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Theisen, Roslyn Marie. "Synthetic models and reactivity of sulfur-ligated iron metalloenzymes /." Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/11585.
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Cooper, Rebecca Elizabeth. "Bacterial iron and manganese reduction driven by organic sulfur electron shuttles." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54894.
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Dissimilatory metal-reducing bacteria (DMRB) play an important role in the biogeochemical cycling of metals. DMRB are unique in that they possess the ability to couple metal reduction with their metabolism. Microbial Fe(III) respiration is a central component of a variety of environmentally important processes, including the biogeochemical cycling of iron and carbon in redox stratified water and sediments, the bioremediation of radionuclide-contaminated water, the degradation of toxic hazardous pollutants, and the generation of electricity in microbial fuel cells. Despite this environmental and evolutionary importance, the molecular mechanism of microbial Fe(III) respiration is poorly understood. Current models of the molecular mechanism of microbial metal respiration are based on direct enzymatic, Fe(III) solubilization, and electron shuttling pathways. Fe(III) oxides are solid at circumneutral pH and therefore unable to come into direct contact with the microbial inner membrane, these bacteria must utilize an alternative strategy for iron reduction. Reduced organic compounds such as thiols are prominent in natural environments where DMRB are found. These thiol compounds are redox reactive and are capable of abiotically reducing Fe(III) oxides at high rates
S. oneidensis wild-type and ΔluxS anaerobic biofilm formation phenotypes were examined under a variety of electron donor-electron acceptor pairs, including lactate or formate as the electron donor and fumarate, thiosulfate, or Fe(III) oxide-coated silica surfaces as the terminal electron acceptor. The rates of biofilm formation under the aforementioned growth conditions as well as in the presence of exogenous thiol compounds indicate that ∆luxS formed biofilms at rates only 5-10% of the wild-type strain and ∆luxS biofilm formation rates were restored to wild-type levels by addition of a variety of exogenous compounds including cysteine, glutathione, homocysteine, methionine, serine, and homoserine. Cell adsorption isotherm analyses results indicate that wild-type is can attach to the surface of hematite particles attachment , but ΔluxS is unable to attach the hematite surfaces. These results indicate that biofilm formation is not required for Fe(III) oxide reduction by S. oneidensis
∆luxS anaerobic biofilm formation rates were restored to wild-type levels by addition of exogenous auntoinducer-2 (AI-2), a by-product of homocysteine production in the Activated Methyl Cycle. This discovery led to subsequent experiments performed to detect the production and utilization of AI-2 by wild-type and ∆luxS strains under aerobic and anaerobic conditions. AI-2 production experiments showed wild-type, but not ΔluxS, was capable of producing AI-2. The addition of exogenous S. oneidensis and Vibrio harveyi-produced AI-2 to wild-type and ∆luxS resulted in the swift depletion of AI-2 from the media. These results provide evidence that S. oneidensis can produce AI-2 and subsequently utilize its’ own AI-2 as well as AI-2 produced by other bacteria as a carbon and electron source in the absence of preferred carbon sources.
S. oneidensis produces and secretes a suite of extracellular thiols under anaerobic Fe(III)-reducing and Mn(III) and Mn(IV)-reducing conditions including cysteine, homocysteine, glutathione, and cyteamine. Exogenous thiols produced by S. oneidensis are intermediates of the Activated Methyl Cycle (AMC) and Transulfurylation Pathway (TSP). Reduced and oxidized thiols were detected, indicating that the thiols are in a constant state of flux between the reduced and oxidized forms and that the concentration of reduced thiols to its’ oxidized counterpart is indicative of the state of metal reduction by the microorganisms. Respiratory phenotypes Based on Fe(III) and Mn(IV) respiratory phenotypes observed in the AMC and TSP pathway mutants (∆luxS, ∆metB, ∆metC and ∆metY) we can infer that cysteine, glutathione, and cysteamine contribute to metal reduction by serving as efficient electron shuttling molecules, while homocysteine is critical for maintenance of the AMC, propagation of thiol biosynthesis, and maintenance of cellular metabolism via the AMC intermediate SAM. Furthermore, these findings suggest that all metal-reducing bacteria require thiol formation to reduce solid metal oxides. Direct contact mechanism is not the dominant means through electrons are transferred and metals are reduced, instead electron shuttles are the maid reduction mechanism.
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Biley, Chris. "Thermodynamic and kinetic modelling of iron (III) reduction with sulfur dioxide gas." Thesis, Stellenbosch : Stellenbosch University, 2015. http://hdl.handle.net/10019.1/97120.
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Thesis (PhD)--Stellenbosch University, 2015.ENGLISH ABSTRACT: Recent developments in the atmospheric treatment of low-grade nickel laterite ores at Anglo American plc has culminated in the conceptual iron-focused laterite (ARFe) process. In addition to the recovery of nickel and cobalt from laterite ore, this process uniquely aims to recover iron as a saleable by-product. The reduction of soluble iron(III) (Fe(III)) by sulfur dioxide gas (SO2) is central to the ARFe concept and represents a complex, multiphase system involving simultaneous gas-liquid mass transfer, thermodynamic speciation and chemical reaction. The chemistry of iron-containing systems is generally poorly understood and accurately predicting their behaviour is challenging, especially under aggressive hydrometallurgical conditions. The primary objective of this work is the development of an engineering model capable of describing the rate and extent of ferric reduction with SO2 under conditions typical of the ARFe process. Thermodynamic considerations provide a rigorous framework for the interpretation of chemical reactions, however little experimental data are openly available for the associated solution species in acidic iron sulfate systems. A key contribution of this work, and critical for the development of the overall model, is the direct measurement of speciation in iron sulfate solutions. Raman and UV-vis spectroscopy were utilised to make direct speciation measurements in the various subsystems of the Fe2(SO4)3-FeSO4-H2SO4-H2O system that were previously unavailable in the open literature. The FeSO+4 and Fe(SO4)– 2 species were explicitly identified and measurements were supported and rationalised by static computational quantum mechanical calculations and ultimately permit the calibration of a robust, ion-interaction solution model with the explicit recognition of the important solution species up to 1.6 mol/kg Fe2(SO4)3, 0.8 mol/kg H2SO4 over 25 – 90 C. Batch and continuous Fe(III) reduction kinetics were measured and the effects of initial Fe2(SO4)3 and H2SO4 concentrations, temperature and in-situ neutralisation quantified. The retardation effect of sulfuric acid was observed to be the most significant factor influencing the initial reaction rate and the achievable extent of reduction at fixed residence time, which varied between about 20 and 80 % after 180 minutes of reaction. A reaction mechanism that is limited by the slow ligand-to-metal electron transfer in the FeIIISO+3 solution species’ decomposition is proposed and spectroscopic measurements and computational quantum mechanical calculations are used to support this mechanism. A kinetic model, comprising a system of differential mass-balance equations, is incorporated into the thermodynamic framework. This reaction model permits the prediction of kinetic profiles over the full range of experimental conditions and can be incorporated into more elaborate simulation models of the ARFe circuit. The specific original contributions of this work are • The direct measurement of aqueous speciation in the Fe2(SO4)3-H2SO4-H2O system by Raman and UV-vis spectroscopy • The development of a modelling framework to characterise speciation, activity coefficients and solubility in the mixed Fe2(SO4)3-FeSO4-H2SO4-H2O system. • The measurement of Fe(III) reduction kinetics using SO2 in concentrated sulfate solutions as a function of initial composition and temperature. • The development of a solution reaction model of Fe(III) reduction with SO2 that accurately predicts the solution speciation and reaction rate with time as a function of composition and temperature. Lastly, the vast complexity of industrial systems will nearly always result in a lack of specific experimental data that are required for the development of phenomenological models. This work emphasises the crucial role that engineering studies hold in the generation of such data to derive maximum practical value for industrial process development and optimisation.
