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1.
Gantasala N. Srinivas 《Inorganica chimica acta》2009,362(7):2172-250
The heavier analogs of C2H2 have been studied at the B3LYP level for their μ and μ4-η2 coordination properties with the transition metals. Based on known alkyne compounds, transition metal fragments [W2(μ-NH)(Cp)2(Cl)2] and [Fe4(CO)12] have been chosen. The SBKJC relativistic effective core potentials and their associated basis sets were used on W, Fe, Sn and Pb, and the 6-31G(d) basis set was used on all other elements. All the complexes of Si2H2, Ge2H2, Sn2H2 and Pb2H2 are found to be local minima. The trans-twist nature of the ligand A2H2 (A = Si-Pb) is large in μ-coordinated complexes of W, and it is very small in μ4-η2 coordinated complexes of Fe. The electronic structure of these complexes was investigated using fragment molecular orbital method (FMO). 相似文献
2.
Bennett T. Farmer II Luciano Müller Edward P. Nikonowicz Arthur Pardi 《Journal of biomolecular NMR》1994,4(1):129-133
Summary A set of three 3D (1H, 13C, 15N) triple-resonance correlation experiments has been designed to provide H1-H8 intraresidue sugar-to-base correlations in purines in an unambiguous and efficient manner. Together, the HsCsNb, HsCs(N)bCb, and HbNbCb experiments correlate the H1 sugar proton to the H8 proton of the attached base by means of the {H1, C1, N9, C8, H8} heteronuclear scalar coupling network. The assignment strategy presented here allows for unambiguous H1-H8 intraresidue correlations, provided that no two purines have both the same H1 and C1 chemical shifts and the same C8 and N9 chemical shifts. These experiments have yielded H1-H8 intraresidue sugar-to-base correlations for all five guanosines in the [13C, 15N] isotopically labeled RNA duplex r(GGCGCUUGCGUC)2. 相似文献
3.
Type 1 pili, anchored to the outer membrane protein FimD, enable uropathogenic Escherichia coli to attach to host cells. During pilus biogenesis, the N-terminal periplasmic domain of FimD (FimD(N)) binds complexes between the chaperone FimC and pilus subunits via its partly disordered N-terminal segment, as recently shown for the FimC-FimH(P)-FimD(N) ternary complex. We report the structure of a new ternary complex (FimC-FimF(t)-FimD(N)) with the subunit FimF(t) instead of FimH(p). FimD(N) recognizes FimC-FimF(t) and FimC-FimH(P) very similarly, predominantly through hydrophobic interactions. The conserved binding mode at a "hot spot" on the chaperone surface could guide the design of pilus assembly inhibitors. 相似文献
4.
Khodayar Gholivand Mohammad Abdollahi Fresia Mojahed Ahlam Madani Alizadehgan Gholamreza Dehghan 《Journal of enzyme inhibition and medicinal chemistry》2013,28(2):566-576
Eight newly synthesized carbacylamidophosphates with the general formula RC(O)NHP(O)Cl2 with R = pCl–C6H4 1a, pBr–C6H4 2a, C6H5 3a, and pMe–C6H4 4a and RC(O)NHP(O)(NC4H8O)2 R = pCl–C6H4 1b, pBr–C6H4 2b, C6H5 3b, pMe–C6H4 4b, were selected to compare the inhibition kinetic parameters, IC50, Ki, kp and KD, on human erythrocyte acetylcholinesterase (hAChE) and bovine serum butyrylcholinesterase (BuChE), Also, the in vivo inhibition potency of compound 2a, 2b and 3a, were studied. The data demonstrates that compound 2a and compound 2b are the potent sensitive as AChE and BuChE inhibitors respectively, and the inhibition of hAChE is about 10-fold greater than that of BuChE. 相似文献
5.
