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1.
Does Iron Deficiency in Pisum sativum Enhance the Activity of the Root Plasmalemma Iron Transport Protein? 总被引:4,自引:3,他引:1
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Roots of Fe-sufficient and Fe-Deficient pea (Pisum sativum L.) were studied to determine the effect of Fe-deficiency on the activity of the root-cell plasmalemma Fe2+ transport protein. Rates of Fe(III) reduction and short-term Fe2+ influx were sequentially determined in excised primary lateral roots using Fe(III)-ethylene-diaminetetraacetic acid (Fe[III]-EDTA). Since the extracellular Fe2+ for membrane transport was generated by root Fe(III) reduction, rates of Fe2+ influx for each root system were normalized on the basis of Fe(III) reducing activity. Ratios of Fe2+ influx to Fe(III) reduction (micromole Fe2+ absorbed/micromole Fe[III] reduced) revealed no enhanced Fe2+ transport capacity in roots of Fe-deficient peas (from the parental genotype, Sparkle) or the functional Fe-deficiency pea mutant, E107 (derived from Sparkle), relative to roots of Fe-sufficient Sparkle plants. Data from studies using 30 to 100 micromolar Fe(III)-EDTA indicated a linear relationship between Fe2+ influx and Fe(III) reduction (Fe2+ generation), while Fe2+ influx saturated at higher concentrations of Fe(III)-EDTA. Estimations based on current data suggest the Fe2+ transport protein may saturate in the range of 10−4.8 to 10−4 molar Fe2+. These results imply that for peas, the physiological rate limitation to Fe acquisition in most well-aerated soils would be the root system's ability to reduce soluble Fe(III)-compounds. 相似文献
2.
The effects of varying concentrations of Fe2+ (5 × 10?5 ?5 × 10?1 M) on benzylglucosinolate degradation in Lepidium sativum seed autolysates were investigated. Increased glucosinolate decomposition was observed over the whole range with a maximum effect at ca 6 × 10?3 M Fe2+, at which point glucosinolate degradation was more than three times that obtained in the absence of added Fe2+ . Nitrile formation was especially enhanced in the presence of all concentrations of Fe2+ studied, and maximum amounts were obtained at ca 6 × 10?3 M Fe2+ when a more than four-fold increase over quantities produced in the absence of Fe2+ was observed. Thiocyanate formation was also promoted with a maximum at ca 4 × 10?3 M Fe2+, but isothiocyanate production was considerably reduced in allcases. It is suggested that Fe2+ inhibits isothiocyanate formation by interfering with the availability of ascorbic acid which is a proven co-factor for most thioglucosidase isoenzymes, but that an Fe2+-ascorbate complex might then be responsible for promoting enzymic production of nitrile. The effects of a limited range of concentrations of Fe3+ and Cu+ were also studied, and results related to those for Fe2+. The relevance of the findings to natural systems and to glucosinolate-containing foods is briefly discussed. 相似文献
3.
Maria Augusta HortaFernando Masarin Jaime RodriguezAndré Ferraz 《International biodeterioration & biodegradation》2011,65(1):164-171
This work evaluates linoleic acid peroxidation reactions initiated by Fe3+-reducing compounds recovered from Eucalyptus grandis, biotreated with the biopulping fungus Ceriporiopsis subvermispora. The aqueous extracts from biotreated wood had the ability to reduce Fe3+ ions from freshly prepared solutions. The compounds responsible for the Fe3+-reducing activity corresponded to UV-absorbing substances with apparent molar masses from 3 kDa to 5 kDa. Linoleic acid peroxidation reactions conducted in the presence of Fe3+ ions and the Fe3+-reducing compounds showed that the rate of O2 consumption during peroxidation was proportional to the Fe3+-reducing activity present in each extract obtained from biotreated wood. This peroxidation reaction was coupled with in-vitro treatment of ball-milled E. grandis wood. Ultraviolet data showed that the reaction system released lignin fragments from the milled wood. Size exclusion chromatography data indicated that the solubilized material contained a minor fraction representing high-molar-mass molecules excluded by the column and a main low-molar-mass peak. Overall evaluation of the data suggested that the Fe3+-reducing compounds formed during wood biodegradation by C. subvermispora can mediate lignin degradation through linoleic acid peroxidation. 相似文献
4.
