Showing papers on "Ferric published in 1994"

Geobacter sulfurreducens sp. nov. , a hydrogen- and acetate-oxidizing dissimilatory metal-reducing microorganism

Abstract: A dissimilatory metal- and sulfur-reducing microorganism was isolated from surface sediments of a hydrocarbon-contaminated ditch in Norman, Okla. The isolate, which was designated strain PCA, was an obligately anaerobic, nonfermentative nonmotile, gram-negative rod. PCA grew in a defined medium with acetate as an electron donor and ferric PPi, ferric oxyhydroxide, ferric citrate, elemental sulfur, Co(III)-EDTA, fumarate, or malate as the sole electron acceptor. PCA also coupled the oxidation of hydrogen to the reduction of Fe(III) but did not reduce Fe(III) with sulfur, glucose, lactate, fumarate, propionate, butyrate, isobutyrate, isovalerate, succinate, yeast extract, phenol, benzoate, ethanol, propanol, or butanol as an electron donor. PCA did not reduce oxygen, Mn(IV), U(VI), nitrate, sulfate, sulfite, or thiosulfate with acetate as the electron donor. Cell suspensions of PCA exhibited dithionite-reduced minus air-oxidized difference spectra which were characteristic of c-type cytochromes. Phylogenetic analysis of the 16S rRNA sequence placed PCA in the delta subgroup of the proteobacteria. Its closest known relative is Geobacter metallireducens. The ability to utilize either hydrogen or acetate as the sole electron donor for Fe(III) reduction makes strain PCA a unique addition to the relatively small group of respiratory metal-reducing microorganisms available in pure culture. A new species name, Geobacter sulfurreducens, is proposed.

Microbial Iron Transport

Abstract: Iron, an essential nutrient, is not readily available in aquatic or terrestrial environments or in animal hosts. Therefore, microbes have developed various strategies for acquiring iron while at the same time protecting themselves from iron's potential toxic effects. The major strategies used by bacteria and fungi to acquire iron include production and utilization of siderophores (ferric specific chelators); utilization of host iron compounds such as heme, transferrin, and lactoferrin; and reduction of Fe(III) to Fe(II) with subsequent transport of Fe(II). Selected examples are discussed with attention to which strategies work best in which environments. The similarities and differences among the different systems with respect to iron binding compounds, receptors, and regulation are also presented.

Soluble guanylate cyclase from bovine lung : activation with nitric oxide and carbon monoxide and spectral characterization of the ferrous and ferric states

Abstract: Nitric oxide (.NO) is a recently discovered signaling agent which plays a role in many biological processes such as vasodilation and neuronal synaptic transmission. The only receptor characterized thus far for .NO is the soluble form of guanylate cyclase (sGC). .NO increases the Vmax of sGC by 100-200-fold, probably by interacting with a heme moiety on the enzyme. Although several procedures exist for purifying sGC, these procedures result in preparations with low heme contents. Using a novel procedure, the enzyme has been purified to homogeneity from bovine lung with a heme content of approximately 1 heme/heterodimer. The UV-visible spectrum of the enzyme contains a Soret peak centered at 431 nm and a single broad alpha/beta peak at 555 nm indicative of a 5-coordinate ferrous heme with histidine as the axial ligand. The heme moiety does not bind oxygen but will readily bind .NO to form a 5-coordinate complex or carbon monoxide (CO) to form a 6-coordinate complex. Oxidation of the heme with ferricyanide shifts the Soret to 393 nm, due most likely to the formation of a 5-coordinate ferric heme. In the ferric state, the heme will apparently not bind water but will bind cyanide with reduced affinity compared to methemoglobin and metmyoglobin. Purified enzyme containing 1 heme/heterodimer is activated 130-fold by .NO and 4.4-fold by CO.

[Fe(OMe)2(O2CCH2Cl)]10, a Molecular Ferric Wheel

Abstract: The synthesis of [Fe(OMe) 2 (O 2 CCH 2 Cl)] 10 , a molecular ferric wheel, from basic iron chloroacetate and ferric nitrate in methanol is described Spectroscopic analysis of methanol solutions used to prepare the compound revealed a (μ-oxo)(μ-carboxylato)diiron(III) intermediate having terminal oxygen donor ligands The structure of the crystalline ferric wheel was revealed in a single crystal X-ray diffraction investigation The molecule has idealized D 5d symmetry and consists of a 20-membered ring comprised of 10 ferric ions linked by 20 bridging methoxide and 10 bridging chloroacetate ligands The 10 iron atoms are approximately coplanar and are coordinated in a distorted octahedral manner by 6 oxygen donor atoms

Mechanisms of cell injury by activated oxygen species.

