Showing papers on "Ferric published in 1987"
TL;DR: The GS-15 organism as mentioned in this paper is not magnetotactic, but reduces amorphic ferric oxide to extracellular magnetite during the reduction of ferric iron as the terminal electron acceptor for organic matter oxidation.
Abstract: The potential contribution of microbial metabolism to the magnetization of sediments has only recently been recognized. In the presence of oxygen, magnetotactic bacteria can form intracellular chains of magnetite while using oxygen or nitrate as the terminal electron acceptor for metabolism1. The production of ultrafine-grained magnetite by magnetotactic bacteria in surficial aerobic sediments may contribute significantly to the natural remanent magnetism of sediments2–4. However, recent studies on iron reduction in anaerobic sediments suggested that bacteria can also generate magnetite in the absence of oxygen5. We report here on a sediment organism, designated GS-15, which produces copious quantities of ultrafine-grained magnetite under anaerobic conditions. GS-15 is not magnetotactic, but reduces amorphic ferric oxide to extracellular magnetite during the reduction of ferric iron as the terminal electron acceptor for organic matter oxidation. This novel metabolism may be the mechanism for the formation of ultrafine-grained magnetite in anaerobic sediments, and couldaccount for the accumulation of magnetite in ancient iron formations and hydrocarbon deposits.
921 citations
TL;DR: A review of the literature indicates that numerous microorganisms can reduce ferric iron during the metabolism of organic matter as mentioned in this paper, and that the reduction of iron appears to be enzymatically catalyzed and may be coupled to an electron transport chain that could generate ATP.
Abstract: A review of the literature indicates that numerous microorganisms can reduce ferric iron during the metabolism of organic matter. In most cases, the reduction of ferric iron appears to be enzymatically catalyzed and, in some instances, may be coupled to an electron transport chain that could generate ATP. However, the physiology and biochemistry of ferric iron reduction are poorly understood. In pure culture, ferric iron‐reducing organisms metabolize fermentable substrates, such as glucose, primarily to typical fermentation products, and transfer only a minor portion of the electron equivalents in the fermentable substrates to ferric iron. However, fermentation products, especially hydrogen and acetate, may be important electron donors for ferric iron reduction in natural environments. The ability of some organisms to couple the oxidation of fermentation products to the reduction of ferric iron means that it is possible for a food chain of iron‐reducing organisms to completely mineralize nonrecal...
360 citations
TL;DR: Investigation of the reaction of nitric oxide with ferric heme proteins and model compounds suggests that the presence of an axial water molecule at the ligand binding site of ferric hemoglobin A prevents it from exhibiting significant cooperativity in its reactions with NO.
Abstract: Rates for the reaction of nitric oxide with several ferric heme proteins and model compounds have been measured. The NO combination rates are markedly affected by the presence or absence of distal histidine. Elephant myoglobin in which the E7 distal histidine has been replaced by glutamine reacts with NO 500-1000 times faster than do the native hemoglobins or myoglobins. By contrast, there is not difference in the CO combination rate constants of sperm whale and elephant myoglobins. Studies on ferric model compounds for the R and T states of hemoglobin indicate that their NO combination rate constants are similar to those observed for the combination of CO with the corresponding ferro derivatives. The last observation suggests that the presence of an axial water molecule at the ligand binding site of ferric hemoglobin A prevents it from exhibiting significant cooperativity in its reactions with NO.
243 citations
Journal Article•
TL;DR: The results suggest that Fe3+-NTA catalyzes the decomposition of hydrogen peroxide to produce hydroxyl radicals, which subsequently cause the strong base alterations of guanine and thymine, and deoxyribose-phosphate backbone breakages.