Dimas Mendes Ribeiro Ana Maria Mapeli Carla Andréa Delatorre Marcelo Augusto Gutierrez Carnelossi Raimundo Santos Barros 《Acta Physiologiae Plantarum》2011,33(6):2117-2123
Dormancy of scarified seeds of Stylosanthes humilis was broken by acidic Al3+ and Fe3+ solutions. Fe+3-stimulated seeds exhibited a high activity of 1-aminocyclopropane-1-carboxylate (ACC) oxidase and produced great amounts
of ethylene, which showed correlated with the germination process. In addition, specific inhibitors of ethylene biosynthesis
and action largely depressed the Fe3+-stimulated germination, leading to the conclusion that the ion broke dormancy by triggering ethylene production by the seeds.
By contrast, inhibitors of ethylene biosynthesis and action did not impair germination of Al3+-stimulated dormant seeds. Moreover, ethylene production and activity of ACC oxidase of Al3+-treated seeds was substantially decreased by inhibitors of ethylene biosynthesis, but germination kept large. Together these
data suggest that ethylene biosynthesis was not required in the chain of events triggered by Al3+ leading to dormancy breakage. Methyl viologen (MV), a reactive oxygen species-generating compound, broke dormancy of seeds
to the same extent as Al3+ did. Germination of both Al3+- and MV-stimulated dormant seeds was inhibited by sodium selenate, an antioxidant compound; selenate, however had no effect
on germination of Fe3+-stimulated seeds. Together these data indicate that the mechanisms underlying the germination of Al3+- and Fe3+-treated seeds are not the same. 相似文献
5.
M. Perl 《Phytochemistry》1981,20(8):1791-1793
An enzyme which splits reduced NAD has been partially purified from pea (Pisum sativum, Kelvedon Wonder) seeds. The activity requires orthophosphate and the products are ADP and probably NMN (dihydro NMN?). The enzyme splits the NADH2 at the pyrophosphate bond and incorporates the phosphate into the AMP residue. NAD, NADP or NADPH2 could not replace NADH2. The enzyme is unstable during storage, is activated by Mg2+ and by Mn2+, and inhibited by Ca2+. K+, Li+ and NH4+ have no effect. The possible role of this enzyme in the synthesis of ATP in seeds at the early stage of germination is discussed. 相似文献
6.
《Inorganica chimica acta》1988,153(1):39-44
Apoenzyme, containing ⩽0.1 zinc atoms and ⩽0.2 Fe atoms per subunit and with ⩽3% of the phosphatase activity, has been prepared from native red kidney bean purple phosphatase. Treatment of this apoenzyme with Fe3+ or Zn2+ separately gave very little recovery of activity, whereas treatment with both Fe3+ and Zn2+ resulted in complete restoration of activity, indicating that both metal ions are essential. ZnFe enzyme with close to one iron and one zinc atom per subunit has been reconstituted by this procedure. Essentially full reactivation was also achieved by addition of Fe3+ together with Fe2+ or Co2+ to the apoenzyme; Fe3+ and Cd2+ gave 27% restoration of activity, whereas Fe3+ with Mn2+, Cu2+, Ni2+ or Hg2+ gave little or no increase in activity. Kinetic parameters for the hydrolysis of p-nitrophenyl phosphate and ATP by the FeFe derivative are reported. 相似文献
7.
