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1.
The Fe3+-doxorubicin complex undergoes reactions that suggest that the complex self-reduces to a ferrous oxidized-doxorubicin free radical species. The Fe3+-doxorubicin system is observed to reduce ferricytochrome c, consume O2 and react with 2,2′-bipyridine. Bipyridine acts as a “ferrous ion scavenger” as it reacts with the ferrous ion produced by Fe3+-doxorubicin self-reduction. In the absence of O2, a ferrous doxorubicin complex accumulates. In the presence of oxygen, Fe2+ recycles back to Fe3+. The rates of these reactions were measured and the Fe3+-doxorubicin self-reduction was determined to be the rate-determining step. The Fe3+-doxorubicin induced inactivation of cytochrome c oxidase and NADH cytochrome c reductase on beef heart submitochondrial particles occurs at a rate similar to Fe3+-doxorubicin self-reduction. Thus the rate at which damage to these mitochondrial enzymes occurs may be controlled by a nonezymatic Fe3+-doxorubicin self-reduction.  相似文献   

2.
Eugene Mochan  Hans Degn 《BBA》1969,189(3):354-359
1. Ferricytochrome c acts as a catalyst in the peroxidation of ferrocytochrome c thereby giving rise to an autocatalytic reaction.

2. The rate of the peroxidation reaction is proportional to the concentration of H2O2 and ferricytochrome c but is independent of the concentration of ferrocytochrome c in the concentration ranges studied.

3. Integration of the rate equation, d[c3+]/dt = k[c3+][H2O2], gives a theoretical expression which fits the experimental time courses for the ferrocytochrome c peroxidation reaction.

4. No direct spectral evidence was found for the formation of a catalytically active ferricytochrome c-H2O2 derivative. Kinetic evidence is presented, however, which indicates the existence of such an intermediate.

5. Ferricytochrome c was more susceptible than ferrocytochrome c to an apparent degradation reaction caused by excess H2O2, thus supporting the idea that the cytochrome c heme iron is more accessible in the oxidized form.  相似文献   


3.
1. The reduction of cytochrome c oxidase by hydrated electrons was studied in the absence and presence of cytochrome c.

2. Hydrated electrons do not readily reduce the heme of cytochrome c oxidase. This observation supports our previous conclusion that heme a is not directly exposed to the solvent.

3. In a mixture of cytochrome c and cytochrome c oxidase, cytochrome c is first reduced by hydrated electrons (k = 4 · 1010 M−1 · s−1 at 22 °C and pH 7.2) after which it transfers electrons to cytochrome c oxidase with a rate constant of 6 · 107 M−1 · s−1 at 22 °C and pH 7.2.

4. It was found that two equivalents of cytochrome c are oxidized initially per equivalent of heme a reduced, showing that one electron is accepted by a second electron acceptor, probably one of the copper atoms of cytochrome c oxidase.

5. After the initial reduction, redistribution of electrons takes place until an equilibrium is reached similar to that found in redox experiments of Tiesjema, R. H., Muijsers, A. O. and Van Gelder, B. F. (1973) Biochim. Biophys. Acta 305, 19–28.  相似文献   


4.
The interaction of horse ferricytochrome c with the reagents [Fe(EDTA)(H2O)] and [Cr(CN)6]3− were studied at pH 7 and 25°C by 1H-NMR spectroscopy. Two binding regions near to the heme crevice of cytochrome c were identified. Both regions bound both reagents but they exhibited different selectivities.

The relevance of this finding to the electron-transfer function of cytochrome c is discussed.  相似文献   


5.
P.Muir Wood 《BBA》1974,357(3):370-379
The rate of electron transfer between reduced cytochrome ƒ and plastocyanin (both purified from parsley) has been measured as k = 3.6 · 107 M−1 · s−1, at 298 °K and pH 7.0, with activation parameters ΔH = 44 kJ · mole−1 and ΔS = +46 J · mole−1 · °K−1. Replacement of cytochrome ƒ with red algal cytochrome c-553, Pseudomonas cytochrome c-551 and mammalian cytochrome c gave rates at least 30 times slower: k = 5 · 105, 7.5 · 105 and 1.0 · 106 M−1 · s−1, respectively.

Similar measurements made with azurin instead of plastocyanin gave k = 6 · 106 and approx. 2 · 107 M−1 · s−1 for reaction of reduced azurin with cytochrome ƒ and algal cytochrome respectively.

