Showing papers on "Ferric published in 1992"
TL;DR: This review will attempt to reassess the function of lactoferrin in the light of the large amount of new information that has accrued since then.
Abstract: Lactoferrin is an iron-binding protein closely related in structure to the serum iron transport protein transferrin. Unlike transferrin, only traces are normally present in serum, and it is instead found mainly in milk and other external secretions, and in the secondary granules of neutrophils. Although lactoferrin was first isolated 30 years ago, its biological role remains unclear. Some aspects of its function were discussed about 12 years ago in this journal,' and this review will attempt to reassess the function of lactoferrin in the light of the large amount of new information that has accrued since then. Knowledge of the structure of lactoferrin has been advanced by recent x ray crystallographic studies, and the structure and iron binding properties of lactoferrin are reviewed in detail elsewhere.2 Briefly lactoferrin, like transferrin, reversibly binds two ferric ions, for which synergistic binding of an anion, usually bicarbonate or carbonate, is necessary. However, its affinity constant for iron is 300 times greater than that of transferrin, and even in the presence of a competing iron chelator such as citrate it can retain iron down to pH 3 or less while transferrin loses it at pH 5. Unlike transferrin, lactoferrin is strongly basic. Human lactoferrin has been cloned and sequenced4 and the recombinant protein expressed in baby hamster kidney cells.5 bearing in mind when considering its possible biological function. Human milk contains 3-6-12-5 ,umol/l of iron, and of this only 60-70% is in the whey fraction, the remainder being in the lipid fraction (11-20%) or bound to casein (2-14%). " As a consequence, milk lactoferrin is only 6-8% saturated with iron, presumably because of the difficulty in gaining access to iron in the lipid fraction or casein micelles.
466 citations
TL;DR: In this article, pseudocubic particles of hematite (mean edge length 1.65 μm) with an exceedingly narrow size distribution (coefficient of variation 6.0%) have been prepared from highly condensed ferric hydroxide gel of approximately 1 mol dm−3 with a nominal excess concentration of ferric ions of 0.10 mol −3 through aging at 100°C for 8 days.
177 citations
TL;DR: In this article, the presence of graphite capsules is shown to limit the maximum fO 2 possible, but places no limit on the minimum FO 2, where the graphite is not inert in such experiments and reacts with Fe 2 O 3 in the melt to form dissolved CO 2 and FeO.
Abstract: Graphite capsules are commonly used to prevent loss of iron from iron-bearing samples in high-pressure melting experiments. The graphite is not inert in such experiments and reacts with Fe 2 O 3 in the melt to form dissolved CO 2 and FeO. This equilibrium can be quantified if the activity-composition relations of CO 2 in the melt are known. The presence of graphite is shown to limit the maximum fO 2 possible, but places no limit on the minimum fO 2 . The fO 2 in the system, the ferric/ferrous ratio in the melt, and the concentration of dissolved CO 2 are proportional to the concentration of ferric iron in the starting material. The dissolved CO 2 content cannot be controlled independently of fO 2 , but for values of fO 2 appropriate to mantle melting, the amount of dissolved CO 2 can be controlled over values ranging from about 0.1 wt% to saturation
168 citations
TL;DR: The Escherichia coli ferric enterobactin esterase gene (fes) was cloned into the vector pGEM3Z under the control of the T7 gene 10 promoter and overexpressed to approximately 15% of the total cellular protein, exhibiting a 4-fold greater activity on the free ligand.
147 citations
TL;DR: This study shows that apoR2 has a very strong affinity for four stable Mn2+ ions, which explains why the spin-exchange interaction between the two ions is very weak and why Mn-R2 is EPR active.
126 citations
TL;DR: The data conclusively demonstrate that two entirely different mechanisms of iron uptake from Tf exist in melanoma cells and that ferric ammonium citrate may be a useful experimental tool to further characterize the specific and nonspecific mechanisms of Fe uptake fromTf.
125 citations
TL;DR: High-resolution resonance Raman spectra of the ferric, ferrous, and carbonmonoxy (CO)-bound forms of wild-type Escherichia coli-expressed Pseudomonas putida cytochrome P450cam and its P420 form are reported.
