Showing papers on "Redox published in 2008"
TL;DR: In situ demonstration of flavin production, and sequestration at surfaces, requires the paradigm of soluble redox shuttles in geochemistry to be adjusted to include binding and modification of surfaces.
Abstract: Bacteria able to transfer electrons to metals are key agents in biogeochemical metal cycling, subsurface bioremediation, and corrosion processes. More recently, these bacteria have gained attention as the transfer of electrons from the cell surface to conductive materials can be used in multiple applications. In this work, we adapted electrochemical techniques to probe intact biofilms of Shewanella oneidensis MR-1 and Shewanella sp. MR-4 grown by using a poised electrode as an electron acceptor. This approach detected redox-active molecules within biofilms, which were involved in electron transfer to the electrode. A combination of methods identified a mixture of riboflavin and riboflavin-5′-phosphate in supernatants from biofilm reactors, with riboflavin representing the dominant component during sustained incubations (>72 h). Removal of riboflavin from biofilms reduced the rate of electron transfer to electrodes by >70%, consistent with a role as a soluble redox shuttle carrying electrons from the cell surface to external acceptors. Differential pulse voltammetry and cyclic voltammetry revealed a layer of flavins adsorbed to electrodes, even after soluble components were removed, especially in older biofilms. Riboflavin adsorbed quickly to other surfaces of geochemical interest, such as Fe(III) and Mn(IV) oxy(hydr)oxides. This in situ demonstration of flavin production, and sequestration at surfaces, requires the paradigm of soluble redox shuttles in geochemistry to be adjusted to include binding and modification of surfaces. Moreover, the known ability of isoalloxazine rings to act as metal chelators, along with their electron shuttling capacity, suggests that extracellular respiration of minerals by Shewanella is more complex than originally conceived.
1,582 citations
TL;DR: A review of the chemistry of the formation and continuing transformation of low-volatility species in the atmosphere can be found in this article, where the primary focus is chemical processes that can change the volatility of organic compounds: oxidation reactions in the gas phase, reaction in the particle phase, and reaction in either phase over several generations.
1,411 citations
TL;DR: Data is summarized supporting a complementary hypothesis for oxidative stress in disease that can occur without free radicals, which is that oxidative stress occurs as a consequence of disruption of thiol redox circuits, which normally function in cell signaling and physiological regulation.
Abstract: Free radical-induced macromolecular damage has been studied extensively as a mechanism of oxidative stress, but large-scale intervention trials with free radical scavenging antioxidant supplements show little benefit in humans. The present review summarizes data supporting a complementary hypothesis for oxidative stress in disease that can occur without free radicals. This hypothesis, which is termed the “redox hypothesis,” is that oxidative stress occurs as a consequence of disruption of thiol redox circuits, which normally function in cell signaling and physiological regulation. The redox states of thiol systems are sensitive to two-electron oxidants and controlled by the thioredoxins (Trx), glutathione (GSH), and cysteine (Cys). Trx and GSH systems are maintained under stable, but nonequilibrium conditions, due to a continuous oxidation of cell thiols at a rate of about 0.5% of the total thiol pool per minute. Redox-sensitive thiols are critical for signal transduction (e.g., H-Ras, PTP-1B), transcription factor binding to DNA (e.g., Nrf-2, nuclear factor-κB), receptor activation (e.g., αIIbβ3 integrin in platelet activation), and other processes. Nonradical oxidants, including peroxides, aldehydes, quinones, and epoxides, are generated enzymatically from both endogenous and exogenous precursors and do not require free radicals as intermediates to oxidize or modify these thiols. Because of the nonequilibrium conditions in the thiol pathways, aberrant generation of nonradical oxidants at rates comparable to normal oxidation may be sufficient to disrupt function. Considerable opportunity exists to elucidate specific thiol control pathways and develop interventional strategies to restore normal redox control and protect against oxidative stress in aging and age-related disease.