Rate constants of 115 and 80 M−1 · s−1 were found for reduction of plastocyanin by ascorbate and hydroquinone at 298 °K and pH 7.0. The rate constants for the oxidation of plastocyanin, cytochrome ƒ, Pseudomonas cytochrome c-551 and red algal cytochrome c-553 by ferricyanide were found to be between 3 · 104 and 8 · 104 M−1 · s−1.

The results are discussed in relation to photosynthetic electron transport.  相似文献   


6.
Akira Kusai  Tateo Yamanaka 《BBA》1973,292(3):621-633
A highly purified preparation of an NAD(P) reductase was obtained from Chlorobium thiosulfatophilum and some of its properties were studied. The enzyme possesses FAD as the prosthetic group, and reduces benzyl viologen, 2,6-dichloro-phenolindophenol and cytochromes c, including cytochrome c-555 (C. thiosulfato-philum), with NADPH or NADH as the electron donor. It reduces NADP+ or NAD+ photosynthetically with spinach chloroplasts in the presence of added spinach ferredoxin. It reduces the pyridine nucleotides with reduced benzyl viologen. The enzyme also shows a pyridine nucleotide transhydrogenase activity. In these reactions, the type of pyridine nucleotide (NADP or NAD) which functions more efficiently with the enzyme varies with the concentration of the nucleotide used; at concentrations lower than approx. 1.0 mM, NADPH (or NADP+) is better electron donor (or acceptor), while NADH (or NAD+) is a better electron donor (or acceptor) at concentrations higher than approx. 1.0 mM. Reduction of dyes or cytochromes c catalysed by the enzyme is strongly inhibited by NADP+, 2′-AMP and and atebrin.  相似文献   

7.
The inorganic sulfane tetrathionate (-O3SSSSO3-) resembles glutathione trisulfide (GSSSG) in that it remarkably activates the reduction of cytochrome c by GSH, both under aerobic and anaerobic conditions. These observations can be explained by the formation of the persulfide GSS-, due to nucleophilic displacements of sulfane sulfur. The GSS- species has previously been proposed to act as a chain carrier in the catalytic reduction of cytochrome c, and perthiyl radicals GSS·, formed in the reduction step, were thought to recycle to sulfane via dimerization to GSSSSG.2 The present study provides some arguments in favour of a chain mechanism involving the GSS· + GS- ⇄ (GSSSG)- equilibrium and sulfane regeneration by a second electron transfer from (GSSSG)· - to cytochrome c.

Thiosulfate sulfurtransferase (rhodanese) is shown to act as a cytochrome c reductase in the presence of thiosulfate and GSH, and again the generation of GSS- can be envisaged to explain this result.  相似文献   

8.
Chelation by citrate was found to promote the autoxidation of Fe2+, measured as the disapperance of 1,10-phenanthroline-chelatable Fe2+. The autoxidation of citrate---2+ could in turn promote the peroxidation of microsomal phospholipid liposomes, as judged by malondialdehyde formation. At low citrate---Fe2+ ratios the autoxidation of Fe2+ was slow and the formation of malondialdehyde was preceded by a lag phase. The lag phase evidence of this, linear initial rates of lipid peroxidation were obtained via the combination of citrate---Fe2+ and citrate---Fe3+, optimum activity occurring at a Fe3+---Fe2+ ratio of 1:1. Evidence is also presented to suggest that the superoxide and the hydrogen peroxide that are formed during the autoxidation of citrate---Fe2+ can either stimulate or inhibit lipid peroxidation by affecting the yield of citrate---Fe3+ from citrate---Fe2+. No evidence was obtained for the participation of the hydroxyl radical in the initiation of lipid peroxidation by citrate---Fe2+.  相似文献   

9.
Y. Lam  D. J. D. Nicholas 《BBA》1969,180(3):459-472
The formation of nitrite reductase and cytochrome c in Micrococcus denitrificans was repressed by O2. The purified nitrite reductase utilized reduced forms of cytochrome c, phenazine methosulphate, benzyl viologen and methyl viologen, respectively, as electron donors. The enzyme was inhibited by KCN, NaN3 and NH2OH each at 1 mM, whereas CO and bathocuproin, diethyl dithiocarbamate, o-phenanthroline and ,'-dipyridyl at 1 mM concentrations were relatively ineffective. The purified enzyme contains cytochromes, probably of the c and a2 types, in one complex. A Km of 46 μM for NO2 and a pH optimum of 6.7 were recorded for the enzyme. The molecular weight of the enzyme was estimated to be around 130000, and its anodic mobility was 6.8·10−6 cm2·sec−1·V−1 at pH 4.55.