Ferrous Iron and Sulfur Oxidation and Ferric Iron Reduction Activities of Thiobacillus ferrooxidans Are Affected by Growth on Ferrous Iron, Sulfur, or a Sulfide Ore 总被引:4,自引:3,他引:1
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Isamu Suzuki Travis L. Takeuchi Trin D. Yuthasastrakosol Jae Key Oh 《Applied microbiology》1990,56(6):1620-1626
Eight strains of Thiobacillus ferrooxidans (laboratory strains Tf-1 [= ATCC 13661] and Tf-2 [= ATCC 19859] and mine isolates SM-1, SM-2, SM-3, SM-4, SM-5, and SM-8) and three strains of Thiobacillus thiooxidans (laboratory strain Tt [= ATCC 8085] and mine isolates SM-6 and SM-7) were grown on ferrous iron (Fe2+), elemental sulfur (S0), or sulfide ore (Fe, Cu, and Zn). The cells were studied for their aerobic Fe2+ - and S0-oxidizing activities (O2 consumption) and anaerobic S0-oxidizing activity with ferric iron (Fe3+) (Fe2+ formation). Fe2+-grown T. ferrooxidans cells oxidized S0 aerobically at a rate of 2 to 4% of the Fe2+ oxidation rate. The rate of anaerobic S0 oxidation with Fe3+ was equal to the aerobic oxidation rate in SM-1, SM-3, SM-4, and SM-5, but was only one-half or less that in Tf-1, Tf-2, SM-2, and SM-8. Transition from growth on Fe2+ to that on S0 produced cells with relatively undiminished Fe2+ oxidation activities and increased S0 oxidation (both aerobic and anaerobic) activities in Tf-2, SM-4, and SM-5, whereas it produced cells with dramatically reduced Fe2+ oxidation and anaerobic S0 oxidation activities in Tf-1, SM-1, SM-2, SM-3, and SM-8. Growth on ore 1 of metal-leaching Fe2+-grown strains and on ore 2 of all Fe2+-grown strains resulted in very high yields of cells with high Fe2+ and S0 oxidation (both aerobic and anaerobic) activities with similar ratios of various activities. Sulfur-grown Tf-2, SM-1, SM-4, SM-6, SM-7, and SM-8 cultures leached metals from ore 3, and Tf-2 and SM-4 cells recovered showed activity ratios similar to those of other ore-grown cells. It is concluded that all the T. ferrooxidans strains studied have the ability to produce cells with Fe2+ and S0 oxidation and Fe3+ reduction activities, but their levels are influenced by growth substrates and strain differences. 相似文献
8.
9.
1. Fructose 1,6-diphosphatase has been purified tenfold from rat liver. The final preparation was not contaminated by either glucose 6-phosphatase or phosphofructokinase. The properties of the enzyme have been investigated in an attempt to define factors that could be of revelance to metabolic control of fructose 1,6-diphosphatase activity. 2. The metal ions Fe2+, Fe3+ and Zn2+ inhibited the activity of fructose 1,6-diphosphatase even in the presence of an excess of mercaptoethanol; other metal ions tested had no effect. The inhibition produced by Zn2+ was reversed by EDTA, but that produced by either Fe2+ or Fe3+ was not reversible. 4. The enzyme has a very low Km for fructose 1,6-diphosphate (2·0μm). Concentrations of fructose 1,6-diphosphate above 75μm inhibited the activity; however, even at very high fructose 1,6-diphosphate concentrations only 70% inhibition was obtained. 5. The activity was also inhibited by low concentrations of AMP, which lowered Vmax. and increased Km for fructose 1,6-diphosphate. Evidence is presented that suggests that AMP can be defined as an allosteric inhibitor of fructose 1,6-diphosphatase. 6. The inhibitions by both fructose 1,6-diphosphate and AMP were extremely specific. Also, the degree of inhibition was not affected by the presence of intermediates of glycolysis, of the tricarboxylic acid cycle, of amino acid metabolism or of fatty acid metabolism. 7. It is suggested that the intracellular concentrations of AMP and fructose 1,6-diphosphate could be of significance in controlling the activity of fructose 1,6-diphosphatase in the liver cell. The possible relationship between these intermediates and the control of gluconeogenesis is discussed. 相似文献
10.
Yongqing Liu Jan H. W. Bergervoet C. H. Ric De Vos Henk W. M. Hilhorst H. Lieke Kraak Cees M. Karssen Raoul J. Bino 《Planta》1994,194(3):368-373
The role of cis-abscisic acid (ABA) and gibberellins (GAs) in the induction of cell-cycle activities has been studied during imbibition and subsequent germination of tomato seeds. Using flow cytometry, nuclear replication activity was investigated in embryo root tips isolated from seeds of the ABA-deficient mutant sit w , the GA-deficient mutant gib-1, and the wild-type (MM) tomato (Lycopersicon esculentum Mill. cv. Moneymaker) upon imbibition in water, 10 μM GA4+7, 5 μM ABA or 5 μM ABA+10 μM GA4+7. The nuclei of fully matured dry MM, sit w and gib-1 seeds predominantly showed 2C DNA signals, indicating that the cell-cycle activity of most root-tip cells had been arrested at the G1 phase of nuclear division. However, ABA-deficient sit w seeds contained a significantly higher amount of G2 cells (4C DNA) compared with the other genotypes, suggesting that, during maturation, cell-cycle activity in sit w seeds is less efficiently arrested in G1. Upon imbibition in water, an induction of the 4C signal, indicating nuclear replication, was observed in the root tip cells of both MM and sit w embroys. The augmentation in the 4C signal occurred before visible germination. Gib-1 seeds did not show cell-cycle activity and did not germinate in water. Upon imbibition in GA4+7, both cell-cycle activity and subsequent germination were enhanced in MM and sit w seeds, and were induced in gib-1. In ABA, the germination of MM and sit w seeds was inhibited while nuclear replication of these seeds was not affected. It is concluded that GA influences germination by acting upon processes that precede cell-cycle activation, while ABA affects growth by acting upon processes that follow cell-cycle activation. 相似文献
11.
