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1.
There are five oxidation-reduction states of horseradish peroxidase which are interconvertible. These states are ferrous, ferric, Compound II (ferryl), Compound I (primary compound of peroxidase and H2O2), and Compound III (oxy-ferrous). The presence of heme-linked ionization groups was confirmed in the ferrous enzyme by spectrophotometric and pH stat titration experiments. The values of pK were 5.87 for isoenzyme A and 7.17 for isoenzymes (B + C). The proton was released when the ferrous enzyme was oxidized to the ferric enzyme while the uptake of the proton occurred when the ferrous enzyme reacted with oxygen to form Compound III. The results could be explained by assuming that the heme-linked ionization group is in the vicinity of the sixth ligand and forms a stable hydrogen bond with the ligand.The measurements of uptake and release of protons in various reactions also yielded the following stoichiometries: Ferric peroxidase + H2O2 → Compound I, Compound I + e? + H+ → Compound II, Compound II + e? + H+ → ferric peroxidase, Compound II + H2O2 → Compound III, Compound III + 3e? + 3H+ → ferric peroxidase.Based on the above stoichiometries and assuming the interaction between the sixth ligand and heme-linked ionization group of the protein, it was possible to picture simple models showing structural relations between five oxidation-reduction states of peroxidase. Tentative formulae are as follows: [Pr·Po·Fe-(II) PrH+·Po·Fe(II)] is for the ferrous enzyme, Pr·Po·Fe(III)OH2 for the ferric one, Pr·Po·Fe(IV)OH? for Compound II, Pr(OH?)·Po+·Fe(IV)OH? for Compound I, and PrH+·Po·Fe(III)O2? for Compound III, in which Pr stands for protein and Po for porphyrin. And by Fe(IV)OH?, for instance, is meant that OH? is coordinated at the sixth position of the heme iron and the formal oxidation state of the iron is four. 相似文献
2.
Sotaro Yamasaki Mitsuo Shoji Megumi Kayanuma Vladimir Sladek Daniel Ken Inaoka Yuichi Matsuo Tomoo Shiba Luke Young Anthony L. Moore Kiyoshi Kita Yasuteru Shigeta 《BBA》2021,1862(4):148356
Alternative oxidase (AOX) catalyzes the four-electron reduction of dioxygen to water as an additional terminal oxidase, and the catalytic reaction is critical for the parasite to survive in its bloodstream form. Recently, the X-ray crystal structure of trypanosome alternative oxidase (TAO) complexed with ferulenol was reported and the molecular structure of the non-heme diiron center was determined. The binding of O2 was a unique side-on type compared to other iron proteins. In order to characterize the O2 binding state of TAO, the O2 binding states were searched at a quantum mechanics/molecular mechanics (QM/MM) theoretical level in the present study. We found that the most stable O2 binding state is the end-on type, and the binding states of the side-on type are higher in energy. Based on the binding energies and electronic structure analyses, O2 binds very weakly to the TAO iron center (ΔE =6.7 kcal mol?1) in the electronic state of Fe(II)…OO, not in the suggested charge transferred state such as the superoxide state (Fe(III)OO· –) as seen in hemerythrin. Coordination of other ligands such as water, Cl?, CN?, CO, N3? and H2O2 was also examined, and H2O2 was found to bind most strongly to the Fe(II) site by ΔE = 14.0 kcal mol?1. This was confirmed experimentally through the measurement of ubiquinol oxidase activity of TAO and Cryptosporidium parvum AOX which was found to be inhibited by H2O2 in a dose-dependent and reversible manner. 相似文献
3.
