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1.
María Eugenia Letelier Sebastián Sánchez-Jofré Liliana Peredo-Silva Juan Cortés-Troncoso Paula Aracena-Parks 《Chemico-biological interactions》2010,188(1):220-227
Iron and copper ions, in their unbound form, may lead to the generation of reactive oxygen species via Haber–Weiss and/or Fenton reactions. In addition, it has been shown that copper ions can irreversibly and non-specifically bind to thiol groups in proteins. This non-specific binding property has not been fully addressed for iron ions. Thus, the present study compares both the pro-oxidant and the non-specific binding properties of Fe3+ and Cu2+, using rat liver cytosol and microsomes as biological systems. Our data show that, in the absence of proteins, Cu2+/ascorbate elicited more oxygen consumption than Fe3+/ascorbate under identical conditions. Presence of cytosolic and microsomal protein, however, differentially altered oxygen consumption patterns. In addition, Cu2+/ascorbate increased microsomal lipid peroxidation and decreased cytosolic and microsomal content of thiol groups more efficiently than Fe3+/ascorbate. Finally, Fe3+/ascorbate and Cu2+/ascorbate inhibited in different ways cytosolic and microsomal glutathione S-transferase (GST) activities, which are differentially sensitive to oxidants. Moreover, in the absence of ascorbate, only Cu2+ decreased the content of cytosolic and microsomal thiol groups and inhibited cytosolic and microsomal GST activities. Catechin partially prevented the damage to thiol groups elicited by Fe3+/ascorbate and Cu2+/ascorbate but not by Cu2+ alone. N-Acetylcysteine completely prevented the damage elicited by Cu2+/ascorbate, Fe3+/ascorbate and Cu2+ alone. N-Acetylcysteine also completely reversed the damage to thiol groups elicited by Fe3+/ascorbate, partially reversed that of Cu2+/ascorbate but failed to reverse the damage promoted by Cu2+ alone. Our data are discussed in terms to the potential damage that the accumulation of iron and copper ions can promote in biological systems. 相似文献
2.
《Biochimica et Biophysica Acta (BBA) - Enzymology》1980,611(1):51-60
Product inhibition of lysyl hydroxylase (peptidyllysine, 2-oxoglutarate:oxygen 5-oxidoreductase, EC 1.14.11.4) was studied with succinate, CO2, dehydroascorbate and hydroxylysine-rich polypeptide chains. The product inhibition patterns and addition data are consistent with a reaction mechanism involving an ordered binding of Fe2+, α-ketoglutarate, O2 and the peptide substrate to the enzyme in this order, and an ordered release of the hydroxylated peptide, CO2, succinate and Fe2+, in which Fe2+ need not leave the enzyme during each catalytic cycle and in which the order of release of the hydroxylated peptide and CO2 is uncertain. Ascorbate probably reacts by a substitution mechanism, either after the release of the hydroxylated peptide, CO2 and succinate or after the release of all products, including Fe2+, and dehydroascorbate is released before the binding of Fe2+. It is suggested that the ascorbate reaction is required to reduce either the enzyme-iron complex or the free enzyme, which may be oxidized by a side-reaction during some catalytic cycles, but not the majority. The mechanisms of the prolyl 4-hydroxylase and lysyl hydroxylase reactions are suggested to be identical.Zn2+, several citric acid cycle intermediates, nitroblue tetrazolium and homogentisic acid inhibited lysyl hydroxylase competitively with regard to Fe2+, α-ketoglutarate, O2 and ascorbate respectively, and epinephrine noncompetitively with regard to all cosubstrates. Apparent Ki values are given for the product and other inhibitors. 相似文献
3.
Shumyantseva VV Bulko TV Kuznetsova GP Lisitsa AV Ponomarenko EA Karuzina II Archakov AI 《Biochemistry. Biokhimii?a》2007,72(6):658-663
The electrochemical reduction of the heme protein sterol-14α-demethylase from Mycobacterium tuberculosis (CYP51b1, or further CYP51) was investigated. Direct electron transfer was demonstrated between CYP51 and graphite screen-printed
electrodes modified with gold nanoparticles and with the membrane-like synthetic surfactant didodecyl dimethylammonium bromide.
