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31.
Giorgio Brandi Flaminio Cattabeni Amedeo Albano Orazio Cantoni 《Free radical research》1989,6(1):47-55
Escherichia coli lethality by hydrogen peroxide is characterized by two modes of killing. In this paper we have found that hydroxyl radicals (OH -) generated by H2O2 and intracellular divalent iron are not involved in the induction of mode one lethality (i.e. cell killing produced by concentrations of H2O2 lower than 2.5 mM). In fact, the OH radical scavengers, thiourea, ethanol and dimethyl sulfoxide, and the iron chelator, desferrioxarnine, did not affect the survival of cells exposed to 2.5mM H2O2. In addition cell vulnerability to the same H2O2 concentration was independent on the intracellular iron content. In contrast, mode two lethality (i.e. cell killing generated by concentrations of H2O2 higher than 10mM) was markedly reduced by OH radical scavengers and desferrioxamine and was augmented by increasing the intracellular iron content.
It is concluded that OH. are required for mode two killing of E. coli by hydrogen peroxide. 相似文献
It is concluded that OH. are required for mode two killing of E. coli by hydrogen peroxide. 相似文献
32.
水稻不育花药中H_2O_2的积累与膜脂过氧化的加剧 总被引:4,自引:0,他引:4
水稻7017、二九矮细胞质雄性不育系及其保持系花药的POD,CAT和SOD活性研究的结果表明,单核早期时不育及可育花药的酶活性差异不明显,单核晚期、二核及三核期的不育花药显著低于可育花药。在不育花药中缺少两条Cu-Zn SOD同工酶带,而且O_2~ 产生效率为可育的4.1~5.5倍,并有H_2O_2和MDA的积累。不育花药中H_2O_2的积累和膜脂过氧化的加剧可能与花粉败育有关。 相似文献
33.
Sadis Matalon Joseph S. Beckman Michael E. Duffey Bruce A. Freeman 《Free radical biology & medicine》1989,6(6):557-564
The purpose of this study was to quantify the effects of extracellularly generated partially reduced oxygen species on active sodium (NA+) transport across the ventral toad skin, a well-studied epithelium. Sections of skin from decapitated toads were mounted in an Ussing chamber, bathed on both sides with electrolyte solution containing 500 μM xanthine and bubbled continuously with room air. The tissues were short-circuited, and short circuit current (Isc) and tissue resistance (Rt were monitored continuously with an automatic voltage clamp apparatus. Fifteen mU/ml of xanthine oxidase (XO), either purchased from Calbiochem or purified from cream, were instilled in either the apical (mucosal) or basolateral (serosal) baths at t = 0 and T = 10 min. Hydrogen peroxide (H2O2) concentrations increased to 200 μM within the first 20 min and then decreased, reaching a value of 40 μM by 60 min. Mean [H2O2] was 90 μM. Instillation of XO in the apical bath resulted in a large decrease in Isc and an increase in Rt, their values being 43% and 160% of their corresponding controls 85 min after the first instillation. Addition of superoxide dismutase and catalase completely prevented these changes. Instillation of XO in the basolateral bath had no effect. Similar physiological responses were obtained using the Calbiochem XO or the purified XO, which contained no measurable protease activity. It was concluded that extracellularly generated partially reduced oxygen species may interfere with active Na+ transport by possibly damaging apical Na+ channel proteins. 相似文献
34.
Vanadate-stimulated oxidation of NAD(P)H 总被引:1,自引:0,他引:1
Vanadate stimulates the oxidation of NAD(P)H by biological membranes because such membranes contain NAD(P)H oxidases which are capable of reducing dioxygen to O2− and because vanadate catalyzes the oxidation of NAD(P)H by O2−, by a free radical chain mechanism. Dihydropyridines, such as reduced nicotinamide mononucleotide (NMNH), which are not substrates for membrane-associated NAD(P)H oxidases, are not oxidized by membranes plus vanadate unless NAD(P)H is present to serve as a source of O2−. When [NMNH] greatly exceeds [NAD(P)H], in such reaction mixtures, one can observe the oxidation of many molecules of NMNH per NAD(P)H consumed. This reflects the chain length of the free radical chain mechanism. We have discussed the mechanism and significance of this process and have tried to clarify the pertinent but confusing literature. 相似文献
35.
The reaction of ribose with horseradish peroxidase in the presence of H2O2 is accompanied by light emission. The detection of horseradish peroxidase Compound II (FeO2+) indicates that the enzyme participates in a normal peroxidatic cycle. Hydrogen peroxide converts horseradish peroxidase into Compound I (FeO3+) which in turn is converted into Compound II by abstracting a hydrogen atom from ribose forming a ribosyl radical. In aerated solutions oxygen rapidly adds to the ribosyl radical. Based on the spectral characteristics and the enhancement of the chemiluminescence by chlorophyll-a, xanthene dyes, D2O and DABCO, it is suggested that the excited species, apparently triplet carbonyls and 1O2, are formed from the bimolecular decay of the peroxyl radicals via the Russell mechanism. 相似文献
36.
John M. C. Gutteridge Melinda West Kent Eneff Robert A. Floyd 《Free radical research》1990,10(3):159-165
Bleomycin, in the presence of ferric salts, oxygen and a suitable reductant, degrades DNA with the release of base propenals, detected as thiobarbituric acid (TBA) reactivity, and the formation of 8-hydroxydeo-xyguanosine (80HdG) detected by HPLC. When xanthine oxidase is added to the incubated mixture of DNA degradation products, TBA-reactivity is destroyed but 80HdG formation is increased. EPR Spin trapping experiments show that hydroxyl radicals (OH) are formed in the reaction mixture and can be inhibited by the inclusion of either superoxide dismutase or catalase. These findings suggest that the base propenals and possibly malondialdehyde, formed from them, are aldehydic substrates for xanthine oxidase and, the product of this reaction is superoxide (O2-) and hydrogen peroxide (H2O2). Thus, TBA reactivity is destroyed in the formation of O2- and H2O2 which stimulate further oxidative damage to DNA resulting in increased 8OHdG formation. 相似文献
37.
