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1.
The oxidative modification of LDL may play an important role in the early events of atherogenesis. Thus the identification of antioxidative compounds may be of therapeutic and prophylactic importance regarding cardiovascular disease. Copper-chlorophyllin (Cu-CHL), a Cu 2+-protoporphyrin IX complex, has been reported to inhibit lipid oxidation in biological membranes and liposomes. Hemin (Fe 3+-protoporphyrin IX) has been shown to bind to LDL thereby inducing lipid peroxidation. As Cu-CHL has a similar structure as hemin, one may assume that Cu-CHL may compete with the hemin action on LDL. Therefore, in the present study Cu-CHL and the related compound magnesium-chlorophyllin (Mg-CHL) were examined in their ability to inhibit LDL oxidation initiated by hemin and other LDL oxidizing systems. LDL oxidation by hemin in presence of H 2O 2 was strongly inhibited by both CHLs. Both chlorophyllins were also capable of effectively inhibiting LDL oxidation initiated by transition metal ions (Cu 2+), human umbilical vein endothelial cells (HUVEC) and tyrosyl radicals generated by myeloperoxidase (MPO) in presence of H 2O 2 and tyrosine. Cu- and Mg-CHL showed radical scavenging ability as demonstrated by the diphenylpicrylhydracylradical (DPPH)-radical assay and estimation of phenoxyl radical generated diphenyl (dityrosine) formation. As assessed by ultracentrifugation the chlorophyllins were found to bind to LDL (and HDL) in serum. The present study shows that copper chlorophyllin (Cu-CHL) and its magnesium analog could act as potent antagonists of atherogenic LDL modification induced by various oxidative stimuli. As inhibitory effects of the CHLs were found at concentrations as low as 1 μmol/l, which can be achieved in humans, the results may be physiologically/therapeutically relevant. 相似文献
2.
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
3.
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
4.
The concentration of nitrite (NO 2−) increases under inflammatory conditions. However, the physiological role of nitrite is so far controversial discussed: it was reported that effects of HOCl (an important inflammation mediator) on phospholipids (PL) may be enhanced but also reduced in the presence of nitrite. In this paper a simple model system was used: unsaturated phosphatidylcholine (PC) vesicles were treated with HOCl in the presence of varying NaNO2 concentrations and the yield of reaction products was determined by MALDI-TOF MS: the extent of chlorohydrin generation was significantly reduced in the presence of NaNO2 because HOCl is consumed by the oxidation of NO2− to NO3−. Similar results were obtained when HOCl was generated by the myeloperoxidase (MPO)/H2O2/Cl− system or the experiments were carried out in the presence of a simple peptide. It is concluded that the transient products of the reaction between HOCl and NO2− do not have a sufficient reactivity to modify PL. 相似文献
5.
Myeloperoxidase (MPO) is a dominating enzyme of circulating polymorphonuclear neutrophils that catalyzes the two-electron oxidation of chloride, thereby producing the strong halogenating agent hypochlorous acid (ClO −/HOCl). In absence of MPO the tripeptide Pro-Gly-Gly reacts with HOCl faster than the amino acid taurine (2-aminoethanesulfonic acid, Tau), while the MPO-mediated chlorination shows reverse order. A comparative study of the enzymatic oxidation of both substrates at pH 4.0–6.0, varying H 2O 2 concentration is presented. Initial and equilibrium rates studies have been carried on, reaction rates in the latter being slower due to the chemical equilibrium between MPO-I and MPO-II–HO 2. A maximum of chlorination rate is observed for Pro-Gly-Gly and Tau when [H 2O 2] ≈ 0.3–0.7 mM and pH ≈ 4.5–5.0. Several mechanistic possibilities are considered, the proposed one implies that chlorination takes place via two pathways. One, for bulkier substrates, involves chlorination by free HOCl outside the heme cavity; ClO − is released from the active center, diffuses away the heme cavity, and undergoes protonation to HOCl. The other implies the existence of compound I–Cl − complex (MPO-I–Cl), capable of chlorinating smaller substrates in the heme pocket. Electronic structure calculations show the size of Pro-Gly-Gly comparable to the available gap in the substrate channel, this tripeptide being unable to reach the active site, and its chlorination is only possible by free HOCl outside the enzyme. 相似文献
6.