Abstract: Reactivities of Fe 3+ chelates of aminopolycarboxylic acids with DNA were investigated by the DNA-sequencing technique using 32 P 5′-end-labeled DNA fragments obtained from the human c-Ha- ras -1 protooncogene, and the reaction mechanism was studied by electron spin resonance spectroscopy. Ferric nitrilotriacetate (Fe 3+ -NTA) plus hydrogen peroxide caused strong DNA cleavage in the presence of albumin. No or little DNA cleavage was observed with ferric chloride or Fe 3+ chelates of other aminopolycarboxylic acids tested in the presence of hydrogen peroxide. The DNA cleavage by Fe 3+ -NTA plus hydrogen peroxide without piperidine treatment occurred at positions of every nucleotide although a specific cleavage was observed, whereas cleavages at the positions of guanine and thymine increased predominantly with piperidine treatment. Electron spin resonance studies using free radical traps demonstrated that of Fe 3+ chelates of aminopolycarboxylic acids, Fe 3+ -NTA was the most effective catalyst in hydrogen peroxide-derived production of hydroxyl radicals under our conditions. The results suggest that Fe 3+ -NTA catalyzes the decomposition of hydrogen peroxide to produce hydroxyl radicals, which subsequently cause the strong base alterations of guanine and thymine, and deoxyribose-phosphate backbone breakages. The possibility that the Fe 3+ -NTA-induced DNA damage is the initiation and/or promotion of carcinogenesis by Fe 3+ -NTA is discussed.
188 citations
TL;DR: These results document the participation of both superoxide anion and hydrogen peroxide in the killing of cultured hepatocytes by acetaminophen and suggest that hydroxyl radicals generated by an iron catalyzed Haber-Weiss reaction mediate the cell injury.
173 citations
TL;DR: The results demonstrate that apical root zones are the main sites both for Fe deficiency-enhanced release of phytosiderophores and for uptake and translocation of iron supplied as FeIII phytOSiderophore.
Abstract: Under iron deficiency the release of so-called phytosiderophores by roots of barley plants (Hordeum vulgare L. cv. Europa) was greater by a factor of 10 to 50 compared to iron-sufficient plants. This enhanced release occurred particularly in apical zones of the seminal roots and in the lateral root zones. Under iron deficiency, uptake rates for iron, supplied as FeIII phytosiderophore, increased by a factor of ca 5 as compared to iron-sufficient plants. This enhanced uptake rate for iron was also much more pronounced in apical than in basal root zones. In contrast, with supply of the synthetic iron chelate, FelII EDDHA (ferric diaminoethane-N, N-di-o-hydroxyphenyl acetic acid), the Fe deficiency-enhanced uptake rates for iron were only small and similar along the roots, except for the lateral root zones. The high selectivity of barley roots for uptake and translocation of FeIII phytosiderophores compared with FeIII EDDHA is reflected by the fact that, at the same external concentration (2 μM), rates of uptake and translocation of iron from FeIII phytosiderophores were between 100 (Fe-sufficient) and 1 000 times higher (Fe-deficient plants) than from FeIII EDDHA. The relatively high rates of uptake and particularly of translocation of iron supplied as FeIII EDDHA in the zone of lateral root formation strongly suggest an apoplastic pathway of radial transport of the synthetic iron chelate into the stele in this root zone.
The results demonstrate that apical root zones are the main sites both for Fe deficiency-enhanced release of phytosiderophores and for uptake and translocation of iron supplied as FeIII phytosiderophores.
165 citations
TL;DR: It is proposed that iron must be reduced to be taken up by the cells in the same way as other divalent cations, and uptake was strongly inhibited by an iron(II)-trapping reagent like ferrozine.
Abstract: Among several parameters affecting the rate and amount of iron uptake by Saccharomyces cerevisiae, the oxidation state of iron appeared to be determinant. Iron presented as Fe(II) was taken up faster than Fe(III) and the kinetic parameters were different. Iron was taken up by the cells from different ferric chelates, at rates that did not depend on their stability constants, and uptake was strongly inhibited by an iron(II)-trapping reagent like ferrozine. Iron was physiologically reduced by a transplasmamembrane redox system, which was induced in iron-deficient conditions. We propose that iron must be reduced to be taken up by the cells in the same way as other divalent cations.