The formal potential of the Fe3+/Fe2+ pair, E
1/2, is equal to −273 mV (vs. Ag/AgCl). The cathodic current corresponding to the reduction of oxygen by immobilized heme protein
was registered in the presence of oxygen. Addition of lanosterol, one of the substrates of the CYP51 family, to the oxygenated
solution caused a concentration-dependent increase in the reduction current in voltammetric and amperometric experiments.
Ketoconazole, an inhibitor of CYP51, inhibited the catalytic cathodic current in the presence of lanosterol. Electrochemical
reduction of CYP51 may serve as an adequate alternative to the reconstituted system, which requires additional redox partners
for the exhibition of catalytic activity of heme proteins of the cytochrome P450 superfamily.
Published in Russian in Biokhimiya, 2007, Vol. 72, No. 6, pp. 805–811. 相似文献
4.
Dynamic equilibria in iron uptake and release by ferritin 总被引:7,自引:0,他引:7
The function of ferritins is to store and release ferrous iron. During oxidative iron uptake, ferritin tends to lower Fe2+ concentration, thus competing with Fenton reactions and limiting hydroxy radical generation. When ferritin functions as a releasing iron agent, the oxidative damage is stimulated. The antioxidant versus pro-oxidant functions of ferritin are studied here in the presence of Fe2+, oxygen and reducing agents. The Fe2+-dependent radical damage is measured using supercoiled DNA as a target molecule. The relaxation of supercoiled DNA is quantitatively correlated to the concentration of exogenous Fe2+, providing an indirect assay for free Fe2+. After addition of ferrous iron to ferritin, Fe2+ is actively taken up and asymptotically reaches a stable concentration of 1–5
m. Comparable equilibrium concentrations are found with plant or horse spleen ferritins, or their apoferritins. After addition of ascorbate, iron release is observed using ferrozine as an iron scavenger. Rates of iron release are dependent on ascorbate concentration. They are about 10 times larger with pea ferritin than with horse ferritin. In the absence of ferrozine, the reaction of ascorbate with ferritins produces a wave of radical damage; its amplitude increases with increased ascorbate concentrations with plant ferritin; the damage is weaker with horse ferritin and less dependent on ascorbate concentrations. 相似文献
5.
The ATP.Mg-dependent type 1 protein phosphatase is inactive as isolated but can be activated in several different ways. In this report, we show that the phosphatase can also be activated by the Fe2+/ascorbate system. Activation of the phosphatase requires both Fe2+ ion and ascorbate and the level of activation is dependent on the concentrations of Fe2+ ion and ascorbate. In the presence of 20 mM ascorbate, the Fe2+ ion concentrations required for half-maximal and maximal activation are about 0.3 and 3mM, respectively. Several common divalent metal ions, including Co2+, Ni2+, Cu2+, Mg2+, and Ca2+ ions, cannot cooperate with ascorbate to activate the phosphatase, and SH-containing reducing agents such as 2-mercaptoethanol and dithiothreitol cannot cooperate with Fe2+ ion to activate the phosphatase, indicating that activation of the phosphatase by the Fe2+/ascorbate system is a specific process. Moreover, H2O2, a strong oxidizer, could significantly diminish the phosphatase activation by the Fe2+/ascorbate system, suggesting that reduction mechanism other than SH-SS interchange is a prerequisite for the Fe2+/ascorbate-mediated phosphatase activation. Taken together, the present study provides initial evidence for a new mode of type 1 protein phosphatase activation mechanism. 相似文献
6.
