Showing papers on "Ferric published in 1990"

Genetic evidence that ferric reductase is required for iron uptake in Saccharomyces cerevisiae.

Abstract: The requirement for a reduction step in cellular iron uptake has been postulated, and the existence of plasma membrane ferric reductase activity has been described in both procaryotic and eucaryotic cells. In the yeast Saccharomyces cerevisiae, there is an externally directed reductase activity that is regulated by the concentration of iron in the growth medium; maximal activity is induced by iron starvation. We report here the isolation of a mutant of S. cerevisiae lacking the reductase activity. This mutant is deficient in the uptake of ferric iron and is extremely sensitive to iron deprivation. Genetic analysis of the mutant demonstrates that the reductase and ferric uptake deficiencies are due to a single mutation that we designate fre1-1. Both phenotypes cosegregate in meiosis, corevert with a frequency of 10(-7), and are complemented by a 3.5-kilobase fragment of genomic DNA from wild-type S. cerevisiae. This fragment contains FRE1, the wild-type allele of the mutant gene. The level of the gene transcript is regulated by iron in the same was as the reductase activity. The ferrous ion product of the reductase must traverse the plasma membrane. A high-affinity (Km = 5 microM) ferrous uptake system is present in both wild-type and mutant cells. Thus, iron uptake in S. cerevisiae is mediated by two plasma membrane components, a reductase and a ferrous transport system.

Oxidation of reduced inorganic sulphur compounds by acidophilic thiobacilli.

Abstract: Acidophilic sulphur-oxidizing bacteria were first isolated from acidic mine effluents [1], where they are the causative agents of the environmental problem acid mine drainage. Furthermore, acidophilic thiobacilli are at least partially responsible for the development of acid sulphate soils [2]. Over the past decades there has been a growing interest in the application of this type of organisms in the biological leaching of metal ores [3] and the biological dcsulphuriz~tion of coal [4,5]. The key reaction in the processes mentioned above is the biological oxidation of pyrite (Fe:S2) to ferric sulphate and sulphuric acid. Thiobacillus ferrooxidans is widely used as a model organism to study the biological oxidation of pyrite. T. ferrooxidans is an obligately chemolithoautotrophic, aerobic. Gram-negative bacterium. Energy sources for autotrophic growth include ferrous iron and a number of reduced inorganic sulphur compounds [6]. Most studies into the physiology and bio-en-

Citrate as a siderophore in Bradyrhizobium japonicum.

Abstract: Under iron-limiting conditions, many bacteria secrete ferric iron-specific ligands, generically termed siderophores, to aid in the sequestering and transport of iron. One strain of the nitrogen-fixing soybean symbiont Bradyrhizobium japonicum, 61A152, was shown to produce a siderophore when 20 B. japonicum strains were screened with all six chemical assays commonly used to detect such production. Production by strain 61A152 was detected via the chrome azurol S assay, a general test for siderophores which is independent of siderophore structure. The iron-chelating compound was neither a catechol nor a hydroxamate and was ninhydrin negative. It was determined to be citric acid via a combination of thin-layer chromatography and high-voltage paper electrophoresis; this identification was verified by a specific enzymatic assay for citric acid. The inverse correlation which was observed between citric acid release and the iron content of the medium suggested that ferric citrate could serve as an iron source. This was confirmed via growth and transport assays. Exogenously added ferric citrate could be used to overcome iron starvation, and iron-deficient cells actively transported radiolabeled ferric citrate. These results, taken together, indicate a role for ferric citrate in the iron nutrition of this strain, which has been shown to be an efficient nitrogen-fixing strain on a variety of soybean cultivars.

Formation of 8-hydroxydeoxyguanosine (8-OH-dG) in rat kidney DNA after intraperitoneal administration of ferric nitrilotriacetate (Fe-NTA).

Abstract: A significant increase of 8-hydroxydeoxyguanosine (8-OH-dG) was observed in the kidney DNA of rats given a renal carcinogen, the ferric complex of nitrilotriacetate (Fe-NTA) by single i.p. injection. By contrast, non- or weakly carcinogenic compounds, aluminum-nitrilotriacetate complex (Al-NTA), non-complexed NTA (Na2NTA) and ferric chloride had no effect on 8-OH-dG production in the kidney DNA. These results suggest the involvement of active oxygen radicals in Fe-NTA carcinogenesis.