1,067 citations
TL;DR: Redox-inert metal ions are used in enzymes to stabilize negative charges and to activate substrates by virtue of their Lewis acid properties, whereas redox-active metal ions can be used both as Lewis acids and as redox centres.
Abstract: We analysed the roles and distribution of metal ions in enzymatic catalysis using available public databases and our new resource Metal-MACiE (http://www.ebi.ac.uk/thornton-srv/databases/Metal_MACiE/home.html). In Metal-MACiE, a database of metal-based reaction mechanisms, 116 entries covering 21% of the metal-dependent enzymes and 70% of the types of enzyme-catalysed chemical transformations are annotated according to metal function. We used Metal-MACiE to assess the functions performed by metals in biological catalysis and the relative frequencies of different metals in different roles, which can be related to their individual chemical properties and availability in the environment. The overall picture emerging from the overview of Metal-MACiE is that redox-inert metal ions are used in enzymes to stabilize negative charges and to activate substrates by virtue of their Lewis acid properties, whereas redox-active metal ions can be used both as Lewis acids and as redox centres. Magnesium and zinc are by far the most common ions of the first type, while calcium is relatively less used. Magnesium, however, is most often bound to phosphate groups of substrates and interacts with the enzyme only transiently, whereas the other metals are stably bound to the enzyme. The most common metal of the second type is iron, which is prevalent in the catalysis of redox reactions, followed by manganese, cobalt, molybdenum, copper and nickel. The control of the reactivity of redox-active metal ions may involve their association with organic cofactors to form stable units. This occurs sometimes for iron and nickel, and quite often for cobalt and molybdenum.
890 citations
TL;DR: Flavin mononucleotide and riboflavin are identified for the first time as the extracellular electron shuttles produced by a range of Shewanella species and shown to act as electron Shuttles and to promote anoxic growth coupled to the accelerated reduction of poorly crystalline Fe(III) oxides.
Abstract: Fe(III)-respiring bacteria such as Shewanella species play an important role in the global cycle of iron, manganese, and trace metals and are useful for many biotechnological applications, including microbial fuel cells and the bioremediation of waters and sediments contaminated with organics, metals, and radionuclides. Several alternative electron transfer pathways have been postulated for the reduction of insoluble extracellular subsurface minerals, such as Fe(III) oxides, by Shewanella species. One such potential mechanism involves the secretion of an electron shuttle. Here we identify for the first time flavin mononucleotide (FMN) and riboflavin as the extracellular electron shuttles produced by a range of Shewanella species. FMN secretion was strongly correlated with growth and exceeded riboflavin secretion, which was not exclusively growth associated but was maximal in the stationary phase of batch cultures. Flavin adenine dinucleotide was the predominant intracellular flavin but was not released by live cells. The flavin yields were similar under both aerobic and anaerobic conditions, with total flavin concentrations of 2.9 and 2.1 μmol per gram of cellular protein, respectively, after 24 h and were similar under dissimilatory Fe(III)-reducing conditions and when fumarate was supplied as the sole electron acceptor. The flavins were shown to act as electron shuttles and to promote anoxic growth coupled to the accelerated reduction of poorly crystalline Fe(III) oxides. The implications of flavin secretion by Shewanella cells living at redox boundaries, where these mineral phases can be significant electron acceptors for growth, are discussed.
787 citations
TL;DR: The use of coupled catalytic systems with electron-transfer mediators usually facilitates the procedures by transporting the electrons from the catalyst to the oxidant along a low-energy pathway, thereby increasing the efficiency of the oxidation and thus complementing the direct oxidation reactions.
Abstract: Oxidation reactions are of fundamental importance in nature, and are key transformations in organic synthesis. The development of new processes that employ transition metals as substrate-selective catalysts and stoichiometric environmentally friendly oxidants, such as molecular oxygen or hydrogen peroxide, is one of the most important goals in oxidation chemistry. Direct oxidation of the catalyst by molecular oxygen or hydrogen peroxide is often kinetically unfavored. The use of coupled catalytic systems with electron-transfer mediators (ETMs) usually facilitates the procedures by transporting the electrons from the catalyst to the oxidant along a low-energy pathway, thereby increasing the efficiency of the oxidation and thus complementing the direct oxidation reactions. As a result of the similarities with biological systems, this can be dubbed a biomimetic approach.