Abstract: Current evidence suggests that O2- and H2O2 injure cells as a result of the generation of a more potent oxidizing species. In addition to O2- and H2O2, the third essential component of the complex that mediates the lethal cell injury is a cellular source of ferric iron. The hypothesis most consistent with all the available data suggests that O2- reduces a cellular source of ferric to ferrous iron, and the latter then reacts with H2O2 to produce a more potent oxidizing species, like the .OH or an equivalently reactive species. In turn, .OH initiates the peroxidative decomposition of the phospholipids of cellular membranes. .OH also damages the inner mitochondrial membrane. Upon mitochondrial deenergization, a sequence of events is initiated that similarly leads to the loss of viability of the cell. DNA represents a third cellular target of .OH. Depending on the cell type, oxidative DNA damage can be coupled to cell killing through a mechanism related to the activation of poly (ADP-ribose) polymerase.

Decreasing Phosphorus Solubility in Poultry Litter with Aluminum, Calcium, and Iron Amendments

Abstract: Arkansas produces approximately one billion broilers (Gallus gallus domesticus) each year Phosphorous runoff from fields receiving poultry litter is believed to be one of the primary factor affecting water quality in northwest Arkansas Poultry litter contains ≃20 g P kg -1 , of which ≃2 g P kg -1 is water soluble The objective of this study was to determine if soluble P levels could be reduced in poultry litter with Al, Ca and/or Fe amendements Poultry litter was amended with alum, sodium aluminate, quick lime, slake lime, calcitic limestone, dolomitic limestone, gypsum, ferrous chloride, ferric chloride, ferrous sulfate, and ferric sulfate, and incubated in the dark at 25 o C for 1 wk

Two distinctly regulated genes are required for ferric reduction, the first step of iron uptake in Saccharomyces cerevisiae.

Abstract: Iron uptake in Saccharomyces cerevisiae involves at least two steps: reduction of ferric to ferrous ions extracellularly and transport of the reduced ions through the plasma membrane. We have cloned and molecularly characterized FRE2, a gene which is shown to account, together with FRE1, for the total membrane-associated ferric reductase activity of the cell. Although not similar at the nucleotide level, the two genes encode proteins with significantly similar primary structures and very similar hydrophobicity profiles. The FRE1 and FRE2 proteins are functionally related, having comparable properties as ferric reductases. FRE2 expression, like FRE1 expression, is induced by iron deprivation, and at least part of this control takes place at the transcriptional level, since 156 nucleotides upstream of the initiator AUG conferred iron-dependent regulation when fused to a heterologous gene. However, the two gene products have distinct temporal regulation of their activities during cell growth.

Bacterial iron transport : coordination properties of pyoverdin paa, a peptidic siderophore of pseudomonas aeruginosa

Abstract: Pyoverdin PaA is a siderophore excreted by Pseudomonas aeruginosa, a common and pathogenic bacterium. It belongs to a family of fluorescent iron(III) biological ligands. Its chemical structure shows three bidentate coordination sites, two hydroxamic acids and a dihydroxyquinoline-type function bound to a peptidic chain. Spectrophotometric, potentiometric and cyclic voltammetric measurements allowed the determination of the acid-base functions of the free siderophore as well as the iron(III) and iron(II) coordination properties. Pyoverdin PaA forms neutral and strong ferric complexes at physiological pH. The thermodynamic stability of its ferric and ferrous complexes is very similar to that of linear trihydroxamate siderophores, such as ferrioxamine B (Desferal) and coprogen, in spite of its anchored structure and of a catechol-type binding site. As for trihydroxamate ligands, the reduction potential was found to be accessible to physiological reductant systems and an iron(III) release mechanism via a reduction step could be proposed. Kinetic studies carried out by either classical or stopped-flow spectrophotometry have provided the kinetic parameters related to the formation and the dissociation of the ferric pyoverdin PaA complexes in acidic conditions. Stepwise mechanisms revealed the flexibility of this strong ligand. The binding of the terminal hydroxamic acid of pyoverdin PaA is proposed to be the rate limiting step of the iron(III) coordination process. The dissociation mechanism showed an unfolding of the siderophore leading to protonated ferric intermediate species corresponding to the successive protonation of the binding sites. Accessible reduction potential to physiological reductants, fast iron(III) uptake kinetics and efficient assistance of the protons to the iron(III) release mechanism are favorable features for iron biological transport by pyoverdin PaA. © 1994 American Chemical Society.