Photocatalytic oxidation of phenol in the presence of hydrogen peroxide and titanium dioxide powders

Abstract: The effect of hydrogen peroxide on the photocatalytic oxidation of phenol on illuminated TiO 2 has been investigated The experimental results indicate that transition metal ions, such as Fe 3+ and Cu 2+ , affect the photocatalytic oxidation of phenol In the absence of added H 2 O 2 the ferric ions induce the occurrence of the photo-Fenton-type reaction so that the phenol removal of an initial 1000 mg 1 −1 solution is enhanced from 23 to 33% within 8 h However, the cupric ions show a negative effect In the presence of added H 2 O 2 , both the ferric and the cupric ions enhance the phenol oxidation rate drastically A 1000 mg 1 −1 phenol solution can be completely decomposed within 1 h and the total organic carbon removal reaches 80% A reaction mechanism which involves the generation of hydroxyl radicals is proposed

Diagenesis in anoxic sediments from the California continental borderland and its influence on iron, sulfur, and magnetite behavior

Abstract: Solid phase and pore water profiles of compounds containing iron and sulfur have been determined by wet chemical, magnetic, and X-ray diffraction techniques in three California continental borderland basins. The observed profiles have been fit by simple reaction-diffusion models in order to determine reaction rates and constrain budgets for iron and sulfur. More than 95% of the solid phase reduced sulfur is pyrite, and down core profiles are well fit by a model in which net sulfate reduction rates decrease exponentially with depth. Net sulfate reduction rates determined from models fit to solid phase reduced sulfur measurements and pore water sulfate profiles yield results that are consistent. Depth integrated sulfate reduction rates for modern sediments in San Pedro, Santa Catalina, and San Nicolas Basins are, 11.4, 6.3, and 6.3–8.8 (μmol cm-2yr-1), respectively. Measurements of solid phase iron species indicate that surficial sediments are enriched in easily-reducible ferric oxyhydroxides. The enrichment is maintained by a combination of oxidation of Fe2+ diffusing upward from underlying anoxic sediments, as well as input of fresh sediment enriched in ferric oxyhydroxides. The three primary sources for iron converted to pyrite and the sequence in which they are utilized are: ferric oxyhydroxides, magnetite and other crystalline oxides, and “exchangeable” iron in phyllosilicates. The majority (50–80%) of the iron converted to pyrite is from the silicates, and budgetary calculations indicate the amount of iron released from San Pedro basin silicates agrees within 35% with the amount of magnesium removed from pore water to solid phases. Fe2+ is enriched in near-surface pore waters because rates of dissolved iron production by oxyhydroxide reduction exceed rates of sulfate reduction and pyrite formation. At depth, pore waters are sulfidic because rates of sulfate reduction exceed rates of iron release from silicates. Sulfide produced at depth diffuses upward until it reaches sediments with available iron, causing a step-like increase in solid phase sulfur concentration. Over 90% of the magnetite present in surficial sediments is dissolved at depth due to reaction with H2S. A model is developed to predict the depth at which magnetite dissolution should occur, based on sulfate reduction rates and the flux of ferric oxyhydroxides. The results of this model predict the onset of dissolution at depths of 5–40 cm in different basins and agree well with the observed depths of magnetite dissolution.

Alteration of sperm whale myoglobin heme axial ligation by site-directed mutagenesis.

Abstract: Three mutant proteins of sperm whale myoglobin (Mb) that exhibit altered axial ligations were constructed by site-directed mutagenesis of a synthetic gene for sperm whale myoglobin. Substitution of distal pocket residues, histidine E7 and valine E11, with tyrosine and glutamic acid generated His(E7)Tyr Mb and Val(E11)Glu Mb. The normal axial ligand residue, histidine F8, was also replaced with tyrosine, resulting in His(F8)Tyr Mb. These proteins are analogous in their substitutions to the naturally occurring hemoglobin M mutants (HbM). Tyrosine coordination to the ferric heme iron of His(E7)Tyr Mb and His(F8)Tyr Mb is suggested by optical absorption and EPR spectra and is verified by similarities to resonance Raman spectral bands assigned for iron-tyrosine proteins. His(E7)Tyr Mb is high-spin, six-coordinate with the ferric heme iron coordinated to the distal tyrosine and the proximal histidine, resembling Hb M Saskatoon [His(beta E7)Tyr], while the ferrous iron of this Mb mutant is high-spin, five-coordinate with ligation provided by the proximal histidine. His(F8)Tyr Mb is high-spin, five-coordinate in both the oxidized and reduced states, with the ferric heme iron liganded to the proximal tyrosine, resembling Hb M Iwate [His(alpha F8)Tyr] and Hb M Hyde Park [His(beta F8)Tyr]. Val(E11)Glu Mb is high-spin, six-coordinate with the ferric heme iron liganded to the F8 histidine. Glutamate coordination to the ferric iron of this mutant is strongly suggested by the optical and EPR spectral features, which are consistent with those observed for Hb M Milwaukee [Val(beta E11)Glu]. The ferrous iron of Val(E11)Glu Mb exhibits a five-coordinate structure with the F8 histidine-iron bond intact.(ABSTRACT TRUNCATED AT 250 WORDS)