The ATP.Mg-dependent type 1 protein phosphatase is inactive as isolated but can be activated in several different ways. In this report, we show that the phosphatase can also be activated by the Fe2+/ascorbate system. Activation of the phosphatase requires both Fe2+ ion and ascorbate and the level of activation is dependent on the concentrations of Fe2+ ion and ascorbate. In the presence of 20 mM ascorbate, the Fe2+ ion concentrations required for half-maximal and maximal activation are about 0.3 and 3mM, respectively. Several common divalent metal ions, including Co2+, Ni2+, Cu2+, Mg2+, and Ca2+ ions, cannot cooperate with ascorbate to activate the phosphatase, and SH-containing reducing agents such as 2-mercaptoethanol and dithiothreitol cannot cooperate with Fe2+ ion to activate the phosphatase, indicating that activation of the phosphatase by the Fe2+/ascorbate system is a specific process. Moreover, H2O2, a strong oxidizer, could significantly diminish the phosphatase activation by the Fe2+/ascorbate system, suggesting that reduction mechanism other than SH-SS interchange is a prerequisite for the Fe2+/ascorbate-mediated phosphatase activation. Taken together, the present study provides initial evidence for a new mode of type 1 protein phosphatase activation mechanism.Abbreviations MAPK
mitogen-activated protein kinase
- MCO
metal ion-catalyzed oxidation
- kinase FA
the activating factor of ATP.Mg-dependent protein phosphatase
- I2
inhibitor-2
- EDTA
ethylenediaminetetraacetic acid
- MBP
myelin basic protein 相似文献
7.
Transmembrane Electron Transport in Plasma Membrane Vesicles Loaded with an NADH-Generating System or Ascorbate 总被引:3,自引:2,他引:1
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Sugar beet (Beta vulgaris L.) leaf plasma membrane vesicles were loaded with an NADH-generating system (or with ascorbate) and were tested spectrophotometrically for their ability to reduce external, membrane-impermeable electron acceptors. Either alcohol dehydrogenase plus NAD+ or 100 millimolar ascorbate was included in the homogenization medium, and right-side-out (apoplastic side-out) plasma membrane vesicles were subsequently prepared using two-phase partitioning. Addition of ethanol to plasma membrane vesicles loaded with the NADH-generating system led to a production of NADH inside the vesicles which could be recorded at 340 nanometers. This system was able to reduce 2,6-dichlorophenolindophenol-3′-sulfonate (DCIP-sulfonate), a strongly hydrophilic electron acceptor. The reduction of DCIP-sulfonate was stimulated severalfold by the K+ ionophore valinomycin, included to abolish membrane potential (outside negative) generated by electrogenic transmembrane electron flow. Fe3+-chelates, such as ferricyanide and ferric citrate, as well as cytochrome c, were not reduced by vesicles loaded with the NADH-generating system. In contrast, right-side-out plasma membrane vesicles loaded with ascorbate supported the reduction of both ferric citrate and DCIP-sulfonate, suggesting that ascorbate also may serve as electron donor for transplasma membrane electron transport. Differences in substrate specificity and inhibitor sensitivity indicate that the electrons from ascorbate and NADH were channelled to external acceptors via different electron transport chains. Transplasma membrane electron transport constituted only about 10% of total plasma membrane electron transport activity, but should still be sufficient to be of physiological significance in, e.g. reduction of Fe3+ to Fe2+ for uptake. 相似文献
8.
Dehydrocyclopeptine epoxidase (DE) activity was determined in cell free preparations of Penicillium cyclopium. The enzyme transforms dehydrocyclopeptine into cyclopenin by a mixed function oxygenation. It needs molecular oxygen and uses NAD(P)H, ascorbate or d,l-6-methyl-5,6,7,8-tetrahydropteridine as cosubstrates. DE is inhibited by CN?, SCN?, 1,10-phenanthroline, EDTA, 2,2′-bipyridine, sodium diethyldithiocarbamate, dicoumarol, p-chloromercuribenzoate and ions of different heavy metals, but not by CO and the lead salt of diethyldithiocarbamate. These properties indicate a specific importance of Fe2+-ions, SH-groups and flavins. DE activity is increased by Fe2+ and FAD. The enzyme may be therefore a Fe2+ activated FAD containing flavoprotein. DE was enriched 268-fold by (NH4)2SO4 precipitation and chromatography on Sephadex G-200. Its MW estimated by Sephadex chromatography, exceeds 480 000. 相似文献
9.
