Showing papers on "Ferric published in 2002"
TL;DR: In this article, the authors measured the kinetics of isotope exchange between aqueous ferrous and ferric species measured over a range of chloride concentrations (0, 11, 110 mM Cl−) and at two temperatures (0 and 22°C) indicate that Fe isotope fractionation is a function of temperature but independent of chloride contents over the range studied.
446 citations
TL;DR: Interactions between transition metal salts and a surrogate environmental particle-ultrafine carbon black suggest ultrafine particles and metals interact by chemical potentiation in a cell-free environment to generate ROS and in the lung, ultra fine particles and iron salts interact in a potentiative manner to generate inflammation.
434 citations
TL;DR: The DNA-binding proteins from starved cells (Dps) are shown to be a Fe-binding and storage protein where Fe(II) oxidation is most effectively accomplished by H2O2 rather than by O2 as in ferritins, and the protective effect of Dps on DNA most likely is exerted through a dual action, the physical association with DNA and the ability to nullify the toxic combination of Fe( II) and H2 O2.
402 citations
TL;DR: It is proposed that the superoxide is the main oxidant of arsenite in the TiO2/UV process and both Fe3+ and HA that were often found with the arsenic in groundwater were beneficial to the photocatalytic oxidation of arsenites, which could be a viable pretreatment method.
Abstract: Arsenite [As(III)] and arsenate [As(V)] are highly toxic aquatic contaminants. Since arsenite is more mobile in natural waters and less efficiently removed in adsorption/coagulation processes than arsenate, the oxidation of arsenite to arsenate is desirable in water treatment. We performed the photocatalytic oxidation of arsenite in aqueous TiO2 suspension and investigated the effects of pH, dissolved oxygen, humic acid (HA), and ferric ions on the kinetics and mechanisms of arsenite oxidation. Arsenite oxidation in UV-illuminated TiO2 suspension was highly efficient in the presence of dissolved oxygen. Homogeneous photooxidation of arsenite in the absence of TiO2 was negligibly slow. Since the addition of excess tert-butyl alcohol (OH radical scavenger) did not reduce the rate of arsenite oxidation, the OH radicals should not be responsible for As(III) oxidation. The addition of HA increased both arsenite oxidation and H2O2 production at pH 3 under illumination, which could be ascribed to the enhanced superoxide generation through sensitization. We propose that the superoxide is the main oxidant of arsenite in the TiO2/UV process. The addition of ferric ions also significantly enhanced the arsenite photooxidation. In this case, the addition of tert-butyl alcohol reduced the arsenite oxidation rate, which implied thatthe OH radical-mediated oxidation path was operative in the presence of ferric ions. Since both Fe3+ and HA that were often found with the arsenic in groundwater were beneficial to the photocatalytic oxidation of arsenite, the TiO2/UV process could be a viable pretreatment method. This can be as simple as exposing the arsenic-polluted water in a TiO2-coated trough to sunlight.
367 citations
01 Apr 2002
TL;DR: In this paper, the authors demonstrate the feasibility of quantification of the ferrous/ferric ratio in minerals by analyzing the Fe L====== 23====== ELNES as a function of the Ferric iron concentration.