Iron reductase systems on the plant plasma membrane-A review

Abstract: Higher plant roots, leaf mesophyll tissue, protoplasts as well as green algae are able to reduce extra-cellular ferricyanide and ferric chelates. In roots of dicotyledonous and nongraminaceous, monocotyledonous plants, the rate of ferric reduction is increased by iron deficiency. This reduction is an obligatory prerequisite for iron uptake and is mediated by redox systems localized on the plasma membrane. Plasma membrane-bound iron reductase systems catalyze the transmembrane electron transport from cytosolic reduced pyridine nucleotides to extracellular iron compounds. Natural and synthetic ferric complexes can act as electron acceptors. This paper gives an overview about the present knowledge on iron reductase systems at the plant plasma membrane with special emphasis on biochemical characteristics and localisation.

Most free-radical injury is iron-related: It is promoted by iron, hemin, holoferritin and vitamin c, and inhibited by desferoxamine and apoferritin

Abstract: Iron is a double-edged sword. In moderate quantities and leashed to protein, it is an essential element in all cell metabolism and growth, but it is toxic when unleashed. Because of its ability to switch back and forth between ferrous and ferric oxidation states, iron is both a strong biological oxidant and reductant. The human diet contains a multitude of natural chemicals which are carcinogens and anticarcinogens, many of which act by generating oxygen radicals, which initiate degenerative processes related to cancer, heart disease and aging (the "oxygen radical hypothesis of aging"). Among these many dietary chemicals are many redox agents, including vitamin C and beta carotene. Free radical damage is produced primarily by the hydroxyl radical (.OH). Most of the .OH generated in vivo comes from iron-dependent reduction of H2O2. Supporting too much iron as a free radical-generating culprit in the risk of cancer, NHANES I data indicated that high body iron stores, manifested by increased transferrin saturation, are associated with an increased cancer risk. Other data shows an increased heart attack risk.

Heme coordination of NO in NO synthase

Abstract: A current question in nitric oxide (NO) biology is whether NO can act as a feedback inhibitor of NO synthase (NOS). We have approached this problem by examining the interaction of NO with neuronal NOS by optical absorption and resonance Raman scattering spectroscopies. Under an inert atmosphere NO coordinated to the heme iron in both the oxidized and reduced forms of NOS. The Soret and visible optical absorption transitions are detected at 436 and at 567 nm, respectively, in the Fe(2+)-NO heme complex and at 440 nm and at 549 and 580 nm, respectively, in the Fe(3+)-NO heme complex. In the resonance Raman spectrum of the ferrous complex the Fe-NO stretching mode is located at 549 cm-1 in the presence of L-arginine and at 536 cm-1 in the absence of L-arginine, whereas in the ferric enzyme the mode is located at 540 cm-1 (in the absence of L-arginine). The interaction between bound L-arginine and the NO indicates that L-arginine binds directly over the heme just as do the substrates in cytochrome P-450s. In the absence of L-arginine, NO readily oxidized the ferrous heme iron. The oxidation was prevented by the presence of bound L-arginine and enabled NOS to form a stable ferrous NO complex. Under oxygen-limited conditions, NO generated by neuronal NOS coordinated to its heme iron and formed a spectrally detectable ferrous-NO complex. Taken together, our results show that NO can bind to both ferric and ferrous NOS and may inhibit NO synthesis through its binding to the heme iron during catalysis.

Mineral Mössbauer spectroscopy: Correlations between chemical shift and quadrupole splitting parameters

Abstract: The variety of coordination numbers, symmetries, distortions and ligand environments in thermally-stable iron-bearing minerals provide wide ranges of chemical shift (δ) and quadrupole splitting (δ) parameters, which serve to characterize the crystal chemistries and site occupancies of Fe2+ and Fe3+ ions in minerals of terrestrial and extraterrestrial origins. Correlations between ferrous and ferric chemical shifts enable thermally-induced electron delocalization behavior in mixed-valence Fe2+-Fe3+ minerals to be identified, while chemical shift versus quadrupole splitting correlations serve to identify nanophase ferric oxides and oxyhydroxides in oxidized minerals and in meteorites subjected to aqueous oxidation before and after they arrived on Earth.

Ferric reductases or flavin reductases

Abstract: Assimilation of iron by microorganisms requires the presence of ferric reductases which participate in the mobilization of iron from ferrisiderophores. The common structural and catalytic properties of these enzymes are described and shown to be identical to those of flavin reductases. This strongly suggests that, in general, the reduction of iron depends on reduced flavins provided by flavin reductases.

