Showing papers on "Ferric published in 1986"
TL;DR: Results indicate that iron reduction can outcompete methanogenic food chains for sediment organic matter when amorphous ferric oxyhydroxides are available in anaerobic sediments, and the transfer of electrons from organic matter to ferric iron can be a major pathway for organic matter decomposition.
Abstract: The potential for ferric iron reduction with fermentable substrates, fermentation products, and complex organic matter as electron donors was investigated with sediments from freshwater and brackish water sites in the Potomac River Estuary. In enrichments with glucose and hematite, iron reduction was a minor pathway for electron flow, and fermentation products accumulated. The substitution of amorphous ferric oxyhydroxide for hematite in glucose enrichments increased iron reduction 50-fold because the fermentation products could also be metabolized with concomitant iron reduction. Acetate, hydrogen, propionate, butyrate, ethanol, methanol, and trimethylamine stimulated the reduction of amorphous ferric oxyhydroxide in enrichments inoculated with sediments but not in uninoculated or heat-killed controls. The addition of ferric iron inhibited methane production in sediments. The degree of inhibition of methane production by various forms of ferric iron was related to the effectiveness of these ferric compounds as electron acceptors for the metabolism of acetate. The addition of acetate or hydrogen relieved the inhibition of methane production by ferric iron. The decrease of electron equivalents proceeding to methane in sediments supplemented with amorphous ferric oxyhydroxides was compensated for by a corresponding increase of electron equivalents in ferrous iron. These results indicate that iron reduction can outcompete methanogenic food chains for sediment organic matter. Thus, when amorphous ferric oxyhydroxides are available in anaerobic sediments, the transfer of electrons from organic matter to ferric iron can be a major pathway for organic matter decomposition.
1,360 citations
TL;DR: The data suggest that the absolute ratio of Fe3+ to Fe2+ was the primary determining factor for the initiation of lipid peroxidation reactions.
593 citations
TL;DR: The difference in binding before and after phosphorylation of a single amino acid residue is demonstrated and affinity elution can be accomplished by inclusion in the buffer of phosphoserine or a displacing metal ion such as Mg2+.
Abstract: Ferric ions are very strongly adsorbed to iminodiacetic acid substituted agarose. This firmly immobilized complex acts as a selective immobilized metal affinity adsorbent for phosphoproteins. Chromatography based on this principle is illustrated by the adsorption-desorption behavior of egg yolk phosvitin before and after dephosphorylation as well as by the change in the chromatographic pattern before and after enzymic phosphorylation of selected histones. The strength of binding is dependent on the phosphate content. The difference is binding before and after phosphorylation of a single amino acid residue is demonstrated. Affinity elution can be accomplished by inclusion in the buffer of (1) phosphoserine or (2) a displacing metal ion such as Mg/sup 2 +/.
158 citations
154 citations
TL;DR: The first spectroscopic evidence for complexes containing iron formally in the IV and V oxidation states in the presence of a simple ligand, i.e., OH/sup -/ and P/sub 2/O/sub 7//sup 4 -/ in alkaline solution is reported.
Abstract: The first spectroscopic evidence for complexes containing iron formally in the IV and V oxidation states in the presence of a simple ligand, i.e., OH/sup -/ and P/sub 2/O/sub 7//sup 4 -/ in alkaline solution is reported. These transient species are obtained by pulse radiolysis of alkaline ferric (Fe(III)) and ferrate (Fe(VI)) solutions by using the hydroxyl radical or its conjugate base, O/sup -/, and the aquated electron, e/sub aq//sup -/, as the respective oxidizing and reducing agents. 18 references, 1 figure.
136 citations
01 Jan 1986
TL;DR: It is proposed that iron deficiency induces production of organic acids in the roots, which in beans leads to both proton excretion and an increased capacity to reduce ferric chelates via the induced electron transfer system in the root epidermis cells.