Abstract: High-resolution resonance Raman spectra of the ferric, ferrous, and carbonmonoxy (CO)-bound forms of wild-type Escherichia coli-expressed Pseudomonas putida cytochrome P450cam and its P420 form are reported. The ferric and ferrous species of P450 and P420 have been studied in both the presence and absence of excess camphor substrate. In ferric, camphor-bound, P450 (mos), the E. coli-expressed P450 is found to be spectroscopically indistinguishable from the native material. Although substrate binding to P450 is known to displace water molecules from the heme pocket, altering the coordination and spin state of the heme iron, the presence of camphor substrate in P420 samples is found to have essentially no effect on the Raman spectra of the heme in either the oxidized or reduced state. A detailed study of the Raman and absorption spectra of P450 and P420 reveals that the P420 heme is in equilibrium between a high-spin, five-coordinate (HS,5C) form and low-spin six-coordinate (LS,6C) form in both the ferric and ferrous oxidation states. In the ferric P420 state, H2O evidently remains as a heme ligand, while alterations of the protein tertiary structure lead to a significant reduction in affinity for Cys(357) thiolate binding to the heme iron. Ferrous P420 also consists of an equilibrium between HS,5C and LS,6C states, with the spectroscopic evidence indicating that H2O and histidine are the most likely axial ligands. The spectral characteristics of the CO complex of P420 are found to be almost identical to those of a low pH of Mb. Moreover, we find that the 10-ns transient Raman spectrum of the photolyzed P420 CO complex possesses a band at 220 cm-1, which is strong evidence in favor of histidine ligation in the CO-bound state. The equilibrium structure of ferrous P420 does not show this band, indicating that Fe-His bond formation is favored when the iron becomes more acidic upon CO binding. Raman spectra of stationary samples of the CO complex of P450 reveal VFe-CO peaks corresponding to both substrate-bound and substrate-free species and demonstrate that substrate dissociation is coupled to CO photolysis. Analysis of the relative band intensities as a function of photolysis indicates that the CO photolysis and rebinding rates are faster than camphor rebinding and that CO binds to the heme faster when camphor is not in the distal pocket.
106 citations
TL;DR: In this article, a new adsorbent media consisting of iron oxide coated onto sand surfaces was used to collect hexavalent chromium from a synthetic waste stream, and better than 99% removal was achieved consistently.
103 citations
TL;DR: In this article, a kinetic model based on the generation of OH. radicals as the rate-determining step is proposed to explain the inverse initial concentration effect of phenol on the apparent rate constant.
Abstract: The kinetics of photocatalytic oxidation of phenol have been studied experimentally. A kinetic model based on the generation of OH . radicals as the rate-determining step is proposed. The results of the theoretical analysis can be used to explain the inverse initial concentration effect of phenol on the apparent rate constant. The model also can explain the experimental findings such as the pseudo-first-order dependence and the effect of the initial pH value on the initial reaction rate. Moreover, the addition of H 2 O 2 with ferric ions enhances the reaction rate significantly. It has also been discovered that the phenol oxidation rate is controlled by the decomposition rate of H 2 O 2 .
97 citations
TL;DR: It was shown that the dose image obtained with an MR scanner deteriorates due to diffusion, and if the MR measurements of a typical depth-dose distribution are carried out within 2 hours of irradiation the diffusion will not have a significant effect on the results.
Abstract: The diffusion of ferric ions produced by irradiation in a dosimeter gel, consisting of a ferrous sulphate solution and agarose gel, has been studied. The diffusion coefficient of ferric ions in the gel was found to be 1.91*10-2 cm2 h-1+or-5%. It was shown that the dose image obtained with an MR scanner deteriorates due to diffusion. This deterioration can be predicted with the aid of the measured diffusion coefficient. It was concluded that if the MR measurements (1/T1 image) of a typical depth-dose distribution are carried out within 2 hours of irradiation the diffusion will not have a significant effect on the results.
97 citations
TL;DR: It was concluded that the white rot fungus might produce hydroxyl radical via a mechanism that includes the secondary metabolites veratryl alcohol and oxalate that may contribute to the ability of this fungus to degrade environmental pollutants.
TL;DR: The Mucorales are the only fungal group where ferritin has been detected so far, suggesting that the substitution of hydroxamate siderophores by complexone siderophile has led to the formation of ferritins as the eucaryotic iron storage proteins.
TL;DR: In this article, an intramolecular water soluble chitosan-Fe(III) complex was prepared by mixing together chitsan powder with a 1·5 m FeCl2 solution at 30°C over 24 h in heterogeneous phase followed by extraction with acetone of the excess ferric chloride.