764 citations
TL;DR: It is demonstrated that the fusion of human glutaredoxin-1 to roGFP2 facilitates specific real-time equilibration between the sensor protein and the glutathione redox couple, which facilitated the observation of redox changes associated with growth factor availability, cell density, mitochondrial depolarization, respiratory burst activity and immune receptor stimulation.
Abstract: Dynamic analysis of redox-based processes in living cells is now restricted by the lack of appropriate redox biosensors. Conventional redox-sensitive GFPs (roGFPs) are limited by undefined specificity and slow response to changes in redox potential. In this study we demonstrate that the fusion of human glutaredoxin-1 (Grx1) to roGFP2 facilitates specific real-time equilibration between the sensor protein and the glutathione redox couple. The Grx1-roGFP2 fusion protein allowed dynamic live imaging of the glutathione redox potential (E(GSH)) in different cellular compartments with high sensitivity and temporal resolution. The biosensor detected nanomolar changes in oxidized glutathione (GSSG) against a backdrop of millimolar reduced glutathione (GSH) on a scale of seconds to minutes. It facilitated the observation of redox changes associated with growth factor availability, cell density, mitochondrial depolarization, respiratory burst activity and immune receptor stimulation.
731 citations
TL;DR: In this paper, the redox control networks of eukaryotic cells have been investigated and further elucidation of these networks within compartments will improve the mechanistic understanding of cell functions and their disruption in disease.
575 citations
TL;DR: Thiol/disulfide pathway, redox potential, and rate information are summarized as a basis for kinetic modeling of sulfur switches and indicates that systems biology could encourage novel therapeutic approaches to protect against oxidative stress by identifying specific redox-sensitive sites which could be targeted for intervention.
524 citations
TL;DR: The aim of this study was to understand the relationship between the redox state of iron-based nanoparticles and their cytotoxicity toward a Gram-negative bacterium, Escherichia coli.
Abstract: Iron-based nanoparticles have been proposed for an increasing number of biomedical or environmental applications although in vitro toxicity has been observed. The aim of this study was to understand the relationship between the redox state of iron-based nanoparticles and their cytotoxicity toward a Gram-negative bacterium, Escherichia coli. While chemically stable nanoparticles (γFe2O3) have no apparent cytotoxicity, nanoparticles containing ferrous and, particularly, zerovalent iron are cytotoxic. The cytotoxic effects appear to be associated principally with an oxidative stress as demonstrated using a mutant strain of E. coli completely devoid of superoxide dismutase activity. This stress can result from the generation of reactive oxygen species with the interplay of oxygen with reduced iron species (FeII and/or Fe0) or from the disturbance of the electronic and/or ionic transport chains due to the strong affinity of the nanoparticles for the cell membrane.
511 citations
TL;DR: This Account describes the mechanistic features of one-electron oxidation reactions of the guanine base in isolated DNA and related model compounds and surveys the analytical methods that can detect low amounts of oxidized bases and nucleosides in cells as they are formed.
Abstract: Nuclear DNA and other molecules in living systems are continuously exposed to endogenously generated oxygen species. Such species range from the unreactive superoxide radical (O2*-)the precursor of hydrogen peroxide (H2O2)to the highly reactive hydroxyl radical (*OH). Exogenous chemical and physical agents, such as ionizing radiation and the UVA component of solar light, can also oxidatively damage both the bases and the 2-deoxyribose moieties of cellular DNA. Over the last two decades, researchers have made major progress in understanding the oxidation degradation pathways of DNA that are most likely to occur from either oxidative metabolism or exposure to various exogenous agents. In the first part of this Account, we describe the mechanistic features of one-electron oxidation reactions of the guanine base in isolated DNA and related model compounds. These reactions illustrate the complexity of the various degradation pathways involved. Then, we briefly survey the analytical methods that can detect low amounts of oxidized bases and nucleosides in cells as they are formed. Recent data on the formation of oxidized guanine residues in cellular DNA following exposure to UVA light, ionizing radiation, and high-intensity UV pulses are also provided. We discuss these chemical reactions in the context of *OH radical, singlet oxygen, and two-quantum photoionization processes.