Nitration of protein tyrosine residues by peroxynitrite (ONOO −) has been implicated in a variety of inflammatory diseases such as acute respiratory distress syndrome (ARDS). Pulmonary surfactant protein A (SP-A) has multiple functions including host defense. We report here that a mixture of hypochlorous acid (HOCl) and nitrite (NO 2−) induces nitration, oxidation, and chlorination of tyrosine residues in human SP-A and inhibits SP-A’s ability to aggregate lipids and bind mannose. Nitration and oxidation of SP-A was not altered by the presence of lipids, suggesting that proteins are preferred targets in lipid-rich mixtures such as pulmonary surfactant. Moreover, both horseradish peroxidase and myeloperoxidase (MPO) can utilize NO 2− and hydrogen peroxide (H 2O 2) as substrates to catalyze tyrosine nitration in SP-A and inhibit its lipid aggregation function. SP-A nitration and oxidation by MPO is markedly enhanced in the presence of physiological concentrations of Cl − and the lipid aggregation function of SP-A is completely abolished. Collectively, our results suggest that MPO released by activated neutrophils during inflammation utilizes physiological or pathological levels of NO 2− to nitrate proteins, and may provide an additional mechanism in addition to ONOO − formation, for tissue injury in ARDS and other inflammatory diseases associated with upregulated •NO and oxidant production. 相似文献
7.
Although the rapid and considerable membrane depolarization response which accompanies activation of the phagocyte NADPH oxidase is due to transmembrane electron fluxes, little is known about the involvement of reactive oxidant species (ROS) in the subsequent repolarization response. In the current study, we have investigated the effects of superoxide dismutase (SOD), catalase, methionine, and the myeloperoxidase (MPO) inhibitors, sodium azide and 4-aminobenzoyl hydrazide (ABAH), as well as those of H 2O 2 and HOCl (both at 100 μM) on the alterations in membrane potential which accompany activation of human neutrophils with the chemoattractant, FMLP (1 μM), and on store-operated uptake of Ca 2+. The generation of ROS by FMLP-activated neutrophils was monitored according to the magnitude of oxygen consumption and autoiodination, while spectrofluorimetric procedures were used to measure alterations in membrane potential and influx of Ca 2+. Treatment of the cells with H 2O 2, and HOCl, significantly impeded membrane repolarization, while sodium azide, ABAH, methionine, and catalase exerted the opposite effects, potentiating both the rates and the magnitudes of membrane repolarization and store-operated uptake of Ca 2+. These observations demonstrate that NADPH oxidase regulates neutrophil membrane potential and Ca 2+ influx not only via its electrogenic activity, but also as a consequence of the generation of ROS. 相似文献
8.
Objective: Al 3+ stimulates Fe 2+ induced lipid oxidation in liposomal and cellular systems. Low-density lipoprotein (LDL) oxidation may render the particle atherogenic. As elevated levels of Al 3+ and increased lipid oxidation of LDL are found in sera of hemodialysis patients, we investigated the influence of Al 3+ on LDL oxidation.
Materials and methods: Using different LDL modifying systems (Fe 2+, Cu 2+, free radical generating compounds, human endothelial cells, hemin/H 2O 2 and HOCl), the influence of Al 3+ on LDL lipid and apoprotein alteration was investigated by altered electrophoretic mobility, lipid hydroperoxide-, conjugated diene- and TBARS formation.