Human non-pancreatic secretory phospholipase A2 (hnpsPLA2) is a group IIA phospholipase A2 which plays an important role in the innate immune response. This enzyme was found to exhibit bactericidal activity toward Gram-positive bacteria, but not Gram-negative ones. Though native hnpsPLA2 is active over a broad pH range, it is only highly active at alkaline conditions with the optimum activity pH of about 8.5. In order to make it highly active at neutral pH, we have obtained two hnpsPLA2 mutants, Glu89Lys and Arg100Glu that work better at neutral pH in a previous study. In the present study, we tested the bactericidal effects of the native hnpsPLA2 and the two mutants. Both native hnpsPLA2 and the two mutants exhibit bactericidal activity toward Gram-positive bacteria. Furthermore, they can also kill Escherichia coli, a Gram-negative bacterium. The two mutants showed better bactericidal activity for E. coli at neutral pH than the native enzyme, which is consistent with the enzyme activities. As hnpsPLA2 is highly stable and biocompatible, it may provide a promising therapy for bacteria infection treatment or other bactericidal applications. 相似文献
6.
7.
Grüber G 《Journal of bioenergetics and biomembranes》2003,35(4):277-280
The vacuolar ATPases (V-type ATPases) are a family of ATP-dependent ion pumps and found in two principal locations, in endomembranes and in plasma membranes. This family of ATPases is responsible for acidification of intracellulare compartments and, in certain cases, ion transport across the plasma membrane of eucaryotic cells. V-ATPases are composed of two distinct domains: a catalytic V1 sector, in which ATP hydrolysis takes place, and the membrane-embedded sector, V0, which functions in ion conduction. In the past decade impressive progress has been made in elucidating the properties structure, function and moleculare biology. These knowledge sheds light also on the evolution of V-ATPases and their related families of A-(A1A0-ATPase) and F-type (F1F0-ATPases)ATPases. 相似文献
8.
Hui Sun Yuqi Ding Jinzhao Duan Qijun Zhang Zhiyong Wang Hui Lou Xiaoming Zheng 《Bioresource technology》2010,101(3):953-958
ZrO2 supported La2O3 catalyst prepared by impregnation method was examined in the transesterification reaction of sunflower oil with methanol to produce biodiesel. It was found that the catalyst with 21 wt% loaded La2O3 and calcined at 600 °C showed the optimum activity. The basic property of the catalyst was studied by CO2-TPD, and the results showed that the fatty acid methyl ester (FAME) yield was related to their basicity. The catalyst was also characterized by TG–DTA, XRD, FTIR, SEM and TEM, and the mechanism for the formation of basic sites was discussed. It was also found that the crystallite size of support ZrO2 decreased by loading of La2O3, and the model of the solid-state reaction on the surface of La2O3/ZrO2 catalyst was proposed. Besides, the influence of various reaction variables on the conversion was investigated. 相似文献
9.
Luth Robin P Germain P Lecomte M Landrain B Li Y Cluzeau D 《Bioresource technology》2011,102(4):3679-3686
Treatment of liquid manure can result in the production of ammonia, nitrous oxide and methane. Earthworms mix and transform nitrogen and carbon without consuming additional energy. The objective of this paper is to analyse whether earthworms modify the emissions of NH3, N2O, CH4 and CO2 during vermifiltration of pig slurry.The experiment used mesocosms of around 50 L, made from a vermifilter treating the diluted manure of a swine house. Three levels of slurry were added to the mesocosms, with or without earthworms, during one month, in triplicate. Earthworm abundance and gas emissions were measured three and five times, respectively.There was a decrease in emissions of ammonia and nitrous oxide and a sink of methane in treatments with earthworms. We suggest that earthworm abundance can be used as a bioindicator of low energy input, and low greenhouse gas and ammonia output in systems using fresh slurry with water recycling. 相似文献
10.