155 citations
TL;DR: Gram-negative, aerobic bacteria capable of facultative growth using ferric ions or thiosulfate or sulfite as electron acceptors were readily isolated from oil field fluids.
Abstract: Gram-negative, aerobic bacteria capable of facultative growth using ferric ions or thiosulfate or sulfite as electron acceptors were readily isolated from oil field fluids. Morphological and bioche...
150 citations
TL;DR: The level of chelatable iron within the cell has a regulatory role in ferritin synthesis through redistribution of the messenger RNAs between the free mRNA pool and the polyribosomes.
Abstract: Acute administration of iron to rats has been previously shown to induce liver ferritin synthesis by increasing the translation of inactive cytoplasmic ferritin mRNAs for both heavy (H) and light (L) subunits by mobilizing them onto polyribosomes. In this report rat hepatoma cells in culture are used to explore the relationship of this response to intracellular iron levels. After adding iron as ferric ammonium citrate to the medium, latent ferritin H- and L-mRNAs were extensively transferred to polyribosomes, accompanied by increased uptake of [35S]methionine into ferritin protein. Because total cellular levels of L- and H-mRNA were not significantly changed by exposure to iron, the increased ferritin mRNAs on polyribosomes most probably come from an inactive cytoplasmic pool, consistent with the inability of actinomycin-D and of cordycepin to inhibit iron-induced ferritin synthesis. When deferoxamine mesylate, an intracellular iron chelator, was added after the addition of iron to the medium, ferritin mRNA on the polyribosomes was reduced, while the free messenger pool increased, and ferritin synthesis diminished. In contrast, the extracellular iron chelator diethylenetriaminepentaacetic acid failed to inhibit the induction of ferritin protein synthesis. Addition of iron in the form of hemin also caused translocation of mRNA to polyribosomes, a response that could be similarly quenched by deferoxamine. Because hemin does not release chelatable iron extracellularly, we conclude that the level of chelatable iron within the cell has a regulatory role in ferritin synthesis through redistribution of the messenger RNAs between the free mRNA pool and the polyribosomes.
148 citations
TL;DR: In this article, the viscosities of two melts in the system Na2O-Fe-FeO -Fe2O3-SiO2 have been measured as a function of oxidation state.
133 citations
TL;DR: In this paper, a sequential combination of ten unique conditions during the cooling history of Mars is suggested which is believed to have generated an environment within Martian permafrost that has stabilized Fe(3+)-SO4(2)-bearing species.
Abstract: Evidence is presented for the possible existence of ferric sulfato complexes and hydroxo ferric sulfate minerals in the permafrost of Mars. A sequential combination of ten unique conditions during the cooling history of Mars is suggested which is believed to have generated an environment within Martian permafrost that has stabilized Fe(3+)-SO4(2-)-bearing species. It is argued that minerals belonging to the jarosite and copiapite groups could be present in Martian regolith analyzed in the Viking XRF measurements at Chryse and Utopia, and that maghemite suspected to be coating the Viking magnet arrays is a hydrolysate of dissolved ferric sulfato complexes from exposed Martian permafrost.
TL;DR: In this paper, the use of loss on ignition (LOI) in whole-rock analysis is evaluated in the modern context, as a measurement of total volatiles, mainly added to the other oxides to assess analytical accuracy by testing whether or not the total is 100.0 ± − 1.0%.
TL;DR: This study concerns magnetic interaction between the tyrosyl radical and the iron center in the two proteins, and finds that for protein M2 the effects are more pronounced than for protein B2, indicating a stronger magnetic interaction.