Yong Peng Chengshan Wang Howard H. Xu Feimeng Zhou 《Journal of inorganic biochemistry》2010,104(4):365-675
Parkinson’s disease (PD) is hallmarked by the abnormal intracellular inclusions (Lewy bodies or LBs) in dopaminergic cells. Amyloidogenic protein α-synuclein (α-syn) and iron (including both Fe(III) and Fe(II)) are both found to be present in LBs. The interaction between iron and α-syn might have important biological relevance to PD etiology. Previously, a moderate binding affinity between α-syn and Fe(II) (5.8 × 103 M−1) has been measured, but studies on the binding between α-syn and Fe(III) have not been reported. In this work, electrospray mass spectrometry (ES-MS), cyclic voltammetry (CV), and fluorescence spectroscopy were used to study the binding between α-syn and Fe(II) and the redox property of the resultant α-syn-Fe(II) complex. The complex is of a 1:1 stoichiometry and can be readily oxidized electrochemically and chemically (by O2) to the putative α-syn-Fe(III) complex, with H2O2 as a co-product. The reduction potential was estimated to be 0.025 V vs. Ag/AgCl, which represents a shift by −0.550 V vs. the standard reduction potential of the free Fe(III)/Fe(II) couple. Such a shift allows a binding constant between α-syn and Fe(III), 1.2 × 1013 M−1, to be deduced. Despite the relatively high binding affinity, α-syn-Fe(III) generated from the oxidation of α-syn-Fe(II) still dissociates due to the stronger tendency of Fe(III) to hydrolyze to Fe(OH)3 and/or ferrihydrite gel. The roles of α-syn and its interaction with Fe(III) and/or Fe(II) are discussed in the context of oxidative stress, metal-catalyzed α-syn aggregation, and iron transfer processes. 相似文献
4.
E. Pecoits M. L. Smith D. C. Catling P. Philippot A. Kappler K. O. Konhauser 《Geobiology》2015,13(1):1-14
It is widely accepted that photosynthetic bacteria played a crucial role in Fe(II) oxidation and the precipitation of iron formations (IF) during the Late Archean–Early Paleoproterozoic (2.7–2.4 Ga). It is less clear whether microbes similarly caused the deposition of the oldest IF at ca. 3.8 Ga, which would imply photosynthesis having already evolved by that time. Abiological alternatives, such as the direct oxidation of dissolved Fe(II) by ultraviolet radiation may have occurred, but its importance has been discounted in environments where the injection of high concentrations of dissolved iron directly into the photic zone led to chemical precipitation reactions that overwhelmed photooxidation rates. However, an outstanding possibility remains with respect to photochemical reactions occurring in the atmosphere that might generate hydrogen peroxide (H2O2), a recognized strong oxidant for ferrous iron. Here, we modeled the amount of H2O2 that could be produced in an Eoarchean atmosphere using updated solar fluxes and plausible CO2, O2, and CH4 mixing ratios. Irrespective of the atmospheric simulations, the upper limit of H2O2 rainout was calculated to be <106 molecules cm?2 s?1. Using conservative Fe(III) sedimentation rates predicted for submarine hydrothermal settings in the Eoarchean, we demonstrate that the flux of H2O2 was insufficient by several orders of magnitude to account for IF deposition (requiring ~1011 H2O2 molecules cm?2 s?1). This finding further constrains the plausible Fe(II) oxidation mechanisms in Eoarchean seawater, leaving, in our opinion, anoxygenic phototrophic Fe(II)‐oxidizing micro‐organisms the most likely mechanism responsible for Earth's oldest IF. 相似文献
5.
Semin BK Davletshina LN Aleksandrov AY Lanchinskaya VY Novakova AA Ivanov II 《Biochemistry. Biokhimii?a》2004,69(3):331-339
Light-induced interaction of Fe(II) cations with the donor side of Mn-depleted photosystem II (PS II(–Mn)) results in the binding of iron cations and blocking of the high-affinity (HAZ) Mn-binding site. The pH dependence of the blocking was measured using the diphenylcarbazide/2,6-dichlorophenolindophenol test. The curve of the pH dependence is bell-shaped with pK 1 = 5.8 and pK 2 = 8.0. The pH dependence of the O2-evolution mediated by PS II membranes is also bellshaped (pK 2 = 7.6). The pH dependence of the process of electron donation from exogenous donors in PS II(–Mn) was studied to determine the location of the alkaline pH sensitive site of the electron transport chain. The data of the study showed that the decrease in the iron cation binding efficiency at pH > 7.0 during blocking was determined by the donor side of the PS II(–Mn). Mössbauer spectroscopy revealed that incubation of PS II(–Mn) membranes in a buffer solution containing 57Fe(II) + 57Fe(III) was accompanied by binding only Fe(III) cations. The pH dependence of the nonspecific Fe(III) cation binding is also described by the same bell-shaped curve with pK 2 = 8.1. The treatment of the PS II(–Mn) membranes with the histidine modifier diethylpyrocarbonate resulted in an increase in the iron binding strength at alkaline pH. It is suggested that blocking efficiency at alkaline pH is determined by competition between OH– and histidine ligand for Fe(III). Because the high-affinity Mn-binding site contains no histidine residue, this fact can be regarded as evidence that histidine is located at another (other than high-affinity) Fe(III) binding site. In other words, this means that the blockage of the high-affinity Mn-binding site is determined by at least two iron cations. We assume that inactivation of oxygen-evolving complex and inhibition of photoactivation in the alkaline pH region are also determined by competition between OH– and a histidine residue involved in coordination of manganese cation outside the high-affinity site. 相似文献
6.