Results: Al 3+ could stimulate the oxidizability of LDL by Fe 2+, but not in the other systems tested. Al 3+ and Fe 2+ were found to bind to LDL and Al 3+could compete with Fe 2+ binding to the lipoprotein. Fluorescence polarization data indicated that Al 3+ does not affect the phospholipid compartment of LDL.
Conclusions:The results indicate that increased LDL oxidation by Fe 2+ in presence of Al 3+ might be due to blockage of Fe 2+ binding sites on LDL making more free Fe 2+ available for lipid oxidation. 相似文献
9.
There is evidence that LDL oxidation may render the lipoprotein atherogenic. The myeloperoxidase-hydrogen peroxide (MPO/H2O2) system of activated phagocytes may be involved in this process. Chloride is supposed to be the major substrate for MPO, generating reactive hypochlorous acid (HOCl), modifying LDL. The pseudo-halide thiocyanate (SCN-) has been shown to be a suitable substrate for MPO, forming reactive HOSCN/SCN*. As relatively abundant levels of SCN- are found in plasma of smokers--a well-known risk group for cardiovascular disease--the ability of SCN- to act as a catalyst of LDL atherogenic modification by MPO/H2O2 was tested. Measurement of conjugated diene and lipid hydroperoxide formation in LDL preparations exposed to MPO/H2O2 revealed that SCN- catalyzed lipid oxidation in LDL. Chloride did not diminish the effect of SCN- on lipid oxidation. Surprisingly, SCN inhibited the HOCl-mediated apoprotein modification in LDL. Nitrite--recently found to be a substrate for MPO--showed some competing properties. MPO-mediated lipid oxidation was inhibited by heme poisons (azide, cyanide) and catalase. Ascorbic acid was the most effective compound in inhibiting the SCN- -catalyzed reaction. Bilirubin showed some action, whereas tocopherol was ineffective. When LDL oxidation was performed with activated human neutrophils, which employ the MPO pathway, SCN- catalyzed the cell-mediated LDL oxidation. The MPO/H2O2/SCN- system may have the potential to play a significant role in the oxidative modification of LDL--an observation further pointing to the link between the long-recognized risk factors of atherosclerosis: elevated levels of LDL and smoking. 相似文献
10.
为了解气体信号硫化氢(H 2S)对盐碱胁迫下裸燕麦( Avena nuda)活性氧(ROS)代谢的调节效应,筛选和确定H 2S最佳的施用时期和适宜浓度。采用盆栽土培试验,研究了在裸燕麦不同时期(幼苗期、拔节期、抽穗期、开花期和灌浆期)喷施0、25、50、100、200、400 μmol·L -1 H 2S供体硫氢化钠(NaHS)对3.0 g·kg -1盐碱混合 (NaCl∶Na 2SO 4∶NaHCO 3∶Na 2CO 3摩尔比为12∶8∶9∶1)胁迫下裸燕麦叶片H 2S含量、H 2S生成关键酶 L-半胱氨酸脱巯基酶(LCD)活性和ROS代谢相关物质含量和酶活性的影响。结果表明:喷施时期和NaHS浓度及其交互作用对盐碱胁迫下裸燕麦叶片中H 2S、超氧阴离子()、过氧化氢(H 2O 2)、丙二醛(MDA)、抗坏血酸(AsA)和谷胱甘肽(GSH)含量及LCD、超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)、抗坏血酸过氧化物酶(APX)和谷胱甘肽还原酶(GR)活性存在显著影响。与喷施0 μmol?L -1 NaHS相比,喷施一定浓度NaHS能够提高H 2S、AsA、GSH含量和LCD、SOD、CAT、POD、APX和GR活性,减少、H 2O 2和MDA积累,但以上各指标最佳的喷施时期和NaHS浓度存在差异。隶属函数综合分析显示,在幼苗期和拔节期喷施25~200 μmol?L -1 NaHS的综合评价值( D)最高,表明在幼苗—拔节期喷施25~200 μmol?L -1 NaHS能更好提高ROS清除能力,从而缓解盐碱胁迫诱导ROS对裸燕麦的氧化伤害。 相似文献
11.