Abstract: Ribonucleotide reductases from Escherichia coli and from mammalian cells are heterodimeric enzymes. One of the subunits, in the bacterial enzyme protein B2 and in the mammalian enzyme protein M2, contains iron and a tyrosyl free radical that both are essential for enzyme activity. The iron center in protein B2 is an antiferromagnetically coupled pair of high-spin ferric ions. This study concerns magnetic interaction between the tyrosyl radical and the iron center in the two proteins. Studies of the temperature dependence of electron paramagnetic resonance (EPR) relaxation and line shape reveal significant differences between the free radicals in proteins B2 and M2. The observed temperature-dependent enhanced EPR relaxation and line broadening of the enzyme radicals are furthermore completely different from those of a model UV-induced free radical in tyrosine. The results are discussed in terms of magnetic dipolar as well as exchange interactions between the free radical and the iron center in both proteins. The free radical and the iron center are thus close enough in space to exhibit magnetic interaction. For protein M2 the effects are more pronounced than for protein B2, indicating a stronger magnetic interaction.
TL;DR: In this article, a new ferric ion sequestering tricatecholate, TRENCAM, has been synthesized from triaminotriethylamine (TREN) in high yield.
Abstract: A new ferric ion sequestering tricatecholate, TRENCAM, has been synthesized from @$',@''-triaminotriethylamine (TREN) in high yield. The solution coordination chemistry of the ligand and its iron(3+,2+) complexes have been studied by means of pH potentiometric, spectrophotometric, and voltammetric methods. The last five stepwise protonation constants (log K ) to (H,TRENCAM)Br are 11.26, 8.75, 8.61, 6.71, and 5.88 (from least-squares refinement of the potentiometric data from pH 3.5 to 10.7). The potentiometric data of the ferric complex have shown that the last three protonation constants are positioned close to one another between pH 5 and 5.6. These are resolved by spectrophotometric data from pH 8 to 5.6, which show that the first protonation constant (log K ) of ferric(TRENCAM) is 5.59. From the reduction potential vs. pH curve of the iron(3+,2+) complexes the corresponding protonation constant (log K ) of the ferrous complex has been determined to be 11.2. The specific affinity of TRENCAM for ferric ion relative to ferrous ion results in a highly negative reduction potential of the iron(3+,2+) center: -1.04 V vs. (NHE). From competition experiments with EDTA, the formation constant (log K ) of ferric(TRENCAM) has been estimated to be 43.6. At pH 7.4, [ligand],, = 10 pM, and [Fe3+],,, = 1 pM, p[Fe3+] = 27.8. Implications of the results for in vivo iron removal are presented.
TL;DR: Results are presented showing that this mechanism could not be responsible for the high rates of ferric reduction shown by roots of iron-deficient bean plants, and indicates a role for the superoxide radical, O(2) ([unk]), as a facultative intermediate electron carrier in the plasma membrane.
Abstract: The recent proposal of Tipton and Thowsen (Plant Physiol 79: 432-435) that iron-deficient plants reduce ferric chelates in cell walls by a system dependent on the leakage of malate from root cells was tested. Results are presented showing that this mechanism could not be responsible for the high rates of ferric reduction shown by roots of iron-deficient bean (Phaseolus vulgaris L. var Prelude) plants. The role of O2 in the reduction of ferric chelates by roots of iron-deficient bean plants was also tested. The rate of Fe(III) reduction was the same in the presence and in the absence of O2. However, in the presence of O2 the reaction was partially inhibited by superoxide dismutase (SOD), which indicates a role for the superoxide radical, O2[unk], as a facultative intermediate electron carrier. The inhibition by SOD increased with substrate pH and with decrease in concentration of the ferrous scavenger bathophenanthroline-disulfonate. The results are consistent with a mechanism for transmembrane electron transport in which a flavin or quinone is the final electron carrier in the plasma membrane. The results are discussed in relation to the ecological importance that O2[unk] may have in the acquisition of ferric iron by dicotyledonous plants.
TL;DR: In this article, Crundwell et al. studied the kinetics of the oxidative dissolution of a zinc sulphide (sphalerite) concentrate in ferric sulphate solutions and showed that the dissolution of the concentrate continued beyond 90% conversion in two hours at 80°C.
TL;DR: The data show that the siderophore system in Anabaena spp.