AFRIKAANSE OPSOMMING: Onlangse ontwikkelinge in die atmosferiese behandeling van lae-graad nikkel lateriet erts by Anglo American plc het gelei tot die konseptuele yster gefokus lateriet (ARFe) proses. Bykommend tot die herwinning van nikkel en kobalt uit laterite erts is hierdie proses uniek en daarop gemik om yster te herwin as ’n verkoopbare by-produk. Die vermindering van oplosbare yster(III) (Fe(III)) met swaeldioksied (SO2) is sentraal tot die ARFe konsep en verteenwoordig ’n komplekse, multifase stelsel wat gelyktydige gas-vloeistof massa-oordrag, termodinamiese spesiasie en chemiese reaksie behels. Die oplossingschemie van ysterstelsels word, oor die algemeen, swak verstaan en om hul gedrag akuraat te voorspel is ’n uitdaging, veral onder aggressiewe hidrometallurgiese kondisies. Die primêre doel van hierdie werk is die ontwikkeling van ’n ingenieursmodel wat die tempo en omvang van yster(III) vermindering met SO2 onder tipiese ARFe proses toestande beskryf. Termodinamiese oorwegings stel ’n streng raamwerk voor vir die interpretasie van chemiese reaksies, alhoewel daar egter min eksperimentele data openlik beskikbaar is vir die gepaardgaande oplossing spesies in suur yster(III) sulfaat stelsels. ’n Belangrike bydrae van hierdie werk, en van kritieke belang vir die ontwikkeling van die algehele model, is die direkte meting van spesiasie in yster(III) sulfaat oplossings. Raman en UV-vis spektroskopie is gebruik om direkte spesiasie metings te maak in die verskillende subsisteme van die Fe2(SO4)3-FeSO4-H2SO4-H2O stelsel wat voorheen nie in die oop literatuur beskikbaar was nie. Die FeSO+4 en Fe(SO4)– 2 spesies is ekplisiet geïdentifiseer, terwyl die metings ondersteun en gerasionaliseer is deur statiese kwantummeganiese berekeninge wat uiteindelik die kalibrasie van ’n robuuste, ioon-interaksie model tot gevolg hê wat ook die belangrike oplossingspesies duidelik beklemtoon tot en met 1.6 mol/kg Fe2(SO4)3, 0.8 mol/kg H2SO4 en tussen 25 – 90°C. Enkellading en kontinue yster(III) verminderingskinetika is gemeet en die gevolge van die aanvanklike Fe2(SO4)3 en H2SO4 konsentrasies, temperatuur en in-situ neutralisasie is gekwantifiseer. Die waargeneemde vertragingseffek van swaelsuur is die mees beduidende faktor wat die aanvanklike reaksietempo en die haalbare reaksie omvangsvermindering na ’n vaste residensietyd van 180 minute bepaal, wat wissel tussen ongeveer 20 en 80%. ’n Reaksiemeganisme word voorgestel wat beperk word deur die stadige ligand-totmetaal elektronoordrag in ontbinding van die Fe(III)SO+3 oplossing-spesies en wat verder deur spektroskopiese metings en kwantummeganiese berekenings ondersteun word. A kinetiese model, wat bestaan uit ’n stelsel van gedifferensieerde massa-balans vergelykings, is in die termodinamiese raamwerk geïnkorporeer. Hierdie reaksie-model laat die voorspelling van kinetiese profiele toe oor die volle omvang van die eksperimentele toestande en kan in meer uitgebreide simulasie modelle van die ARFe proces geinkorporeer word. Die spesifieke en oorspronklike bydraes van hierdie werk is • Die direkte meting van die spesiasie in die Fe2(SO4)3-H2SO4-H2O stelsel deur Raman en UV-vis spektroskopie • Die ontwikkeling van ’n modelraamwerk om spesiasie, aktiwiteitskoëffisiënte en oplosbaarheid in die gemengde Fe2(SO4)3-FeSO4-H2SO4-H2O stelsel te karakteriseer. • Die meting van yster(III) vermideringskinetieka deur SO2 in gekonsentreerde sulfate oplossings te gebruik as ’n funksie van die aanvanklike samestelling en temperatuur. • Die ontwikkeling van ’n oplossingsreaksie-model van yster(III) vermindering met SO2 wat die oplossing-spesiasie en reaksietempo met die tyd as ’n funksie van samestelling en temperatuur akkuraat voorspel. Laastens, die oorgrote kompleksiteit van industriële stelsels sal byna altyd lei tot ’n gebrek van spesifieke eksperimentele data wat nodig is vir die ontwikkeling van fenomenologiese modelle. Hierdie werk beklemtoon die belangrike rol wat ingenieursstudies speel in die generasie van data wat sodanig tot maksimum praktiese waarde vir industriële prosesontwikkeling en optimalisering lei.
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Hennig, Sandra Elisabeth. "Insights into the ATP-dependent reductive activation of the Corrinoid/Iron-Sulfur Protein of Carboxydothermus hydrogenoformans." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2014. http://dx.doi.org/10.18452/16984.
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Die Verknüpfung einer exergonischen mit einer endergonischen Reaktion zur Ermöglichung der letzteren ist eine in biologischen Systemen weit verbreitete Strategie. Energetisch benachteiligte Elektronenübertragungsreaktionen im Rahmen der reduktiven Aktivierung von Nitrogenasen, Radikal-abhängigen β,α-Dehydratasen, der zu diesen verwandten Benzoyl-CoA-Reduktasen und diversen Cobalamin-abhängigen Methyltransferasen sind gekoppelt an die Hydrolyse von ATP. Der Methylgruppentransfer des reduktiven Acetyl-CoA-Weges von Carboxydothermus hydrogenoformans erfordert den Co(I)-Zustand des Corrinoid/Eisen-Schwefel Proteins (CoFeSP). Um diese superreduzierte Form nach einer oxidativen Inaktivierung zu regenerieren ist ein „Reparaturmechanismus“ erforderlich. Ein offenes Leseraster (orf7), welches möglicherweise für eine reduktive Aktivase von Corrinoid Enzymen (RACE) kodiert, wurde in dem Gencluster der am reduktiven Acetyl-CoA-Weg beteiligten Proteine entdeckt. Im Rahmen dieser Arbeit wurde dieses potenzielle RACE Protein biochemisch und strukturell charakterisiert und die ATP-abhängige reduktive Aktivierung von CoFeSP untersucht. Auf Grundlage der in dieser Arbeit gewonnenen Ergebnisse wurde ein Mechanismus für die ATP-abhängige Aktivierung entworfen. Dieser gibt Einblicke wie die durch ATP-Hydrolyse bereitgestellte Energie einen energetisch ungünstigen Elektronentransfer ermöglichen kann. Hierzu kombiniert RACo das Ausgleichen von Bindungsenergien mit Modulationen am Elektronenakzeptor. Eine vergleichbare Strategie wurde bisher in keinem anderen ATP-abhängigen Elektronenübertragungssystem wie dem von Nitrogenasen, Radikal-abhängigen β,α-Dehydratasen oder Benzoyl-CoA-Reduktasen beobachtet und könnte ein für RACE Proteine allgemein gültige Eigenschaft darstellen.The principle of coupling an exergonic to an endergonic reaction to enable the latter is a widespread strategy in biological systems. Unfavoured electron transfer reactions in the reductive activation of nitrogenases, radical-dependent β,α-dehydratases and the related benzoyl- CoA reductases, as well as different cobalamin-dependent methyltransferases are coupled to the hydrolysis of ATP. The reductive acetyl-CoA pathway of Carboxydothermus hydrogenoformans relies on the superreduced Co(I)-state of the corrinoid/iron-sulfur protein (CoFeSP) that requires a “repair mechanism” in case of incidental oxidation. An open reading frame (orf7) coding for a putative reductive activase of corrinoid enzymes (RACE) was discovered in the gene cluster of proteins involved in the reductive acetyl-CoA pathway. In this work, this putative RACE protein was biochemically and structurally characterised and the ATP-dependent reductive activation of CoFeSP was investigated. Based on the results of this study, a mechanism for the ATP-dependent reactivation of CoFeSP was deduced providing insights into how the energy provided by ATP could trigger this unfavourable electron transfer. The reductive activator of CoFeSP combines balance of binding energies and modulations of the electron acceptor to promote the uphill electron transfer to CoFeSP. A comparable strategy has not been observed in other ATP-dependent electron transfer systems like nitrogenases, radical-dependent β,α-dehydratases and benzoyl- CoA reductases and could be a universal feature of RACE proteins.