The most highly purified nitrite reductase still exhibited cytochrome c oxidase activity with a Km of 27 μM for O2. This activity was also inhibited by KCN, NaN3 and NH2OH and by NO2.

A constitutive cytochrome oxidase associated with membranes was also isolated from cells grown anaerobically with NO2. It was inhibited by smaller amounts of KCN, NaN3 and NH2OH than the cytochrome oxidase activity of the nitrite reductase enzyme and also differed in having a pH optimum of about 8 and a Km for O2 of less than 0.1 μM. Spectroscopically, cytochromes b and c were found to be associated with the constitutive oxidase in the particulate preparation. Its activity was also inhibited by NO2.

The physiological role of the cytochrome oxidase activity associated with the purified nitrite reductase is likely to be of secondary importance for the following reasons: (a) it accounts for less than 10% of total cytochrome c oxidase activity of cell extracts; (b) the constitutive cytochrome c oxidase has a smaller Km for O2 and would therefore be expected to function more efficiently especially at low concentrations of O2.  相似文献   


10.
J. Butler  G.G. Jayson  A.J. Swallow 《BBA》1975,408(3):215-222

1. 1. The superoxide anion radical (O2) reacts with ferricytochrome c to form ferrocytochrome c. No intermediate complexes are observable. No reaction could be detected between O2 and ferrocytochrome c.

2. 2. At 20 °C the rate constant for the reaction at pH 4.7 to 6.7 is 1.4 · 106 M−1 · s−1 and as the pH increases above 6.7 the rate constant steadily decreases. The dependence on pH is the same for tuna heart and horse heart cytochrome c. No reaction could be demonstrated between O2 and the form of cytochrome c which exists above pH ≈ 9.2. The dependence of the rate constant on pH can be explained if cytochrome c has pKs of 7.45 and 9.2, and O2 reacts with the form present below pH 7.45 with k = 1.4 · 106 M−1 · s−1, the form above pH 7.45 with k = 3.0 · 105 M−1 · s−1, and the form present above pH 9.2 with k = 0.

3. 3. The reaction has an activation energy of 20 kJ mol−1 and an enthalpy of activation at 25 °C of 18 kJ mol−1 both above and below pH 7.45. It is suggested that O2 may reduce cytochrome c through a track composed of aromatic amino acids, and that little protein rearrangement is required for the formation of the activated complex.

4. 4. No reduction of ferricytochrome c by HO2 radicals could be demonstrated at pH 1.2–6.2 but at pH 5.3, HO2 radicals oxidize ferrocytochrome c with a rate constant of about 5 · 105–5 · 106 M−1 · s−1

.  相似文献   


11.
Direct evidence obtained by means of the technique of pulse radiolysis-kinetic spectrometry, with measurements in the time range 10−6 to 1 s, is presented that, consequent upon reaction of a single H-atom with a single molecule of ferricytochrome c, a reducing equivalent is transmitted via the protein structure to the ferriheme moiety. Such transmission accounts for at least 70% of the total reduction of the ferri to the ferro state of cytochrome c. The remainder of the total reduction takes place without stages resolvable on the time scale of these experiments. Reduction brought about by H atoms appears to follow a different course than reduction by hydrated electrons. In the latter case, intramolecular transmission of reducing equivalents could not be demonstrated (Lichtin, N. N., Shafferman, A. and Stein, G. (1973) Biochim. Biophys. Acta 314, 117–135).

Not every H-atom reacts with ferricytochrome c at a site which results in conversion of the Fe(III) state to the Fe(II) state. Approximately half of reacting H-atoms do not produce reduction.

The following second order rate constants have been determined in solutions of low ionic strength at 20±2 °C: k[H+ferricytochrome c] = (1.0±0.2) · 1010 M−1 · s−1 at pH 3.0 and 6.7; k[H+ferrocytochrome c] = (1.3±0.2) · 1010 M−1 · s−1 at pH 3.0; k[eaq + ferrocytochrome c] = (1.9±0.4) · 1010 M−1 · s−1 at pH 6.7.  相似文献   