Y. Zhang Y. P. Wang P. Liu J. M. Song G. D. Xu G. H. Zheng 《Russian Journal of Plant Physiology》2012,59(6):766-771
Root border cells are a population of rhizosphere cells surrounding the root tips but separated from them. The root tip is a major target of Fe2+ toxicity; thus, it was hypothesized that the border cells might protect or exacerbate Fe2+ toxicity. To explore the effects of excess Fe2+ on the border cells in rice (Oryza sativa L.), experiments were carried out using the border cells in vitro (Shanyou No. 10). The border cells were precultured under ??hanging in the air?? and detached from the root tips. The shape, numbers, and viability of border cells were examined during exposure to toxic levels of Fe2+. When the root was 1 mm long, there were 205 border cells on average. With the growth of the root, more border cells were observed. When the root grew to 25 mm long, the total number of border cells reached a maximum, while the maximum activity of border cells appeared when the root was 20 mm long. The pectin methyl esterase (PME) activity of the root cap peaked at a root length of 2 mm. Border cell development was related to PME activity in rice. Excessive Fe2+ was toxic to detached border cells. After treatment with 200 ??M Fe2+ solution for 48 h, cell viability decreased by 72.70%. However, when treated with 400 ??M Fe2+ solution, the number of viable cells was actually higher, suggesting the induction of a cellular self-protection response. The activity of PME first increased under high concentrations of Fe2+ and then decreased. These results indicate that toxic levels of Fe2+ modulate PME activity and border cell survival. 相似文献
12.
An enzyme that rapidly catalyzes the hydrolysis of denatured DNA has been partially purified from germinated pea (Pisum sativum) seeds. The nuclease has been characterised as having endonucleolytic activity degrading single stranded DNA at a 15- to 20-fold higher rate than native DNA. From exclusion chromatography on Sephadex G-200 the molecular weight of the enzyme was calculated to be 42,000. The small extent of hydrolysis of native DNA is suggested to be due to the degradation of partially denatured areas in the native molecule. The enzyme shows activity over a broad range of pH but was most active between pH 6.5 and 8.0. The maximum hydrolysis of denatured DNA was observed at 45 °C while with native DNA the temperature optima was 60 °C. The nuclease does not show an absolute requirement for added divalent cations. However, the addition of Mg2+ and Ca2+ results in 40 and 60% stimulation, respectively. EDTA has no effect on enzymatic activity, whereas 8-hydroxyquinoline was inhibitory. 相似文献
13.
Chang-Jun Ji Jung-Hoon Kim Young-Bin Won Yeh-Eun Lee Tae-Woo Choi Shin-Yeong Ju Hwan Youn John D. Helmann Jin-Won Lee 《The Journal of biological chemistry》2015,290(33):20374-20386
In many Gram-positive bacteria PerR is a major peroxide sensor whose repressor activity is dependent on a bound metal cofactor. The prototype for PerR sensors, the Bacillus subtilis PerRBS protein, represses target genes when bound to either Mn2+ or Fe2+ as corepressor, but only the Fe2+-bound form responds to H2O2. The orthologous protein in the human pathogen Staphylococcus aureus, PerRSA, plays important roles in H2O2 resistance and virulence. However, PerRSA is reported to only respond to Mn2+ as corepressor, which suggests that it might rely on a distinct, iron-independent mechanism for H2O2 sensing. Here we demonstrate that PerRSA uses either Fe2+ or Mn2+ as corepressor, and that, like PerRBS, the Fe2+-bound form of PerRSA senses physiological levels of H2O2 by iron-mediated histidine oxidation. Moreover, we show that PerRSA is poised to sense very low levels of endogenous H2O2, which normally cannot be sensed by B. subtilis PerRBS. This hypersensitivity of PerRSA accounts for the apparent lack of Fe2+-dependent repressor activity and consequent Mn2+-specific repressor activity under aerobic conditions. We also provide evidence that the activity of PerRSA is directly correlated with virulence, whereas it is inversely correlated with H2O2 resistance, suggesting that PerRSA may be an attractive target for the control of S. aureus pathogenesis. 相似文献
14.