Hydrogen peroxide, produced by inflammatory and vascular cells, induces oxidative stress that may contribute to endothelial dysfunction. In smooth muscle cells, H 2O 2 induces production of O 2− by activating NADPH oxidase. However, the mechanisms whereby H 2O 2 induces oxidative stress in endothelial cells are poorly understood. We examined the effects of H 2O 2 on O 2− levels on porcine aortic endothelial cells (PAEC). Treatment with 60 μmol/L H 2O 2 markedly increased intracellular O 2− levels (determined by conversion of dihydroethidium to hydroxyethidium) and produced cytotoxicity (determined by propidium iodide staining) in PAEC. Overexpression of human manganese superoxide dismutase in PAEC reduced O 2− levels and attenuated cytotoxicity resulting from treatment with H 2O 2. L-NAME, an inhibitor of nitric oxide synthase (NOS), and apocynin, an inhibitor of NADPH oxidase, reduced O 2− levels in PAEC treated with H 2O 2, suggesting that both NOS and NADPH oxidase contribute to H 2O 2-induced O 2− in PAEC. Inhibition of NADPH oxidase using apocynin and NOS rescue with L-sepiapterin together reduced O 2− levels in PAEC treated with H 2O 2 to control levels. This suggests interaction-distinct NOS and NADPH oxidase pathways to superoxide. We conclude that H 2O 2 produces oxidative stress in endothelial cells by increasing intracellular O 2− levels through NOS and NADPH oxidase. These findings suggest a complex interaction between H 2O 2 and oxidant-generating enzymes that may contribute to endothelial dysfunction. 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.
以烟草悬浮细胞BY-2(Nicotiana tabacum L.cv.Bright Yellow-2)为材料,探讨了在铜离子胁迫下植物细胞死亡发生过程中胞外H 2O 2及NADPH氧化酶所扮演的角色。实验结果表明,随着外源CuCl 2浓度的上升(从0~700 μmol·L -1),细胞死亡水平不断上升,且胞外H 2O 2的水平也不断增加。在300 μmol·L -1的CuCl 2诱导细胞死亡的过程中,加入H 2O 2清除剂N-N-二甲基硫脲(DMTU)降低了胞外CuCl 2胁迫下H 2O 2含量增加的同时也降低了细胞死亡水平的上升,这一观察表明了铜离子胁迫所导致的细胞死亡的发生和胞外H 2O 2的增加有关。进一步的研究表明,300 μmol·L -1 CuCl 2的胁迫导致了NADPH氧化酶活性的显著性上升,而加入NADPH氧化酶的抑制剂(二亚苯基碘,DPI,)则降低了CuCl 2胁迫所导致的细胞死亡和胞外H 2O 2含量的上升。上述结果表明,胞外H 2O 2和NADPH氧化酶参与了CuCl 2对植物细胞死亡的诱导作用。 相似文献
14.
1. Single reduced methyl viologen (MV .+) acts as an electron donor in a number of enzyme systems. The large changes in extinction coefficient upon oxidation (λ max 600 nm; MV .+, = 1.3 · 10 4 M −1 · cm −1; oxidised form of methyl viologen (MV 2+), = 0.0) make it ideally suited to kinetic studies of electron transfer reactions using stopped-flow and standard spectrophotometric techniques. 2. A convenient electrochemical preparation of large amounts of MV.+ has been developed. 3. A commercial stopped-flow apparatus was modified in order to obtain a high degree of anaerobicity. 4. The reaction of MV.+ with O2 produced H2O2 (k > 5 · 106 M−1 · s−1, pH 7.5, 25 °C). H2O2 subsequently reacted with excess MV.+ (k = 2.3 · 103 M−1 · s−1, pH 7.5, 25 °C) to produce water. The kinetics of this reaction were complex and have only been interpreted over a limited range of concentrations. 5. The results support the theory that the herbicidal action of methyl viologen (Paraquat, Gramoxone) is due to H2O2 (or radicals derived from H2O2) induced damage of plant cell membrane. 相似文献
15.