12.
The Mechanism of Iron (III) Stimulation of Lipid Peroxidation   总被引:1,自引:0,他引:1  
A study conducted on Fe2+ autoxidation showed that its rate was extremely slow at acidic pH values and increased by increasing the pH; it was stimulated by Fe3+ addition but the stimulation did not present a maximum at a Fe2+/Fe3+ ratio approaching 1:1. The species generated during Fe3+-catalyzed Fe2+ autoxidation was able to oxidize deoxyribose; the increased Fe2+ oxidation observed at higher pHs was paralleled by increased deoxyribose degradation. The species generated during Fe3+-catalyzed Fe2+ autoxidation could not initiate lipid peroxidation in phosphatidylcholine liposomes from which lipid hydroperoxides (LOOH) had been removed by treatment with triph-enylphosphine. Neither Fe2+ oxidation nor changes in the oxidation index of the liposomes due to lipid peroxidation were observed at pHs where the Fe3+ effect on Fe2+ autoxidation and on deoxyribose degradation was evident. In our experimental system, a Fe2+/Fe3+ ratio ranging from 1:3 to 2:1 was unable to initiate lipid peroxidation in LOOH-free phosphatidylcholine liposomes. By contrast Fe3+ stimulated the peroxidation of liposomes where increasing amounts of cumene hydroperoxide were incorporated. These results argue against the participation of Fe3+ in the initiation of LOOH-independent lipid peroxidation and suggest its possible involvement in LOOH-dependent lipid peroxidation.  相似文献   

13.
1. NADPH-dependent iron and drug redox cycling, as well as lipid peroxidation process were investigated in microsomes isolated from human term placenta. 2. Paraquat and menadione were found to undergo redox cycling, catalyzed by NADPH:cytochrome P-450 reductase in placental microsomes. 3. The drug redox cycling was able to initiate microsomal lipid peroxidation in the presence of micromolar concentrations of iron and ethylenediaminetetraacetate (EDTA). 4. Superoxide was essential for the microsomal lipid peroxidation in the presence of iron and EDTA. 5. Drastic peroxidative conditions involving superoxide and prolonged incubation in the presence of iron were found to destroy flavin nucleotides, inhibit NADPH:cytochrome P-450 reductase and inhibit propagation step of lipid peroxidation. 6. Reactive oxo-complex formed between iron and superoxide is proposed as an ultimate species for the initiation of lipid peroxidation in microsomes from human term placenta as well as for the destruction of flavin nucleotides and inhibition of NADPH:cytochrome P-450 reductase as well as for impairment of promotion of lipid peroxidation under drastic peroxidative conditions.  相似文献   

14.
The antioxidant action of a series of benzylisoquinoline alkaloids has been investigated. Laudanosoline, protopapaverine, anonaine, apomorphine, glaucine, boldine, bulbocapnine, tetrahydroberberine and stepholidine produced a dose-dependent inhibition of microsomal lipid peroxidation induced by Fe2+/ascorbate, CCl4/NADPH or by Fe3+ADP/NADPH. Apomorphine exerted the highest inhibitory effects in the three systems of induction used, with a potency higher than propyl gallate. Laudanosoline was particularly effective in the first system, while bulbocapnine and anonaine were more potent when CCl4/NADPH or Fe3+ -ADP/NADPH were used as inducers. Laudanosoline, protopapaverine, apomorphine, tetrahydroberberine and stepholidine were also potent inhibitors of nitroblue tetrazolium (NBT) reduction. The presence of a free hydroxyl group or preferably of a catechol group is a feature relevant for inhibition of lipid peroxidation and NBT reduction, nevertheless the antioxidant activity of benzylisoquinoline alkaloids cannot be only ascribed to the formation of phenoxy radicals and other free radical species may be formed during aporphine and tetrahydroprotoberberine oxidation. The influence of this series of compounds on the time course of lipid peroxidation suggests that some of them, like apomorphine and boldine act as chain-breaking antioxidants.  相似文献   

15.
Objective: Al3+ stimulates Fe2+ induced lipid oxidation in liposomal and cellular systems. Low-density lipoprotein (LDL) oxidation may render the particle atherogenic. As elevated levels of Al3+ and increased lipid oxidation of LDL are found in sera of hemodialysis patients, we investigated the influence of Al3+ on LDL oxidation.

Materials and methods: Using different LDL modifying systems (Fe2+, Cu2+, free radical generating compounds, human endothelial cells, hemin/H2O2 and HOCl), the influence of Al3+ on LDL lipid and apoprotein alteration was investigated by altered electrophoretic mobility, lipid hydroperoxide-, conjugated diene- and TBARS formation.