[35] Synthesis and determination of thiosulfate and polythionates

Abstract: Publisher Summary This chapter discusses synthesis and determination of thiosulfate and polythionates. Thiosulfate and polythionates react with cyanide to form thiocyanate, which can be determined colorimetrically as ferric thiocyanate. Differences in the reactivity of the thionates with cyanide enable the quantitative characterization and determination of mixtures of several compounds: trithionate is stable at high pH values and reacts with cyanide only at elevated temperatures, thiosulfate reacts with cyanide at room temperature only in the presence of copper(II) as a catalyst, whereas the higher polythionates react rapidly with cyanide at room temperature to form thiosulfate and sulfite. Thiocyanate formation can be quantified by reference to a calibration curve using thiocyanate or thiosulfate standards. In all the procedures in which ferric thiocyanate is measured, caution needs to be exercised, as the color is light sensitive and readings should be made at once or samples stored in darkness after addition of ferric reagent. The sensitivity of the procedure can be enhanced by using small volumes of more concentrated reagents and reading optical density in long light path (4 cm) cuvettes.

The mammalian transferrin-independent iron transport system may involve a surface ferrireductase activity.

Abstract: Mammalian cells accumulate iron from ferric citrate or ferric nitrilotriacetate through the activity of a transferrin-independent iron transport system [Sturrock, Alexander, Lamb, Craven and Kaplan (1990) J. Biol. Chem. 265, 3139-3145]. The uptake system might recognize and transport ferric-anion complexes, or cells may reduce ferric iron at the surface and then transport ferrous iron. To distinguish between these possibilities we exposed cells to either [59Fe]ferric citrate or ferric [14C]citrate and determined whether accumulation of iron was accompanied by the obligatory accumulation of citrate. In HeLa cells and human skin fibroblasts the rate of accumulation of iron was three to five times greater than that of citrate. Incubation of fibroblasts with ferric citrate or ferric ammonium citrate resulted in an enhanced accumulation of iron and citrate; the molar ratio of accumulation approaching unity. A similar rate of citrate accumulation, however, was observed when ferric citrate-incubated cells were exposed to [14C]citrate alone. Further studies demonstrated the independence of iron and citrate accumulation: addition of unlabelled citrate to cells decreased the uptake of labelled citrate without affecting the accumulation of 59Fe; iron uptake was decreased by the addition of ferrous chelators whereas the uptake of citrate was unaffected; reduction of ferric iron by ascorbate increased the uptake of iron but had no effect on the uptake of citrate. When HeLa cells were depleted of calcium, iron uptake decreased, but there was little effect on citrate uptake. These results indicate that transport of iron does not require the obligatory transport of citrate and vice versa. The mammalian transferrin-independent iron transport system appears functionally similar to iron transport systems in both the bacterial and plant kingdoms which require the activities of both a surface reductase and a ferrous metal transporter.

Solubilization of Minerals by Bacteria: Electrophoretic Mobility of Thiobacillus ferrooxidans in the Presence of Iron, Pyrite, and Sulfur

Abstract: Thiobacillus ferroxidans is an obligate acidophile that respires aerobically on pyrite, elemental sulfur, or soluble ferrous ions. The electrophoretic mobility of the bacterium was determined by laser Doppler velocimetry under physiological conditions. When grown on pyrite or ferrous ions, washed cells were negatively charged at pH 2.0. The density of the negative charge depended on whether the conjugate base was sulfate, perchlorate, chloride, or nitrate. The addition of ferric ions shifted the net charge on the surface asymptotically to a positive value. When grown on elemental sulfur, washed cells were close to their isoelectric point at pH 2.0. Both pyrite and colloidal sulfur were negatively charged under the same conditions. The electrical double layer around the bacterial cells under physiological conditions exerted minimal electrostatic repulsion in possible interactions between the cell and either of its charged insoluble substrates. When Thiobacillus ferrooxidans was mixed with either pyrite or colloidal sulfur at pH 2.0, the mobility spectra of the free components disappeared with time to be replaced with a new colloidal particle whose electrophoretic properties were intermediate between those of the starting components. This new particle had the charge and size properties anticipated for a complex between the bacterium and its insoluble substrates. The utility of such measurements for the study of the interactions of chemolithotrophic bacteria with their insoluble substrates is discussed. Images

The Action of Nine Chelators on Iron-Dependent Radical Damage

Abstract: Nine iron chelators were tested in five systems for their effects on radical-generation and conversion at chelator: iron molar ratios from 0.1 to 10. Stimulatory actions might distinguish toxic from safer chelators. Radical-generating reactions which represent different aspects of iron (ferrous and ferric) availability were studied: a) the reaction with hydrogen peroxide to hydroxylate benzoate; b) the oxidation of ascorbate; c) the reaction with hydrogen peroxide to fragment proteins; d) the reaction with hydrogen peroxide to permit amplified chemiluminescence; and e) the induction of peroxidation of mitochondrial membrane lipids. The compounds used were HBED, CP130, Desferal, EDTA, pyridine-hydrazone (CGP 43′902B), Ferrozine, CP 94 (CGP 46′700), LI (CGP 37 391) and rhodotorulic acid (CGP 45 274). Only the hexadentate compounds HBED, CP130 and Desferal were uniformly inhibitory (“protective”). The protective compounds were also apparently more stable during radical fluxes than the other chelators.