TL;DR: In this article, the effects of bicarbonate, phosphate and high pH on the ferric reducing capacity of the roots of plants grown with iron deficiency were studied, and the results showed that the negative effect of these factors depended on its co-existence with other factors.
Abstract: Bicarbonate, phosphate and high pH are factors considered to induce or aggravate iron chlorosis. We have studied the effects of these factors on the ferric reducing capacity of the roots of plants grown with iron deficiency. Three kinds of experiments were performed with young sunflower (Helianthus annuus L., line RHA 274) and cucumber (Cucumis sativus L., cv “Burpee pickler"), plants grown in nutrient solution with the following results: i) Once the reducing capacity had been increased by iron deficiency, bicarbonate and high pH inhibited the reduction of ferric ethylenediaminetetraacetate to a similar extent, while phosphate had no effect. ii) When the considered factors were present during the period of growth without iron, the development of reducing capacity was inhibited more by bicarbonate than by a treatment with the same high pH value buffered with N‐[2‐Hydroxyethyl]piperazine‐N ‐[2‐ethanesulfonic acid] (Hepes). A negative effect of bicarbonate on the reducing capacity depended on its co...
TL;DR: The results support the hypothesis that the apoplastic pH shift caused by H+ excretion stimulated Fe[III] reduction and shed light on the way by which the strong buffering effect of HCO3-in some soils may be involved in iron deficiency encountered by some of the plants which grow in them.
Abstract: We have studied the mechanism of the response to iron deficiency in rape (Brassica napus L.), taking into account our previous results: net H(+) extrusion maintains a pH shift between the root apoplast and the solution, and the magnitude of the pH shift decreases as the buffering power in the solution increases. The ferric stress increased the ability of roots to reduce Fe[III]EDTA. Buffering the bulk solution (without change in pH) inhibited Fe[III]EDTA reduction. At constant bulk pH, the inhibition (ratio of the Fe[III]EDTA-reduction rates measured in the presence and in the absence of buffer) increased with the rate of H(+) extrusion (modulated by the length of a pretreatment in 0.2 mM CaSO4). These results support the hypothesis that the apoplastic pH shift caused by H(+) excretion stimulated Fe[III] reduction. The shape of the curves describing the pH-dependency of Fe[III]EDTA reduction in the presence and in the absence of a buffer fitted this hypothesis. When compared to the titration curves of Fe[III]citrate and of Fe[III]EDTA, the curves describing the dependency of the reduction rate of these chelates on pH indicated that the stimulation of Fe[III] reduction by the apoplastic pH shift due to H(+) excretion could result from changes in electrostatic interactions between the chelates and the fixed chargers of the cell wall and-or plasmalemma. Blocking H(+) excretion by vanadate resulted in complete inhibiton of Fe[III] reduction, even in an acidic medium in which there was neither a pH shift nor an inhibitory effect of a buffer. This indicates that the apoplastic pH shift resulting from H(+) pumping is not the only mechanism which is involved in the coupling of Fe[III] reduction to H(+) transport. Our results shed light on the way by which the strong buffering effect of HCO 3 (-) in some soils may be involved in iron deficiency encountered by some of the plants which grow in them.
TL;DR: The Escherichia coli haemoglobin-like flavohaemoprotein (Hmp) has been purified to near homogeneity using two chromatographic steps and characteristics indicate that the b-type haem is attached to the protein through a nitrogenous ligand, probably originating from a histidine residue.
Abstract: The Escherichia coli haemoglobin-like flavohaemoprotein (Hmp) has been purified to near homogeneity using two chromatographic steps. The prosthetic groups are identified as FAD and protohaem IX. SDS/PAGE has indicated a molecular mass of 44 kDa for the monomeric protein consistent with the amino-acid sequence deduced from the hmp+ gene. The protein, as isolated, is in the Fe(III) state, exhibiting absorbance maxima at 403.5, 540 (shoulder) and 627 nm. The ferrous and carbonmonoxyferrous states resemble those of haemoglobin, showing maxima at 431.5 and 558 nm, and 421, 542 and 566 nm respectively. Upon aerobic addition of NAD(P)H, the ferric state is reduced to the oxygenated Fe(II) state, characterized by maxima at 413, 544 and 580 nm. This oxy form is not stable and slowly decays to the ferric state. Addition of dithionite and nitrite to the ferric protein results in the formation of a nitrosyl complex, whose e.p.r. characteristics indicate that the b-type haem is attached to the protein through a nitrogenous ligand, probably originating from a histidine residue.