Abstract: Iron deficiency in higher plants causes accumulation of salts of organic acids in the roots, the most characteristic being citrate. We show that citrate and malate accumulate in beans (Phaseolus vulgaris L. var Prelude), not because of a lack of the iron-containing enzyme aconitase (EC 4.2.1.3), but in close coupling to the extrusion of protons during rhizosphere acidification, one of the 'Fe-efficiency' reactions of dicotyledonous plants. When proton excretion is induced in roots of control bean plants by addition of fusicoccin, only malate, not citrate, is accumulated. We propose that iron deficiency induces production of organic acids in the roots, which in beans leads to both proton excretion and an increased capacity to reduce ferric chelates via the induced electron transfer system in the root epidermis cells. Plants growing under iron deficiency may employ different strategies to increase iron uptake: (a) dicotyledons and non-grass monocotyledons develop a strong ferric reduction activity at the root surface (2); moreover, they may acidify the rhizosphere by
120 citations
TL;DR: Resonance Raman spectra of ferrous and ferric cytochrome c peroxidase and Compound ES and their pH dependences were investigated in resonance with Soret band and it was inferred that a water molecule suggested to occupy the sixth coordination position of the heme iron is not coordinated to theHeme iron at pH 6 but that protonation of the pKa = 5.5 residue induces an appreciable structural change, allowing the coordination of the water molecule to the
118 citations
TL;DR: In this article, it was shown that iron deficiency induces production of organic acids in the roots, which in beans leads to both proton excretion and an increased capacity to reduce ferric chelates via the induced electron transfer system in root epidermis cells.
Abstract: Iron deficiency in higher plants causes accumulation of salts of organic acids in the roots, the most characteristic being citrate. We show that citrate and malate accumulate in beans ( Phaseolus vulgaris L. var Prelude), not because of a lack of the iron-containing enzyme aconitase (EC 4.2.1.3), but in close coupling to the extrusion of protons during rhizosphere acidification, one of the `Fe-efficiency9 reactions of dicotyledonous plants. When proton excretion is induced in roots of control bean plants by addition of fusicoccin, only malate, not citrate, is accumulated. We propose that iron deficiency induces production of organic acids in the roots, which in beans leads to both proton excretion and an increased capacity to reduce ferric chelates via the induced electron transfer system in the root epidermis cells.
116 citations
TL;DR: Results show that Ca2+ functions in maintaining the protein structure in the heme environments as well as the spin state of theheme iron, in favor of the enzymatic activity of HRP.
113 citations
TL;DR: In this article, the optimum operating conditions for diffusion dialysis were studied for the recovery of nitric acid and hydrofluoric acid from mixed solutions containing these acids and ferric ions.
104 citations
TL;DR: Chloroperoxidase, in spite of the previously established close spectroscopic and heme iron coordination structure similarities to the P-450 enzymes, clearly belongs to the hydroperoxidases in terms of its ligand binding properties and active site heme environment.
Abstract: Equilibrium binding studies of exogenous ligands and halides to the active site heme iron of chloroperoxidase have been carried out from pH 2 to 7. Over twenty ligands have been studied including C, N, O, P, and S donors and the four halides. As judged from changes in the optical absorption spectra, direct binding of the ligands to the heme iron of ferric or ferrous chloroperoxidase occurs in all cases; this has been ascertained for the ferric enzyme in several cases through competition experiments with cyanide. All of the ligands except for the halides, nitrate, and acetate form exclusively low-spin complexes in analogy to results obtained with the spectroscopically related protein, cytochrome P-450-CAM [Sono, M., & Dawson, J.H. (1982) J. Biol. Chem. 257, 5496-5502]. The titration results show that, for the ferric enzyme, (i) weakly acidic ligands (pKa greater than 3) bind to the enzyme in their neutral (protonated) form, followed by deprotonation upon ligation to the heme iron. In contrast, (ii) strongly acidic ligands (pKa less than 0) including SCN-, NO3-, and the halides except for F- likely bind in their anionic (deprotonated) form to the acid form of the enzyme: a single ionizable group on the protein with a pKa less than 2 is involved in this binding. For the ferrous enzyme, (iii) a single ionizable group with the pKa value of 5.5 affects ligand binding. These results reveal that chloroperoxidase, in spite of the previously established close spectroscopic and heme iron coordination structure similarities to the P-450 enzymes, clearly belongs to the hydroperoxidases in terms of its ligand binding properties and active site heme environment. Magnetic circular dichroism studies indicate that the alkaline form (pH 9.5) of ferric chloroperoxidase has an RS-ferric heme-N donor ligand coordination structure with the N donor likely derived from histidine imidazole.
TL;DR: The results suggest a mechanism of active transport of unmodified coordination complex across the outer membrane with possible accumulation in the periplasm.