Heme-Heme Oxygenase Complex: Structure and Properties of the Catalytic Site from Resonance Raman Scattering

Abstract: The resonance Raman spectra of ferric and ferrous forms of the heme-heme oxygenase (HO) complex (isoform 1) clarify several structural features of the catalytic active site. Isotopic substitution studies of the central iron atom of the heme demonstrate that the line at 218 cm-1 in the ferrous ligand-free form of the complex originates from the iron-histidine stretching mode. The presence of a Raman line at this frequency confirms that the fifth ligand coordinating to the heme is a neutral imidazole from a histidine residue. The modes associated with CO in the carboxy derivative of the ferrous enzyme complex have typical frequencies of histidine-bound heme proteins such as myoglobin. In the ferric form of the complex, at alkaline pH, hydroxide is identified as the bound exogenous ligand, and at neutral pH we infer that water is bound. Thus, the coordination of the heme-HO complex is the same as that in myoglobin. However, in a comparison of the low-frequency vibrational modes in the resonance Raman spectrum of the heme-HO complex to those of myoglobin, the spectra are found to be very different, indicating that the interactions between the heme and its amino acid pocket in these two proteins are quite different. The neutral imidazole may play several important roles in the physiological function of the heme-HO complex.

Oxidative Dissolution of Arsenopyrite by Mesophilic and Moderately Thermophilic Acidophiles

Abstract: The purpose of this work was to determine solution- and solid-phase changes associated with the oxidative leaching of arsenopyrite (FeAsS) by Thiobacillus ferrooxidans and a moderately thermoacidophilic mixed culture. Jarosite [KFe3(SO4)2(OH)6], elemental sulfur (S0), and amorphous ferric arsenate were detected by X-ray diffraction as solid-phase products. The oxidation was not a strongly acid-producing reaction and was accompanied by a relatively low redox level. The X-ray diffraction lines of jarosite increased considerably when ferrous sulfate was used as an additional substrate for T. ferroxidans. A moderately thermoacidophilic mixed culture oxidized arsenopyrite faster at 45°C than did T. ferroxidans at 22°C, and the oxidation was accompanied by a nearly stoichiometric release of Fe and As. The redox potential was initially low but subsequently increased during arsenopyrite oxidation by the thermoacidophiles. Jarosite, S0, and amorphous ferric arsenate were also formed under these conditions.

Oxidation-Reduction Properties of Compounds I and II of Arthromyces ramosus Peroxidase

Abstract: At neutral pH, compound I of Arthromyces ramosus peroxidase (ARP) was stable and was reduced to ferric ARP without apparent formation of compound II upon titration with ascorbate or hydroquinone. In the titration experiments, compound II was seen as an intermediate only at alkaline pH. However, measuring a difference spectrum in the Soret region by a stopped-flow method, we found that compound II was formed during the catalytic oxidation of ascorbate even at neutral pH. Using an EPR spectrometer with a microflow system, we measured the steady-state concentration of benzosemiquinone formed in the ARP-catalyzed oxidation of hydroquinone. The results clearly showed that ARP catalyzes the oxidation of hydroquinone by a one-electron-transfer mechanism, as does horseradish peroxidase. These observations led to the conclusion that compound I is reduced to compound II through a one-electron reduction by ascorbate or hydroquinone. Therefore, we concluded that ARP compound II is unusually unstable and is rapidly reduced to ferric enzyme without accumulation in the titration experiment. The unusual instability of ARP compound II is explained in terms of the high reduction potential of compound II. The reduction potentials (E0') of compounds I and II were measured at several pH values from redox equilibria with potassium hexachloroiridate on the basis of E0' = 0.90 V for the IrCL6(2)-IrCl6(3)- couple. These values were determined to be 0.915 and 0.982 V at pH 7, respectively, and decreased with increasing pH. This pH dependence was markedly changed by the buffer concentration.(ABSTRACT TRUNCATED AT 250 WORDS)