Róbert Huszánk György Lendvay Ottó Horváth 《Journal of biological inorganic chemistry》2007,12(5):681-690
Preparation of the water-soluble, kinetically labile, high-spin iron(II) tetrakis(4-sulfonatophenyl)porphyrin, Fe(II)TPPS4−, has been realized in neutral or weakly acidic solutions containing acetate buffer. The buffer played a double role in these
systems: it was used for both adjusting pH and, via formation of an acetato complex, trapping trace amounts of iron(III) ions,
which would convert the iron(II) porphyrins to the corresponding iron(III) species. Fe(II)TPPS4− proved to be stable in these solutions even after saturation with air or oxygen. In the absence of acetate ions, however,
iron(II) ions play a catalytic role in the formation of iron(III) porphyrins. While the kinetically inert iron(III) porphyrin,
Fe(III)TPPS3−, is a regular one with no emission and photoredox properties, the corresponding iron(II) porphyrin displays photoinduced
features which are typical of sitting-atop complexes (redshifted Soret absorption and blueshifted emission and Q absorption
bands, photoinduced porphyrin ligand-to-metal charge transfer, LMCT, reaction). In the photolysis of Fe(II)TPPS4− the LMCT process is followed by detachment of the reduced metal center and an irreversible ring-opening of the porphyrin
ligand, resulting in the degradation of the complex. Possible oxygen-binding ability of Fe(II)TPPS4− (as a heme model) has been studied as well. Density functional theory calculations revealed that in solutions with high acetate
concentration there is very little chance for iron(II) porpyrin to bind and release O2, deviating from heme in a hydrophobic microenvironment in hemoglobin. In the presence of an iron(III)-trapping additive that
is much less strongly coordinated to the iron(II) center than the acetate ion, Fe(II)TPPS4− may function as a heme model. 相似文献
7.
We present a quantitative molecular interpretation of binding between the five B subunits of cholera enterotoxin and the oligosaccharide of ganglioside GM1, based on the currently accepted quaternary structure of the toxin and principles of multiple equilibria. A sequential binding equation is derived and fitted to published binding data obtained by equilibrium dialysis. In one study of binding to reduced toxin (I), intact toxin (II), and isolated B subunits (III) at low concentrations, analysis by the Hill equation suggested that binding was positively cooperative and that there were only four binding sites per toxin molecule; individual affinity constants could not be estimated because of the empirical nature of the Hill equation. Our analysis suggests that the evidence for positive cooperativity is stronger for I and III than for II. Affinity constants for the first binding step are about 2.0–2.1 μM?1 for I and 2.5–2.7 μM?1 for II and III; those for the second binding step are about 3.5–5.0 μM?1 for I and III, but only 2.5 μM?1 for II. Constants for later binding steps are apparently within the range of 2–7 μM?1. Predictions of the sequential model at higher ligand concentrations diverge substantially from those of the Hill equation, and are supported by data obtained at higher protein and ligand concentrations. Thus all available equilibrium dialysis data are consistent with a single set of affinity constants and with the hypothesis of five equivalent binding sites. 相似文献
8.