Alasdair J. Carmichael 《Free radical research》1990,10(1):37-45
Vanadyl reacts with hydrogen peroxide forming hydroxyl radicals in a Fenton-like reaction. The hydroxyl radicals were spin trapped and identified using 5.5-dimethyl-I-pyrroline-N-oxide (DMPO). The quantity of hydroxyl radicals spin trapped during the reaction between vanadyl and hydrogen peroxide are equal to half of the hydroxyl radicals spin trapped during the reaction between ferrous ions and hydrogen peroxide. Experiments in the presence of formate show that this hydroxyl radical scavenger effectively competes with DMPO preventing the formation of the DMPO-OH adduct. However. in experiments using ethanol as the hydroxyl radical scavenger it was not possible to completely prevent the formation of DMPO-OH. The formation of this additional DMPO-OH in the presence of ethanol does not depend on the concentration of dissolved oxygen, but does depend on the concentration of hydrogen peroxide added to the vanadyl solution. The results suggest that the additional DMPO-OH formed in the presence of ethanol originates from a vanadium (V) intermediate. This intermediate may oxidize DMPO leading to the formation of DMPO-0; which rapidly decomposes forming DMPO-OH. 相似文献
38.
Most carcinogens, including polycyclic aromatic hydrocarbons (PAH), require metabolic activation to produce the ultimate electrophilic species that bind covalently with cellular macromolecules to trigger the cancer process. Metabolic activation of PAH can be understood in terms of two main pathways: one-electron oxidation to yield reactive intermediate radical cations and monooxygenation to produce bay-region diol epoxides. The reason we have postulated that one-electron oxidation plays an important role in the activation of PAH derives from certain common characteristics of the radical cation chemistry of the most potent carcinogenic PAH. Two main features common to these PAH are: 1) a relatively low ionization potential, which allows easy metabolic removal of one electron, and 2) charge localization in the PAH radical cation that renders this intermediate specifically and efficiently reactive toward nucleophiles. Equally important, cytochrome P-450 and mammalian peroxidases catalyze one-electron oxidation. This mechanism plays a role in the binding of PAH to DNA. Chemical, biochemical and biological evidence will be presented supporting the important role of one-electron oxidation in the activation of PAH leading to initiation of cancer. 相似文献
39.
How to Characterize a Biological Antioxidant 总被引:15,自引:0,他引:15
Barry Halliwell 《Free radical research》1990,9(1):1-32
An antioxidant is a substance that, when present at low concentrations compared to those of an oxidizable substrate, significantly delays or prevents oxidation of that substrate. Many substances have been suggested to act as antioxidants in vivo, but few have been proved to do so. The present review addresses the criteria necessary to evaluate a proposed antioxidant activity. Simple methods for assessing the possibility of physiologically-feasible scavenging of important biological oxidants (superoxide, hydrogen peroxide, hydroxyl radical, hypochlorous acid, haem-associated ferryl species, radicals derived from activated phagocytes, and peroxyl radicals, both lipid-soluble and water-soluble) are presented, and the appropriate control experiments are described. Methods that may be used to gain evidence that a compound actually does function as an antioxidant in vivo are discussed. A review of the pro-oxidant and anti-oxidant properties of ascorbic acid that have been reported in the literature leads to the conclusion that this compound acts as an antioxidant in vivo under most circumstances. 相似文献
40.
Studies documenting spin trapping of lipid radicals in defined model systems have shown some surprising solvent effects with the spin trap DMPO. In aqueous reactions comparing the reduction of H2O2 and methyl linoleate hydroperoxide (MLOOH) by Fez+, hydroxyl (HO·) and lipid alkoxyl (LO·) radicals produce identical four-line spectra with line intensities 1:2:2:1. Both types of radicals react with commonly-used HO· scavengers, e.g. with ethanol to produce ·C(CH3)HOH and with dirnethylsulfoxide (DMSO)togive ·CH3. However, DMSO radicals (either ·CH3or ·OOCH3) react further with lipids, and when radicals are trapped in these MLOOH systems, multiple adducts are evident. When acetonitrile is added to the aqueous reaction systems in increasing concentrations, ·CH2CN radicals resulting from HO· attack on acetonitrile are evident, even with trace quantities of that solvent. In contrast, little, if any, reaction of LO· with acetonitrile occurs, even in 100% acetonitrile. A single four-line signal persists in the lipid systems as long as any water is present, although the relative intensity of the two center lines decreases as solvent-induced changes gradually dissociate the nitrogen and β-hydrogen splitting constants. Extraction of the aqueous-phase adducts into ethyl acetate shows clearly that the identical four-line spectra in the H202 and MLOOH systems arise from different radical species in this study, but the lack of stability of the adducts to phase transfer may limit the use of this technique for routine adduct identification in more complex systems. These results indicate that the four-line 1:2:2:1. aN = aH = 14.9G spectrum from DMPO cannot automatically be assigned to the HO· adduct in reaction systems where lipid is present, even when the expected spin adducts from ethanol or DMSO appear confirmatory for HO-. Conclusive distinction between HO· and LO· ultimately will require use of 13C-labelled DMPO or HPLC-MS separation and specific identification of adducts when DMPO is used as the spin trap. 相似文献