Cornelis M. Visser 《Bioorganic chemistry》1980,9(2):261-271
The proposition is made that the enzymes that catalyze ascorbate-dependent hydroxylation reactions in metabolism make use of a primordial dioxygen fixation system, in which a ferrous ascorbate complex is the central and permanent catalytic unit. It is suggested that dioxygen on bonding to the complex becomes a nucleophile that will react with an electrophilic and easily oxidizable compound, such as an α-ketoacid. This gives rise to a presumably fairly stable intermediate ferryl ascorbate complex that acts as an electrophilic oxenoid both in ascorbate-dependent oxygenase reactions and in chemical models thereof, such as Udenfriend's system (ascorbate and Fe2?, with or without EDTA in water). A similar ferryl species with easily oxidizable ligands is suggested to be the oxenoid in other oxygenase reactions such as the tetrahydrobiopterin and the cytochrome P-450-dependent monooxygenases. 相似文献
10.
Aldo Escobar Victoria Gaete Marco Tulio Núñez 《Journal of bioenergetics and biomembranes》1992,24(2):227-233
Externally added ascorbate or NADH effectively reduced ferricyanide and promoted the exit of Fe3+ originated from acid-destabilized transferrin contained inside endocytic vesicles. The effect of ascorbate was mediated by an ascorbate uptake system, and the effect of NADH was mediated by the membrane-associated oxidoreductase. At physiological concentrations of both ascorbate and NADH, the ascorbate transport and the NADH-oxidoreductase system were additive as measured by the rate of reduction of ferricyanide and by the mobilization of transferrin-associated iron. The results indicate that Fe3+ reduction may occur by a nonenzymatic reaction with ascorbate transported into the vesicle lumen. The ascorbate-mediated reduction of iron derived from transferrin occurring in the endosome could play a major role in cellular iron uptake. 相似文献
11.
Ying Liu Ana Pocivavsek Vassilios Papadopoulos 《The Journal of steroid biochemistry and molecular biology》2009,115(3-5):86-90
Cytochrome P450 17α-hydroxylase/17, 20 lyase (CYP17) is a microsomal enzyme reported to have two distinct catalytic activities, 17α-hydroxylase and 17, 20 lyase, that are essential for the biosynthesis of peripheral androgens such as dehydroepiandrosterone (DHEA). Paradoxically, DHEA is present and plays a role in learning and memory in the adult rodent brain, while CYP17 activity and protein are undetectable. To determine if CYP17 is required for DHEA formation and function in the adult rodent brain, we generated CYP17 chimeric mice that had reduced circulating testosterone levels. There were no detectable differences in cognitive spatial learning between CYP17 chimeric and wild-type mice. In addition, while CYP17 mRNA levels were reduced in CYP17 chimeric compared to wild-type mouse brain, the levels of brain DHEA levels were comparable. To determine if adult brain DHEA is formed by an alternative Fe2+-dependent pathway, brain microsomes were isolated from wild-type and CYP17 chimeric mice and treated with FeSO4. Fe2+ caused comparable levels of DHEA production by both wild-type and CYP17 chimeric mouse brain microsomes; DHEA production was not reduced by a CYP17 inhibitor. Taken together these in vivo studies suggest that in the adult mouse brain DHEA is formed via a Fe2+-sensitive CYP17-independent pathway. 相似文献
12.
Ghosh Mrinal K. Mukhopadhyay Mau Chatterjee Indu B. 《Molecular and cellular biochemistry》1997,166(1-2):35-44
In this paper we demonstrate that ascorbic acid specifically prevents NADPH-initiated cytochrome P450 (P450)-mediated microsomal lipid peroxidation in the absence of free iron. Lipid peroxidation has been evidenced by the formations of conjugated dienes, lipid hydroperoxide and malondialdehyde. Other scavengers of reactive oxygen species including superoxide dismutase, catalase, glutathione, -tocopherol, uric acid, thiourea, mannitol, histidine, -carotene and probucol are ineffective to prevent the NADPH-initiated P450-mediated free iron-independent microsomal lipid peroxidation. Using a reconstituted system comprised of purified NADPH-P450 reductase, P450 and isolated microsomal lipid or pure L--phosphatidylcholine diarachidoyl, a mechanism has been proposed for the iron-independent microsomal lipid peroxidation and its prevention by ascorbic acid. It is proposed that the perferryl moiety P450 Fe3+. O2 initiates lipid peroxidation by abstracting methylene hydrogen from polyunsaturated lipid to form lipid radical, which then combines with oxygen to produce the chain propagating peroxyl radical for subsequent formation of lipid peroxides. Apparently, ascorbic acid prevents initiation of lipid peroxidation by interacting with P450 Fe3+. O2. (Mol Cell Biochem 166: 35-44, 1997) 相似文献
13.