TL;DR: In this article, the reduction/oxidation (redox) conditions in 15 principal aquifer (PA) systems of the United States, and their impact on several water quality issues, were assessed from a large data base collected by the National Water-Quality Assessment Program of the USGS.
Abstract: Reduction/oxidation (redox) conditions in 15 principal aquifer (PA) systems of the United States, and their impact on several water quality issues, were assessed from a large data base collected by the National Water-Quality Assessment Program of the USGS. The logic of these assessments was based on the observed ecological succession of electron acceptors such as dissolved oxygen, nitrate, and sulfate and threshold concentrations of these substrates needed to support active microbial metabolism. Similarly, the utilization of solid-phase electron acceptors such as Mn(IV) and Fe(III) is indicated by the production of dissolved manganese and iron. An internally consistent set of threshold concentration criteria was developed and applied to a large data set of 1692 water samples from the PAs to assess ambient redox conditions. The indicated redox conditions then were related to the occurrence of selected natural (arsenic) and anthropogenic (nitrate and volatile organic compounds) contaminants in ground water. For the natural and anthropogenic contaminants assessed in this study, considering redox conditions as defined by this framework of redox indicator species and threshold concentrations explained many water quality trends observed at a regional scale. An important finding of this study was that samples indicating mixed redox processes provide information on redox heterogeneity that is useful for assessing common water quality issues. Given the interpretive power of the redox framework and given that it is relatively inexpensive and easy to measure the chemical parameters included in the framework, those parameters should be included in routine water quality monitoring programs whenever possible.
TL;DR: The analysis of such stepwise mechanisms both in aprotic media and in water is reviewed, with particular recent emphasis on electrochemical and theoretical approaches to proton-coupled electron transfer processes.
Abstract: The coupling between electron and proton transfers has a long experimental and theoretical history in chemistry and biochemistry. To take just one example, the fact that acceptance of an electron triggers the addition of an acid or the removal of a base and vice versa for oxidations towers over all understanding of organic electrochemistry. Protoncoupled electron transfer (PCET) reactions also play a critical role in a wide range of biological processes, including enzyme reactions, photosynthesis, and respiration. A recent impressive review describes PCET reactions and phenomena. PCET is employed here as a general term for reactions in which both an electron and a proton are transferred, either in two separate steps or in a single step. Reactions in which the electron and proton transfer between the same donor and acceptor, that is, hydrogen atom transfer, are, of course, not considered here because we consider electrochemical PCET reactions in which electrons are flowing into or from an electrode while protons are transferred between acid and base. Molecular electrochemistry, through nondestructive techniques such as cyclic voltammetry, has proved to be very useful in characterizing electron transfers and deciphering mechanisms in which chemical reactions are associated with electron transfer. Therefore, it has been a convenient tool for the mechanistic study of reactions in which electron transfer is coupled to proton transfer, that is, in which an electron leaves or enters an electrode while a proton is transferred from or to the redox species. Until recently, PCET has been mostly thought of as stepwise electron and proton transfer (ET-PT or PT-ET). We thus review in an initial section (section 2) the analysis of such stepwise mechanisms both in aprotic media and in water. In aprotic media, * E-mail address: cyrille.costentin@univ-paris-diderot.fr. Cyrille Costentin was born in Normandy, France, in 1972. He received his undergraduate education at Ecole Normale Superieure (Cachan, France) and pursued his graduate studies under the guidance of Prof. Jean-Michel Saveant and Dr. Philippe Hapiot at the University of ParisDiderot (Paris 7), where he received his Ph.D. in 2000. After a year as a postdoctoral fellow at the University of Rochester, working with Prof. J. P. Dinnocenzo, he joined the faculty at the University of Paris-Diderot as an associate professor. He was promoted to professor in 2007. His interests include mechanisms and reactivity in electron transfer chemistry with particular recent emphasis on electrochemical and theoretical approaches to proton-coupled electron transfer processes. Chem. Rev. 2008, 108, 2145–2179 2145
TL;DR: Two series of mononuclear ruthenium(II) complexes involving polypyridine-type ligands have been prepared, and their ability to act as catalysts for water oxidation has been examined.