TL;DR: It is demonstrated that H2O2 generated during air oxidation of thiols is the main factor in non-turnover-dependent inactivation of purified recombinant human 5-lipoxygenase, and the optimisation of assay conditions have facilitated the purification of large quantities of relatively stable enzyme that will be useful for further kinetic and physical studies.
Abstract: Human 5-lipoxygenase is a non-heme iron protein which is reported to be highly unstable in the presence of oxygen. The results of this investigation demonstrate that H2O2 generated during air oxidation of thiols is the main factor in non-turnover-dependent inactivation of purified recombinant human 5-lipoxygenase for the following reasons: catalase protects against oxygen-dependent inactivation of the enzyme in the presence of dithiothreitol; the active, stable enzyme can be prepared under aerobic conditions with the exclusion of dithiothreitol and contaminating metal ions; 10 microM H2O2 causes the rapid inactivation of the enzyme. The native (ferrous) enzyme is approximately seven times more sensitive to inactivation by H2O2 than the ferric enzyme, suggesting that the mechanism of inactivation involves a Fenton-type reaction of the ferrous enzyme with H2O2, resulting in the formation of an activated oxygen species. Purification of 5-lipoxygenase under aerobic conditions (no dithiothreitol) results in an increase in both the specific activity of the purified protein [up to 70 mumol 5(S)-hydroperoxy-6-trans-8, 11, 14-cis-icosatetraenoic acid (5-HPETE)/mg protein] and in the ratio of specific activity to enzyme iron content compared to enzyme purified under anaerobic conditions in the presence of dithiothreitol. The reaction of the highly active 5-lipoxygenase enzyme shows a dependence on physiological intracellular calcium concentrations, half-maximal product formation being obtained at 0.9 microM free Ca2+. The maximal enzyme activity is also dependent on EDTA and dithiothreitol and low amounts of carrier protein, as well as the known activators PtdCho and ATP. Ca2+ can be substituted by Mn2+, Ba2+ and Sr2+, although lower levels of stimulation are obtained. 5-Lipoxygenase is strongly inhibited by low concentrations (< or = 10 microM) of Zn2+ and Cu2+. The inhibition by Cu2+ is apparently irreversible, whereas that by Zn2+ is slowly reversed (t1/2 = 2 min) in the presence of excess EDTA. These observations on the mechanism of non-turnover-dependent inactivation of 5-lipoxygenase, and the optimisation of assay conditions, have facilitated the purification of large quantities of relatively stable enzyme that will be useful for further kinetic and physical studies.
TL;DR: The present study characterizes the serial reactions of H2O2 with compounds I and II of lignin peroxidase isozyme H1, and provides evidence that demonstrates that the spectral data are merely an artifact caused by enzyme instability and rule out the existence of compound III*.
TL;DR: In this paper, a gene designated FUP1, for ‘ferric utilization proficient’, was isolated by this approach, and DNA sequencing showed that FUP 1 encodes a hydrophilic 43 kDa protein identical to MSN1, a gene encoding a transcriptional activator implicated in carbon source regulation.
Abstract: SUMMARY: We have selected for genes that, when present in multiple copies, enhance growth of wild-type cells of Saccharomyces cerevisiae in an iron-limiting medium. A gene designated FUP1, for ‘ferric utilization proficient’, was isolated by this approach. Increased dosage of FUP1 reduces the concentration of iron in the medium required for efficient growth and confers elevated levels of iron uptake activity in iron-limited cells. Disruption of the FUP1 locus reduces wild-type iron uptake rates by 2-fold in cells grown on raffinose medium but has no effect on glucose-grown cells. DNA sequencing showed that FUP1 encodes a hydrophilic 43 kDa protein identical to MSN1, a gene encoding a transcriptional activator implicated in carbon source regulation. Our results suggest that FUP1/MSN1 also regulates synthesis of gene products involved in iron uptake.
TL;DR: In this article, the zeta potential vs pH relationship of pyrite in the presence and absence of xanthate has been analyzed in terms of a model which assumes that dissolution of iron from the pyritic surface occurs, followed by the adsorption of iron hydroxide species and iron hydride-xanthate complexes onto this surface.