Abstract: Growth of Anabaena sp. strain 7120 (in the absence of chelators or added iron) was inhibited by the addition of 2.1 to 6.5 microM copper and was abolished by copper concentration of 10 microM or higher. When the copper was chelated to schizokinen (the siderophore produced by this organism in response to iron starvation), the toxic effects were eliminated. Analysis of culture filtrates showed that the cupric schizokinen remains in the medium, thereby lowering the amount of copper taken up by the cells. Although this organism actively transports ferric schizokinen, it apparently does not recognize the cupric complex. Thus, Anabaena sp. is protected from copper toxicity under conditions in which siderophore is being produced. For cells grown in low iron, the accumulation of extracellular schizokinen was observed to parallel cell growth and continue well into stationary phase. The actual iron status of the organism was monitored by using iron uptake velocity as an assay. Cultures grown on 0.1 microM added iron were found to be severely iron limited upon reaching stationary phase, thus explaining the continued production of schizokinen. These data show that the siderophore system in Anabaena spp. has developed primarily as a response to iron starvation and that additional functions such as alleviation of copper toxicity or allelopathic inhibition of other algal species are merely secondary benefits.
01 Sep 1987-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this article, the leaching kinetics of chalcopyrite with ferric sulfate was studied and the morphology and electrochemical properties of the leach surface were investigated.
Abstract: The leaching kinetics of natural chalcopyrite crystals with ferric sulfate was studied. The morphology of the leached chalcopyrite and the electrochemical properties of chalcopyrite electrodes also were investigated. The leaching of chalcopyrite showed parabolic-like kinetics initially and then showed linear kinetics. In the initial stage, a dense sulfur layer formed on the chalcopyrite surface. The growth of the layer caused it to peel from the surface, leaving a rough surface. In the linear stage, no thick sulfur layer was observed. In this investigation, chalcopyrite leaching in the linear stage was principally studied. The apparent activation energy for chalcopyrite leaching was found to range from 76.8 to 87.7 kJ mol−1, and this suggests that the leaching of chalcopyrite is chemically controlled. The leaching rate of chalcopyrite increases with an increase in Fe(SO4)1.5 concentration up to 0.1 mol dm−3, but a further increase of the Fe(SO4)1.5 concentration has little effect on the leaching rate. The dependency of the mixed potential upon Fe(SO4)1.5 concentration was found to be 79 mV decade−1 from 0.01 mol dm−3 to 1 mol dm−3 Fe(SO4)1.5. Both the leaching rate and the mixed potential decreased with an increased FeSO4 concentration. The anodic current of Fe(II) oxidation on the chalcopyrite surface in a sulfate medium was larger than that in a chloride medium.
TL;DR: It is observed by ESR spectroscopy that both phosphatases were able to promote hydroxyl radical formation and the iron complex of diethylenetriamine penta-acetic acid was investigated and found to promote Haber-Weiss-Fenton chemistry.
TL;DR: In this paper, the catalytic effect of five ferric chelate compounds was studied under different conditions and the coulombic yields of the cells containing the microorganism Erwinia dissolvens indicate a large degree of energy conversion in the systems studied, and were even larger than those reported in the literature for Escherichia coli.
TL;DR: The photochemistry of metalloporphyrins and related macrocycles is of intense current interest as discussed by the authors, and the photochemical properties of ferric porphyrin and heme proteins remain largely unexplored and not well understood.
Abstract: The photochemistry of metalloporphyrins and related macrocycles is of intense current interest. Nonetheless, the photochemistry of ferric porphyrins and heme proteins remains largely unexplored and not well understood. The ability of Fe(III) porphyrins to act as catalysts for hydrocarbon oxidations with various oxidants suggested to us their possible use as photocatalysts. In this paper, they assign a near-ultraviolet absorption in Fe/sup III/(TPP)(X) (where X = F, Cl, Br, I, N/sub 3/; TPP = 5,10,15,20-tetraphenylporphyrinate(-2)) as a halide ligand-to-metal charge-transfer (LMCT) transition. Irradiation into this band leads to rapid photoreduction of the iron atom and dissociation of X/sup 0/. In the presence of O/sub 2/, photoinitiation of hydrocarbon oxidation occurs.