Neutrophilic Fe(II) oxidizing microorganisms are found in many natural environments. It has been hypothesized that, at low oxygen concentrations, microbial iron oxidation is favored over abiotic oxidation. Here, we compare the kinetics of abiotic Fe(II) oxidation to oxidation in the presence of the bacterium Leptothrix cholodnii Appels isolated from a wetland sediment. Rates of Fe(II) oxidation were determined in batch experiments at 20°C, pH 7 and oxygen concentrations between 3 and 120 μmol/l. The reaction progress in experiments with and without cells exhibited two distinct phases. During the initial phase, the oxygen dependency of microbial Fe(II) oxidation followed a Michaelis-Menten rate expression (KM = 24.5 ± 10 μmol O2/l, vmax = 1.8 ± 0.2 μmol Fe(II)/(l min) for 108 cells/ml). In contrast, abiotic rates increased linearly with increasing oxygen concentrations. At similar oxygen concentrations, initial Fe(II) oxidation rates were faster in the experiments with bacteria. During the second phase, the accumulated iron oxides catalyzed further oxidative iron precipitation in both abiotic and microbial reaction systems. That is, abiotic oxidation also dominated the reaction progress in the presence of bacteria. In fact, in some experiments with bacteria, iron oxidation during the second phase proceeded slower than in the absence of bacteria, possibly due to an inhibitory effect of extracellular polymeric substances on the growth of Fe(III) oxides. Thus, our results suggest that the competitive advantage of microbial iron oxidation in low oxygen environments may be limited by the autocatalytic nature of abiotic Fe(III) oxide precipitation, unless the accumulation of Fe(III) oxides is prevented, for example, through a close coupling of Fe(II) oxidation and Fe(III) reduction. 相似文献
9.
F. Macrì E. Braidot E. Petrussa M. Zancani A. Vianello 《Plant biology (Stuttgart, Germany)》1992,105(2):97-103
This work was undertaken to verify whether surface NADH oxidases or peroxidases are involved in the apoplastic reduction of Fe(III). The reduction of Fe(III)-ADP, linked to NADH-dependent activity of horseradish peroxidase (HRP), protoplasts and cells of Acer pseudoplatanus, was measured as Fe(II)-bathophenanthrolinedisulfonate (BPDS) chelate formation. In the presence of BPDS in the incubation medium (method 1), NADH-dependent HRP activity was associated with a rapid Fe(III)-ADP reduction that was almost completely inhibited by superoxide dismutase (SOD), while catalase only slowed down the rate of reduction. A. pseudoplatanus protoplasts and cells reduced extracellular Fe(III)-ADP in the absence of exogenously supplied NADH. The addition of NADH stimulated the reduction. SOD and catalase only inhibited the NADH-dependent Fe(III)-ADP reduction. Mn(II), known for its ability to scavenge O?2, inhibited both the independent and NADH-dependent Fe(III)-ADP reduction. The reductase activity of protoplasts and cells was also monitored in the absence of BPDS (method 2). The latter was added only at the end of the reaction to evaluate Fe(II) formed. Also, in this case, both preparations reduced Fe(III)-ADP. However, the addition of NADH did not stimulate Fe(III)-ADP reduction but, instead, lowered it. This may be related to a re-oxidation of Fe(II) by H2O2 that could also be produced during NADH-dependent peroxidase activity. Catalase and SOD made the Fe(III)-ADP reduction more efficient because, by removing H2O2 (catalase) or preventing H2O2 formation (SOD), they hindered the re-oxidation of Fe(II) not chelated by BPDS. As with the result obtained by method 1, Mn(II) inhibited Fe(III)-ADP reduction carried out in the presence or absence of NADH. The different effects of SOD and Mn(II), both scavengers of O?2, may depend on the ability of Mn(II) to permeate the cells more easily than SOD. These results show that A. pseudoplatanus protoplasts and cells reduce extracellular Fe(III)-ADP. Exogenously supplied NADH induces an additional reduction of Fe(III) by the activity of NADH peroxidases of the plasmalemma or cell wall. However, the latter can also trigger the formation of H2O2 that, reacting with Fe(II) (not chelated by BPDS), generates hydroxyl radicals and converts Fe(II) to Fe(III) (Fenton's reaction). 相似文献
10.