Abstract: Determination of Fe3+/ΣFe in minerals at submicrometre scale has been a long-standing objective in analytical mineralogy. Detailed analysis of energy-loss near-edge structures (ELNES) of the Fe L
23
core-loss edges recorded in a transmission electron microscope (TEM) provides chemical information about the iron oxidation state. The valence-specific multiplet structures are used as valence fingerprints. Systematic investigations on the Fe L
23
ELNES of mono and mixed-valence Fe-bearing natural minerals and synthetic solid solutions of garnets (almandine-skiagite and andradite-skiagite), pyroxenes (acmite-hedenbergite) and spinels (magnetite-hercynite) are presented where the presence of multiple valence states is distinguished by a splitting of the Fe L
3
edge. We demonstrate the feasibility of quantification of the ferrous/ferric ratio in minerals by analyzing the Fe L
23
ELNES as a function of the ferric iron concentration resulting in three independent methods: (1) The method of the modified integral intensity ratio of the Fe L
23
white lines employs two 2-eV-wide integration windows centring around both the Fe L
3
maximum for Fe3+ and the Fe L
2
maximum for Fe2+. This refined routine, compared to the previously published quantification method of the ferrous/ferric ratio in minerals, leads to an improved universal curve with acceptable absolute errors of about ±0.03 to ±0.04 for Fe3+/ΣFe ratios. (2) The second method uses a simple mathematical description of the valence-dependent splitting of Fe L
3
ELNES by fitting several Gaussian functions and an arctan function. The systematic analysis of the integral portions of the individual Gaussian curves for different mineral groups provides a further Fe3+/ΣFe quantification method with an absolute error of about ±0.02 to ±0.03. (3) The Fe L
3
ELNES can also be modelled with the help of reference spectra, whereby the Fe3+/ΣFe ratio can be determined with an absolute error of ca. ±0.02.
321 citations
TL;DR: In this article, the rate of evolution of NH3, which is indicative of the overall rate of degradation, was measured continuously in a batch system sparged with air at 55 °C, typical of absorbers for CO2 removal from flue gas.
Abstract: Oxidative degradation of monoethanolamine (MEA) was studied at 55 °C, typical of absorbers for CO2 removal from flue gas. The rate of evolution of NH3, which was indicative of the overall rate of degradation, was measured continuously in a batch system sparged with air. Dissolved iron from 0.0001 to 1 mM yielded oxidation rates from 0.37 to 2 mM/h in MEA solutions loaded with 0.4 mol CO2/mol MEA. Ethylenediaminetetraacetic acid (EDTA) and N,N-bis(2-hydroxyethyl)glycine effectively decreased the rate of oxidation in the presence of iron by 40−50%. Ferrous caused oxidation in unloaded MEA with stoichiometry from 0.1 to 0.33 mol NH3/mol Fe2+. Fe2+ from 0.0001 to 3.2 mM yielded rates from 0.12 to 1.1 mM/h. Ferric did not appear to catalyze oxidation in unloaded MEA.
290 citations
TL;DR: A system in which influx of iron into brain is by regulated receptor‐mediated transport and in which efflux is by bulk flow is ideal for homeostasis of brain iron.
Abstract: Iron is an important constituent in brain and, in certain regions, e.g., the basal nuclei, reaches concentrations equivalent to those in liver. It has a role in electron transfer and is a cofactor for certain enzymes, including those involved in catecholamine and myelin synthesis. Iron in CSF is likely to be representative of that in interstitial fluid of brain. Transferrin in CSF is fully saturated, and the excess iron may be loosely bound as Fe(II). Brain iron is regulated in iron depletion, suggesting a role for the blood-brain barrier (BBB). Iron crosses the luminal membrane of the capillary endothelium by receptor-mediated endocytosis of ferric transferrin. This results in an initial linear uptake of radioactive iron into brain at an average rate relative to serum of about 3.3 x 10(-3) ml x g of brain(-1) x h(-1) in the adult rat. This corresponds to about 80 nmol x kg(-1) x h(-1). Much higher rates occur in the postnatal rat. These increase during the first 15 days of life and decline thereafter. Within the endothelium, most of the iron is separated from transferrin, presumably by the general mechanism of acidification within the endosome. Iron appears to be absorbed from the vesicular system into cytoplasm and transported across the abluminal plasma membrane into interstitial fluid as one or more species of low molecular weight. There is some evidence that ionic Fe(II) is involved. Certainly Fe(II) ions presented on the luminal side rapidly cross the complete BBB, i.e., luminal and abluminal membranes. Within interstitial fluid, transported iron will bind with any unsaturated transferrin synthesized or transported into the brain-CSF system. Oligodendrocytes are one site of synthesis. From interstitial fluid, ferric transferrin is taken up by neurones and glial cells by the usual receptor-mediated endocytosis. Calculations of the amount of iron leaving the system with the bulk flow of CSF indicate that most iron entering brain across the capillary endothelium finally leaves the system with the bulk outflow of CSF through arachnoid villi and other channels. A system in which influx of iron into brain is by regulated receptor-mediated transport and in which efflux is by bulk flow is ideal for homeostasis of brain iron.