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Holanda, Roseanne. "A study of novel acidophilic Firmicutes and their potential applications in biohydrometallurgy." Thesis, Bangor University, 2018. https://research.bangor.ac.uk/portal/en/theses/a-study-of-novel-acidophilic-firmicutes-and-their-potential-applications-in-biohydrometallurgy(50564a50-13ed-4663-bec0-efa149957493).html.
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The application of biotechnologies in the mining sector has intensified over the last 30 years, driven by the increasing demand for metals associated with the rise in energy costs and the awareness for environmentally responsible mining practices. Acidophilic prokaryotes play an important role in biohydrometallurgy, facilitating the solubilisation and recovery of base metals from ores and waste materials. The potential of novel acidophiles of the phylum Firmicutes for applications in biohydrometallurgical processes is examined in this thesis. Eight strains of extremely acidophilic bacteria were studied and shown to belong to the proposed novel genus “Acidibacillus”. These had been isolated previously from several distinct global locations and were shown to be obligately heterotrophic bacteria with potential to carry out tasks critical to biomining such as regenerating ferric iron (by catalysing the dissimilatory oxidation of ferrous iron), generating sulfuric acid (by the oxidation of zero-valent sulfur and tetrathionate; two strains only), and removing potentially inhibitory dissolved organic carbon. These isolates also demonstrated the ability to catalyse the dissimilatory reduction of ferric iron in anaerobic conditions. Results obtained during this study provide the basis for future research to assess their potential roles in microbial consortia applied in the bio-processing of metal ores. A novel obligately anaerobic acidophilic Firmicute (strain I2511) isolated from sediment obtained from an abandoned copper mine, was characterised in terms of its phylogeny and physiology. This isolate formed a separated clade within the Firmicutes, and was considered to represent a novel candidate genus. It also displayed a unique set of physiological traits, distinct from currently validated species of acidophilic Firmicutes. The isolate was an obligate anaerobe that grew via zero-valent sulfur (ZVS) respiration, generating H2S over a wide pH range (1.8 - 5.0), and also catalysed the dissimilatory reduction of ferric iron. Strains of acidophilic sulfatereducing bacteria (aSRB), also Firmicutes, were shown to reduce ZVS at pH as low as 3. These aSRB, together with isolate I2511, populated a novel variant of a low pH sulfidogenic bioreactor. The “hybrid sulfidogenic bioreactor” (HSB) operated using both sulfate and ZVS as electron acceptors, and glycerol as electron donor. The bioreactor successfully remediated and recovered zinc from circum-neutral pH mine-impacted waters with distinct chemical composition collected from two abandoned lead/zinc mines in the U.K. The microbial consortium used in this system proved to be robust, in which the HSB generated H2S consistently under a wide pH range (2 – 7). Experiments demonstrated that H2S could also be generated abiotically in a non-inoculated low pH reactor, by the chemical reaction of ZVS and zero-valent iron to form iron sulfide, and the consequent acid dissolution of the latter. Operational costs and the advantages of biogenic and abiotic generation of H2S for recovery of transition metals from mine waters are discussed.
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Hennig, Sandra Elisabeth [Verfasser], Holger [Akademischer Betreuer] Dobbek, Erwin [Akademischer Betreuer] Schneider, and Peter [Akademischer Betreuer] Hildebrandt. "Insights into the ATP-dependent reductive activation of the Corrinoid/Iron-Sulfur Protein of Carboxydothermus hydrogenoformans / Sandra Elisabeth Hennig. Gutachter: Holger Dobbek ; Erwin Schneider ; Peter Hildebrandt." Berlin : Humboldt Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2014. http://d-nb.info/105259686X/34.
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Pham, Huynh Anh. "The dynamics of microbial ferric and sulfate reduction in acidic mine lake sediments and their impact on water quality." University of Western Australia. School of Environmental Systems Engineering, 2009. http://theses.library.uwa.edu.au/adt-WU2010.0004.
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[Truncated abstract] Acidic mine lakes are formed as a result of the oxidation and dissolution of metal sulfide minerals and are primarily characterized by low pH values of 2 4. Many strategies for the bioremediation of acidic mine lakes depend on the alkalinity generation capabilities of microbial ferric and/or sulfate reducing bacteria. However nearly all mine lakes are oligotrophic, with very low concentrations of available organic carbon and nutrients; all required for healthy microbial growth. There is also an unusual class of mine lakes characterized by low concentrations of organic carbon and also very low concentrations of dissolved iron and sulfate. Our ability to promote microbial activity in these systems is especially challenging. This study focuses on one of these systems, Lake Kepwari, a coal mine lake in Western Australia. Numerical modeling of remediation strategies is an efficient way of testing scenarios prior to expensive in-field trials. However such modeling relies on good descriptions of microbial processes, including kinetic parameterizations of ferric and sulfate reduction. There has been little research to date on the study of kinetic parameterizations of the chemical and biological alkalinity generation in acidic mine lakes. The objectives of this thesis were to investigate the viability of microbial ferric and sulfate reduction in an ultraoligotrophic, acidic mine lake, to assess the impact of these microbial processes on water quality and to parameterize the Dual Monod kinetics of neutralization under dual limitation conditions. Molecular analyses including most probable number, DNA extraction, polymerase chain reaction, polymerase chain reaction denaturing gradient gel electrophoresis were used to examine the microbial communities in the lake sediments. ... The Monod maximum specific microbial growth rates with respect to dissolved organic carbon and ferric, and as determined in batch experiments, were 0.07 ± 0.01 and 0.048 ± 0.02 day-1, respectively, and their corresponding Monod half saturation constants and were 14.37 and 5.6 mmol L-1. The Monod maximum consumption rates under ferric and OC limitation were also estimated. The Monod maximum specific microbial growth rates with respect to dissolved organic carbon and sulfate, , and were 0.05 ± 0.01, 0.08 ± 0.01 and 0.07 ± 0.02 day-1, respectively, and their corresponding Monod half saturation constants, and were 75.5, 131.8 and 10.2 mmol L-1. The Monod maximum consumption rates under sulfate and OC limitation were also estimated. The results of this study suggest that strategies for the remediation of ultraoligotrophic, acidic mine lakes may rely on microbial ferric and sulfate reduction, however additions of both organic carbon and sulfate/ferric are essential. These results can be immediately applied to mesocosm studies in outdoor enclosures and to the management of acidic mine lakes. Furthermore, this thesis has provided a new, valuable understanding on the Dual Monod kinetic parameterizations of neutralization for an ultraoligotrophic, acidic mine lake environment. These parameterizations are essential for the lake ecological models that will be used to investigate remediation scenarios for acidic mine lakes.