TL;DR: A heterotrophic bacterium, isolated from an acidic stream in a disused pyrite mine which contained copious growths of "acid streamers," displayed characteristics which differentiated it from previously described mesophilic acidophiles, including members of the Sphaerotilus-Leptothrix group of filamentous bacteria.
Abstract: A heterotrophic bacterium, isolated from an acidic stream in a disused pyrite mine which contained copious growths of "acid streamers," displayed characteristics which differentiated it from previously described mesophilic acidophiles. The isolate was obligately acidophilic, with a pH range of 2.0 to 4.4 and an optimum pH of 3.0. The bacterium was unable to fix carbon dioxide but oxidized ferrous iron, although at a slower rate than either Thiobacillus ferrooxidans or Leptospirillum ferrooxidans. Elemental sulfur and manganese(II) were not oxidized. In liquid media, the isolate produced macroscopic streamerlike growths. Microscopic examination revealed that the bacterium formed long (greater than 100 microns) filaments which tended to disintegrate during later growth stages, producing single, motile cells and small filaments. The isolate did not appear to utilize the energy from ferrous iron oxidation. Both iron (ferrous or ferric) and an organic substrate were necessary to promote growth. The isolate displayed a lower tolerance to heavy metals than other iron-oxidizing acidophiles, and growth was inhibited by exposure to light. There was evidence of extracellular sheath production by the isolate. In this and some other respects, the isolate resembles members of the Sphaerotilus-Leptothrix group of filamentous bacteria. The guanine-plus-cytosine content of the isolate was 62 mol%, which is less than that recorded for Sphaerotilus-Leptothrix spp. and greater than those of L. ferrooxidans and most T. ferrooxidans isolates. Images
TL;DR: Reactions involving changes that affect the function of leghemoglobin (Lb) are reviewed and mechanisms must operate in nodules to maintain Lb in the Lb(2+) state.
Abstract: Reactions involving changes that affect the function of leghemoglobin (Lb) are reviewed. The chemical nature of Lb and conditions inside nodules, such as slightly acid pH and the presence of metal ions, chelators, and toxic metabolites (nitrite, superoxide radical, peroxides), are conducive for oxidation of ferrous Lb (Lb2+) or its oxygenated form (LbO2) to nonfunctional ferric Lb (Lb3+) and ferryl Lb. Because Lb3+ is nearly nonexistent in nodules and undergoes observable reduction in vivo, mechanisms must operate in nodules to maintain Lb in the Lb2+ state. Redox reactions of Lb are mediated, for the most part, by activated oxygen species: (a) oxidation of LbO2 to Lb3+ involves superoxide; (b) excess peroxide oxidizes LbO2 and Lb3+ to ferryl Lb and may cause breakdown of heme, release of iron, and generation of hydroxyl radicals (protein radicals may be formed in this process); (c) enzymatic reduction of Lb3+ requires active flavin and thiol groups and involves formation of peroxide; and (d) direct reduction of Lb3+ by NADH is mediated by superoxide and peroxide. Transition metal ions and certain small molecules of nodules such as flavins may act as intermediate electron carriers between NADH and Lb3+, increasing the rate of reaction, which then proceeds via superoxide or flavin radicals, respectively.
TL;DR: In this paper, the zero-field tensor (D) was derived from the Mhsbauer spectra of the picket-fence porphyrin in the presence of weak antiferromagnetic exchange coupling between the paramagnetic iron centers.