《Bioscience, biotechnology, and biochemistry》2013,77(6):1324-1331
Phosvitin, a phosphoprotein known as an iron-carrier in egg yolk, binds almost all the yolk iron. In this study, we investigated the effect of phosvitin on Fe(II)-catalyzed hydroxyl radical (?OH) formation from H2O2 in the Fenton reaction system. Using electron spin resonance (ESR) with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and deoxyribose degradation assays, we observed by both assays that phosvitin more effectively inhibited ?OH formation than iron-binding proteins such as ferritin and transferrin. The effectiveness of phosvitin was related to the iron concentration, indicating that phosvitin acts as an antioxidant by chelating iron ions. Phosvitin accelerates Fe(II) autoxidation and thus decreases the availability of Fe(II) for participation in the ?OH-generating Fenton reaction. Furthermore, using the plasmid DNA strand breakage assay, phosvitin protected DNA against oxidative damage induced by Fe(II) and H2O2. These results provide insight into the mechanism of protection of the developing embryo against iron-dependent oxidative damage in ovo. 相似文献
11.
Regulation of Dissimilatory Fe(III) Reduction Activity in Shewanella putrefaciens 总被引:5,自引:4,他引:5
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Robert G. Arnold Michael R. Hoffmann Thomas J. DiChristina Flynn W. Picardal 《Applied microbiology》1990,56(9):2811-2817
Under anaerobic conditions, Shewanella putrefaciens is capable of respiratory-chain-linked, high-rate dissimilatory iron reduction via both a constitutive and inducible Fe(III)-reducing system. In the presence of low levels of dissolved oxygen, however, iron reduction by this microorganism is extremely slow. Fe(II)-trapping experiments in which Fe(III) and O2 were presented simultaneously to batch cultures of S. putrefaciens indicated that autoxidation of Fe(II) was not responsible for the absence of Fe(III) reduction. Inhibition of cytochrome oxidase with CN− resulted in a high rate of Fe(III) reduction in the presence of dissolved O2, which suggested that respiratory control mechanisms did not involve inhibition of Fe(III) reductase activities or Fe(III) transport by molecular oxygen. Decreasing the intracellular ATP concentrations by using an uncoupler, 2,4-dinitrophenol, did not increase Fe(III) reduction, indicating that the reduction rate was not controlled by the energy status of the cell. Control of electron transport at branch points could account for the observed pattern of respiration in the presence of the competing electron acceptors Fe(III) and O2. 相似文献
12.
《Luminescence》2003,18(5):259-267
High‐valent oxo‐iron(IV) species are commonly proposed as the key intermediates in the catalytic mechanisms of iron enzymes. Water‐soluble iron(III) tetrakis‐5,10,15,20‐(N‐methyl‐4‐pyridyl)porphyrin (Fe(III)TMPyP) has been used as a model of heme‐enzyme to catalyse the hydrogen peroxide (H2O2) oxidation of various organic compounds. However, the mechanism of the reaction of Fe(III)TMPyP with H2O2 has not been fully established. In this study, we have explored the kinetic simulation of the reaction of Fe(III)TMPyP with H2O2 and of the catalytic reactivity of FeTMPyP in the luminescent peroxidation of luminol. According to the mechanism that has been established in this work, Fe(III)TMPyP is oxidized by H2O2 to produce (TMPyP)·+Fe(IV)=O (k1 = 4.5 × 104/mol/L/s) as a precursor of TMPyPFe(IV)=O. The intermediate, (TMPyP)·+Fe(IV)=O, represented nearly 2% of Fe(III)TMPyP but it does not accumulate in suf?cient concentration to be detected because its decay rate is too fast. Kinetic simulations showed that the proposed scheme is capable of reproducing the observed time courses of FeTMPyP in various oxidation states and the decay pro?les of the luminol chemiluminescence. It also shows that (TMPyP)·+Fe(IV)=O is 100 times more reactive than TMPyPFe(IV)=O in most of the reactions. These two species are responsible for the initial sharp and the sustained luminol emissions, respectively. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
13.