TL;DR: Newcastle laboratory experiments suggest that bovine lactoferrin (Lf) has no effect on iron absorption in rats, and a study carried out in newborn infants to measure the effects of If on iron retention confirms the previous findings in rats that If does not influence the availability of nonheme iron.
Abstract: Results from experiments in this laboratory using 59Fe suggest that bovine lactoferrin (Lf) has no effect on iron absorption in rats. A study was therefore carried out in newborn infants to measure the effects of Lf on iron retention. Bovine Lf was labeled with the stable isotope 58Fe and fed to 7-day-old infants in a standard milk formula. Iron retention was estimated by measuring the unabsorbed 58Fe excreted in the feces during the following 3 days using neutron activation analysis. The results were compared with those obtained from a group of infants fed a similar level of iron as ferric chloride, labeled with 58Fe, together with 30 mg ascorbic acid. There was a very wide variation in percent iron retention amongst the infants but no overall difference between the Lf and ferric chloride groups. This confirms the previous findings in rats that Lf does not influence the availability of nonheme iron.
TL;DR: It is clearly shown that the Fe(III) in the distinctive environment is polynuclear (Fe atoms with Fe-Fe = 3.5 A and TB = 7 K), and the arrangement of atoms is such that Fe( III) atoms appear to have both carboxylate-like ligands, presumably from apoferritin, and oxo bridges to the other iron atoms.
Abstract: Ferritin is a complex of a hollow, spherical protein and a hydrous, ferric oxide core of less than or equal to4500 iron atoms inside the apoprotein coat; the apoprotein has multiple binding sites for monoatomic metal ions, e.g., Fe(II), V(IV), Tb(III), that may be important in the initiation of iron core formation. In an earlier study the authors observed that the oxidation of Fe(II) vacated some, but not all, of the metal-binding sites, suggesting migration of some Fe during oxidation, possibly to form nucleation clusters; some Fe(III) remained bound to the protein. Preliminary extended X-ray absorbance fine structure (EXAFS) analysis of the same Fe(III)-apoferritin complex showed an environment distinct from ferritin cores, but the data did not allow a test of the Fe cluster hypothesis. In this paper, with improved EXAFS data and with Moessbauer data on the same complex formed with /sup 57/Fe, they clearly show that the Fe(III) in the distinctive environment is polynuclear. Moreover, the arrangement of atoms is such that Fe(III) atoms appear to have both carboxylate-like ligands, presumably from apoferritin, and oxo bridges to the other iron atoms. Thus the protein provides sites not only for initiation but also for nucleation of the iron core.more » Sites commodious enough and with sufficient conserved carboxylate ligands to accommodate such a nucleus occur inside the protein coat at the subunit dimer interfaces. Such Fe(III)-apoferritin nucleation complexes can be used to study the properties of the several members of the apoferritin family.« less
TL;DR: Decarreau et al. as discussed by the authors showed that the crystal growth of a dioctahedral smectite, containing only Fe 3+ atoms in the octahedral sheet, is possible under strictly oxidizing conditions.