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Yuvaniyama, Pramvadee. "Biosynthesis of Iron-Sulfur Clusters." Diss., Virginia Tech, 1999. http://hdl.handle.net/10919/40388.
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It is not known whether biosynthesis of [Fe-S] clusters occurs through a spontaneous self-assembly process or an enzymatic process. However, in the Azotobacter vinelandii nitrogenase system, it has been proposed that NifS and NifU are involved in the mobilization of sulfur and iron necessary for nitrogenase-specific [Fe-S] cluster assembly. The NifS protein has been shown to have cysteine desulfurase activity and can be used to supply sulfur for the in vitro catalytic formation of [Fe-S] clusters. The activity of the NifU protein has not yet been established, but NifU could have functions complementary to NifS by mobilizing iron or serving as an intermediate site necessary for nitrogenase-specific [Fe-S] cluster assembly. A second iron-binding site within NifU was predicted to serve these functions because two identical [2Fe-2S] clusters that had previously been identified within the homodimeric NifU are tightly bound, and the NifU primary sequence is rich in cysteine residues. In this dissertation, I examined the possibility that NifU might mobilize iron or serve as an intermediate site for [Fe-S] cluster assembly, as well as the possibility that NifU could work in concert with NifS.
Primary sequence comparisons, amino acid substitution experiments, and biophysical characterization of recombinantly-produced NifU fragments were used to show that NifU has a modular structure. One module is contained in approximately the C-terminal half of NifU and provides the binding site for the [2Fe-2S] cluster previously identified (the permanent [2Fe-2S] cluster). Cysteine residues Cys¹³⁷, Cys¹³⁹, Cys¹⁷⁵, and Cys¹⁷⁵ serve as ligands to the [2Fe-2S] cluster. Another module (referred to as NifU-1) is contained in approximately the N-terminal third of NifU and provides a second iron-binding site (rubredoxin-like Fe(III)-binding site). Cysteine residues Cys35, Cys⁶², Cys¹⁰⁶>, and a putative non-cysteine ligand of unknown origin provide coordination to the iron at this site. The significance of these iron-binding sites was also accessed by showing that cysteine residues involved in providing the rubredoxin-like Fe(III)-binding site and those that provide the [2Fe-2S] cluster binding site are all required for the full physiological function of NifU. The two other cysteine residues contained within NifU, Cys²⁷² and Cys²⁷⁵, are neither necessary for binding iron at either site nor are they required for the full physiological function of NifU.
These results provide the basis for a model where iron bound at the rubredoxin-like sites within NifU-1 (one iron per monomer) is proposed to be destined for [Fe-S] cluster formation. It was possible to find in vitro evidence supporting this idea. First, it was demonstrated that NifU and NifS are able to form a transient complex. Second, in the presence of NifS as well as L-cysteine and a reducing agent, the Fe(III) contained at the rubredoxin-like sites within the NifU-1 or NifU homodimer can rearrange to form a transient [2Fe-2S] cluster between the two subunits. Finally, a mutant form of NifU-1 was isolated that appears to be trapped in the [2Fe-2S] cluster-containing form, and this [2Fe-2S] cluster (the transient [2Fe-2S] cluster) can be released from the polypeptide matrix upon reduction with dithionite.
Previous work has shown that the permanent [2Fe-2S] clusters of as-isolated NifU are in the oxidized form but can be reduced chemically. The transient [2Fe-2S] cluster formed between rubredoxin-like sites, in contrast, is reductively labile. If the transient cluster serves as an intermediate [Fe-S] cluster to be destined for [Fe-S] cluster assembly, I propose that the permanent [2Fe-2S] clusters could have redox roles participating in either one or all of the following events. The permanent [2Fe-2S] clusters could have a redox function in the acquisition of iron for initial binding at the mononuclear sites. They could also provide reducing equivalents for releasing the transient [2Fe-2S] cluster. In addition, upon releasing the transient [2Fe-2S] cluster, the permanent [2Fe-2S] clusters could provide the appropriate oxidation state of the irons to be destined to nitrogenase metallocluster core formation.
Finally, because proteins homologous to NifU and NifS are widely distributed in nature, it is suggested that the mechanism for NifU and NifS in the formation of nitrogenase-specific [Fe-S] clusters could represent a general mechanism for [Fe-S] cluster synthesis in other systems.Ph. D.
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Wu, Shu-Pao. "Iron-sulfur cluster biosynthesis. Iron-sulfur cluster transfer from Holo ISU and ISA to Apo Fd." The Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=osu1078866123.
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Wu, Shu-Pao. "Iron-sulfur cluster biosynthesis. Iron-sulfur cluster transfer from holo ISU and ISA to apo ferredoxin." Connect to this title online, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1078866123.
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Thesis (Ph. D.)--Ohio State University, 2004.Title from first page of PDF file. Document formatted into pages; contains xx, 161 p.; also includes graphics Includes bibliographical references (p. 153-161). Available online via OhioLINK's ETD Center
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Yucel, Mustafa. "New perspectives in sulfur-iron cycling at the ocean-seafloor interface the Black Sea sediments and deep-sea hydrothermal vents /." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 203 p, 2010. http://proquest.umi.com/pqdweb?did=1997524241&sid=5&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Fawcett, Sarah E. J. "Reactions of iron-sulfur clusters in proteins." Thesis, University of Oxford, 1998. https://ora.ox.ac.uk/objects/uuid:87b10a8e-67a8-476b-ae20-49e6892051f5.
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This thesis describes the investigation of reactions of iron-sulfur clusters in proteins using direct electrochemistry. The influence of potential on metal uptake to generate the [M3Fe-4S] cluster from the [3Fe-4S] cluster of Desulfovibrio africanus Fd III is studied. The influence of potential was complex: rapid and reversible interconversions (M = Fe and Zn) occurred only between the states [M3Fe-4S]2+ and [3Fe-4S]0, with [3Fe-4S]1+ having little affinity for M. The [M3Fe-4S]1+ cubanes and the hyper-reduced [3Fe-4S]2- were relatively unreactive. The reactivity of the transformed cluster, [M3Fe-4S] (M = Fe, Zn, Co), from the 7Fe Fd of Desulfovibrio africanus was studied and was found to react with a number of small thiol molecules, indicating that either ligand addition or exchange takes place at the transformed M site of the cluster. No reaction was observed with oxygenic ligands. In all cases, with the exception of imidazole, negative shifts in reduction potentials were observed. Reactions of the [2Fe-2S] cluster from the ferredoxin of Clostridium pasteurianum and a number of site-directed mutants of this ferredoxin are studied. The cysteine ligands of the cluster were identified and evidence was obtained for serinate ligation of the cluster in a number of mutants. The reduction potentials of these serinateligated clusters were found to have a notable dependence on pH. A mutant ferredoxin containing only three cysteine ligands was investigated, which was found to interact with an exogenous thiolate ligand and, in addition, displayed a second reduction couple, indicating the formation of the [2Fe-2S]0 state. Reactions of the [3Fe-4S] cluster and various [M3Fe-4S] adducts, from the ferredoxin of the hyperthermophile Pyrococcus furiosus, are studied. The [3Fe-4S] cluster exhibited a complex pH dependence over a wide pH range. The formation of the hyper-reduced [3Fe-4S]2- state was observed, which required 3H+ for the overall 3e⧠reduction from [3Fe-4S]1+. Metal uptake reactions for M = Fe, Zn, Cd, were found to be slower than for its mesophilic counterpart, the 7Fe Fd III from Desulfovibrio africanus. Conversely, Tl uptake was found to be rapid, suggesting that co-ordination of Tl does not require reorganisation of the protein structure.