Degradation of the ferric chelate of EDTA by a pure culture of an Agrobacterium sp.

Abstract: A pure culture of an Agrobacterium sp. (deposited as ATCC 55002) that mineralizes the ferric chelate of EDTA (ferric-EDTA) was isolated by selective enrichment from a treatment facility receiving industrial waste containing ferric-EDTA. The isolate grew on ferric-EDTA as the sole carbon source at concentrations exceeding 100 mM. As the degradation proceeded, carbon dioxide, ammonia, and an unidentified metabolite(s) were produced; the pH increased, and iron was precipitated from solution. The maximum rate of degradation observed with sodium ferric-EDTA as the substrate was 24 mM/day. At a substrate concentration of 35 mM, 90% of the substrate was degraded in 3 days and 70% of the associated chemical oxygen demand was removed from solution. Less than 15% of the carbon initially present was incorporated into the cell mass. Significant growth of this strain was not observed with uncomplexed EDTA as the sole carbon source at comparable concentrations; however, the ferric chelate of propylenediaminetetraacetic acid (ferric-PDTA) did support growth.

Porewater oxidation, dissolved phosphate and the iron curtain: iron-phosphorus relations in tidal freshwater marshes

Abstract: The process of dissolved phosphate removal from aqueous solution, which occurs during oxidation of soluble ferrous compounds to insoluble ferric forms, was examined in soils of two tidal freshwater marshes. Sites of amorphous iron deposition and sorption or co-precipitation of phosphate were found to be in surface soils and along creekbanks, where both ion diffusion and porewater advection move dissolved iron and phosphate from reduced to oxidized regions. Profiles of extractable iron and total phosphorus from creekbank and interior soils were consistent with hypothesized differences between a high and a low marsh. Porewater concentrations of dissolved phosphate were higher in creekbank soils of the high marsh, compared with water actually discharging from the creekbank during tidal exposure. We propose that an iron curtain of ferric hydroxides functions as a barrier to diffusive and advective movement of dissolved phosphate along surfaces of tidal freshwater marshes, and has important implications for the distribution and availability of phosphorus in other types of wetlands and aqueous systems.

Superoxide dismutase and Fenton chemistry. Reaction of ferric-EDTA complex and ferric-bipyridyl complex with hydrogen peroxide without the apparent formation of iron(II).

Abstract: A ferric-EDTA complex, prepared directly from FeCl3 or from an oxidized ferrous salt, reacts with H2O2 to form hydroxyl radicals (.OH), which degrade deoxyribose and benzoate with the release of thiobarbituric acid-reactive material, hydroxylate benzoate to form fluorescent dihydroxy products and react with 5,5-dimethylpyrrolidine N-oxide (DMPO) to form a DMPO-OH adduct. Degradation of deoxyribose and benzoate and the hydroxylation of benzoate are substantially inhibited by superoxide dismutase and .OH-radical scavengers such as formate, thiourea and mannitol. Inhibition by the enzyme superoxide dismutase implies that the reduction of the ferric-EDTA complex for participation in the Fenton reaction is superoxide-(O2.-)-dependent, and not H2O2-dependent as frequently implied. When ferric-bipyridyl complex at a molar ratio of 1:4 is substituted for ferric-EDTA complex (molar ratio 1:1) and the same experiments are conducted, oxidant damage is low and deoxyribose and benzoate degradation were poorly if at all inhibited by superoxide dismutase and .OH-radical scavengers. Benzoate hydroxylation, although weak, was, however, more effectively inhibited by superoxide dismutase and .OH-radical scavengers, implicating some role for .OH. The iron-bipyridyl complex had available iron-binding capacity and therefore would not allow iron to remain bound to buffer or detector molecules. Most .OH radicals produced by the iron-bipyridyl complex and H2O2 are likely to damage the bipyridyl molecules first, with few reacting in free solution with the detector molecules. Deoxyribose and benzoate degradation appeared to be mediated by an oxidant species not typical of .OH, and species such as the ferryl ion-bipyridyl complex may have contributed to the damage observed.