277 citations
TL;DR: It is concluded that relatively low average mixing speeds for coagulation and flocculation are essential for efficient operation for DAF separation.
275 citations
TL;DR: In this article, a method for simultaneous measurement of ferrous and ferric iron concentrations in drainage and other waters is reported, which is based on the colorimetric measurement of red-colored ferric-sulfosalicylate complex formed at low pH.
222 citations
TL;DR: The kinetics of formation and breakdown of the putative active oxygenating intermediate in cytochrome P 450, a ferryl-oxo-(π) porphyrin cation radical (Compound I), have been analyzed in the reaction of a thermostable P450, CYP119, with meta-chloroperoxybenzoic acid (m-CPBA).
209 citations
TL;DR: In this article, an efficient synthesis of 3,4-dihydropyrimidinones from the aldehyde, β-keto ester and urea in ethanol, using ferric chloride hexahydrate or nickel chloride hexahedrate as the catalyst, is described.
Abstract: An efficient synthesis of 3,4-dihydropyrimidinones from the aldehyde, β-keto ester and urea in ethanol, using ferric chloride hexahydrate or nickel chloride hexahydrate as the catalyst, is described. Compared with the classical Biginelli reaction conditions, this new method has the advantage of excellent yields (53-97%) and short reaction time (4-5 hours).
TL;DR: Direct inhibition of E. coli Fur activity by NO is established by using chromosomal Fur-regulated lacZ reporter fusion in E. Escherichia coli to establish a link between control of iron metabolism and the response to NO effects.
Abstract: Ferric uptake regulation protein (Fur) is a bacterial global regulator that uses iron as a cofactor to bind to specific DNA sequences. The function of Fur is not limited to iron homeostasis. A wide variety of genes involved in various mechanisms such as oxidative and acid stresses are under Fur control. Flavohemoglobin (Hmp) is an NO-detoxifying enzyme induced by NO and nitrosothiol compounds. Fur recently was found to regulate hmp in Salmonella typhimurium, and in Escherichia coli, the iron-chelating agent 2,2'-dipyridyl induces hmp expression. We now establish direct inhibition of E. coli Fur activity by NO. By using chromosomal Fur-regulated lacZ reporter fusion in E. coli, Fur activity is switched off by NO at micromolar concentration. In vitro Fur DNA-binding activity, as measured by protection of restriction site in aerobactin promoter, is directly sensitive to NO. NO reacts with Fe(II) in purified FeFur protein to form a S = 12 low-spin FeFur-NO complex with a g = 2.03 EPR signal. Appearance of the same EPR signal in NO-treated cells links nitrosylation of the iron with Fur inhibition. The nitrosylated Fur protein is still a dimer and is stable in anaerobiosis but slowly decays in air. This inhibition probably arises from a conformational switch, leading to an inactive dimeric protein. These data establish a link between control of iron metabolism and the response to NO effects.
TL;DR: The removal of HA is not caused by adsorbing onto the iron hydroxide resulted from PFS hydrolysis, but through the complex-formation between the PFS and the HA, demonstrating that the coagulation of HA by PFS at low pH is mainly due to charge-neutralization.
TL;DR: The ferrous oxidation in xylenol orange (FOX) assay for hydroperoxides suffers from very narrow pH optimum in the range 1.7-1.8, and substitution of perchloric for the sulfuric acid resulted in a lowering of the optimum pH of the assay to 1.1, a decreased dependence of the absorbance of the ferric-xylenl orange complex on acid concentration and decreased sensitivity to added compounds.
TL;DR: In a short overview of iron chemistry, some of the pitfalls using standard redox potentials are pointed out, the interaction of ferric complexes with hydrogen peroxide to give hydroxyl radicals are commented on, and the role of dissimilatory ferric reduction in microbial respiration and biomineralization is discussed.