Abstract: Two series of mononuclear ruthenium(II) complexes involving polypyridine-type ligands have been prepared, and their ability to act as catalysts for water oxidation has been examined. One series is of the type [Ru(tpy)(NN)Cl](PF6) (tpy = 2,2′; 6,2′′-terpyridine), where NN is one of 12 different bidentate ligands, and the other series includes various combinations of 4-picoline, 2,2′-bipyridine (bpy), and tpy as well as the tetradentate 2,9-dipyrid-2′-yl-1,10-phenanthroline (dpp). The electronic absorption and redox data for these compounds have been measured and reported. The long-wavelength metal-to-ligand charge-transfer absorption and the first oxidation and reduction potentials are found to be consistent with the structure of the complex. Of the 23 complexes, 14 catalyze water oxidation and all of these contain a tpy or dpp. Kinetic measurements indicate a first-order reaction and together with a catalyst recovery experiment argue against the involvement of RuO2. A tentative mechanism is proposed that ...
TL;DR: In this article, the feasibility of using ilmenite as an oxygen carrier in chemical-looping combustion has been investigated, and it was found that the resulting oxygen is an attractive and inexpensive oxygen carrier.
Abstract: The feasibility of using ilmenite as oxygen carrier in chemical-looping combustion has been investigated. Itwas found that ilmenite is an attractive and inexpensive oxygen carrier for chemical-looping combustion.Alaboratory fluidizedbed reactor system, simulating chemical-looping combustion by exposing the sample to alternating reducing and oxidizing conditions,was used to investigate the reactivity. During the reducing phase, 15 g of ilmenite with a particle
size of 125–180μm was exposed to a flow of 450mLn/min of either methane or syngas (50% CO, 50% H2) and during the oxidizing phase to a flow of 1000mLn/min of 5% O2 in nitrogen. The ilmenite particles showed no decrease in reactivity in the laboratory experiments after 37 cycles of oxidation and reduction. Equilibrium calculations indicate that the reduced ilmenite is in the form FeTiO3 and the oxidized carrier is in the form Fe2TiO5 +TiO2. The theoretical oxygen transfer capacity between these oxidation states is 5%. The same oxygen transfer capacity was obtained in the laboratory experiments with syngas. Equilibrium calculations indicate that ilmenite should be able to give high conversion of the gases with the equilibrium ratios CO/(CO2 + CO) and H2/(H2O+H2) of 0.0006 and 0.0004, respectively. Laboratory experiments suggest a similar ratio for CO. The equilibrium calculations give a reaction enthalpy of the overall oxidation that is 11% higher than for the oxidation of methane per kmol of oxygen. Thus, the reduction from
Fe2TiO5 +TiO2 to FeTiO3 with methane is endothermic, but less endothermic compared to NiO/Ni and Fe2O3/Fe3O4, and almost similar to Mn3O4/MnO.
TL;DR: In this article, the authors demonstrate operation of an aqueous electrochemical cell with an atmospheric-pressure microplasma cathode and a solid metal anode for the rapid production of colloidal metal nanoparticles.
Abstract: We demonstrate operation of an aqueous electrochemical cell with an atmospheric-pressure microplasma cathode and a solid metal anode for the rapid production of colloidal metal nanoparticles. Microplasmas are miniaturized versions of low-pressure glow discharges that operate nonthermally at high pressures (∼1atm) and contain energetic electrons. Aqueous metal cations are directly reduced by electrons in the microplasma without the presence of a solid cathode or chemical reducing agents. Kinetic studies performed by UV-visible absorbance spectroscopy suggest that particle nucleation and growth are coupled to redox reactions initiated in the electrochemical cell through plasma-liquid interactions.