The potential for C4 photosynthesis was investigated in five C3-C4 intermediate species, one C3 species, and one C4 species in the genus Flaveria, using 14CO2 pulse-12CO2 chase techniques and quantum-yield measurements. All five intermediate species were capable of incorporating 14CO2 into the C4 acids malate and aspartate, following an 8-s pulse. The proportion of 14C label in these C4 products ranged from 50–55% to 20–26% in the C3-C4 intermediates F. floridana Johnston and F. linearis Lag. respectively. All of the intermediate species incorporated as much, or more, 14CO2 into aspartate as into malate. Generally, about 5–15% of the initial label in these species appeared as other organic acids. There was variation in the capacity for C4 photosynthesis among the intermediate species based on the apparent rate of conversion of 14C label from the C4 cycle to the C3 cycle. In intermediate species such as F. pubescens Rydb., F. ramosissima Klatt., and F. floridana we observed a substantial decrease in label of C4-cycle products and an increase in percentage label in C3-cycle products during chase periods with 12CO2, although the rate of change was slower than in the C4 species, F. palmeri. In these C3-C4 intermediates both sucrose and fumarate were predominant products after a 20-min chase period. In the C3-C4 intermediates, F. anomala Robinson and f. linearis we observed no significant decrease in the label of C4-cycle products during a 3-min chase period and a slow turnover during a 20-min chase, indicating a lower level of functional integration between the C4 and C3 cycles in these species, relative to the other intermediates. Although F. cronquistii Powell was previously identified as a C3 species, 7–18% of the initial label was in malate+aspartate. However, only 40–50% of this label was in the C-4 position, indicating C4-acid formation as secondary products of photosynthesis in F. cronquistii. In 21% O2, the absorbed quantum yields for CO2 uptake (in mol CO2·[mol quanta]-1) averaged 0.053 in F. cronquistii (C3), 0.051 in F. trinervia (Spreng.) Mohr (C4), 0.052 in F. ramosissima (C3-C4), 0.051 in F. anomala (C3-C4), 0.050 in F. linearis (C3-C4), 0.046 in F. floridana (C3-C4), and 0.044 in F. pubescens (C3-C4). In 2% O2 an enhancement of the quantum yield was observed in all of the C3-C4 intermediate species, ranging from 21% in F. ramosissima to 43% in F. pubescens. In all intermediates the quantum yields in 2% O2 were intermediate in value to the C3 and C4 species, indicating a co-function of the C3 and C4 cycles in CO2 assimilation. The low quantum-yield values for F. pubescens and F. floridana in 21% O2 presumably reflect an ineffcient transfer of carbon from the C4 to the C3 cycle. The response of the quantum yield to four increasing O2 concentrations (2–35%) showed lower levels of O2 inhibition in the C3-C4 intermediate F. ramosissima, relative to the C3 species. This indicates that the co-function of the C3 and C4 cycles in this intermediate species leads to an increased CO2 concentration at the site of ribulose-1,5-bisphosphate carboxylase/oxygenase and a concomitant decrease in the competitive inhibition by O2.Abbreviations PEP
phosphoenolpyruvate
- PGA
3-phosphoglycerate
- RuBP
ribulose-1,5-bisphosphate 相似文献
11.
Assessing the Impact of Advected African Dust on Air Quality and Health in the Eastern United States
Joseph M. Prospero 《人类与生态风险评估》1999,5(3):471-479
Large quantities of African dust are carried into the southeastern United States each summer with concentrations typically in the range of 10 to 100?µg m?3. Because approximately one-third to one-half of the dust mass is in the size range under 2.5?µm diameter, the advection of African dust has implications for the EPA's newly implemented standard for PM2.5 particulate matter and for the assessment of human health effects. It will be difficult to assess the impact of African dust events on air quality because they occur during the summer (maximum in July) when photochemical pollution events are frequent and intense in the eastern United States. Indeed, the presence of dust could affect the evolution of photochemical dust events. In order to assess the role of African dust in air quality in the United States, it will be necessary to develop a set of diagnostic indicators; it appears that dust mineralogy and elemental composition might be useful for this purpose. Various satellite products can be used to characterize the spatial coverage of dust events and, when coupled with meteorological tools, to predict impact regions. 相似文献
12.