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O'Carroll, Ina Puleri. "Assembly of Iron-Sulfur Clusters In Vivo." Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/26289.
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Iron-sulfur [Fe-S] clusters are protein cofactors that facilitate various life-sustaining biological processes. Their in vivo assembly is accomplished by three different systems known to date. These are: the NIF system which provides [Fe-S] clusters for nitrogenase and other nitrogen-fixing proteins, the SUF system which is induced during conditions of oxidative stress and iron starvation in E. coli, and the ISC system which serves as the housekeeping assembly apparatus. The latter is the focus of this dissertation and includes the proteins IscR, IscS, IscU, IscA, HscB, HscA, Fdx, and IscX. IscU is purified in its cluster-less (apo) form, but can serve as a scaffold to assemble [Fe-S] clusters in vitro in the presence of excess iron and sulfide. To test the scaffold hypothesis and gain insight into the events that occur during [Fe-S] cluster assembly and delivery, we developed two methods that allow the isolation of IscU and other ISC proteins in vivo. In the first method, Azotobacter vinelandii IscU is isolated from its native host, whereas in the second, it is isolated recombinantly from E. coli using a vector that allows expression of the entire isc operon. We found that IscU exists in vivo in two forms: apo-IscU and [2Fe-2S]2+ cluster-loaded IscU which are believed to be conformationally distinct. Both transient and stable IscU-IscS complexes were identified, indicating that the two proteins interact in vivo in a manner that involves their association and dissociation. The [2Fe-2S]2+-IscU species was present as a single entity, whereas significant amounts of apo-IscU were found associated with IscS, suggesting that IscU-IscS dissociation is triggered by the completion of [2Fe-2S] clusters. Both apo and [2Fe-2S]2+-IscU were predominantly monomeric whereas IscU-IscS complexes were determined to have an α2β2 composition. IscU was purified in the absence of the chaperones HscA and HscB and was also shown to accommodate a [2Fe-2S]2+ cluster similar to the one bound to IscU isolated from wild type cells. The findings suggest that [2Fe-2S]2+-IscU exists in one conformation in vivo and that any conformational changes on IscU are exerted after [2Fe-2S] cluster formation. In silico studies showed that a flexible loop containing the conserved LPPVK motif, which is responsible for interactions with HscA, may facilitate cluster exposure to either mediate its delivery to acceptor proteins or participation in the construction of [4Fe-4S] clusters. Experiments with NfuA, a protein similar to the C-terminal domain of NifU, demonstrated that NfuA and similar proteins might serve as [Fe-S] cluster carriers to accomplish the efficient delivery of nascent cofactors to the various recipient proteins.Ph. D.
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Gelling, Cristy Lee Biotechnology & Biomolecular Sciences Faculty of Science UNSW. "Tetrahydrofolate and iron-sulfur metabolism in Saccharomyces cerevisiae." Publisher:University of New South Wales. Biotechnology & Biomolecular Sciences, 2008. http://handle.unsw.edu.au/1959.4/43270.
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Tetrahydrofolate-mediated one-carbon metabolism is required for the biosynthesis of many central metabolites, including some amino acids, nucleobases, and nucleotides, and hence dysfunction of one-carbon metabolism is associated with many human diseases and disorders. The mitochondrial glycine decarboxylase complex (GDC) is an important component of one-carbon metabolism, generating 5,10-methylene-tetrahydrofolate (5,10-CH2-H??4folate) from glycine. Previous work has shown that the genes encoding the unique sub-units of the Saccharomyces cerevisiae GDC (GCV1, GCV2 and GCV3) are regulated in response to changes in the levels of cytosolic 5,10-CH2-H??4folate (Piper et al., 2000). Given the centrality of 5,10-CH2-H??4folate to many aspects of metabolism, it was hypothesised that other genes may be regulated by the same mechanism. Using microarray analysis of S. cerevisiae under a number of conditions that affect 5,10-CH2-H??4folate levels, the ??one-carbon regulon??, a group of genes that were co-regulated with the GCV genes was identified. The one-carbon regulon corresponds closely to genes whose promoters are bound by the purine biosynthesis regulator Bas1p, but not all one-carbon regulon members are significantly purine regulated. Genetic approaches demonstrated that the one-carbon unit response and the purine response are distinct, though both depend on the presence of Bas1p. This demonstrated that the close metabolic connections of one-carbon and purine metabolism are reflected in over-lapping, but separable regulatory mechanisms. The identity of the sensor of one-carbon unit depletion remains unknown, but in the course of investigation of the candidate regulator Caf17p, it was demonstrated that Caf17p is in fact involved in Fe/S cluster protein maturation. Examination of the effects of Caf17p depletion revealed that Caf17p is required for the function and maturation of the related mitochondrial Fe/S proteins aconitase and homoaconitase, as well as the function of, but not de novo iron incorporation into, the mitochondrial radical-SAM Fe/S protein biotin synthase. Because other Fe/S proteins were unaffected, Caf17p appears to be a specialised Fe/S maturation factor. The presence of a putative H4folate binding site indicates that Caf17p may constitute a metabolic link between one-carbon and iron metabolism.
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Friemann, Rosmarie. "Structure-function studies of iron-sulfur enzyme systems /." Uppsala : Dept. of Molecular Biology, Swedish Univ. of Agricultural Sciences, 2004. http://epsilon.slu.se/a504-ab.html.
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Adedeji, Dolapo A. Duin Evert C. "Isoprenoid synthesis new roles for iron sulfur clusters /." Auburn, Ala., 2007. http://repo.lib.auburn.edu/Send%2002-04-08/ADEDEJI_DOLAPO_4.pdf.
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Tilley, Gareth John. "Electrochemical investigations into iron-sulfur cluster containing proteins." Thesis, University of Oxford, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365300.
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Bates, Katie. "Unusual reactivity of synthetic iron-sulfur based clusters." Thesis, University of Newcastle Upon Tyne, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492081.
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Dizin, Eric Michel. "Insights On Iron-Sulfur Cluster Assembly Donor Proteins." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1208532379.
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Ding, Shu. "Thermodynamic studies on iron-sulfur cluster assembly proteins." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1316472363.
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Qi, Wenbin. "Studies of Iron-Sulfur Cluster Biogenesis and Trafficking." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1325099104.
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Li, Jingwei. "Studies of Iron Sulfur Cluster Maturation and Transport." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1429695967.
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Friemann, Rosmarie. "Structure-function studies of iron-sulfur enzyme systems /." Uppsala : Dept. of Molecular Biology, Swedish Univ. of Agricultural Sciences, 2005. http://epsilon.slu.se/a504.pdf.
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Shiers, Denis. "Iron and sulfur utilisation patterns in chemolithotrophic cultures." Thesis, Shiers, Denis (2012) Iron and sulfur utilisation patterns in chemolithotrophic cultures. PhD thesis, Murdoch University, 2012. https://researchrepository.murdoch.edu.au/id/eprint/12863/.
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In this study, the growth and behaviour of chemolithotrophic organisms in the presence of both ferrous and tetrathionate ions was investigated. Given the impact of chemolithotrophic metabolic activity upon the chemistry and leaching of mineral sulfide systems, investigations were conducted to determine the effects of solution variables on substrate utilisation.