Abstract: In biological systems, the predominant form of iron is the trivalent Fe(III) form, which is potentially not readily bioavailable because of its hydrolysis and polymerization to insoluble forms. It is also the easiest of the two predominant forms of iron to chelate selectively. In a short overview of iron chemistry, we point out some of the pitfalls using standard redox potentials, comment on the interaction of ferric complexes with hydrogen peroxide to give hydroxyl radicals and address the release of iron from ferrisiderophores. In biological systems there are two classes of ferric reductases, the soluble flavin reductases found in prokaryotes, and the membrane-bound cytochrome b-like reductases found in eukaryotes. Finally the role of dissimilatory ferric reduction in microbial respiration and biomineralization is discussed.
TL;DR: In this paper, a microwave hydrothermal (MH) reaction of ferrous sulphate and sodium hydroxide in the temperature range of 90-200 °C was reported.
TL;DR: This work investigated the association of uranium with the amorphous and crystalline forms of iron oxides commonly formed on corroding steel surfaces and found that uranium was incorporated with the oxide by addition during the formation of ferrihydrite, goethite, green rust II, lepidocrocite, maghemite, and magnetite.
Abstract: Decontamination of metal surfaces contaminated with low levels of radionuclides is a major concern at Department of Energy facilities. The development of an environmentally friendly and cost-effective decontamination process requires an understanding of their association with the corroding surfaces. We investigated the association of uranium with the amorphous and crystalline forms of iron oxides commonly formed on corroding steel surfaces. Uranium was incorporated with the oxide by addition during the formation of ferrihydrite, goethite, green rust II, lepidocrocite, maghemite, and magnetite. X-ray diffraction confirmed the mineralogical form of the oxide. EXAFS analysis at the U L(III) edge showed that uranium was present in hexavalent form as a uranyl oxyhydroxide species with goethite, maghemite, and magnetite and as a bidentate inner-sphere complex with ferrihydrite and lepidocrocite. Iron was present in the ferric form with ferrihydrite, goethite, lepidocrocite, and maghemite; whereas with magnetite and green rust II, both ferrous and ferric forms were present with characteristic ferrous:total iron ratios of 0.65 and 0.73, respectively. In the presence of the uranyl ion, green rust II was converted to magnetite with concomitantreduction of uranium to its tetravalent form. The rate and extent of uranium dissolution in dilute HCl depended on its association with the oxide: uranium present as oxyhydroxide species underwent rapid dissolution followed by a slow dissolution of iron; whereas uranium present as an inner-sphere complex with iron resulted in concomitant dissolution of the uranium and iron.
TL;DR: The opposite regulation of two iron permease genes and the role of TUP1 indicate that the process of iron acquisition by C. albicans may be more complex and potentially more adaptable than by S. cerevisiae.
Abstract: High-affinity iron uptake by a ferrous permease in the opportunistic pathogen Candida albicans is required for virulence. Here this iron uptake system has been characterized by investigating three distinct activities: an externally directed surface ferric reductase, a membrane-associated PPD (p-phenylenediamine) oxidase and a cellular ferrous iron transport activity. Copper was required for the PPD oxidase and ferrous transport activities. In contrast, copper was not required for iron uptake from siderophores. Addition of iron to the growth medium repressed ferric reductase and ferrous transport, indicating homeostatic regulation. To identify the genes involved, orthologous mutants of Saccharomyces cerevisiae were transformed with a genomic library of C. albicans. CFL95, a gene with sequence similarity to ferric reductases, restored reductase activity to the orthologous S. cerevisiae mutant. CaFTR2 and CaFTR1, genes with homology to ferrous permeases, conferred ferrous transport activity to the orthologous S. cerevisiae mutant. However, neither a genomic library nor CaFET99, a multicopper oxidase homologue and candidate gene for the PPD oxidase, complemented the S. cerevisiae mutant, possibly because of problems with targeting or assembly. Transcripts for CFL95, CaFTR1 and CaFET99 were strongly repressed by iron, whereas the CaFTR2 transcript was induced by iron. Deletion of the TUP1 regulator perturbed the homeostatic control of reductive iron uptake. Incidentally, iron starvation was noted to induce flavin production and this was misregulated in the absence of TUP1 control. The opposite regulation of two iron permease genes and the role of TUP1 indicate that the process of iron acquisition by C. albicans may be more complex and potentially more adaptable than by S. cerevisiae.