Abstract: The specificity of the outer membrane protein receptor for ferric enterobactin transport in Escherichia coli and the mechanism of enterobactin-mediated transport of ferric ions across the outer membrane have been studied. Transport kinetic and inhibition studies with ferric enterobactin and synthetic structural analogs have mapped the parts of the molecule important for receptor binding. The ferric complex of the synthetic structural analog of enterobactin, 1,3,5-N,N',N''-tris-(2,3-dihydroxybenzoyl)triaminomethylbenzene (MECAM), was transported with the same maximum velocity as was ferric enterobactin. A double-label transport assay with [59Fe, 3H]MECAM showed that the ligand and the metal are transported across the outer membrane at an identical rate. Under the growth conditions used, large fractions of the transported complexes were available for exchange across the outer membrane when a large excess of extracellular complex was added to the cell suspension; at least 60% of the internalized [59Fe]enterobactin exchanged with extracellular [55Fe]enterobactin. Internalized [59Fe, 3H]MECAM was released from the cell as the intact complex when either unlabeled Fe-MECAM or Fe-enterobactin was added extracellularly. The results suggest a mechanism of active transport of unmodified coordination complex across the outer membrane with possible accumulation in the periplasm.
TL;DR: In this paper, an electrochemical charge transfer model for the leaching of a sphaleritic flotation concentrate in an acidic ferric sulphate solution is described, in which the mineral surface potential is approximated by the solution redox potential for the ferrous-ferric redox couple.
TL;DR: Titration of both forms of mono(ferric)transferrin indicates that unlike other metal ions, Ni2+ binds preferentially to the N-terminal binding site, but that the site preference is rather small.
TL;DR: A marked increase in 1/T2 is observed at higher iron loadings that the authors are unable to account for within the framework of the theory of outer sphere relaxation, even when the effects arising from inhomogeneities in the local magnetic field are included.
Abstract: The magnetic field dependence of 1/T1 over the range 0.01 to 50 MHz proton Larmor frequency (NMRD profile) is reported for water protons in solutions of horse spleen apoferritin, and of ferritin reconstituted at both low and high iron levels. The apoferritin results are in every way typical of diamagnetic spherical proteins of their size (K. Hallenga and S. H. Koenig, Biochemistry 15, 4255 (1976)). Titration of up to 24 ferrous ions per protein molecule, with subsequent oxidation to ferric, shows a nonlinear saturating contribution to the NMRD profile which is interpreted as arising from a small number of ferric ions (six to eight) bound close to the outside of each ferritin molecule, and a comparable number of interior sites. The latter become multiply occupied as the core grows and do not contribute measurably to 1/T1 in this state. The former sites are never more than singly occupied, and their contribution to the solvent proton relaxation rates is independent of the loading of the core. Measurements of 1/T2 at 20 MHz are quite in accord with theoretical expectations for apoferritin and ferritin with up to 24 ferric ions per molecule. However, a marked increase in 1/T2 is observed at higher iron loadings that we are unable to account for within the framework of the theory of outer sphere relaxation, even when the effects arising from inhomogeneities in the local magnetic field are included. A sample of human spleen hemosiderin was found to have the same 1/T1 NMRD profile as a comparable sample of ferritin.
TL;DR: In this paper, two lithium ions per formula unit can be inserted into the structure; the inserted lithium ions displace the tetrahedral ferric ions of the spinel into neighbouring vacant octahedral sites to yield a rocksalt phase Li3Fe5O8.
TL;DR: The preparation and characterization of synthetic ferritin-like particles produced by precipitation of magnetite from a mixture of ferrous and ferric ions in the presence of dextran are described and a 400-fold enrichment for Legionella was obtained.
TL;DR: In this article, the compositional dependence of the redox ratio (FeO/FeO1.5) has been experimentally determined in K2O-Al2O3-SiO2-Fe2O 3-FeO (KASFF) silicate melts.