A set of eight organisms, capable of oxidising ferrous ions or reduced sulfur compounds, were adapted to ferrous or tetrathionate ions. These cell lines were cultured in media containing 2.5 mM of tetrathionate, with either high or low concentrations of ferrous ions present. Sb.xthermosulfidooxidans and M. hakonensis grew in a diauxic growth pattern utilising ferrous ions preferentially, irrespective of adaptive history or ferrous concentration. At. ferrooxidans, Sb. acidophilus, Sb.xsibiricus, Sb. thermotolerans, A.xbrierleyi and S. metallicus exhibited simultaneous substrate utilisation and a single phase of growth under at least one of the four conditions tested. Preferential utilisation of tetrathionate was not observed under any of the four conditions tested. Planktonic cell numbers were not consistently proportional to the total quantity of the reduced substrate(s) oxidised.
Reduced sulfur species were detected during batch culture growth of At. caldus on tetrathionate. Formation of elemental sulfur, thiosulfate, sulfite, penta- and hexathionate were consistent with the enzymatic hydrolysis of tetrathionate and subsequent chemical reactions. Growth yields were comparatively low with an average value of 3.53 g(dry wt.) mol(S4O6)-1. However, a significant quantity of reduced organic material was detected dissolved in solution. Yield data obtained from this study was compared with other reports and analysed using a thermodynamic framework derived from studies of heterotrophic growth. This analysis indicated that the conserved substrate had a sulfur(IV) atom oxidised to sulfur(VI).
The addition of nitrate significantly modified substrate oxidation patterns in a growth medium containing ferrous and tetrathionate ions. Ferrous ion oxidation processes were inhibited to a greater extent than tetrathionate utilisation. Tetrathionate-adapted cultures of Sb. acidophilus and Sb. sibiricus demonstrated preferential oxidation of tetrathionate at nitrate concentrations of 20–40 mM. Iron-adapted cultures of M.xhakonensis preferentially oxidised ferrous ions in the presence of nitrate at all concentrations where growth was observed. Responses of other test species varied, depending on the nitrate concentration and adaptive history of the organism.
Nitrate was added to control the redox potential of the solution in cultures bioleaching chalcopyrite. Redox potentials were not controlled at 30 and 45 °C. Copper extraction was equal to, or less than that seen in cultures without nitrate present. The addition of nitrate to cultures at 60 °C maintained the redox potential between 430–460 mV (Ag/AgCl). Copper extraction in these systems was increased compared with cultures where nitrate was absent.
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Bridge, Toni A. M. "Iron reduction by acidophilic bacteria." Thesis, Bangor University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.295276.
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Lau, Ngai Ting. "Catalytic reduction of sulfur dioxide and nitric oxide /." View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?CENG%202006%20LAU.
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Yoon, Taejin. "Functionaland structural studies of human frataxin: An iron chaperone protein for mitochondrial iron-sulfur cluster and heme biosyntheses." The Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=osu1124287807.
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Dembowa, Aneta. "Synthesis and Characterization of Amphiphilic Iron-Sulfur Core Dendrimers." NCSU, 2005. http://www.lib.ncsu.edu/theses/available/etd-01022005-192535/.
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Synthesis of water soluble carboxylate-terminated Fe4S4-core was carried out. Convergent method was chosen to build three generations of dendrons. Several synthetic schemes were explored. The syntheses were conducted with 4,4-bis(hydroxyphenyl)penthanol as a repeat unit and N,N-dimethyl thiocarbamate and methyl ester or methoxy-methyl as protecting groups. The conditions for deprotection and ligand exchange have been proposed. 1H, 13C and MALDI-MS were used to characterize synthesized molecules.
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Roessler, Maxie M. "EPR investigations of iron-sulfur cluster relays in enzymes." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:ac6fa892-f54a-490d-927b-161231f00777.
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Electron paramagnetic resonance (EPR) spectroscopy is a powerful tool for obtaining structural information about chemical centres with unpaired electrons. In complex biological systems, EPR spectroscopy can be used to probe these paramagnetic centres and the long-range interactions between them. This thesis investigates two important types of enzymes, and in particular the role of the iron-sulfur electron-transfer centres they contain, with a variety of EPR techniques. Complex I (NADH:Ubiquinone Oxidoreductase) plays a key role in the electron transfer chain essential to the formation of ATP, and its malfunction has been related to numerous human diseases. It is a giant enzyme that contains the longest relay of iron-sulfur clusters known. EPR experiments conducted on complex I from bovine mitochondria yield crucial insight into the mechanism of efficient long-range electron transfer and bring us a step closer to understanding the functioning of this important complex. Hydrogenases are produced by micro-organisms and catalyse the reversible oxidation of H2. Most hydrogenases, including Hyd-2 from Escherichia coli, are very air-sensitive, but some, including E. coli Hyd-1 and Salmonella Hyd-5, are able to function in the presence of atmospheric levels of O2. Understanding the origins of this 'O2-tolerance' is of paramount importance if hydrogenases are to be exploited in future energy technologies. In this thesis, native E. coli Hyd-1 and Hyd-2, Salmonella Hyd-5, as well as O2-tolerant and O2-sensitive variants of E. coli Hyd-1 are characterised using EPR. The EPR investigations elucidate properties of the active site and the electron-transfer relay and, in conjunction with other techniques, reveal structural and mechanistic details of how a highly unusual iron-sulfur cluster in the electron-transfer chain enables some hydrogenases to sustain catalytic activity in the presence of O2.
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Warek, Ujwala. "Genes from Arabidopsis involved in iron-sulfur cluster biogenesis." Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/29847.
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Iron sulfur [Fe-S] proteins are essential components of many major biological processes including electron transport, respiration, photosynthesis, hormone biosynthesis, and environmental sensing. The process of [Fe-S] cluster assembly in living cells is a controlled mechanism that is highly conserved across all kingdoms. Considerable progress has been made in deciphering this mechanism in bacteria, yeast, and mammals. The key players are the NifS/IscS/SufS proteins, which act as the sulfur donor, and the NifU/IscU/SufU proteins, which serve as a scaffold that binds Fe and upon which the cluster is assembled. Additional proteins are involved in the maturation and transport of the clusters. In eukaryotes there is redundancy in the proteins involved in this mechanism and the process is compartmentalized.
Not much is known about the [Fe-S] cluster assembly mechanism in plants. In addition to the redundancy and compartmentalization seen in this machinery in eukaryotes, plants present a further challenge by offering chloroplasts as an additional site for [Fe-S] cluster assembly. The objective of this project has been to characterize Arabidopsis AtNFS1 and AtISU1-3, which show high homology to NifS/IscS and NifU/IscU, respectively, and are hypothesized to be key players in [Fe-S] cluster biogenesis in plants. Subcellular localization results of the AtNFS1 and AtISU1-3 proteins fused to GFP from this study are consistent with the presence of dual machinery in plants, with both mitochondria and chloroplasts as sites for [Fe-S] cluster assembly. Furthermore, observations also showed that AtISU2 mRNA may be unstable. The results of these experiments, together with promoter analysis described in this dissertation using GUS fusions suggested that the genes encoding the AtISU scaffold proteins are regulated at the transcriptional and probably also at the posttranscriptional level.
Gene silencing experiments performed in this dissertation research using antisense and RNAi constructs indicated that these genes have the potential to impact respiration, photosynthesis, phytohormone biosynthesis, and environmental sensing, diverse processes that rely on [Fe-S] proteins. These observations, together with previous in vitro evidence that AtNFS1 and AtISU1 can participate in [Fe-S] cluster assembly, provide strong evidence that these proteins are part of two distinct cluster assembly systems that function in different subcellular locations and perhaps under different environmental conditions. Information gathered here has made it possible to begin developing a detailed model of [Fe-S] cluster biogenesis in plants.Ph. D.
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Luo, Wen-I. "The Role of Chaperones in Iron-Sulfur Cluster Biogenesis." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1325168796.
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Parker, Ceth Woodward. "Microbial Iron Reduction In The Development of Iron Formation Caves." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1542892784053378.
