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81.
82.
Stefan Mebs Ramona Kositzki Jifu Duan Leonie Kertess Moritz Senger Florian Wittkamp Ulf-Peter Apfel Thomas Happe Sven T. Stripp Martin Winkler Michael Haumann 《BBA》2018,1859(1):28-41
[FeFe]-hydrogenases are superior hydrogen conversion catalysts. They bind a cofactor (H-cluster) comprising a four-iron and a diiron unit with three carbon monoxide (CO) and two cyanide (CN?) ligands. Hydrogen (H2) and oxygen (O2) binding at the H-cluster was studied in the C169A variant of [FeFe]-hydrogenase HYDA1, in comparison to the active oxidized (Hox) and CO-inhibited (Hox-CO) species in wildtype enzyme. 57Fe labeling of the diiron site was achieved by in vitro maturation with a synthetic cofactor analogue. Site-selective X-ray absorption, emission, and nuclear inelastic/forward scattering methods and infrared spectroscopy were combined with quantum chemical calculations to determine the molecular and electronic structure and vibrational dynamics of detected cofactor species. Hox reveals an apical vacancy at Fed in a [4Fe4S-2Fe]3 ? complex with the net spin on Fed whereas Hox-CO shows an apical CN? at Fed in a [4Fe4S-2Fe(CO)]3 ? complex with net spin sharing among Fep and Fed (proximal or distal iron ions in [2Fe]). At ambient O2 pressure, a novel H-cluster species (Hox-O2) accumulated in C169A, assigned to a [4Fe4S-2Fe(O2)]3 ? complex with an apical superoxide (O2?) carrying the net spin bound at Fed. H2 exposure populated the two-electron reduced Hhyd species in C169A, assigned as a [(H)4Fe4S-2Fe(H)]3 ? complex with the net spin on the reduced cubane, an apical hydride at Fed, and a proton at a cysteine ligand. Hox-O2 and Hhyd are stabilized by impaired O2– protonation or proton release after H2 cleavage due to interruption of the proton path towards and out of the active site. 相似文献
83.
G. J. D. Kirk 《Plant and Soil》2002,245(1):49-57
Theory for coupled diffusion processes in soil is briefly described and three examples of its application to understand root-induced solubilization of nutrients given. The examples are: (1) solubilization of P through root-induced pH changes in the rhizosphere of rice plants growing in flooded soil; (2) solubilization of P through excretion of organic chelating agents from rice roots growing in aerobic soil; and (3) the effects of root geometry on P solubilization, particularly cylindrical versus planar geometry and the effect of excretion of a solubilizing agent being localized along the root axis. The theory is tested by comparing measured concentration profiles of P near roots with the predictions of the theory made using independently measured parameter values. In the examples given, the agreement between the observed and predicted concentration profiles is very good, indicating that the theory is sound and the processes involved well understood. 相似文献
84.
《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
85.
The late‐stage “ferruginization” of the Ediacara Member (Rawnsley Quartzite,South Australia): Insights from uranium isotopes 下载免费PDF全文
L. G. Tarhan N. J. Planavsky X. Wang E. J. Bellefroid M. L. Droser J. G. Gehling 《Geobiology》2018,16(1):35-48
The paleoenvironmental setting in which the Ediacara Biota lived, died, and was preserved in the eponymous Ediacara Member of the Rawnsley Quartzite of South Australia is an issue of long‐standing interest and recent debate. Over the past few decades, interpretations have ranged from deep marine to shallow marine to terrestrial. One of the key features invoked by adherents of the terrestrial paleoenvironment hypothesis is the presence of iron oxide coatings, inferred to represent the upper horizons of paleosols, along fossiliferous sandstone beds of the Ediacara Member. We find that these surficial oxides are characterized by (234U/238U) values which are not in secular equilibrium, indicating extensive fluid‐rich alteration of these surfaces within the past approximately 2 million years. Specifically, the oxide coatings are characterized by (234U/238U) values >1, indicating interaction with high‐(234U/238U) fluids derived from alpha‐recoil discharge. These oxides are also characterized by light “stable” δ238/235U values, consistent with a groundwater U source. These U isotope data thus corroborate sedimentological observations that ferric oxides along fossiliferous surfaces of the Ediacara Member consist of surficial, non‐bedform‐parallel staining, and sharply irregular patches, strongly reflecting post‐depositional, late‐stage processes. Therefore, both sedimentological and geochemical evidence indicate that Ediacara iron oxides do not reflect synsedimentary ferruginization and that the presence of iron oxides cannot be used to either invoke a terrestrial paleoenvironmental setting for or reconstruct the taphonomic pathways responsible for preservation of the Ediacara Biota. These findings demonstrate that careful assessment of paleoenvironmental parameters is essential to the reconstruction of the habitat of the Ediacara Biota and the factors that led to the fossilization of these early complex ecosystems. 相似文献
86.