Abstract: A B S T R A C T : Silico-ferric coprecipitates, with chemical formula S i4Fe23 + O.. nHzO, were aged in suspension at 75 ~ 100 ~ and 150~ and the structural evolution of solids with time studied by XRD, TEM, and IR, Mfssbauer and EXAFS spectroscopy. The initial Si-Fe coprecipitate was found to be amorphous but showed local order similar to that of a smectite layer. At 75~ only a weak structural evolution of the silico-ferric product towards a smectite-like structure was observed. Experiments performed at 100 ~ and 150~ led to synthesis of a ferric smectite with �9 e 3+ C structural formula Sl4F j.s30~0(OH)z %.26. During syntheses a highly soluble silico-ferric complex appeared; the Si/Fe atomic ratio of this complex was 3, and the apparent concentration of Fe 3+ in solution reached 27 mM/l. These syntheses prove that the crystallization of a dioctahedral smectite, containing only Fe 3+ atoms in the octahedral sheet, is possible under strictly oxidizing conditions. However, crystal growth of a ferric smectite under these conditions is slow and only syntheses carried out at sufficiently high temperatures give convincing results. In a previous paper (Decarreau & Bonnin, 1986), we reviewed the conditions of crystallization of iron-rich dioctahedral ferric smectites, both under natural and experimental conditions. It was demonstrated that a ferric end-member of dioctahedral smectite could be synthesised at low temperature in initially reducing then oxidizing conditions. These results were an experimental corroboration of a crystal-growth process suggested by Pedro et al. (1978) and Bischoff (1972) for the genesi s of nontronitic smectite. Following the experimental studies of Caillere et al. (1955), and more recently Harder (1976, 1977, 1978), one of the most important questions about iron-rich ferric smectite ~,enesis was: is it possible to observe the crystal growth of such smectites in atmospheric oxidizing conditions ? Aging experiments on silico-ferric solids coprecipitated in aqueous suspension, between 75 ~ and 150~ have been carried out to address this question.
TL;DR: It is suggested that the iron-stimulated production of free radicals leading to lipid peroxidation is the major cause of ferric nitrilotriacetate-mediated renal toxicity and vitamin E, a known scavenger ofFree radicals, is effective in protecting against this iron-induced toxicity.
01 Dec 1987-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this paper, a mixture of synthetic ilmenite and graphite was heated in argon at 1000 to 1100 °C and the rate of reduction was followed gravimetrically.
Abstract: Pellets prepared from mixtures of synthetic ilmenite and graphite were heated in argon at 1000 to 1100 °C and the rate of reduction was followed gravimetrically. No measurable reaction was obtained at 1000 °C but the rate was high at 1100 °C. An inflection in the reduction curve at about 2 pct weight loss at 1050 and 1100 °C was due to the difficulty in nucleating iron. The rate is increased significantly by the addition of ferric chloride which promotes the nucleation of iron. The addition of rutile decreases the rate of reduction and the addition of manganese stabilizes a pseudobrookite phase.
TL;DR: The ferric spin-state equilibrium and relaxation rate of cytochrome P-450 has been examined with temperature jump spectroscopy using a number of camphor analogues known to induce different mixed spin states in the substrate-bound complexes, and a strong correlation between the fraction of high-spin species and the rate constant, k-1, is observed.
Abstract: The ferric spin-state equilibrium and relaxation rate of cytochrome P-450 has been examined with temperature jump spectroscopy using a number of camphor analogues known to induce different mixed spin states in the substrate-bound complexes [Gould, P., Gelb, M., & Sligar, S. G. (1981) J. Biol. Chem. 256, 6686]. All temperature-induced spectral changes were monophasic, and the spin-state relaxation rate reached a limiting value at high substrate concentrations. The ferric spin equilibrium constant, Kspin, is defined in terms of the rate constants k1 and k-1 via Kspin = k1/k-1 = [P-450(HS)]/[P-450(LS)] where HS and LS represent high-spin (S = 5/2) and low-spin (S = 1/2) ferric iron, respectively, and the spectrally observed spin-state relaxation rate by kobsd = k1 + k-1. A strong correlation between the fraction of high-spin species and the rate constant, k-1, is observed. For a 3 degrees C temperature jump (from 10 to 13 degrees C), the 23% high-spin tetramethylcyclohexanone complex (Kd = 45 +/- 20 microM) is characterized by a ferric spin relaxation rate of kobsd = 1990 s-1, while the rates for the d-fenchone (41% high spin, Kd = 42 +/- 10 microM) and kobsd = 1990 s-1, while the rates for the d-fenchone (41% high spin, Kd = 42 +/- 10 microM) and camphoroquinone (75% high spin, Kd = 15 +/- 5 microM) complexes are 1430 and 346 s-1, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: Pyoverdinpss was isolated, chemically characterized, and found to resemble previously characterized pyoverdins in spectral traits, size, and amino acid composition, but was structurally unique since amino acid analysis of reductive hydrolysates yielded β-hydroxyaspartic acid, serine, threonine, and lysine in a 2-2:2:1 ratio.