Trimetazidine is a well-established anti-ischemic drug, which has been used for long time in the treatment of pathological conditions related with the generation of reactive oxygen species. However, although extensively studied, its molecular mode of action remains largely unknown. In the present study, the ability of trimetazidine to protect low-density lipoproteins (LDL) from oxidation and cultured cells from H 2O 2-induced DNA damage was investigated. Trimetazidine, tested at concentrations 0.02 to 2.20 mM, was shown to offer significant protection to LDL exposed to three different oxidizing systems, namely copper, Fe/ascorbate, and met-myoglobin/H 2O 2. The oxidizability of LDL was estimated by measuring, (i) the lag period, (ii) the maximal rate of conjugated diene formation, (iii) the total amount of conjugated dienes formed, (iv) the electrophoretic migration of LDL protein in agarose gels (REM), and (v) the inactivation of the enzyme PAF-acetylhydrolase present in LDL. In addition, the presence of trimetazidine decreased considerably the DNA damage in H 2O 2-exposed Jurkat cells in culture. H 2O 2 was continuously generated by the action of glucose oxidase at a rate of 11.8 ± 1.5 μM per min (60 ng enzyme per 100 μl), and DNA damage was assessed by the single cell gel electrophoresis assay (also called comet assay). The protection offered by trimetazidine in this system (about 30% at best) was transient, indicating modification of this agent during its action. These results indicate that trimetazidine can modulate the action of oxidizing agents in different systems. Although its mode of action is not clarified, the possibility that it acts as a lipid barrier permeable transition metal chelator is considered. 相似文献
16.
Human neutrophils activatd by PMA were found to induced the formation of a nitroxide radical from DFO. The presence of SOD was necessary to permit the formation of the DFO radical. The inactive phorbol ester did not induce DFO radical, and
_sphinganine suppressed the radical produced by the active phorbol ester. Other cell stimuli (Zymocel and the chemotactic peptide) also induced the formation of the DFO radical, although radical concentration was very much lower than with PMA. Participation of .NO, ,OH or 1O 2 was ruled out by the inability of N G-methyl-L-arginine, N G-nitro-L-arginine, DMSO, mannitol, histidine, and methionine to inhibit the formation of DFO radical produced by PMA-activated cells. Furthermore, PMA-activated cells dod not produce detectable levels of NO 2−, as a stable oxidation product of .NO, and D 2, which enhances the lifetime of singlet oxygen, did not modify the intensity or the lifetime of DFO radical. The involvement of cell MPO was suggested by the inhibition of the DFO radical observed after treatment with catalase or with antihuman MPO antibodies. Also, HOCI was found to induce the DFO radical in cell-free reactions, but our data indicate that the reaction leading to DFO radical formation by neutrophils involves the reduction of MPO compound II back to active enzyme (ferric-MPO). Anti-inflammatory drugs strongly increased the DFO radical produced by activated neutrophils. On the contrary, none of these drugs was able to increase the DFO radical produced by HOCl. Histidine and methionine that inhibited the DFO radical intensity in cell-free reactions, were shown to act directly onm HOCl. Experiments with MPO-H 2O 2 in SOD- and Cl −-free conditions showed the formation of DFO radical and confirmed the hypothesis of the involvement of compound II. The conversion of compound II to ferric MPO by DFO optimized the enzymatic activity of neurophils, and in the presence of monochlorodimedon (compound II promoting agent) we measured an increased HOCl production. When DFO was modified by conjugation with hydroxyethyl starch, it lost the ability to produce the radical either by neutrophils or by MPO-H 2O 2 and did not increase HOCl production. The inability of these DFO derivatives to produce potentially toxic species migh explain their reported lower toxicity in vivo. 相似文献
17.