Hydrothermal (200 degrees C) synthesis and crystal chemistry of iron-rich kaolinites

Abstract: In order to study Al-Fe substitution, Fe-kaolinites were synthesized at 200°C from glasses (Si/(Al + Fe) = 1) with varying Fe content. XRD and IR spectroscopy showed that kaolinites with increasing Fe contents could be synthesized, and Mossbauer spectroscopy indicated that the iron is strictly ferric. Chemical analyses (STEM) of kaolinite particles determined up to almost 7% Fe2O3, which probably does not represent a structural limit. The effect of Fe3+ content is evident on growth kinetics and particle size of kaolinites, both decreasing with % Fe2O3. However, it is not possible to establish a general correlation between Fe content and percentage of structural defects. Acccording to IR spectroscopy, some synthesized Fe-rich kaolinites can have relatively good crystallinity.

Superoxide-dependent formation of hydroxyl radicals from ferric-complexes and hydrogen peroxide: an evaluation of fourteen iron chelators.

Abstract: When a variety of ferric chelates are reacted with hydrogen peroxide in phosphate buffer deoxyribose is damaged and this damage is protected against by formate, thiourea and mannitol. Damage done by ferric complexes of citrate, EDTA, NTA, EGTA and HEDA is substantially inhibited by superoxide dismutase (SOD) whereas complexes of PLA. ADP and CDTA are moderately inhibited by SOD. The effects of SOD argue against hydrogen peroxide acting as a reductant in Fenton chemistry driven by ferric complexes and hydrogen peroxide. EDTA has proved to be a useful model for Fenton chemistry that is inhibited by SOD although, it is not unique in this respect.

Effects of added manganic and ferric oxides on sulfate reduction and sulfide oxidation in intertidal sediments

Abstract: Freshly precipitated iron or manganese oxides were added to surface sediments from a salt marsh and from the intertidal region of Lowes Cove, Maine In the presence of added manganese, sulfate was formed under anoxic conditions, suggesting a manganese dependent sulfide oxidation Sulfate formation was not observed with iron additions Sulfate reduction was substantially but not completely inhibited by either metal oxide, even though both were added at levels well in excess though both were added at levels well in excess of natural concentrations Manganese-catalysed sulfide oxidation was further documented using a combination of radiolabel, metal oxide, and inhibitor additions, Results from this study suggested that losses of radiolabelled sulfide could result in underestimates of gross sulfate reduction rates in the presence of significant manganic oxide concentrations In addition, manganic oxides may facilitate the anaerobic regeneration of sulfate from sulfides

Iron magnetic moments in iron/silica gel nanocomposites

Abstract: Homogeneous gelled composites of iron and silica containing 11–40 wt. % Fe have been prepared by low‐temperature polymerization of aqueous solutions of ferric nitrate, tetraethoxysilane, and ethanol (with an HF catalyst). X‐ray diffraction, electron microscopy, Mossbauer effect, and magnetization measurements have been used to show that these bulk materials are paramagnetic composites at room temperature and remain in that state to 10 K. In this condition the Fe is present in nanometer‐sized regions and exists in ionic form (both Fe3+ and Fe2+ ). It possesses a large magnetic moment which decreases linearly from 3.9 μB/ Fe atom to 2.8 μB /Fe atom as the Fe content increased from 11% to 40%. For this composition increase, a negative Curie‐Weiss temperature was found which increased in magnitude linearly from −13 to −46 K. It is suggested that many of the iron atoms in the as‐cured nanocomposites interact antiferromagnetically, and that the magnitude of the effect increases with the Fe concentration. After ...

Possible role of bacterial siderophores in inflammation. Iron bound to the Pseudomonas siderophore pyochelin can function as a hydroxyl radical catalyst.