Abstract: The compositional dependence of the redox ratio (FeO/FeO1.5) has been experimentally determined in K2O-Al2O3-SiO2-Fe2O3-FeO (KASFF) and K2O-CaO-Al2O3-SiO2-Fe2O3-FeO (KCASFF) silicate melts. Compositions were equilibrated at 1,450° C in air, with 78 mol % SiO2. KASFF melts have from 1 to 5 mol % Fe2O3 and include both peraluminous (K2O Al2O3) compositions. KCASFF melts have 1 mol % Fe2O3 encompassing peraluminous, metaluminous (CaO+K2O>Al2O3) and peralkaline compositions. Peralkaline KASFF melts with 1 mol % Fe2O3 have low and constant values for the redox ratio, whereas in peraluminous melts the redox ratio increases with increasing (K2O/Al2O3). Increasing total iron concentration increases the redox ratio in peraluminous melts and slightly decreases the redox ratio in peralkaline melts. Substituting CaO for K2O at fixed total iron (1 mol %) increases the redox ratio in both peraluminous and metaluminous KCASFF melts; however, the redox ratio in peralkaline KCASFF melts is not affected by this exchange. These data indicate that Fe3+ is in four-fold coordination, with K+ or Ca2+ providing local charge balance. The tetrahedral ferric species is most stable in peralkaline melts and least stable in peraluminous melts, due to the competition between Al3+ and Fe3+ for charge balancing cations in the latter melt. Tetrahedral Fe3+ is also less stable when Ca2+ provides local charge balance. The data are consistent with a network modifying role for Fe2+ in the melt.
TL;DR: In this paper, the synthesis of ferric smectites was performed at low temperature (75° C) by aging coprecipitated gels of silica and Fe2+-sulphate under initially reducing then oxidizing conditions.
Abstract: Syntheses of ferric smectites were performed at low temperature (75° C by aging coprecipitated gels of silica and Fe2+-sulphate under initially reducing then oxidizing conditions. Under strictly reducing conditions only nuclei of a trioctahedral ferrous stevensite were observed and crystal growth did not take place. When a spontaneous oxidization, in contact with air, was effected, the ferrous smectite nuclei transformed rapidly into a ferric, nontronite-like, smectite. Crystallogenesis of the ferric smectite was studied by XRD, IR, DTA, Mossbauer and EPR spectroscopies. The end-synthesis smectite contained only Fe3+ ions, all located in the octahedral sheet. This clay was mixed with a cryptocrystalline iron oxide phase containing one-third of the iron atoms and undetectable by XRD.
TL;DR: It is demonstrated here that Ga(III) can effectively displace iron under reducing conditions and the physiological significance of this reaction to the clinical use of gallium is discussed.
Abstract: Siderophores are iron transport compounds produced by numerous microorganisms and which strongly chelate Fe(III), but not Fe(II). Other trivalent metals, such as Al(III), Cr(III), or Ga(III), are not capable of significantly displacing iron from siderophores. However, I demonstrate here that Ga(III) can effectively displace iron under reducing conditions. With ascorbate as reductant and ferrozine as Fe(II) trapping agent, the kinetics of reductive displacement of iron by Ga(III) were followed spectroscopically by the increase of absorbance at 562 nm due to formation of the Fe(II)-ferrozine complex. No significant reduction of siderophore occurred in the absence of Ga(III). With excess Ga(III), the displacement was quantitative and very rapid. The rate of metal exchange was pseudo first order with respect to Ga(III) concentration and highly pH dependent, suggesting that siderophore ligands are displaced from the iron in a concerted mechanism by Ga(III) and protonation to expose the Fe(III) to reduction by ascorbate. Reaction rates were dependent upon the structure of the siderophore, being greatest for ferric rhodotorulic acid and slowest for ferrichrome A at pH 5.4. The pH profile for ferric rhodotorulic acid was unusual in that it showed a maximum at pH 6.5, while all other siderophores examined showed an increase in rate as pH was lowered from 7.0. The physiological significance of this reaction to the clinical use of gallium is discussed.
TL;DR: In this paper, the authors investigated charge, solubility, and molecular-size characteristics of dissolved organic carbon in raw and treated water from a Virginia reservoir to determine the types of organic compounds removed by ferric sulfate, coagulation, and settling.
Abstract: Charge, solubility, and molecular-size characteristics of dissolved organic carbon in raw and treated water from a Virginia reservoir were investigated to determine the types of organic compounds removed by ferric sulfate, coagulation, and settling. All three parameters influenced removal of dissolved organic carbon. Larger molecules were more readily precipitated than smaller ones. Ionic compounds were more effectively removed than neutral compounds. Hydrophilic and hydrophobic organics were preferentially removed over compounds of intermediate solubility. Two main groups of organic halide precursors were identified. Fulvic acids were the dominant precursors in raw water- they reacted rapidly with chlorine and had high specific yields, but were readily precipitated. Low-molecular-weight neutral compounds were the dominant precursor group remaining in treated waters. These molecules reacted more slowly with chlorine and had lower organohalide yields.