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Heim, Heiko Christian [Verfasser]. "Mimicking the active centers of iron sulfur proteins via reactions of iron sulfur cations in a linear octopole ion trap / Heiko Christian Heim." Ulm : Universität Ulm, 2017. http://d-nb.info/1135265712/34.
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Monsen, Bodil Elisabeth. "Iron ore concentrates : oxidation and reduction." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 1992. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-5747.
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Raud, Pettersson Laura. "Mathematical Modelling of Reversed Sulfur Reduction in Microaerobic Biofilm." Thesis, KTH, Skolan för kemi, bioteknologi och hälsa (CBH), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-278841.
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Alenezi, Khalaf. "Electrochemical transformation of alkanes, carbon dioxide and protons at iron-porphyrins and iron-sulfur clusters." Thesis, University of East Anglia, 2013. https://ueaeprints.uea.ac.uk/47965/.
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The work contained in this thesis focuses on (i) chemical and electrochemical alkane oxidation using Fe-porphyrin complexes as catalysts (ii) electrochemical and photoelectrochemical CO2 reduction using Fe-porphyrin complexes (iii) electrochemical and photoelectrochemical generation of hydrogen using iron-sulfur cluster. Chapter 1 gives a general overview of the electrochemical techniques which underpin the work presenedt in this thesis. Chapter 2 reports the chemical and electrocatalytic oxidation of hydrocarbons to alcohols and epoxides by using iron (III) porphyrins as catalysts. A series of new basket-handle thiolate Fe (III) porphyrins have been used to mediate anodic oxidation of hydrocarbons, specifically adamantane hydroxylation and cyclooctene epoxidation. The electrocatalytic and chemical catalytic activity oxidation of the thiolate porphyrins are benchmarked against Fe (III) tetraphenyl porphyrin chloride and its tetrapentafluorophenyl analogue. Chapter 3 describes the electrochemical and photoelectrochemical reduction of carbon dioxide to carbon monoxide. This chapter shows that iron (III) porphyrin complexes are capable of carrying out electrocatalytic reduction of carbon dioxide at both vitreous carbon and illuminated p-type silicon surfaces, with reasonable current efficiencies. At illuminated p-type silicon photovoltages of ca 500mV are obtained. 7 Chapter 4 describes the electrochemical and photoelectrochemical reduction of proton to H2 using [Fe4S4 (SPh)4]2- as an electrocatalyst at both vitreous carbon and at illuminated p-type Si electrodes.
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Dunford, Adrian J. "Kinetic studies on synthetic and biological iron-sulfur based clusters." Thesis, University of Newcastle Upon Tyne, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270825.
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Garrett, Brendan. "Substitution and protonation reactions at synthetic iron-sulfur-based clusters." Thesis, University of Newcastle Upon Tyne, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.437982.
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Raulfs, Estella Callie. "Isolation of in vivo intermediates in iron sulfur cluster biogenesis." Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/26949.
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Iron-sulfur clusters are simple inorganic cofactors that are ubiquitous in living systems. The assembly of iron sulfur clusters is an essential process and must be carefully controlled in order to limit the release of toxic free iron or sulfide. Thus far there are three known protein systems for iron sulfur cluster assembly including the nif, suf, and isc systems. The nif system makes iron-sulfur clusters for nitrogenase production, while both the suf and isc systems provide iron-sulfur clusters for general cellular use. In Azotobacter vinelandii the isc operon contains eight genes which are transcribed together as a single operon: iscR iscS iscU iscA hscB hscA fdx iscX. The two central isc players include IscS, a cysteine desulfurase, and IscU the proposed site of iron-sulfur cluster assembly.
Using A. vinelandii as a model organism, we have sought to better understand the mechanism of in vivo isc cluster assembly. In order test the scaffold hypothesis, we constructed strains that allowed for quick and rapid isolation of IscU. The purification of IscU with a bound [2Fe-2S] cluster strongly supports the model that IscU serves as the site of cluster synthesis in vivo. Additionally, using this same genetic system we isolated an IscU39DA variant with an oxygen stable bound [2Fe-2S] cluster. The IscU39DA scaffold came in tight α₂β₂ complex with IscS and was not separated by high salt, size exclusion, or reducing conditions. On the other hand, wild-type IscU also associated with IscS in a α₂β₂ complex, but readily dissociated upon increased salt concentration. The tight association of IscU39DA and IscS was found to occur regardless of the presence of a bound [Fe-S] cluster. We conclude that the IscU Asp-39 residue is essential for mediating the dissociation of IscU and IscS.
In addition to studying IscS and IscU, we were interested to further understand how the isc system is regulated in response to external factors. Previous work has demonstrated that IscR controls expression of the isc operon in Escherichia coli. When IscR is holo this protein represses isc expression, while in its apo-form it allows isc expression. In A. vinelandii we found that ∆iscR strains exhibit in a 5 – 7 fold elevation of isc expression. Additionally, ∆iscR strains reveal a small growth phenotype on plates, and a tendency to form spontaneous suppressor mutations allowing reversion to wild-type growth. Loss of apo-IscR function was found to cause a more severe effect on growth than the loss of holo-IscR function, suggesting IscR has cellular roles in addition to the regulation of the isc operon.Ph. D.
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Mansy, Sheref S. "Structure and function of iron-sulfur cluster biosynthesis proteins and the influence of oxygen ligation." Connect to this title online, 2003. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1059664189.
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Thesis (Ph. D.)--Ohio State University, 2003.Title from first page of PDF file. Document formatted into pages; contains xxi, 250 p.; also includes graphics (some col.) Includes bibliographical references (p. 226-250). Available online via OhioLINK's ETD Center
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Bejarano, Cesar. "Carbothermal reduction of sulfur dioxide using oil-sands fluid coke." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0016/MQ53340.pdf.
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Bakke, Bruce W. "Reduction of sulfur release through indigester oxidation in kraft pulping." Thesis, Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/11691.
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Sim, Min Sub. "Physiology of multiple sulfur isotope fractionation during microbial sulfate reduction." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/77788.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references.
Microbial sulfate reduction (MSR) utilizes sulfate as an electron acceptor and produces sulfide that is depleted in heavy isotopes of sulfur relative to starting sulfate. The fractionation of S-isotopes is commonly used to trace the biogeochemical cycling of sulfur in nature, but a mechanistic understanding of factors that control the range of isotope fractionation is still lacking. This thesis investigates links between the physiology of sulfate reducing bacteria in pure cultures and multiple sulfur isotope (³², ³³, ³⁴34S, and ³⁶S) fractionation during MSR in batch and continuous culture experiments. Experiments address the influence of nutrient and electron donor conditions, including organic carbon, nitrogen, and iron, in cultures of a newly isolated marine sulfate reducing bacterium (DMSS-1). An actively growing culture of DMSS-1 produced sulfide depleted in ³⁴S by 6 to 66%o, depending on the availability and chemistry of organic electron donors. The magnitude of isotope effect correlated well with the cell specific sulfate reduction rate (csSRR), and the largest isotope effects occurred when cultures grew slowly on glucose, a recalcitrant organic substrate. These findings bridge the long-standing discrepancy between the upper limit for S-isotope effect in laboratory cultures and the corresponding observations in nature and indicate that the large (>46 %o) fractionation of S-isotopes does not unambiguously record the oxidative sulfurrecycling. When the availability of iron was limited, the increase in S-isotope fractionation was accompanied by a decrease in the cytochrome c content as well as csSRR. In contrast, growth in nitrogenlimited cultures increased both csSRR and S-isotope fractionation. The influence of individual enzymes and electron carriers involved in sulfate respiration on the fractionation of S-isotopes was also investigated in cultures of mutant strains of Desulfovibrio vulgaris Hildenborough. The mutant lacking Type I tetraheme cytochrome c₃ fractionated ³⁴S/³²S ratio 50% greater relative to the wild type. The increasing S-isotope fractionation accompanied the evolution of H2 in the headspace and the decreasing csSRR. These results further demonstrate that the flow of electrons to terminal reductases imparts the primary control on the magnitude of the fractionation of S-isotopes, suggested by culture experiments using DMSS-1.
by Min Sub Sim.