Abstract: Tissue injury has been linked to neutrophil associated hydroxyl radical (.OH) generation, a process that requires an exogenous transition metal catalyst such as iron. In vivo most iron is bound in a noncatalytic form. To obtain iron required for growth, many bacteria secrete iron chelators (siderophores). Since Pseudomonas aeruginosa infections are associated with considerable tissue destruction, we examined whether iron bound to the Pseudomonas siderophores pyochelin (PCH) and pyoverdin (PVD) could act as .OH catalysts. Purified PCH and PVD were iron loaded (Fe-PCH, Fe-PVD) and added to a hypoxanthine/xanthine oxidase superoxide- (.O2-) and hydrogen peroxide (H2O2)-generating system. Evidence for .OH generation was then sought using two different spin-trapping agents (5.5 dimethyl-pyrroline-1-oxide or N-t-butyl-alpha-phenylnitrone), as well as the deoxyribose oxidation assay. Regardless of methodology, .OH generation was detected in the presence of Fe-PCH but not Fe-PVD. Inhibition of the process by catalase and/or SOD suggested .OH formation with Fe-PCH occurred via the Haber-Weiss reaction. Similar results were obtained when stimulated neutrophils were used as the source of .O2- and H2O2. Addition of Fe-PCH but not Fe-PVD to stimulated neutrophils yielded .OH as detected by the above assay systems. Since PCH and PVD bind ferric (Fe3+) but not ferrous (Fe2+) iron, .OH catalysis with Fe-PCH would likely involve .O2(-)-mediated reduction of Fe3+ to Fe2+ with subsequent release of "free" Fe2+. This was confirmed by measuring formation of the Fe2(+)-ferrozine complex after exposure of Fe-PCH, but not Fe-PVD, to enzymatically generated .O2-. These data show that Fe-PCH, but not Fe-PVD, is capable of catalyzing generation of .OH. Such a process could represent as yet another mechanism of tissue injury at sites of infection with P. aeruginosa.

The role of Fe2+ and Fe3+ in synthetic Fe-substituted tetrahedrite

Abstract: Tetrahedrites with the composition between Cu12Sb4S13 and Cu10Fe2Sb4S13 were synthesized at 457 °C and 500 °C from the elements and carefully studied by Mossbauer spectroscopy of57Fe. Between Cu12Sb4S13 and Cu11Fe1Sb4S13 iron is predominantly ferric. Between Cu11Fe1Sb4S13 and Cu10Fe2Sb4S13 iron is predominantly ferrous and occupies the tetrahedral M1-sites.

An EXAFS study of the interaction of substrate with the ferric active site of protocatechuate 3,4-dioxygenase

Abstract: X-ray crystallographic studies of the intradiol cleaving protocatechuate 3,4-dioxygenase from Pseudomonas aeruginosa have shown that the enzyme has a trigonal bipyramidal ferric active site with two histidines, two tyrosines, and a solvent molecule as ligands. Fe K-edge EXAFS studies of the spectroscopically similar protocatechuate 3,4-dioxygenase from Brevibacterium fuscum are consistent with a pentacoordinate geometry of the iron active site with 3 O/N ligands at 1.90 {angstrom} and 2 O/N ligands at 2.08 {angstrom}. The 2.08-{angstrom} bonds are assigned to the two histidines, while the 1.90-{angstrom} bonds are associated with the two tyrosines and the coordinated solvent. The short Fe-O distance for the solvent suggests that it coordinates as hydroxide rather than water. When the inhibitor terephthalate is bound to the enzyme, the XANES data indicate that the ferric site becomes 6-coordinate and the EXAFS data show a beat pattern which can only be simulated with an additional Fe-O/N interaction at 2.46 {angstrom}. Together, the data suggest that the oxygens of the carboxylate group in terephthalate displace the hydroxide and chelate to the ferric site but in an asymmetric fashion. In contrast, protocatechuate 3,4-dioxygenase remains 5-coordinate upon the addition of the slow substrate homoprotocatechuic acid (HPCA). Previous EPR data have indicatedmore » that HPCA forms an iron chelate via the two hydroxyl functions. For the iron site to remain 5-coordinate and the HPCA to be chelated to the iron, the substrate must displace not only the hydroxide but also a ligand from the protein backbone, probably a histidine. The mechanistic implications of the displacement of hydroxide and a protein ligand in the active site are discussed.« less