TL;DR: Specific interaction of both roGFPs with glutaredoxin in vitro strongly suggests that in situ both variants preferentially act as sensors for the glutathione redox potential, suggesting that roG FP2 is a reliable probe for dynamic redox imaging in planta.
Abstract: Reduction-oxidation-sensitive green fluorescent protein (roGFP1 and roGFP2) were expressed in different sub-cellular compartments of Arabidopsis and tobacco leaves to empirically determine their performance as ratiometric redox sensors for confocal imaging in planta. A lower redox-dependent change in fluorescence in combination with reduced excitation efficiency at 488 nm resulted in a significantly lower dynamic range of roGFP1 than for roGFP2. Nevertheless, when targeted to the cytosol and mitochondria of Arabidopsis leaves both roGFPs consistently indicated redox potentials of about -320 mV in the cytosol and -360 mV in the mitochondria after pH correction for the more alkaline matrix pH. Ratio measurements were consistent throughout the epidermal cell layer, but results might be attenuated deeper within the leaf tissue. Specific interaction of both roGFPs with glutaredoxin in vitro strongly suggests that in situ both variants preferentially act as sensors for the glutathione redox potential. roGFP2 targeted to plastids and peroxisomes in epidermal cells of tobacco leaves was slightly less reduced than in other plasmatic compartments, but still indicated a highly reduced glutathione pool. The only oxidizing compartment was the lumen of the endoplasmic reticulum, in which roGFP2 was almost completely oxidized. In all compartments tested, roGFP2 reversibly responded to perfusion with H(2)O(2) and DTT, further emphasizing that roGFP2 is a reliable probe for dynamic redox imaging in planta. Reliability of roGFP1 measurements might be obscured though in extended time courses as it was observed that intense irradiation of roGFP1 at 405 nm can lead to progressive photoisomerization and thus a redox-independent change of fluorescence excitation ratios.
TL;DR: In this paper, the authors have demonstrated the reasons why CeO2 becomes an active catalyst for diesel particulate (soot) abatement, which attracts recent worldwide attention in the development of clean diesel automobiles.
Abstract: The present work has demonstrated the reasons why CeO2 becomes an active catalyst for diesel particulate (soot) abatement, which attracts recent worldwide attention in the development of clean diesel automobiles. Four typical fluorite-type oxides, CeO2, ZrO2, Pr6O11, and a CeO2−ZrO2 solid solution have been studied as model catalysts for soot oxidation in conjunction with the redox property and the reactivity of solid oxygen species. It was found that the redox property measured in terms of oxygen storage/release capacity was not the sole determining factor for the observed catalytic activity decreasing in the order of CeO2 ≫ Pr6O11 ≈ CeO2−ZrO2 > ZrO2. The reactivity of oxygen species involved in the redox cycles would rather be important. The ESR measurement showed that admission of O2 to the pre-reduced CeO2 surface generated superoxide ions (O2−). Such reactive oxygen species were less abundant on CeO2−ZrO2 and were not detected on ZrO2 and Pr6O11. The labeled and unlabeled O2 pulse experiments demonst...
TL;DR: It is shown here that reduction-oxidation-sensitive GFP (roGFP), when expressed in plants, is an artificial target protein of GRXs, which results in continuous formation and release of the roGFP disulfide bridge depending on the actual redox potential of the cellular glutathione buffer.
TL;DR: It is shown here that the presence of both an iodido ligand and a σ-donor/π-acceptor phenylazopyridine ligand confers remarkable inertness toward ligand substitution on the half-sandwich ruthenium arene complexes, which are highly cytotoxic to human ovarian A2780 and human lung A549 cancer cells.