Iron content of sediment and phosphate adsorption properties 总被引:7,自引:2,他引:7
Phosphorus can occur in sediments in different forms and accordingly its availability varies. The distinction between the phosphorus fractions is made with two chemical extraction methods; an ammonium oxalate-oxalic acid extraction and an extraction according to Hieltjes & Lijklema (1980).The iron and aluminum liberated with the ammonium oxalate-oxalic acid extraction method is linearly correlated (r
2 = 0.73) with the phosphorus liberated in the first two steps of the Hieltjes and Lijklema extraction by: P = 0.035 (Fe + Al) + 0.001 (P, Fe and Al in mmol g–1).The iron and aluminum (hydr)oxides are very important fractions in the sediment adsorption capacity for phosphorus. The phosphorus sorption capacity (PSC) is 0.080 mol P (mol (Fe + Al))–1 and the adsorption constant (k) is 11.9 µmol P l–1. Here it is assumed that iron and aluminum (hydr)oxide have the same affinity for phosphorus. 相似文献
87.
Xingzhi Jing Ting Du Tao Li Xiaoxia Yang Guodong Wang Xiaoyang Liu Zhensong Jiang Xingang Cui 《Journal of cellular and molecular medicine》2021,25(12):5671-5680
Iron overload is common in elderly people which is implicated in the disease progression of osteoarthritis (OA), however, how iron homeostasis is regulated during the onset and progression of OA and how it contributes to the pathological transition of articular chondrocytes remain unknown. In the present study, we developed an in vitro approach to investigate the roles of iron homeostasis and iron overload mediated oxidative stress in chondrocytes under an inflammatory environment. We found that pro-inflammatory cytokines could disrupt chondrocytes iron homeostasis via upregulating iron influx transporter TfR1 and downregulating iron efflux transporter FPN, thus leading to chondrocytes iron overload. Iron overload would promote the expression of chondrocytes catabolic markers, MMP3 and MMP13 expression. In addition, we found that oxidative stress and mitochondrial dysfunction played important roles in iron overload-induced cartilage degeneration, reducing iron concentration using iron chelator or antioxidant drugs could inhibit iron overload-induced OA-related catabolic markers and mitochondrial dysfunction. Our results suggest that pro-inflammatory cytokines could disrupt chondrocytes iron homeostasis and promote iron influx, iron overload-induced oxidative stress and mitochondrial dysfunction play important roles in iron overload-induced cartilage degeneration. 相似文献
88.
Kiyotaka Watanabe Naoko Muranishi Yoshiko Murata Kouichi Orino Shozo Okano Shinji Yamamoto 《Biometals》2000,13(4):319-324
A sandwich enzyme-linked immunosorbent assay using H-subunit-rich canine heart ferritin as a standard has been developed for measuring canine serum ferritin which is H-subunit-rich. Serum ferritin concentrations in 51 normal dogs ranged from 143 to 1766 ng ml–1, with a mean value of 479±286 (SD) ng ml–1. Serum ferritin iron concentrations as determined by an immunoprecipitation technique ranged from 30.4 to 115.9 ng ml–1 in 15 normal dogs with serum ferritin protein levels of 298 to 959 ng ml–1. There was a significant linear correlation between the serum ferritin iron and protein levels (r=0.9441, P<0.001), and the mean iron/protein ratio of serum ferritin was 0.112±0.017. When canine sera were incubated with concanavalin A-Sepharose 4B, we observed the apparent binding of serum ferritin to concanavalin A. However, ferritin obtained by heat-treating the sera at pH 4.8 to remove the ferritin-binding proteins did not bind to the lectin. These results suggest that canine serum ferritin contains a considerable amount of iron but no concanavalin A-binding G subunit present in human serum ferritin. 相似文献
89.
Wiesinger JA Buwen JP Cifelli CJ Unger EL Jones BC Beard JL 《Journal of neurochemistry》2007,100(1):167-179
Neurological development and functioning of dopamine (DA) neurotransmission is adversely affected by iron deficiency in early life. Iron-deficient rats demonstrate significant elevations in extracellular DA and a reduction in dopamine transporter (DAT) densities in the caudate putamen and nucleus accumbens. To explore possible mechanisms by which cellular iron concentrations control DAT functioning, endogenous DAT-expressing PC12 cells were used to determine the effect of iron chelation on DAT protein and mRNA expression patterns. In addition, we used human DAT (hDAT)-transfected Neuro2a (N2A) cells to examine DAT degradation and trafficking patterns. A 50 microM treatment for 24 h with the iron chelator, desferrioxamine (DFO), significantly decreased dopamine uptake in a dose-dependent manner, with no apparent change in K(m), in both PC12 and N2A cells. Reduced DA uptake was accompanied by concentration- and time-dependent reductions in total DAT protein levels in both cell lines. Exposure to increasing concentrations of DFO did not significantly alter DAT mRNA in either PC12 or N2A cells. However, DAT degradation rates increased three-fivefold in both cell types exposed to 50 microM DFO for 24 h. Biotinylation studies in N2A cells indicate a more dramatic loss of DAT in the membrane fraction, while OptiPrep fractionation experiments revealed an increase in lysosomal DAT with iron chelation. Inhibition of protein kinase C activation with staurosporin prevented the effect of iron chelation on DAT function, suggesting that in vitro iron chelation affects DAT primarily through the effects on trafficking rather than on synthesis. 相似文献