《Inorganica chimica acta》1988,152(4):227-231
Mössbauer and electronic absorbance spectroscopic studies on the reactions of iron(II): ascorbic acid with molecular oxygen in aqueous and methanolic solutions are reported. Both spectroscopic techniques show that in the starting mixtures there are no iron(II): ascorbate complexes. On mixing the iron(II)/ascorbate solution with solutions containing molecular oxygen at pH 6–7 high spin iron(III) is observed in the Mössbauer spectrum. Coloured intermediates, the lifetimes of which are solvent dependent, are seen by stopped-flow spectrophotometry. We assign these coloured intermediates as iron(III) ascorbate complexes. The stoichiometry of the initial reaction between iron(II) and oxygen is shown to be 2Fe(II):O2 by stopped-flow methods. A scheme for the overall reactions is discussed. 相似文献
14.
《Free radical research》2013,47(4-6):259-270
Using the pulse radiolysis technique, we have demonstrated that bleomycin-Fe(III) is stoichiometrically reduced by CO2? to bleomycin-Fe(II) with a rate of (1.9 ± 0.2) × 108M?1s?1. In the presence of calf thymus DNA, the reduction proceeds through free bleomycin-Fe(III) and the binding constant of bleomycin-Fe(III) to DNA has been determined to be (3.8 ± 0.5) x 104 M?1. It has also been demonstrated that in the absence of DNA O2?1 reacts with bleomycin-Fe(III) to yield bleomycin-Fe(II)O2, which is in rapid equilibrium with molecular oxygen, and decomposes at room temperature with a rate of (700 ± 200) s?1. The resulting product of the decomposition reaction is Fe(III) which is bound to a modified bleomycin molecule. We have demonstrated that during the reaction of bleomycin-Fe(II) with O2, modification or self-destruction of the drug occurs, while in the presence of DNA no destruction occurs, possibly because the reaction causes degradation of DNA. 相似文献
15.
《BBA》2019,1860(12):148060
Oxygen (O2) activation is a central challenge in chemistry and catalyzed at prototypic dimetal cofactors in biological enzymes with diverse functions. Analysis of intermediates is required to elucidate the reaction paths of reductive O2 cleavage. An oxidase protein from the bacterium Geobacillus kaustophilus, R2lox, was used for aerobic in-vitro reconstitution with only 57Fe(II) or Mn(II) plus 57Fe(II) ions to yield [FeFe] or [MnFe] cofactors under various oxygen and solvent isotopic conditions including 16/18O and H/D exchange. 57Fe-specific X-ray scattering techniques were employed to collect nuclear forward scattering (NFS) and nuclear resonance vibrational spectroscopy (NRVS) data of the R2lox proteins. NFS revealed Fe/Mn(III)Fe(III) cofactor states and Mössbauer quadrupole splitting energies. Quantum chemical calculations of NRVS spectra assigned molecular structures, vibrational modes, and protonation patterns of the cofactors, featuring a terminal water (H2O) bound at iron or manganese in site 1 and a metal-bridging hydroxide (μOH−) ligand. A procedure for quantitation and correlation of experimental and computational NRVS difference signals due to isotope labeling was developed. This approach revealed that the protons of the ligands as well as the terminal water at the R2lox cofactors exchange with the bulk solvent whereas 18O from 18O2 cleavage is incorporated in the hydroxide bridge. In R2lox, the two water molecules from four-electron O2 reduction are released in a two-step reaction to the solvent. These results establish combined NRVS and QM/MM for tracking of iron-based oxygen activation in biological and chemical catalysts and clarify the reductive O2 cleavage route in an enzyme. 相似文献
16.