TL;DR: A computer-controlled reactor was designed to function as a "potentiostat"-bioreactor by arresting the air supply to the reactor when the redox potential in solution was greater than a designated setpoint, and it was found to improve chalcopyrite dissolution.
Abstract: Shake flask and stirred tank bioleaching experiments showed that the dissolution of chalcopyrite is inhibited by ferric ion concentrations as low as 200 mg L(-1) and redox potentials >420 mV (vs. Ag/AgCl). Chemical leaching of chalcopyrite (4% suspension, surface area 2.3 m2 g(-1)) was enhanced fourfold in the presence of 0.1 M ferrous sulphate compared with 0.1 M ferric sulphate. A computer-controlled reactor was designed to function as a "potentiostat"-bioreactor by arresting the air supply to the reactor when the redox potential in solution was greater than a designated setpoint. Leaching at a low, constant redox potential (380 mV vs. Ag/AgCl) achieved final copper recoveries of 52%-61%, which was twice that achieved with a continuous supply of oxygen (<30% extraction). The bacterial populations were observed to continue growing under oxygen limitation but in a controlled manner that was found to improve chalcopyrite dissolution. As the control mechanism is easily established and is likely to decrease production cost, the use of this technology may find application in industry.
TL;DR: In the hemoglobin repletion experiments carried out on newly weaned rats with anemia induced by a low-iron diet, supplementation of the diet with the Fe(3+)-peptide complex was as efficient as supplementation with iron sulfate in the conversion from diet to hemoglobin iron.
Abstract: The properties of an Fe3+−peptide complex containing 5.6% Fe, obtained by the reaction of ferric chloride with an enzymatic hydrolysate of casein, are described. The major site of iron binding corresponds primarily to the carboxylate groups and to a lesser extent to the peptide bonds. The Fe3+−peptide complex is insoluble at acid pH and completely soluble at neutral to alkaline pH. When soluble, the Fe3+ is tightly bound to the complex peptide mixture but can be displaced and complexed by a low molecular weight ligand such as cysteine. Its efficacy in relation to iron sulfate was compared in rats. Both iron sources were administrated in Milli-Q water by gastric gavage to male Wistar rats (180−200 g) after an 18 h fast with water ad libitum. Fe3+ from the Fe3+−peptide complex was transferred to the blood in a dose-dependent manner (1−8 mg of Fe/kg), and the serum iron levels were significantly higher (p < 0.001) than in a similar group of rats treated with iron sulfate. In the comparative kinetics experime...
TL;DR: In this article, the authors proposed a reaction model to interpret the catalytic effect of silver ions on chalcopyrite leaching in sulfuric acid solutions, and applied the model to analyze the effect of the presence of silver ion on the performance of chal copyrite extraction.
TL;DR: Experimental results showed that ferric chloride had lower fluorescence quenching than polyferric sulfate (PFS), indicating more rapid hydrolysis of the monomeric ferric ion in the coagulation and dilution process, and from the pH study, it was found that sludge formed from PFS coagulations was more stable than that from FeCl3 coagulated.
TL;DR: Analysis of sediments shows a pronounced signature of this deposition with elevated sediment concentrations of iron, arsenic, and manganese relative to a control site, and hypothesize that this phase persists in the recently deposited sediment despite reducing conditions due to slow dissolution kinetics.