Abstract: P2,/n. The five-coordinate iron atom is bonded to four porphyrinato nitrogens (Fe-N,) = 2.107 (14) A and to an oxygen atom of the acetate ion (FA,, = 2.034 (3) A), placed inside the molecular cavity of the picket-fence porphyrin. Mhsbauer spectra were recorded in the two oxidation states of the complex at temperatures varying from 1.5 to 200 K in fields of 0-6.21 T. The ferrous complex has a large quadrupole splitting, AEQ = 4.25 mm s-I, nearly independent of temperature. In the ferric species, the quadrupole splitting, AEQ = 1.1 mm s-', is as normally found in ferric high-spin iron porphyrins. The spin-Hamiltonian analysis of the spectra yields the zero-field parameters D = -0.9 cm-' and E/D = 0.33 and the magnetic hyperfine parameters A,, = -17 T and A, = -13.3 T in the ferrous complex (spin S = 2) and D = 7.5 cm-I, E/D = 0 and Ax,,= = -20 T in the ferric species (S = 5/2). The values of the zero-field parameters of the ferric species are confirmed by EPR analysis; the g values are g, = 1.960, g, = 2.017, and g, = 2.00. The zero-field splittings and effective g values in the ferric complex are interpreted in terms of a crystal-field model. Theoretical estimates of the quadrupole splitting and zero-field parameters in the ferrous complex are given on the basis of molecular-orbital calculations. The relation between the zero-field tensor (D) and electronic and X-ray structure in the ferrous species is discussed. Parallel to the discovery of the unusually large quadrupole splitting, PE - 4 mm s-', in the ferrous state of the prosthetic group term4 p460 of the multiheme enzyme hydroxylamine oxidoreductase from the bacterium Nitrosomonas europeae,'V2 comparably large splittings were observed in a number of synthetic five-coordinate porphyrins of the formula [Fe(X)(Porph)]-, where X is an anionic oxygen- or nitrogen-donor ligand or a halide ion.38 In order to gain more insight into the electronic structure of the iron ions in these complexes, field- and temperature-dependent MBssbauer measurements have been performed in the synthetic phenolato porphyrinato complex [ Fe"(OC6H,)(TPP)]- by Lang et a1.* For the derivation of a set of zero-field parameters consistent with both the susceptibility and MBssbauer data in the phenolate complex, these authors introduced weak antiferromagnetic exchange coupling between the paramagnetic iron centers.8 Strong correlations between the sign and magnitude of the zero-field parameter D and the value of the exchange-coupling constant were found in the simulations of the magnetic susceptibility data. However, the spin-Hamiltonian parameters inferred from the Mbsbauer spectra are rather insensitive to the weak intermolecular couplings. The value of the zero-field parameter D obtained by Lang et al. is small and negative (see Table I). The principal components of the magnetic hyperfine tensor (A) in the complex are negative, which is characteristic of a dominant Fermi contact interaction. Furthermore, the A tensor shows anisotropy, lAll < IA, 1, originating from spin-dipolar interaction. The anisotropy ob the A tensor and the positive sign of the main component of the electric-field-gradient (EFG) tensor indicate that the iron(I1) ion in the phenolate complex possesses a half-filled subshell of spin-parallel electrons plus an "excessn electron of opposite spin in an oblate orbital of d, ty~,~*,' The weak temperature dependence of the quadrupole sphttmg in the range 1-300 K shows that the ground orbital state is energetically well-separated from excited orbital states by energy gaps typically 1 order
TL;DR: A novel iron-sulfur protein was purified from the extract of Desulfovibrio desulfuricans to homogeneity as judged by polyacrylamide gel electrophoresis, providing direct spectroscopic evidence for the presence of a 6Fe cluster in this newly purified protein.
TL;DR: In this paper, the effects of silicate and phosphate ions on the formation of α- and β-FeOOH particles were studied, and it was shown that α-FeOH particles formed at a higher concentration of these anions.
Abstract: The effects of silicate and phosphate ions on the formation of α- and β-FeOOH particles were studied. The formation and crystallization of α-FeOOH particles were inhibited by both the anions, and their particle size decreased with increasing concentration of the anions added. This inhibition was caused not only by complexing with ferric ions but also by adsorption on the particle surface. For α-FeOOH the amorphous particles were formed at a higher concentration of these anions. On the other hand, in the case of β-FeOOH the effects of both the anions were little, especially for silicate ions. This difference between α- and β-FeOOH particles could be explained by the difference between their preparation pH. The α-FeOOH particles prepared in the presence of these anions showed a microporosity.
TL;DR: In this article, the polycarboxylate siderophore, rhizoferrin, and its dehydration products were separated by preparative HPLC and characterized by 13C-NMR, 1H-nMR, UV, circular dichroism (CD) and IR spectroscopy, and also by capillary electrophoresis.
Abstract: The polycarboxylate siderophore, rhizoferrin, and its dehydration products were separated by preparative HPLC and characterized by13C-NMR,1H-NMR, UV, circular dichroism (CD) and IR spectroscopy, and also by capillary electrophoresis. Assginment of all carbon atoms and protons by NMR spectra confirmed the structure of rhizoferrin and gave evidence for the presence of the cyclized dehydration byproducts, imidorhizoferrin and bis-imidorhizoferrin. The imido forms were also characterized by their mobility during capillary electrophoresis. UV spectra revealed a 1∶1 iron:ligand ratio above pH 3. Based on the absorption maximum of the metal ligand charge transfer hand at 335 nm a molar extinction coefficient of 2300m−1 cm−1 was calculated for ferric rhizoferrin. CD measurements revealed that the quarternary carbon atoms of the two citric acid residues possess anR,R configuration and that the iron complex of rhizoferrin adopts a A configuration around the metal center.