W H Fuchsman C H Barlow W J Wallace W S Caughey 《Biochemical and biophysical research communications》1974,61(2):635-643
Solid dipyridine hemes which are unreactive toward oxygen lose both pyridine ligands upon heating under vacuum to give a solid which takes up O2, reversibly, one O2 per heme. Replacement of 16O2 by 18O2 reduces only infrared bands near 1660 and 1590 cm?1, frequencies near the vibrational band for gaseous O2. No FeO bands are detected. EPR spectra reveal a free radical and ferric iron; Mössbauer, NMR and infrared spectra support an iron(III) oxidation state. Limited molecular weight data indicate a dimer. Possibly two dioxygen molecules are held sandwich fashion between two porphyrins via donor-acceptor interactions, which are facilitated by electron transfer from iron(II) into the porphyrin forming a π-anion. Such O2 bonding is not found in oxy Hb and Mb or in oxyhemerythrin but may occur with cytochrome oxidase and other oxygen utilizing (or producing) heme and other proteins. 相似文献
17.
Iron oxidation stimulates organic matter decomposition in humid tropical forest soils 总被引:2,自引:0,他引:2
Humid tropical forests have the fastest rates of organic matter decomposition globally, which often coincide with fluctuating oxygen (O2) availability in surface soils. Microbial iron (Fe) reduction generates reduced iron [Fe(II)] under anaerobic conditions, which oxidizes to Fe(III) under subsequent aerobic conditions. We demonstrate that Fe (II) oxidation stimulates organic matter decomposition via two mechanisms: (i) organic matter oxidation, likely driven by reactive oxygen species; and (ii) increased dissolved organic carbon (DOC) availability, likely driven by acidification. Phenol oxidative activity increased linearly with Fe(II) concentrations (P < 0.0001, pseudo R2 = 0.79) in soils sampled within and among five tropical forest sites. A similar pattern occurred in the absence of soil, suggesting an abiotic driver of this reaction. No phenol oxidative activity occurred in soils under anaerobic conditions, implying the importance of oxidants such as O2 or hydrogen peroxide (H2O2) in addition to Fe(II). Reactions between Fe(II) and H2O2 generate hydroxyl radical, a strong nonselective oxidant of organic compounds. We found increasing consumption of H2O2 as soil Fe(II) concentrations increased, suggesting that reactive oxygen species produced by Fe(II) oxidation explained variation in phenol oxidative activity among samples. Amending soils with Fe(II) at field concentrations stimulated short‐term C mineralization by up to 270%, likely via a second mechanism. Oxidation of Fe(II) drove a decrease in pH and a monotonic increase in DOC; a decline of two pH units doubled DOC, likely stimulating microbial respiration. We obtained similar results by manipulating soil acidity independently of Fe(II), implying that Fe(II) oxidation affected C substrate availability via pH fluctuations, in addition to producing reactive oxygen species. Iron oxidation coupled to organic matter decomposition contributes to rapid rates of C cycling across humid tropical forests in spite of periodic O2 limitation, and may help explain the rapid turnover of complex C molecules in these soils. 相似文献
18.
Claudia Lüdecke Marco Reiche Karin Eusterhues Sandor Nietzsche Kirsten Küsel 《Environmental microbiology》2010,12(10):2814-2825
The ecological importance of Fe(II)‐oxidizing bacteria (FeOB) at circumneutral pH is often masked in the presence of O2 where rapid chemical oxidation of Fe(II) predominates. This study addresses the abundance, diversity and activity of microaerophilic FeOB in an acidic fen (pH ~5) located in northern Bavaria, Germany. Mean O2 penetration depth reached 16 cm where the highest dissolved Fe(II) concentrations (up to 140 µM) were present in soil water. Acid‐tolerant FeOB cultivated in gradient tubes were most abundant (106 cells g?1 peat) at the 10–20 cm depth interval. A stable enrichment culture was active at up to 29% O2 saturation and Fe(III) accumulated 1.6 times faster than in abiotic controls. An acid‐tolerant, microaerophilic isolate (strain CL21) was obtained which was closely related to the neutrophilic, lithoautotrophic FeOB Sideroxydans lithotrophicus strain LD‐1. CL21 oxidized Fe(II) between pH 4 and 6.0, and produced nanoscale‐goethites with a clearly lower mean coherence length (7 nm) perpendicular to the (110) plane than those formed abiotically (10 nm). Our results suggest that an acid‐tolerant population of FeOB is thriving at redox interfaces formed by diffusion‐limited O2 transport in acidic peatlands. Furthermore, this well‐adapted population is successfully competing with chemical oxidation and thereby playing an important role in the microbial iron cycle. 相似文献
19.