Abstract: Organometallic complexes offer chemistry that is not accessible to purely organic molecules and, hence, potentially new mechanisms of drug action We show here that the presence of both an iodido ligand and a σ-donor/π-acceptor phenylazopyridine ligand confers remarkable inertness toward ligand substitution on the half-sandwich “piano-stool” ruthenium arene complexes [(η6-arene)Ru(azpy)I]+ (where arene = p-cymene or biphenyl, and azpy = N,N-dimethylphenyl- or hydroxyphenyl-azopyridine) in aqueous solution Surprisingly, despite this inertness, these complexes are highly cytotoxic to human ovarian A2780 and human lung A549 cancer cells Fluorescence-trapping experiments in A549 cells suggest that the cytotoxicity arises from an increase in reactive oxygen species Redox activity of these azopyridine RuII complexes was confirmed by electrochemical measurements The first one-electron reduction step (half-wave potential −02 to −04 V) is assignable to reduction of the azo group of the ligand In contrast, the unbound azopyridine ligands are not readily reduced Intriguingly the ruthenium complex acted as a catalyst in reactions with the tripeptide glutathione (γ-l-Glu-l-Cys-Gly), a strong reducing agent present in cells at millimolar concentrations; millimolar amounts of glutathione were oxidized to glutathione disulfide in the presence of micromolar ruthenium concentrations A redox cycle involving glutathione attack on the azo bond of coordinated azopyridine is proposed Such ligand-based redox reactions provide new concepts for the design of catalytic drugs
TL;DR: In this article, a cyclic voltammogram of NiCu alloy demonstrates the formation of β/β crystallographic forms of the nickel oxyhydroxide under prolonged repetitive potential cycling in alkaline solution.
TL;DR: Green fluorescent protein-based redox sensor targeted to the intermembrane space (IMS) and matrix of yeast mitochondria indicates that redox control in the cytosol and matrix are maintained separately by cytosolic and mitochondrial isoforms of GSSG reductase.
TL;DR: A different role of the oxygen species produced by these sources is apparent as oxidants derived from NADPH oxidase are involved mainly in signaling processes, whereas those produced by mitochondria induce cell death in pathways including also the thioredoxin system, presently considered an important target for cancer chemotherapy.
Abstract: The oxidation chemistry of thiols and disulfides of biologic relevance is described. The review focuses on the interaction and kinetics of hydrogen peroxide with low-molecular-weight thiols and protein thiols and, in particular, on sulfenic acid groups, which are recognized as key intermediates in several thiol oxidation processes. In particular, sulfenic and selenenic acids are formed during the catalytic cycle of peroxiredoxins and glutathione peroxidases, respectively. In turn, these enzymes are in close redox communication with the thioredoxin and glutathione systems, which are the major controllers of the thiol redox state. Oxidants formed in the cell originate from several different sources, but the major producers are NADPH oxidases and mitochondria. However, a different role of the oxygen species produced by these sources is apparent as oxidants derived from NADPH oxidase are involved mainly in signaling processes, whereas those produced by mitochondria induce cell death in pathways inclu...
TL;DR: In this article, the best current structural model of the inorganic ion cluster, based on polarized EXAFS experiments on crystals of the photosystem, shows Ca2+ ligated by carboxyl groups from amino acid residues (alanine, glutamate) that bridge to Mn atoms.
TL;DR: In this paper, the peak potential of the peak was linearly dependent on pH with dEp/dpH as 42mV/pH and a comparison of peak potential value of 2′,3′-dideoxyadenosine with adenosine and 2′-deoxyadensoine indicated that the difference is insignificant which has further been supported by calculations of difference of energies of lowest unoccupied and highest occupied molecular orbitals.
TL;DR: In this paper, the results of these tests have showed that active centres for CO-PROX contain copper in the +2 oxidation state, which promoted H 2 -rich conditions at 70-210°C.