TL;DR: In this paper, 13 desferrioxamine-type siderophores were obtained from cultures of Streptomyces olivaceus Tu 2718 by supplementing the production medium with ornithine or 1,4-diaminobutane, 1,6diaminohexane, bis(2-aminoethyl) ether, S-(2-amide)cysteine, and N-glycylethylenediamine.
Abstract: Thirteen new desferrioxamine-type siderophores, designated X 1 -X 6 , Et 1 -Et 3 , Te 1 -Te 3 , and P 1 , were obtained from cultures of Streptomyces olivaceus Tu 2718 by supplementing the production medium with ornithine or 1,4-diaminobutane, 1,6-diaminohexane, bis(2-aminoethyl) ether, S-(2-aminoethyl)cysteine, and N-glycylethylenediamine
TL;DR: Absorption minima developed with the addition of ferric sulfate in the dithionite reduced cell suspension demonstrated that the ferric ion could accept electrons from the cytochrome system of this bacterium.
Abstract: Anaerobic growth on elemental sulfur using dissimilar iron reduction by Thiobacillus ferrooxidans has been demonstrated. The ferric ion reducing activity (FIR) of the anaerobic cells was double that of the aerobic cells. Significant differences in inhibition of FIR by respiratory inhibitors were observed between aerobic and anaerobic cells. A higher amount of cytochrome was detected in anaerobic cells compared to aerobic cells. Absorption minima developed with the addition of ferric sulfate in the dithionite reduced cell suspension demonstrated that the ferric ion could accept electrons from the cytochrome system of this bacterium. The possibility of two different electron transport chains in ferric ion reduction is discussed.
TL;DR: It is proposed that apo mammalian ferritin (apoMF) contains six redox centers that can be fully oxidized forming oxidized apoferritin(apoMFox) or fully reduced forming apoMFred, and the yellow color of apo MF appears to be an integral characteristic of the apoMF and is possibly associated with its redox activity.
Abstract: Apo horse spleen ferritin undergoes a 6.3 +/- 0.5 electron redox reaction at -310 mV at pH 6.0-8.5 and 25 degrees C to form reduced apoferritin (apoMFred). Reconstituted ferritin containing up to 50 ferric ions undergoes reduction at the same potential, taking up one electron per ferric ion and six additional electrons by the protein. We propose that apo mammalian ferritin (apoMF) contains six redox centers that can be fully oxidized forming oxidized apoferritin (apoMFox) or fully reduced forming apoMFred. ApoMFred can be prepared conveniently by dithionite or methyl viologen reduction. ApoMFred is slowly oxidized by molecular oxygen but more rapidly by Fe(CN)6(3-) to apoMFox. Fe(III)-cytochrome c readily oxidizes apoMFred to apoMFox with a stoichiometry of 6 Fe(III)-cytochrome c per apoMFred, demonstrating a rapid interprotein electron-transfer reaction. Both redox states of apoMF react with added Fe3+ and Fe2+. Addition of eight Fe2+ to apoMFox under anaerobic conditions produced apoMFred and Fe3+, as evidenced by the presence of a strong g = 4.3 EPR signal. Subsequent addition of bipyridyl produced at least six Fe(bipyd)3(2+) per MF, establishing the reversibility of this internal electron-transfer process between the redox centers of apoMF and bound iron. Incubation of apoMFred with the Fe(3+)-ATP complex under anaerobic conditions resulted in the formation and binding of two Fe2+ and four Fe3+ by the protein. The various redox states formed by the binding of Fe2+ and Fe3+ to apoMFox and apoMFred are proposed and discussed. The yellow color of apoMF appears to be an integral characteristic of the apoMF and is possibly associated with its redox activity.
TL;DR: Gallium and iron appear to share the same Tf-independent cellular uptake system in HL60 cells, and exposure of cells to gallium results in the activation of cell membrane non-Tf iron carriers that may play a role in overcoming the T f-independent growth-inhibitory effects of gallium.