Results: Al3+ could stimulate the oxidizability of LDL by Fe2+, but not in the other systems tested. Al3+ and Fe2+ were found to bind to LDL and Al3+could compete with Fe2+ binding to the lipoprotein. Fluorescence polarization data indicated that Al3+ does not affect the phospholipid compartment of LDL.

Conclusions:The results indicate that increased LDL oxidation by Fe2+ in presence of Al3+ might be due to blockage of Fe2+ binding sites on LDL making more free Fe2+ available for lipid oxidation.  相似文献   

16.
K.A. Davis  Y. Hatefi  K.L. Poff  W.L. Butler 《BBA》1973,325(3):341-356

1. 1. Three b-type cytochromes (b557.5, b560, and b562.5), plus a chromophore with an absorption peak at 558 nm at 77 °K, have been found to be associated with the electron transport system of bovine heart mitochondria. The reduced minus oxidized spectra of these components at 77 °K, as well as that of cytochrome c1, have been recorded with a wavelength accuracy of ± 0.1 nm and presented to the nearest 0.5 nm. All the major and β absorption peaks of cytochromes b557.5, b560, b562.5, c1 and c have been shown by fourth derivative analysis to be present in the dithionite-reduced minus oxidized spectra of mitochondria and submitochondrial particles.

2. 2. The distribution of the above components has been studied in the four electron transfer complexes of the respiratory chain. Cytochromes b560, b562.5 and c1, as well as chromophore-558, were found to fractionate into Complex III (reduced ubiquinone-cytochrome c reductase), whereas cytochrome b557.5 was found in Complex II (succinate-ubiquinone reductase).

3. 3. Cytochrome b560 was readily reduced by NADH or succinate, but b562.5 was not reduced by substrates unless the preparation was treated with antimycin A. In antimycin-treated preparations pre-reduction of c1 with ascorbate inhibited the subsequent reduction of b562.5 by substrates. These results indicate that b560 and b562.5 correspond, respectively, to bK and bT previously described by Chance et al.14 (1970, Proc. Natl. Acad. Sci. U.S. 66, 1175–1182).

4. 4. Similar to b560, chromophore-558 can be reduced by substrates in the absence or presence of antimycin A. However, in antimycin-treated preparations, pre-reduction of c1 inhibits its subsequent reduction by substrates. This property is similar to that of b562.5.

5. 5. Cytochrome b557.5, which occurs in Complex II, appears to have a low mid-point potential. It can be reduced with dithionite and oxidized by fumarate or ubiquinone. CO treatment of dithionite-reduced b557.5 neither modified the spectrum of this cytochrome nor diminished the extent of b557.5 reoxidation by fumarate.

6. 6. Antimycin A treatment does not appear to alter the spectra of the above cytochromes. However, small amounts (< 4%) of ethanol or methanol, which are usually added to particles as solvent for antimycin A, have a pronounced effect on the peaks of cytochrome c1. The spectrum of cytochrome c1 at 77 °K as modified by 3% (v/v) ethanol is shown.

Abbreviations: ETP, non-phosphorylating electron transport particle preparation; ETPH, phosphorylating electron transport particle preparation; TMPD, tetramethylphenylenediamine; Complexes I, preparations of NADH-ubiquinone reductase; Complexes II, succinate-ubiquinone reductase; Complexes III, reduced ubiquinone-cytochrome c reductase; Complexes I-III, NADH-cytochrome c reductase; Complexes II-III, succinate-cytochrome c reductase  相似文献   


17.
Horse-heart ferrocytochrome c has been labeled with N-(2,2,5,5-tetramethyl-3-pyrrolidinyl-1-oxyl) iodoacetamide at methionine-65. The paramagnetic resonance spectrum of labeled ferricytochrome c indicates a weak immobilization of the radical (τc = 9.3·10−10 sec) which becomes stronger upon binding of labeled cytochrome c to cytochrome c-depleted mitochondrial membranes (τc = 3.3·10−9 sec). The hyperfine coupling constant remains, however, unchanged (16.7 ± 0.1 gauss) indicating that the cytochrome c binding site is highly polar. The region where cytochrome c is bound to the membrane is insensitive to large variations of medium viscosity.  相似文献   

18.
Scott Power  Graham Palmer 《BBA》1980,593(2):400-413
We have prepared and characterized resealed erythrocyte ghosts in which the only discernible pigment is cytochrome c. The resealed ghosts have the normal orientation and are free of ‘leaky’ species; they are stable and can be maintained at 4°C for many days without lysis.

