydroxylated 3-CCA formation was linearly increased with H2O2 concentrations. All the data obtained in the present experiments suggested that the Fe3+-lactate (1:2) complex formed in the Fenton reaction system reacts directly with H2O2 to produce additional ·OH in the Fenton reaction by other mechanisms than lactate or lactate/Fe3+ mediated promotion of Fe3+/Fe2+ redox cycling.  相似文献   

19.
The weak luminescence that accompanies the aerobic xanthine oxidase reaction is inhibited by superoxide dismutase, by catalase, and by scavengers of hydroxyl radicals. It is also entirely dependent upon the presence of carbonate. It thus appears that the O2 and H2O2 produced during the aerobic action of xanthine oxidase interact to generate OH which, in turn, reacts with carbonate to yield the carbonate radical (CO3?). The species that is directly responsible for light emission appears to be produced by a dimerization of carbonate radicals, since the light intensity was a function of the square of the carbonate concentration. The data provide no reason to suppose that the light-emitting species is singlet oxygen.  相似文献   

20.
Exogenous hydrogen peroxide (H2O2) induces oxidative stress and apoptosis in cancer cells. This study evaluated the antiapoptotic effects of pan-caspase and caspase-3, -8, or -9 inhibitors on H2O2-treated Calu-6 and A549 lung cancer cells in relation to reactive oxygen species (ROS) and glutathione (GSH). Treatment with 50–500 μM H2O2 inhibited the growth of Calu-6 and A549 cells at 24 h and induced apoptosis in these cells. All the tested caspase inhibitors significantly prevented cell death in H2O2-treated lung cancer cells. H2O2 increased intracellular ROS levels, including that of O 2 ·? , at 1 and 24 h. It also increased the activity of catalase but decreased the activity of SOD. In addition, H2O2 triggered GSH deletion in Calu-6 and A549 cells at 24 h. It reduced GSH levels in Calu-6 cells at 1 h but increased them at 24 h. Caspase inhibitors decreased O 2 ·? levels in H2O2-treated Calu-6 cells at 1 h and these inhibitors decreased ROS levels, including that of O 2 ·? , in H2O2-treated A549 cells at 24 h. Caspase inhibitors partially attenuated GSH depletion in H2O2-treated A549 cells and increased GSH levels in these cells at 24 h. However, the inhibitors did not affect GSH deletion and levels in Calu-6 cells at 24 h. In conclusion, H2O2 induced caspase-dependent apoptosis in Calu-6 and A549 cells, which was accompanied by increases in ROS and GSH depletion. The antiapoptotic effects of caspase inhibitors were somewhat related to the suppression of H2O2-induced oxidative stress and GSH depletion.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号