Abstract: Deposition of arsenic to the sediments of Haiwee Reservoir (Olancha, CA) has dramatically increased since March 1996 as a result of an interim strategy for arsenic management in the Los Angeles Aqueduct (LAA) water supply. Ferric chloride and cationic polymer are introduced into the Aqueduct at the Cottonwood treatment plant, 27 km north of the Haiwee Reservoir. This treatment decreases the average arsenic concentration from 25 μg/L above Cottonwood to 8.3 μg/L below Haiwee. Iron- and arsenic-rich flocculated solids are removed by deposition to the reservoir sediments. Analysis of sediments shows a pronounced signature of this deposition with elevated sediment concentrations of iron, arsenic, and manganese relative to a control site. Sediment concentrations of these elements remain elevated throughout the core length sampled (ca. 4% iron and 600 and 200 μg/g of manganese and arsenic, respectively, on a dry weight basis). A pore water profile revealed a strong redox gradient in the sediment. Manganese in the pore waters increased below 5 cm; iron and arsenic increased below 10 cm and were strongly correlated, consistent with reductive dissolution of iron oxyhydroxides and concurrent release of associated arsenic to solution. X-ray absorption near-edge spectroscopy revealed inorganic As(V) present only in the uppermost sediment (0-2.5 cm) in addition to inorganic As(III). In the deeper sediments (to 44 cm), only oxygen-coordinated As(III) was detected. Analysis of the extended X-ray absorption fine structure spectrum indicates that the As(III) at depth remains associated with iron oxyhydroxide. We hypothesize that this phase persists in the recently deposited sediment despite reducing conditions due to slow dissolution kinetics.
TL;DR: Surprisingly, imidazole, cyanide, and azide binding profiles at equilibrium are not accounted for by a single site titration curve but are biphasic and strongly suggest the presence of two distinct conformers within the liganded species.
TL;DR: In this article, reverse osmosis (RO) membranes were tested at three different treatment plants in southern California, using either aluminum sulfate (alum) or ferric chloride coagulants and chloramines.
TL;DR: Iron is taken up by human colon cells and participates in the induction of oxidative DNA damage, which means that iron or its capacity to catalyse ROS-formation, is an important colon cancer risk factor.
Abstract: Dietary iron may contribute to colon cancer risk via production of reactive oxygen species (ROS). The aim of the study was to determine whether physiological ferric/ferrous iron induces oxidative DNA damage in human colon cells. Therefore, differentiated human colon tumour cells (HT29 clone 19A) were incubated with ferric-nitrilotriacetate (Fe-NTA) or with haemoglobin and DNA breaks and oxidised bases were determined by microgelelectrophoresis. The effects of Fe-NTA were measured with additional H(2)O(2) (75microM) and quercetin (25-100microM) treatment. Analytic detection of iron in cell cultures, treated with 250microM Fe-NTA for 15 min to 24h, showed that 48.02+/-5.14 to 68.31+/-2.11% were rapidly absorbed and then detectable in the cellular fraction. Fe-NTA (250-1000microM) induced DNA breaks and oxidised bases, which were enhanced by subsequent H(2)O(2) exposure. Simultaneous incubation of HT29 clone 19A cells with Fe-NTA and H(2)O(2) for 15 min, 37 degrees C did not change the effect of H(2)O(2) alone. The impact of Fe-NTA and H(2)O(2)-induced oxidative damage is reduced by the antioxidant quercetin (75-67% of H(2)O(2)-control). Haemoglobin was as effective as Fe-NTA in inducing DNA damage. From these results we can conclude that iron is taken up by human colon cells and participates in the induction of oxidative DNA damage. Thus, iron or its capacity to catalyse ROS-formation, is an important colon cancer risk factor. Inhibition of damage by quercetin reflects the potential of antioxidative compounds to influence this risk factor. Quantitative data on the genotoxic impact of ferrous iron (e.g. from red meat) relative to the concentrations of antioxidants (from plant foods) in the gut are now needed to determine the optimal balance of food intake that will reduce exposure to this type of colon cancer risk factor.
TL;DR: Comparison of sorbed and dissolved Fe(II) concentrations between cultures amended with cysteine and with other organic chelators showed that solubilization is not the main factor in Cysteine-stimulated Fe(III) reduction.