Two wheat varieties were grown in artificially created sodic soils in pots at a range of sodicity levels (exchangeable sodium
percentage (ESP) 15–52), with and without an anionic polyacrylamide soil conditioner (PAM) to stabilise soil aggregates. Increasing
sodicity decreased the % water stable aggregates (% WSA) in soil and survival, grain and straw yield of wheat. Plants grown
at high sodicity also had higher Na+, lower K+ and Ca2+ concentrations and lower K+/Na+ ratio in flag leaf sap than plants grown in control (non-sodic) soil. Sodicity had no effect on the concentrations of Cu2+, Fe2+, Mn2+ and Zn2+ in grains and straw, but total uptake of these micronutrients was deceased due to lower dry weight of these tissues per plant.
At all sodicity levels treatment of sodic soil with PAM increased the % WSA to values greater than in the non-sodic control
soil, and slightly lowered ESP. Over the range ESP 15–44 the effects of PAM on wheat grain yield increased as sodicity increased,
so that at ESP 44 grain yield in the treatment with PAM was only 25% lower than in the non-sodic control. However at ESP 52
the effects of PAM were smaller, and grain yield was 86% lower than in the control. At this sodicity level the decreases in
grain yield due to sodicity and the increases in reponse to treatment of sodic soil with PAM were similar in the two varieties
tested. At high sodicity levels (ESP 44 and 52) treatment of sodic soil with PAM decreased the concentration of Na+ and increased K+ and K+/Na+ ratio in flag leaf sap. However, at the highest sodicity level (ESP 52), flag leaf Na+ concentration remained above the level (100 mol m-3) at which it has been found to be toxic. Concentrations of Cu2+, Fe2+, Mn2+ and Zn2+ in grain and straw were unaffected by PAM. These results suggest that at ESP up to 40–50 adverse physical characteristics
are the major cause of low wheat yield in sodic soils, either due to their direct effects in decreasing growth, or their indirect
effects in increasing uptake of Na+ and decreasing uptake of K+. Above ESP 50, roots are less able to exclude Na+, even in the presence of improved soil physical conditions, so that at these sodicity levels, both adverse physical and adverse
chemical properties contribute to the decreased yield.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
15.
The effects of various salts on the proteolytic activity of extracts from Schistosoma mansoni cercariae were tested. Using an Azocoll substrate, stimulation (2 to 2.5-fold) of activity by the monovalent cations Na+ and K+ was demonstrated, with maximum stimulation at 20–40 mM concentrations. The divalent cations Mg2+ and Ca2+ stimulated proteolytic activity at low concentrations (between 0 and 10 mM) but inhibited activity at higher concentrations. The divalent cations Zn2+, Cu2+, Fe2+, and Co2+ were inhibitory even at very low concentrations. The results presented here are discussed in relation to previously described ion effects on cercarial infectivity. 相似文献
16.
Role of Ferrous Ions in Synthetic Cobaltous Sulfide Leaching of Thiobacillus ferrooxidans 总被引:3,自引:6,他引:3
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Microbiological leaching of synthetic cobaltous sulfide (CoS) was investigated with a pure strain of Thiobacillus ferroxidans. The strain could not grow on CoS-salts medium in the absence of ferrous ions (Fe2+). However, in CoS-salts medium supplemented with 18 mM Fe2+, the strain utilized both Fe2+ and the sulfur moiety in CoS for growth, resulting in an enhanced solubilization of Co2+. Cell growth on sulfur-salts medium was strongly inhibited by Co2+, and this inhibition was completely protected by Fe2+. Cobalt-resistant cells, obtained by subculturing the strain in medium supplemented with both Fe2+ and Co2+, brought a marked decrease in the amount of Fe2+ absolutely required for cell growth on CoS-salts medium. As one mechanism of protection by Fe2+, it is proposed that the strain utilizes one part of Fe2+ externally added to CoS-salts medium to synthesize the cobalt-resistant system. Since a similar protective effect by Fe2+ was also observed for cell inhibition by stannous, nickel, zinc, silver, and mercuric ions, a new role of Fe2+ in bacterial leaching in T. ferrooxidans is proposed. 相似文献
17.