Deferiprone (L1) is an effective iron-chelating drug that is widely used for the treatment of iron-overload diseases. It is known that in aqueous solutions Fe2+ and Fe3+ ions can produce hydroxyl radicals via Fenton and photo-Fenton reactions. Although previous studies with Fe2+ have reported ferroxidase activity by L1 followed by the formation of Fe3+ chelate complexes and potential inhibition of Fenton reaction, no detailed data are available on the molecular antioxidant mechanisms involved. Similarly, in vitro studies have also shown that L1–Fe3+ complexes exhibit intense absorption bands up to 800 nm and might be potential sources of phototoxicity. In this study we have applied an EPR spin trapping technique to answer two questions: (1) does L1 inhibit the Fenton reaction catalyzed by Fe2+ and Fe3+ ions and (2) does UV–Vis irradiation of the L1–Fe3+ complex result in the formation of reactive oxygen species. PBN and TMIO spin traps were used for detection of oxygen free radicals, and TEMP was used to trap singlet oxygen if it was formed via energy transfer from L1 in the triplet excited state. It was demonstrated that irradiation of Fe3+ aqua complexes by UV and visible light in the presence of spin traps results in the appearance of an EPR signal of the OH spin adduct (TMIO–OH, a(N)=14.15 G, a(H)=16.25 G; PBN–OH, a(N)=16.0 G, a(H)=2.7 G). The presence of L1 completely inhibited the OH radical production. The mechanism of OH spin adduct formation was confirmed by the detection of methyl radicals in the presence of dimethyl sulfoxide. No formation of singlet oxygen was detected under irradiation of L1 or its iron complexes. Furthermore, the interaction of L1 with Fe2+ ions completely inhibited hydroxyl radical production in the presence of hydrogen peroxide. These findings confirm an antioxidant targeting potential of L1 in diseases related to oxidative damage. 相似文献
14.
《Free radical research》2013,47(1-5):141-150
The interaction of superoxide ion and ascorbate anion with anthracycline antibiotics (adriamycin and aclacinimycin A) as well as with their Fe3+ complexes has been studied in aprotic and protic media. It was found that both superoxide and ascorbate reduce anthracyclines to deoxyaglycons via a one-electron transfer mechanism under all conditions studied. The reaction of ascorbate anion with adriamycin and aclacinomycin A in aqueous solution proceeded only in the presence of Fe3+ ions; it is supposed that an active catalytic species was Fe3+ adriamycin. It is also supposed that the reduction of anthracycline antibiotics by O,7 and ascorbate in cells may increase their anticancer effect. 相似文献
15.
E. D. Wills 《The Biochemical journal》1969,113(2):325-332
1. Metal ion-chelating agents such as EDTA, o-phenanthroline or desferrioxamine inhibit lipid peroxide formation when rat liver microsomes prepared from homogenates made in pure sucrose are incubated with ascorbate or NADPH. 2. Microsomes treated with metal ion-chelating agents do not form peroxide on incubation unless inorganic iron (Fe2+ or Fe3+) in a low concentration is added subsequently. No other metal ion can replace inorganic iron adequately. 3. Microsomes prepared from sucrose homogenates containing EDTA (1mm) do not form lipid peroxide on incubation with ascorbate or NADPH unless Fe2+ is added. Washing the microsomes with sucrose after preparation restores most of the capacity to form lipid peroxide. 4. Lipid peroxide formation in microsomes prepared from sucrose is stimulated to a small extent by inorganic iron but to a greater extent if adenine nucleotides, containing iron compounds as a contaminant, are added. 5. The iron contained in normal microsome preparations exists in haem and in non-haem forms. One non-haem component in which the iron may be linked to phosphate is considered to be essential for both the ascorbate system and NADPH system that catalyse lipid peroxidation in microsomes. 相似文献
16.