G. Park F. H. Lu N. Ye M. W. Brechbiel S. V. Torti F. M. Torti R. P. Planalp 《Journal of biological inorganic chemistry》1998,3(5):449-457
The interaction of Fe(II) and Fe(III) with the novel Fe(II) chelator N,N′N″-tris(2-pyridylmethyl)-cis,cis-1,3,5-triaminocyclohexane (referred to as tachpyr) gives rise to six-coordinate, low-spin, cationic complexes of Fe(II).
Tachpyr also displays a cytotoxicity toward cultured bladder cancer cells that is believed to involve coordination of intracellular
iron. The anaerobic reaction of tachpyr with Fe(II) salts affords the Fe(II)-tachpyr2+ complex, but in presence of oxygen, oxidative dehydrogenation of one or two of the aminomethylene group(s) of the ligand
occurs, with formal loss of H2: R—N(H)—C(H)2—(2-py) → R—N=C(H)—(2-py)+H2. The resulting mono- and diimino Fe(II) complexes (denoted as [Fe(tachpyr-H2)]2+ and [Fe(tachpyr-2H2)]2+) are an inseparable mixture, but they may be fully oxidized by H2O2 to the known tris(imino) complex Fe(II)[cis,cis-1,3,5-tris(pyridine-2-carboxaldimino)cyclohexane]2+ (or [Fe(tachpyr-3H2)]2+). Cyclic voltammetry of the imino complex mixture reveals an irreversible anodic wave at +0.78 V vs. NHE. Tachpyr acts as
a reducing agent toward Fe(IIII) salts, affording the same two Fe(II) imino complexes as products. Tachpyr also reductively
removes Fe(III) from an Fe(III)(ATP)3 complex (which is a putative form of intracellular iron), producing the two Fe(II) imino complexes. Novel N-alkylated derivatives of tachpyr have been synthesized. N-Alkylation has two effects on tachpyr: lowering metal affinity through increased steric hindrance, and preventing Fe(III)
reduction because oxidative dehydrogenation of nitrogen is blocked. The N-methyl tachpyr derivative binds Fe(II) only weakly as a high-spin complex, and no complexation or reduction of Fe(III) is
observed. Corresponding to their inability to bind iron, the N-alkylated chelators are nontoxic to cultured bladder cancer cells. A tach-based chelator with three N-propyleneamino arms is also synthesized. Studies of the chemical and biochemical properties of this chelator further support
a relationship between intracellular iron chelation, iron reduction, and cytotoxicity.
Received: 23 March 1998 / Accepted: 1 June 1998 相似文献
20.
Evidence for rapid microscale bacterial redox cycling of iron in circumneutral environments 总被引:3,自引:0,他引:3
The potential for microscale bacterial Fe redox cycling was investigated in microcosms containing ferrihydrite-coated sand
and a coculture of a lithotrophic Fe(II)-oxidizing bacterium (strain TW2) and a dissimilatory Fe(III)-reducing bacterium (Shewanella alga strain BrY). The Fe(II)-oxidizing organism was isolated from freshwater wetland surface sediments which are characterized
by steep gradients of dissolved O2 and high concentrations of dissolved and solid-phase Fe(II) within mm of the sediment–water interface, and which support
comparable numbers (105–106 mL−1) of culturable Fe(II)-oxidizing and Fe(III)-reducing reducing. The coculture systems showed minimal Fe(III) oxide accumulation
at the sand-water interface, despite intensive O2 input from the atmosphere and measurable dissolved O2 to a depth of 2 mm below the sand–water interface. In contrast, a distinct layer of oxide precipitates formed in systems
containing Fe(III)-reducing bacteria alone. Examination of materials from the cocultures by fluorescence in situ hybridization
indicated close physical juxtapositioning of Fe(II)-oxidizing and Fe(III)-reducing bacteria in the upper few mm of sand. Our
results indicate that Fe(II)-oxidizing bacteria have the potential to enhance the coupling of Fe(II) oxidation and Fe(III)
reduction at redox interfaces, thereby promoting rapid microscale cycling of Fe.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献