TL;DR: The bond strengths of two cements to enamel and dentine were increased by as much as 183 per cent by the use of surface treatments of polyacrylic acid and ferric oxalate.
Abstract: Adhesive bond strengths of glass ionomer and polycarboxylate cements to human enamel and dentine were measured in vitro on untreated surfaces and on surfaces treated with cement liquid or polyacrylic acid, ferric oxalate, and ferric chloride. The bond strengths of two cements to enamel and dentine were increased by as much as 183 per cent by the use of surface treatments of polyacrylic acid and ferric oxalate.
TL;DR: It is likely that either singlet oxygen or superoxide and hydroxyl radicals are involved in the attack on heme iron, because inactivation correlates with oxygen production and can be decreased to a certain degree by scavengers such as ethanol, 1-propanol, 2-pro panol, or mannitol.
TL;DR: Rhizobium leguminosarum GF160 required iron for growth under aerobic conditions in a chemically defined medium and released a Fe3+-reducing agent that was identified as anthranilic acid that reached concentrations up to 1 mM.
TL;DR: Urate produced during the reaction of xanthine oxidase and hypoxanthine limits deoxyribose degradation as well as the effectiveness of the superoxide dismutase enzymes to inhibit damage to deoxy ribose by H2O2 and the Fe3+-EDTA chelate.
Abstract: When OH. radicals are formed in a superoxide-driven Fenton reaction, in which O2.- is generated enzymically, deoxyribose degradation is effectively inhibited by CuZn- and Mn-superoxide dismutases. The products of this reaction are H2O2 and a Fe3+-EDTA chelate. The mixing of H2O2 and a Fe3+-EDTA chelate also generates OH. radicals able to degrade deoxyribose with the release of thiobarbituric acid-reactive material. This reaction too is inhibited by CuZn- and Mn-superoxide dismutases, suggesting that most of the OH. is formed by a non-enzymic O2.--dependent reduction of the Fe3+-EDTA chelate. Since the reaction between the Fe3+-EDTA chelate and H2O2 leads to a superoxide dismutase-inhibitable formation of OH. radicals, it could suggest a much wider protective role for the superoxide dismutase enzymes in biological systems. Urate produced during the reaction of xanthine oxidase and hypoxanthine limits deoxyribose degradation as well as the effectiveness of the superoxide dismutase enzymes to inhibit damage to deoxyribose by H2O2 and the Fe3+-EDTA chelate. Some of this damage may result from an O2.--independent pathway to OH. formation in which urate reduces the ferric complex.
TL;DR: Ferric chloride, when boiled with hydrazine hydrate and cacodylic acid, is converted into a fine cationic iron colloid which consists of 0.5-1.5 nm electron-dense granules, and gives a distinct Prussian blue reaction.
Abstract: Ferric chloride, when boiled with hydrazine hydrate and cacodylic acid, is converted into a fine cationic iron (ferric hydroxide) colloid which consists of 0.5-1.5 nm electron-dense granules, and gives a distinct Prussian blue reaction. This colloid allows light and electron microscopic detection of ionized anionic sites in tissues at a wide pH range of 0.8-7.6. It is smaller in size and more stable, and assures longer and greater staining of tissues, especially at low pH levels, than the iron colloid prepared with sodium or ammonium cacodylate by Seno and his associates (1983, 1984, 1985). Some light and electron micrographs of the rat kidney, spleen and other organs stained with our colloid are presented as examples. These micrographs confirm that the glomerular podocyte end-foot surface facing the Bowman's capsular space is strongly negative-charged. They also show that almost all lymphoid cells around the arteries in the splenic white pulp and thymic cortex contain strongly negative-charged nuclei and that the distal convoluted and collecting urinary tubules are more negative-charged than the proximal convoluted tubules.
TL;DR: EPR studies of this enzyme indicate the presence of a high-spin ferric center in a rhombic environment, as evidenced by a signal at g = 4.3 with the correct intensity for the measured iron content.
TL;DR: Resonance Raman (RR) spectra obtained at three excitation wavelengths are reported for various ferric, ferrous, and ferryl derivatives of bovine lactoperoxidase, indicating a nonheme binding site for the thiol substrates.