K Sugioka H Nakano T Noguchi J Tsuchiya M Nakano 《Biochemical and biophysical research communications》1981,100(3):1251-1258
The system, which contains NADPH, purified cytochrome P-450 reductase, and adriamycin, produces H2O2 and in appreciable amounts with oxygen consumption and NADPH oxidation under aerobic conditions. Such an adriamycin-induced NADPH oxidation system, however, does not cause the decomposition of unsaturated fatty acids in microsomal phospholipid micelles, suggesting no direct participation of the active oxygen species and semiquinone radicals of adriamycin in lipid peroxidation. Adriamycin produces a co-ordination complex with Fe3+ and ADP, which, but no Fe3+-ADP complex, could be reduced by NADPH-cytochrome P-450 reductase at the expence of NADPH. The decomposition of unsaturated fatty acids in phospholipid micelles is achieved by the Fe3+-ADP-adriamycin complex and strikingly enhanced by enzymatically reduced iron-ADP-adriamycin complex. 相似文献
17.
Pharmacological ascorbate has been shown to induce toxicity in a wide range of cancer cell lines. Pharmacological ascorbate in animal models has shown promise for use in cancer treatment. At pharmacological concentrations the oxidation of ascorbate produces a high flux of H2O2 via the formation of ascorbate radical (Asc•-). The rate of oxidation of ascorbate is principally a function of the level of catalytically active metals. Iron in cell culture media contributes significantly to the rate of H2O2 generation. We hypothesized that increasing intracellular iron would enhance ascorbate-induced cytotoxicity and that iron chelators could modulate the catalytic efficiency with respect to ascorbate oxidation. Treatment of cells with the iron-chelators deferoxamine (DFO) or dipyridyl (DPD) in the presence of 2 mM ascorbate decreased the flux of H2O2 generated by pharmacological ascorbate and reversed ascorbate-induced toxicity. Conversely, increasing the level of intracellular iron by preincubating cells with Fe-hydroxyquinoline (HQ) increased ascorbate toxicity and decreased clonogenic survival. These findings indicate that redox metal metals, e.g., Fe3+/Fe2+, have an important role in ascorbate-induced cytotoxicity. Approaches that increase catalytic iron could potentially enhance the cytotoxicity of pharmacological ascorbate in vivo. 相似文献
18.
Role of a Ferric Ion-Reducing System in Sulfur Oxidation of Thiobacillus ferrooxidans 总被引:4,自引:9,他引:4
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Tsuyoshi Sugio Chitoshi Domatsu Osamu Munakata Tatsuo Tano Kazutami Imai 《Applied microbiology》1985,49(6):1401-1406
The properties of a ferric ion-reducing system which catalyzes the reduction of ferric ion with elemental sulfur was investigated with a pure strain of Thiobacillus ferrooxidans. In anaerobic conditions, washed intact cells of the strain reduced 6 mol of Fe3+ with 1 mol of elemental sulfur to give 6 mol of Fe2+, 1 mol of sulfate, and a small amount of sulfite. In aerobic conditions, the 6 mol of Fe2+ produced was immediately reoxidized by the iron oxidase of the cell, with a consumption of 1.5 mol of oxygen. As a result, Fe2+ production was never observed under aerobic conditions. However, in the presence of 5 mM cyanide, which completely inhibits the iron oxidase of the cell, an amount of Fe2+ production comparable to that formed under anaerobic conditions was observed under aerobic conditions. The ferric ion-reducing system had a pH optimum between 2.0 and 3.8, and the activity was completely destroyed by 10 min of incubation at 60°C. A short treatment of the strain with 0.5% phenol completely destroyed the ferric ion-reducing system of the cell. However, this treatment did not affect the iron oxidase of the cell. Since a concomitant complete loss of the activity of sulfur oxidation by molecular oxygen was observed in 0.5% phenol-treated cells, it was concluded that the ferric ion-reducing system plays an important role in the sulfur oxidation activity of this strain, and a new sulfur-oxidizing route is proposed for T. ferrooxidans. 相似文献
19.