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
18.
以盆栽平邑甜茶为试材,分别将盆浸没于5种浓度硫化氢(H 2S)释放剂硫氢化钠(NaHS;0、0.02、0.05、0.1、0.2 mmol·L -1)水溶液,以及添加有次牛磺酸(HT;H 2S清除剂)的NaHS水溶液中,10 d后调查根系形态构型、叶片活性氧生成和光合气体交换参数以及植株生长的变化.结果表明: 在淹水处理液中加入0.02~0.1 mmol·L -1 NaHS,能增加土壤淹水时根系总长度、表面积、体积、直径、根尖数、分形维数、一级侧根数量和根系活力,降低叶片超氧阴离子(O 2-·)生成速率和过氧化氢(H 2O 2)含量,提高叶片光合速率(P n)、蒸腾速率(T r)、气孔导度(g s)、水分利用效率(WUE)和表观CO 2利用效率(CUE),还提高幼苗株高和植株生物量,其中NaHS在浓度0.1 mmol·L -1 时作用效果最显著;当NaHS施用浓度达到0.2 mmol·L -1或在0.1 mmol·L -1 NaHS中加施次牛磺酸时,上述指标均降回到单纯淹水时的水平.这说明添加适量H 2S能够有效缓解土壤淹水对平邑甜茶根系生长的抑制,可以通过减少活性氧产生以及提高CUE,从而减轻淹水胁迫对叶片光合性能和植株生长的不利影响. 相似文献
19.
Myeloperoxidase (MPO), a heme enzyme secreted by activated phagocytes, catalyzes the oxidation of halides to hypohalous acids. At plasma concentrations of halides, hypochlorous acid (HOCl) is the major strong oxidant produced. In contrast, the related enzyme eosinophil peroxidase preferentially generates hypobromous acid (HOBr). Since reagent and MPO-derived HOCl converts low-density lipoprotein (LDL) to a potentially atherogenic form, we investigated the effects of HOBr on LDL modification. Compared to HOCl, HOBr caused 2-3-fold greater oxidation of tryptophan and cysteine residues of the protein moiety (apoB) of LDL and 4-fold greater formation of fatty acid halohydrins from the lipids in LDL. In contrast, HOBr was 2-fold less reactive than HOCl with lysine residues and caused little formation of N-bromamines. Nevertheless, HOBr caused an equivalent increase in the relative electrophoretic mobility of LDL as HOCl, which was not reversed upon subsequent incubation with ascorbate, in contrast to the shift in mobility caused by HOCl. Similar apoB modifications were observed with HOBr generated by MPO/H(2)O(2)/Br(-). In the presence of equivalent concentrations of Cl(-) and Br(-), modifications of LDL by MPO resembled those seen in the presence of Br(-) alone. Interestingly, even at physiological concentrations of the two halides (100 mM Cl(-), 100 microM Br(-)), MPO utilized a portion of the Br(-) to oxidize apoB cysteine residues. MPO also utilized the pseudohalide thiocyanate to oxidize apoB cysteine residues. Our data show that even though HOBr has different reactivities than HOCl with apoB, it is able to alter the charge of LDL, converting it into a potentially atherogenic particle. 相似文献
20.
The effect of H 2O 2 on the primary structure of OxyHb was studied. Upon treatment of Oxy Hb with H 2O 2 ([Heme]/[H 2O 2] =I), tryptophan and methionine residues of the /-chain were modified. Treatment of ApoHb with H 2O 2 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 H 2O 2. The modification of histidine residues in ApoHb may be mediated by a metal-catalyzed oxidation system comprised of H 2O 2 and histidine-bound iron. The H 2O 2-mediated modification of tryptophan in the OxyHb β-chain. however, requires the heme moiety. 相似文献
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