Abstract: Pseudomonas syringae pv. syringae B301D produces a yellow-green, fluorescent siderophore, pyoverdinpss, in large quantities under iron-limited growth conditions. Maximum yields of pyoverdinpss of approximately 50 μg/ml occurred after 24 h of incubation in a deferrated synthetic medium. Increasing increments of Fe(III) coordinately repressed siderophore production until repression was complete at concentrations of ≥ 10 μM. Pyoverdinpss was isolated, chemically characterized, and found to resemble previously characterized pyoverdins in spectral traits (absorbance maxima of 365 and 410 nm for pyoverdinpss and its ferric chelate, respectively), size (1,175 molecular weight), and amino acid composition. Nevertheless, pyoverdinpss was structurally unique since amino acid analysis of reductive hydrolysates yielded β-hydroxyaspartic acid, serine, threonine, and lysine in a 2:2:2:1 ratio. Pyoverdinpss exhibited a relatively high affinity constant for Fe(III), with values of 1025 at pH 7.0 and 1032 at pH 10.0. Iron uptake assays with [55Fe]pyoverdinpss demonstrated rapid active uptake of 55Fe(III) by P. syringae pv. syringae B301D, while no uptake was observed for a mutant strain unable to acquire Fe(III) from ferric pyoverdinpss. The chemical and biological properties of pyoverdinpss are discussed in relation to virulence and iron uptake during plant pathogenesis.
TL;DR: Resonance Raman spectroscopy of lignin peroxidase from the basidiomycete Phanerochaete chrysosporium suggests two different coordination states for the native ferric enzyme, and results presented herein indicate this hypothesis is indeed correct.
Abstract: Resonance Raman (RR) spectroscopy of lignin peroxidase (ligninase, dairylpropane oxygenase) from the basidiomycete Phanerochaete chrysosporium suggests two different coordination states for the native ferric enzyme. Evidence for a high-spin, hexacoordinate ferric protoporphyrin IX was presented by Andersson et al. [Andersson, L. A., Renganathan, V., Chiu, A.A., Loehr, T. M., & Gold, M. H. (1985) J. Biol. Chem. 260, 6080-6087], whereas Kuila et al. [Kuila, D., Tien, M., Fee, J. A., & Ondrias, M. R. (1985) Biochemistry 24, 3394-3397] proposed a high-spin, pentacoordinate ferric system. Because the two RR spectral studies were performed at different temperatures, we explored the possibility that lignin peroxidase might exhibit temperature-dependent coordination-state equilibria. Resonance Raman results presented herein indicate that this hypothesis is indeed correct. At or near 25 degrees C, the ferric iron of lignin peroxidase is predominantly high spin, pentacoordinate; however, at less than or equal to 2 degrees C, the high-spin, hexacoordinate state dominates, as indicated by the frequencies of well-documented spin- and coordination-state marker bands for iron protoporphyrin IX. The temperature-dependent behavior of lignin peroxidase is thus similar to that of cytochrome c peroxidase (CCP). Furthermore, lignin peroxidase, like horseradish peroxidase (HRP) and CCP, clearly has a vacant coordination site trans to the native fifth ligand at ambient temperature. High-frequency RR spectra of compound II of lignin peroxidase are also presented. The observed shifts to higher frequency for both the oxidation-state marker band v4 and the spin- and coordination-state marker band v10 are similar to those reported for the compound II forms of HRP and lactoperoxidase and for ferryl myoglobin.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: Anhydrous FeCl3 in CH2Cl2 cleaves benzyl and p-phenylbenzyl ethers of sugars in 15-30 minutes and 2-3 minutes, respectively, at room temperature in >70% yields; methyl ethers and acyl groups are not affected as mentioned in this paper.