Ming Tien Lee A. Morehouse John R. Bucher Steven D. Aust 《Archives of biochemistry and biophysics》1982,218(2):450-458
Experiments were performed which illustrate the various ways EDTA can influence lipid peroxidation. Either detergent-dispersed linoleate, or liposomes made from extracted microsomal phospholipids were utilized as substrates for peroxidation. Peroxidation was accomplished using Fe2+ or Fe3+. In systems utilizing Fe2+, EDTA chelation facilitated Fe2+ autoxidation which in turn caused peroxidation of detergent-dispersed linoleate. Peroxidation was not initiated during EDTA-Fe2+ autoxidation when the substrate lipids were in a liposomal configuration. Systems utilizing Fe3+ required an enzyme (either xanthine oxidase or NADPH-cytochrome P450 reductase) to reduce the iron for peroxidative activity. EDTA chelation of Fe3+ enhanced the xanthine oxidase and NADPH-cytochrome P450 reductase-catalyzed peroxidation of detergent-dispersed linoleate, presumably by facilitating the reduction of Fe3+. Catalase and mannitol inhibited both EDTA-Fe2+- and EDTA-Fe3+-dependent lipid peroxidation. EDTA-Fe3+ was not capable of initiating peroxidation of phospholipid liposomes following enzymatic reduction by either enzyme, but ADP-chelated iron effectively initiated liposomal peroxidation in similar systems. With xanthine oxidase-catalyzed peroxidation of liposomes with ADP-Fe3+, the inclusion of EDTA-Fe3+ caused a modest enhancement of activity. EDTA-Fe3+ greatly stimulated NADPH-cytochrome P450 reductase-catalyzed peroxidation of liposomes with ADP-Fe3+. In contrast, the addition of EDTA, rather than EDTA-Fe3+ inhibited the liposomal peroxidation catalyzed by either enzyme with ADP-Fe3+ when the EDTA concentration exceeded the concentration of Fe3+. 相似文献
20.
The effects of ascorbate and a-tocopherol as antioxidants and as co-operative factors against NADPH-dependent lipid peroxidation in human placental mitochondria have been studied. The addition of ascorbate at low concentration (up to 50 M) to the NADPH-generating system resulted in increasing lipid peroxidation and Fe3+ to Fe2+ reduction. High concentration of ascorbate (150 M), which produced maximal rate of ascorbate-dependent lipid peroxidation, was found to inhibit almost completely NADPH-dependent lipid peroxidation by maintaining too much iron in its reduced form. Either stimulatory or inhibitory effect of ascorbate on NADPH-dependent lipid peroxidation depends on the appropriate Fe3+/Fe2+ ratio. -Tocopherol caused a decrease of NADPH-dependent lipid peroxidation, inhibiting completely this process at 150 M concentration. The inhibitory effect of -tocopherol increased rapidly with the increasing ascorbate concentration, almost complete inhibition of NADPH-dependent lipid peroxidation being obtained at 25 M -tocopherol and 50 M ascorbate. This strong inhibitory combined effect of -tocopherol and ascorbate was independent of the Fe3+/Fe2+ ratio, as a-tocopherol is not able to reduce Fe3+ to Fe2+ under the conditions employed. These findings suggest that antioxidant effects of ascorbate in placental mitochondria are mediated by recycling of a-tocopherol rather than by strong reduction of Fe3+ to Fe2+. On the basis of the results obtained, we assume that adequate concentrations of a-tocopherol and ascorbate in placental tissue may prevent the release of lipid peroxide from placental mitochondria and therefore could be protective against the development of preeclampsia. 相似文献