Abstract: CuO/CeO 2 catalysts with CuO content ranging from 0.5 wt.% to 8 wt.%, prepared by wet impregnation of commercial ceria, have been tested for the preferential oxidation of CO (CO-PROX) under H 2 -rich conditions at 70–210 °C. Catalytic activity increases up to 4 wt.% CuO content, with less concentrated catalysts showing higher intrinsic activity. Catalysts have been characterized by means of XRD, BET analysis and UV spectroscopy. Formation of segregated CuO clusters has been detected for Cu richest CuO/CeO 2 sample. Redox properties have been deeply investigated using TP analysis (H 2 TPR, CO TPR, TPO) of fresh or pre-treated samples. Participation of surface ceria, induced by the strong interaction with copper, to reduction/oxidation reactions in the temperature range explored (up to 430 °C) has been demonstrated. Different copper species and their reactivity towards H 2 and CO have been individuated by comparing TPR of fully oxidized catalysts with those of partially oxidized catalysts. Active species have been identified as copper-ceria sites able to oxidize CO even at room temperature and to be re-oxidized by O 2 at the same temperature. Transient experiments have been carried out at different temperature using a diluted mixture starting from oxidized or reduced catalysts and followed by a H 2 TPR of the used samples. The results of these tests have showed that active centres for CO oxidation contain copper in the +2 oxidation state. At T > 100 °C some reduced copper sites are stabilized which promote H 2 oxidation thus lowering the selectivity of the CO-PROX process.
TL;DR: In this article, the chloroplast is considered a primary sensor of environmental change through a redox sensing/signalling mechanism that acts synergistically with other signal transduction pathways to elicit the appropriate molecular and physiological responses.
Abstract: A basic requirement of all photosynthetic organisms is a balance between overall energy supply through temperature-independent photochemical reactions and energy consumption through the temperature-dependent biochemical reactions of photosynthetic electron transport and contiguous metabolic pathways. Since the turnover of photosystem II (PSII) reaction centers is a limiting step in the conversion of light energy into ATP and NADPH, any energy imbalance may be sensed through modulation of the redox state of PSII. This can be estimated in vivo by chlorophyll a fluorescence as changes in the redox state of PSII, or photosystem II excitation pressure, which reflects changes in the redox poise of intersystem electron transport carriers. Through comparisons of photosynthetic adjustment, we show that growth at low temperature mimics growth at high light. We conclude that terrestrial plants, green algae and cyanobacteria do not respond to changes in growth temperature or growth irradiance per se, but rather, respond to changes in the redox state of intersystem electron transport as reflected by changes in PSII excitation pressure, We suggest that this chloroplastic redox sensing mechanism may be an important component for sensing abiotic stresses in general. Thus, in addition to its role in energy transduction, the chloroplast may also be considered a primary sensor of environmental change through a redox sensing/signalling mechanism that acts synergistically with other signal transduction pathways to elicit the appropriate molecular and physiological responses.
TL;DR: In this article, the effect of redox potential on chalcopyrite leaching was evaluated in stirred Erlenmeyer flasks with 0.5 g of pure chal copyrite and 100mL of a Fe 3+ /Fe 2+ sulphate solution.
TL;DR: The results showed that Mnx+ cations entered into the ceria lattice to form solid solutions, which increased the amount of oxygen vacancies and promoted surface oxygen chemisorption as mentioned in this paper.
TL;DR: The review focuses on conditions that, by promoting cellular oxidative stress, lead to the generation of abnormal calcium signals, and how this calcium imbalance may cause a variety of human diseases including, in particular, degenerative diseases of the central nervous system and cardiac pathologies.
Abstract: Studies done many years ago established unequivocally the key role of calcium as a universal second messenger. In contrast, the second messenger roles of reactive oxygen and nitrogen species have emerged only recently. Therefore, their contributions to physiological cell signaling pathways have not yet become universally accepted, and many biological researchers still regard them only as cellular noxious agents. Furthermore, it is becoming increasingly apparent that there are significant interactions between calcium and redox species, and that these interactions modify a variety of proteins that participate in signaling transduction pathways and in other fundamental cellular functions that determine cell life or death. This review article addresses first the central aspects of calcium and redox signaling pathways in animal cells, and continues with the molecular mechanisms that underlie crosstalk between calcium and redox signals under a number of physiological or pathological conditions. To conclude, the...