The internal cytochrome c participates in redox reactions with both soluble and insolubilized cytochrome c present externally, and with external cytochrome b5. No reaction was observed with plastocyanin, cytochrome c oxidase or NADPH-cytochrome c reductase.

A study has been made of the reaction of the internal cytochrome c with the low molecular weight reductants, ascorbate and glutathione. Complex kinetics are observed with both reagents: with ascorbate the results are best explained by assuming the existence, in the membrane, of a redox-active species able to undergo dedimerization. A protein bound disulfide bond would satisfy the requirement.  相似文献   


19.
J. A. Berden  E. C. Slater 《BBA》1970,216(2):237-249
1. Succinate-cytochrome c reductase activity was reconstituted by incubating a mixture of succinate dehydrogenase, cytochrome c1, ubiquinone-10, phospholipid and a preparation of cytochrome b, made by the method of .

2. Preparations of cytochrome b active in reconstitution contained 5–28% native cytochrome b, as adjudged by reducibility with succinate in the reconstituted preparation and by lack of reaction with CO. Preparations of cytochrome b containing no native cytochrome b according to this criterion were inactive in reconstitution.

3. With a fixed amount of cytochrome b, the activity of the reconstituted preparation increased with increasing amounts of cytochrome c1 until a ratio of about 2b (total): 1c1 (allowing for the cytochrome c1 present in the cytochrome b preparation) was reached.

4. The amount of antimycin necessary for maximal inhibition of the reconstituted enzyme is a function of the amount of the cytochrome b and is independent of the amount of cytochrome c1. It is equal to about one half the amount of native cytochrome b.

5. Preparations of intact or reconstituted succinate-cytochrome c reductase or of cytochrome b completely quench the fluorescence of added antimycin, until an amount of antimycin equal to onehalf the amount of native cytochrome b present was added. Antimycin added in excess of this amount fluoresces with normal intensity. The quenching is only partial in the presence of Na2S2O4. Denatured cytochrome b does not quench the fluorescence.

6. Since preparations of cytochrome b active in reconstitution contained cytochrome c1 in an amount exceeding one half the amount of native cytochrome b present in the preparation, there is no evidence that native cytochrome b has been resolved from cytochrome c1. The stimulatory action of cytochrome c1 may be due to the restoration of a damaged membrane conformation.

7. Based on the assumption that the bc1 segment of the respiratory chain contains 2b:1c1:1 antimycin-binding sites, the specific quenching of antimycin fluorescence by binding to cytochrome b enables an accurate determination of the absorbance coefficients of cytochromes b and c1. These are 25.6 and 20.1 mM−1×cm−1 for the wavelength pairs 563–577 nm and 553–539 nm, respectively, in the difference spectrum reduced minus oxidized.  相似文献   


20.
Superoxide generation, assessed as the rate of acetylated cytochrome c reduction inhibited by superoxide dismutase, by purified NADPH cytochrome P-450 reductase or intact rat liver microsomes was found to account for only a small fraction of their respective NADPH oxidase activities. DTPA-Fe3+ and EDTA-FE3+ greatly stimulated NADPH oxidation, acetylated cytochrome c reduction, and O(2) production by the reductase and intact microsomes. In contrast, all ferric chelates tested caused modest inhibition of acetylated cytochrome c reduction and O(2) generation by xanthine oxidase. Although both EDTA-Fe3+ and DTPA-Fe3+ were directly reduced by the reductase under anaerobic conditions, ADP-Fe3+ was not reduced by the reductase under aerobic or anaerobic conditions. Desferrioxamine-Fe3+ was unique among the chelates tested in that it was a relatively inert iron chelate in these assays, having only minor effects on NADPH oxidation and/or O(2) generation by the purified reductase, intact microsomes, or xanthine oxidase. Desferrioxamine inhibited microsomal lipid peroxidation promoted by ADP-Fe3+ in a concentration-dependent fashion, with complete inhibition occurring at a concentration equal to that of exogenously added ferric iron. The participation of O(2) generated by the reductase in NADPH-dependent lipid peroxidation was also investigated and compared with results obtained with a xanthine oxidase-dependent lipid peroxidation system. NADPH-dependent peroxidation of either phospholipid liposomes or rat liver microsomes in the presence of ADP-Fe3+ was demonstrated to be independent of O(2) generation by the reductase.  相似文献   

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