Ph.D.
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Son, Ahjeong. "Microbial reduction of perchlorate with elemental iron." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 1.83 Mb., 152 p, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:3200522.
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Hall, Mark Andrew. "Iron-catalysed cross-coupling and reduction reactions." Thesis, University of Bristol, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.551314.
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Iron nanoparticles of size 6-16 nm have been successfully prepared by the reduction of FeCb with 3-pentylmagnesium bromide in the presence of polyethylene glycol. These nanoparticles show excellent activity in the catalytic dehalogenation of a range of alkyl and aryl halides when used at 5 mol% loadings, if an excess of the Grignard is present to ensure the regeneration of the catalyst. Alkyl halides react to give mixtures of alkane, alkene and homocoupled products, with good selectivity of the alkane product being observed. Aryl halides undergo hydrodehalogenation cleanly and do not undergo homocoupling. A general methodology, previously developed within the group for the cross-coupling of benzyl halides with diarylzinc reagents has been applied to other substrates. This includes 2-halopyridines and N-(bromomethyl)phthalimide, with the former exhibiting slower reaction rates so higher temperatures were required. Surprisingly, in the case of N-(bromomethyl)phthalimide, the coupling reaction was found to proceed without the need for a catalyst. This has been demonstrated for a number of diarylzinc reagents, which resulted in the cross-coupled product being formed in good to excellent yields. Furthermore,. this substrate undergoes cross- coupling with a range of boronic acids via transmetallation to diethylzinc.
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Bayerköhler, Frieder [Verfasser], and Philipp [Akademischer Betreuer] Kurz. "Iron-molybdenum sulphides as proton reduction catalysts." Freiburg : Universität, 2017. http://d-nb.info/1144148901/34.
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Nixon, Sophie Louise. "Microbial iron reduction on Earth and Mars." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/9974.
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The search for life beyond Earth is the driving force behind several future missions to Mars. An essential task in the lead-up to these missions is a critical assessment of the habitability for, and feasibility of, life. However, little research has been conducted on this issue, and our understanding of the plausibility for life on Mars remains unconstrained. Owing to the anoxic and iron-rich nature of Mars, microbial iron reduction (MIR) represents a compelling candidate metabolism to operate in the Martian subsurface, past and present. The objectives of this thesis are to address the feasibility of MIR on Mars by i) better defining the habitability of MIR on Earth, and ii) assessing the range and availability of organic electron donors in the subsurface of Earth and Mars. Samples collected from Mars-relevant environments on Earth were used to initiate MIR enrichment cultures at 4°C, 15°C and 30°C. Results indicate MIR is widespread in riverbed and subglacial sediments but not sediments from desert or recent volcanic plains. The iron-reducing microorganisms in subglacial enrichments are at least psychrotolerant and in some cases psychrophilc. Culture-independent methods highlighted the changes in diversity between temperature conditions for subglacial sediments, and indicated that members of the prolific MIR Geobacteraceae family are common. The genera Geobacter and Desulfosporosinus are responsible for MIR in the majority of enrichments. Long-term anoxia and the availability of redox constituents are the major factors controlling MIR in these environments. A MIR enrichment culture was unable to use shales and kerogens as the sole source of electron donors for MIR, despite the presence of known electron donors. Furthermore, MIR was inhibited by the presence of certain kerogens. The causes of inhibition are unknown, and are likely to be a combination of chemical and physical factors. Experiments were conducted to assess the ability of three pure strains and a MIR enrichment to use non-proteinogenic amino acids common to carbonaceous meteorites as electron donors for MIR. Results demonstrate that γ-aminobutyric acid served as an electron donor for the enrichment culture, but no other amino acids supported MIR by this or other iron-reducing cultures. The D-form of chiral amino acids was found to exert a strong inhibitory effect, which decreased in line with concentration. Theoretical calculations using published meteoritic accretion rates onto the surface of Mars indicate that the build up inhibitory amino acids may place important constrains on habitability over geologic time scales. Contamination of a pure strain of Geobacter metallireducens with a strain of Clostridium revealed a syntrophic relationship between these microorganisms. Anaerobic heterotrophs are likely to play an important role in maintaining an available supply of electron donors for MIR and similar chemoorganic metabolisms operating in the subsurface. This research indicates that MIR remains a feasible metabolism to operate on Mars providing a readily available redox couple is present. However, given the observed inhibition in the presence of bulk carbonaceous material and certain amino acids found in meteorites, the use of extraterrestrial carbonaceous material in the Martian subsurface for microbial iron reduction is questionable, and should be the focus of future research.
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HUANG, HE. "REDUCTION OF PERCHLORATE BY ZERO VALENT IRON." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1131047520.
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Joshi, Neelambari. "Investigating the role of iron sulfur cluster binding residues of HYDF." Thesis, Montana State University, 2012. http://etd.lib.montana.edu/etd/2012/joshi/JoshiN0512.pdf.
Full textAbstract:
[FeFe]-hydrogenases are metalloenzymes found in many bacteria and lower eukaryotes. The catalytic active site of [FeFe]-hydrogenases termed as H-cluster consists of a [4Fe-4S] cubane bridged to a 2Fe subcluster. The two iron atoms of the 2Fe subcluster are decorated by carbon monoxide, cyanide ligands as well as a bridging dithiolate ligand. The assembly of this complex H cluster involves the role of three accessory enzymes namely HydE, HydG and HydF. The maturase, HydF is a GTPase and contains two types of clusters, a [4Fe-4S] and a [2Fe-2S] cluster. The [2Fe-2S] cluster is transformed into an H-cluster precursor by action of HydE and HydG. It is suggested from EPR spectroscopic data of both reduced HydF DeltaEG and Oxidized HydF EG that the [2Fe-2S] cluster and the [4Fe-4S] cluster are not bound to each other. Since an H-cluster like signal was observed in oxidized HydF EG suggested that the two clusters are arranged in same manner as the H-cluster itself. This aforementioned hypothesis drove us to investigate the ligand arrangement of both a [4Fe-4S] and most importantly the [2Fe-2S] clusters in HydF. The apo HydF structure does not provide us with significant insights into Fe-S cluster coordination details, therefore we have attempted to experimentally identify the residues that act as ligands to both the clusters. To that end, we substituted each of the conserved Fe-S cluster binding residues and observed the effects of these mutations on both clusters by spectroscopic methods like UV-Vis spectroscopy and EPR. Our observations indicated that among the three conserved cysteines, C304 and C356 are absolutely quintessential for iron sulfur cluster assembly in HydF DeltaEG while C353 and H306 have some capacity to bind iron sulfur clusters. Further in vitro hydrogenase assays suggested importance of C353 residue as it affected the assembly of the 2Fe subcluster. Thus we propose a dimeric/ tetrameric model of HydF where both the [2Fe-2S] and the [4Fe-4S] clusters are ligated by eight conserved, four putative Fe-S cluster binding residues from each monomer. In our proposed model we discuss the possible occurrence of non cysteinyl ligation for iron sulfur clusters.
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Camba, Acosta Raul O. "Reaction mechanisms of iron-sulfur proteins studied by protein-film voltammetry." Thesis, University of Oxford, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365860.
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