A novel copper, zinc superoxide dismutase (CuZnSOD) was purified to homogeneity from the liver of an animal well adapted to the stressful living conditions of the desert, the camel (Camelus dromedarius). The biochemical properties of camel liver CuZnSOD were examined. The purified enzyme had a native molecular weight of 28 kDa, as judged by gel filtration chromatography, and showed a single band at 27 kDa on SDS-PAGE, indicating that it is a monomeric protein. Optimal activity of the purified enzyme occurred at 43 °C and pH 6.0, and the activation energy was 1.42 kJ/mol. CuZnSOD activity was strongly inhibited by β-ME, DTT, H2O2 and SDS and slightly inhibited by EDTA, NaN3 and PMSF. Al3+, Ca2+, Cd2+, Mg2+ and Zn2+ stimulated CuZnSOD activity, whereas Ba2+, Co2+, Fe2+ and Ni2+ inhibited it. The purified enzyme contained 0.010 µg of Cu and 0.69 µg of Zn per mg of protein. Km, Vmax, kcat and kcat/Km values for NBT and riboflavin were 16.27 and 0.16 µM, 20.85 and 21.54 U/mg, 9.65 and 9.97 s−1, and 0.59 and 62.33 s-1 µM−1, respectively. Camel liver CuZnSOD exhibited unique biochemical properties compared to those of other CuZnSODs, including lower molecular weight with a monomeric structure, higher optimum temperature, very low Ea, very low optimum pH, very low contents of Cu and Zn, and higher affinity, turnover number and catalytic efficiency for riboflavin. These unique properties of camel liver CuZnSOD might be related to the ability of this animal to inhabit stressful desert conditions. 相似文献
18.
Hydroxylation of gibberellin-[3H] A1 (GA1-[3H]) to GA8-[3H] by the 95000 g supernatant fluid from imbibed bean seeds required Fe2+ or Fe3+ and O2 but was insensitive to CO. The hydroxylating enzyme has a sedimentation coefficient of 4·5 S, and was precipitated by (NH4)2SO4 at 35–60% saturation. This hydroxylase was specific for GA1 and did not hydroxylate either pseudo-GA1-[3H] or 16-ketoGA1-[3H]. Virtually all hydroxylase activity was localized in the cotyledons. 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.
In cells, mitochondria, endoplasmic reticulum, and peroxisomes are the major sources of reactive oxygen species (ROS) under physiological and pathophysiological conditions. Cytochrome c (cyt c) is known to participate in mitochondrial electron transport and has antioxidant and peroxidase activities. Under oxidative or nitrative stress, the peroxidase activity of Fe3+cyt c is increased. The level of NADH is also increased under pathophysiological conditions such as ischemia and diabetes and a concurrent increase in hydrogen peroxide (H2O2) production occurs. Studies were performed to understand the related mechanisms of radical generation and NADH oxidation by Fe3+cyt c in the presence of H2O2. Electron paramagnetic resonance (EPR) spin trapping studies using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) were performed with NADH, Fe3+cyt c, and H2O2 in the presence of methyl-β-cyclodextrin. An EPR spectrum corresponding to the superoxide radical adduct of DMPO encapsulated in methyl-β-cyclodextrin was obtained. This EPR signal was quenched by the addition of the superoxide scavenging enzyme Cu,Zn-superoxide dismutase (SOD1). The amount of superoxide radical adduct formed from the oxidation of NADH by the peroxidase activity of Fe3+cyt c increased with NADH and H2O2 concentration. From these results, we propose a mechanism in which the peroxidase activity of Fe3+cyt c oxidizes NADH to NAD•, which in turn donates an electron to O2, resulting in superoxide radical formation. A UV-visible spectroscopic study shows that Fe3+cyt c is reduced in the presence of both NADH and H2O2. Our results suggest that Fe3+cyt c could have a novel role in the deleterious effects of ischemia/reperfusion and diabetes due to increased production of superoxide radical. In addition, Fe3+cyt c may play a key role in the mitochondrial “ROS-induced ROS-release” signaling and in mitochondrial and cellular injury/death. The increased oxidation of NADH and generation of superoxide radical by this mechanism may have implications for the regulation of apoptotic cell death, endothelial dysfunction, and neurological diseases. We also propose an alternative electron transfer pathway, which may protect mitochondria and mitochondrial proteins from oxidative damage. 相似文献