Abstract: The reductive dissolution of poorly crystalline ferric oxides in the presence of cysteine was investigated to evaluate the potential of cysteine as a possible electron carrier to stimulate the reduction of iron(III) oxides by Geobacter sulfurreducens. The extent and rate of biotic and abiotic reduction of iron(III) oxides in the presence of cysteine at various concentrations were compared. Iron(III) oxides were reduced abiotically by cysteine. The initial rate and extent of iron(III) oxide reduction were correlated linearly with the cysteine concentration ranging from 0 to 6 mM. Also, addition of 0.5-2 mM cysteine significantly stimulated the rate and the extent of iron(III) oxide reduction in cultures of G. sulfurreducens. The cysteine concentration decreased in accordance with the increase of Fe(II) concentration and reached a nearly constant residual concentration. Cysteine depletion followed first-order kinetics and increased linearly with the cysteine concentration. An 8- to 11-fold increase in the extent of iron(III) oxide reduction relative to the abiotic system was observed. Comparison of sorbed and dissolved Fe(II) concentrations between cultures amended with cysteine and with other organic chelators showed that solubilization is not the main factor in cysteine-stimulated Fe(III) reduction. Addition of cystine could enhanced the extent of iron(III) oxide reduction, concomitant with the increase of the regenerated cysteine concentration and support the hypothesis that cysteine could serve as an electron carrier to transfer electrons from G. sulfurreducens to poorly crystalline iron(III) oxides.
TL;DR: In this paper, the interference of acid-soluble ferric minerals on the analysis of sulfides using cold diffusion procedures and the effectiveness of two amendments, i.e., SnCl2 and ascorbic acid (AA), respectively, to prevent the interference.
TL;DR: Dcytb expression and function were modulated by iron and DMT1, both predominantly localised in the apical region of the duodenum were up-regulated in iron deficiency.
Abstract: Dcytb has been identified as the mammalian transplasma ferric reductase that catalyzes the reduction of ferric to ferrous iron in the process of iron absorption. Its mRNA and protein levels are up-regulated by several independent stimulators of iron absorption. Furthermore, its cDNA encodes putative binding sites for heme and ascorbic acid. Using Northern and Western blots, RT-PCR and confocal microscopy, we studied the expression and localisation of Dcytb in cell lines and tissues of CD1 mice. Dcytb expression and function were modulated by iron. Dcytb and DMT1, both predominantly localised in the apical region of the duodenum were up-regulated in iron deficiency. Dcytb, the iron regulated ferric reductase may also utilize cytoplasmic ascorbate as electron donor for transmembrane reduction of iron. Dcytb expression was found in other tissues apart from the duodenum and its regulation and functions at these other sites are of interest in iron metabolism.
TL;DR: The role of H. pylori Fur in regulation of H-pylori iron uptake is determined and it is found that Fur homologs are involved in the regulation of bacterial iron‐responsive regulation.
Abstract: Background. Availability of the essential nutrient iron is thought to vary greatly in the gastric mucosa, and thus the human gastric pathogen Helicobacter pylori requires regulatory responses to these environmental changes. Bacterial iron-responsive regulation is often mediated by Ferric Uptake Regulator (Fur) homologs, and in this study we have determined the role of H. pylori Fur in regulation of H. pylori iron uptake.
Methods. Wild-type H. pylori and fur mutant derivatives were compared after growth in iron-restricted and iron-replete conditions. Iron-uptake was measured using 55Fe-labeled iron, whereas gene expression was monitored at the transcriptional level using Northern hybridization and lacZ reporter gene fusions.
Results. Iron-uptake and total cellular iron content were approximately five-fold increased in the fur mutant compared with the wild-type strain, which indicated that in the fur mutant iron-uptake is not repressed by excess iron. A comprehensive screening of all H. pylori genes encoding putative iron-uptake proteins indicated that some of these H. pylori genes are constitutively expressed, while others are iron- and Fur-regulated.
Conclusions. Iron uptake in H. pylori is in part differently regulated compared with other bacteria, since in H. pylori some iron-uptake systems are constitutively expressed. However, other iron uptake systems of H. pylori display the iron- and Fur-mediated repression that is common in bacteria. Taken together, this Fur-mediated modulation of iron-uptake capacity may be a specific adaptation to the conditions in the human stomach, where iron starvation and iron overload can be encountered in relatively short time intervals.