Hydrogen peroxide (H2O2)-induced aggregation of calf platelets and its modification by agents with specific properties were characterized employing
a spectrophotometric assay. An Arrhenius activation energy of 20 ± 1 kcal/mol was found in the temperature range of 25‡-36‡C.
Rate inhibition occurred on either side of this temperature range, and under anaerobic conditions. Exogenous Ca2+ ions were not required but Ca2+ ions, at 1 mM-concentration, optimally increased rates and extent of aggregation at suboptimal H2O2 concentrations but only extent of aggregation at optimal H2O2 concentrations. Ba2+, Sr2+, Cd2+, Mn2+ and Ni2+ ions (1 mM) and Zn2+, Pb2+ and Hg2+ ions (10 mM) were inhibitory. The cyclo-oxygenase inhibitor, indomethacin (10-30 mM) exerted only mild inhibition by a competitive
mechanism. Another cyclo-oxygenase inhibitor, aspirin, functioned to increase aggregation. Ligands acting directly at the
prostaglandin H2/thromboxane A, receptor (5Z. 9, 11, 13E, 15(S) 15-hydroxy 9(11) epoxy methano prosta 5, 13-dien-1-oic acid, pinane thromboxane
A2, arachidonic acid, eicosapentaenoic acid, and N-ethylmaleimide) functioned as competitive inhibitors. Another platelet-activating
sulphydryl reagent, thimerosal, also inhibited competitively while the protein kinase C inhibitor, sphingosine, and the protein
kinase C modulator, Zn2+ ions, inhibited by different mechanisms. The results indicate direct action of H2O2 at the prostaglandin H2/thromboxane A2 receptor, possibly its sulphydryls, to activate the protein kinase C pathway, independently of cyclo-oxygenase products.
The results underscored the power of the kinetic approach for investigating mechanisms of platelet activation. 相似文献
13.
Schäfer IB Bailer SM Düser MG Börsch M Bernal RA Stock D Grüber G 《Journal of molecular biology》2006,358(3):725-740
The A1Ao ATP synthase from archaea represents a class of chimeric ATPases/synthases, whose function and general structural design share characteristics both with vacuolar V1Vo ATPases and with F1Fo ATP synthases. The primary sequences of the two large polypeptides A and B, from the catalytic part, are closely related to the eukaryotic V1Vo ATPases. The chimeric nature of the A1Ao ATP synthase from the archaeon Methanosarcina mazei G?1 was investigated in terms of nucleotide interaction. Here, we demonstrate the ability of the overexpressed A and B subunits to bind ADP and ATP by photoaffinity labeling. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was used to map the peptide of subunit B involved in nucleotide interaction. Nucleotide affinities in both subunits were determined by fluorescence correlation spectroscopy, indicating a weaker binding of nucleotide analogues to subunit B than to A. In addition, the nucleotide-free crystal structure of subunit B is presented at 1.5 A resolution, providing the first view of the so-called non-catalytic subunit of the A1Ao ATP synthase. Superposition of the A-ATP synthase non-catalytic B subunit and the F-ATP synthase non-catalytic alpha subunit provides new insights into the similarities and differences of these nucleotide-binding ATPase subunits in particular, and into nucleotide binding in general. The arrangement of subunit B within the intact A1Ao ATP synthase is presented. 相似文献
14.
The peroxiredoxins (Prxs) constitute a very large and highly conserved family of thiol-based peroxidases that has been discovered only very recently. We consider here these enzymes through the angle of their discovery, and of some features of their molecular and physiological functions, focusing on complex phenotypes of the gene mutations of the 2-Cys Prxs subtype in yeast. As scavengers of the low levels of H2O2 and as H2O2 receptors and transducers, 2-Cys Prxs have been highly instrumental to understand the biological impact of H2O2, and in particular its signaling function. 2-Cys Prxs can also become potent chaperone holdases, and unveiling the in vivo relevance of this function, which is still not established, should further increase our knowledge of the biological impact and toxicity of H2O2. The diverse molecular functions of 2-Cys Prx explain the often-hard task of relating them to peroxiredoxin genes phenotypes, which underscores the pleiotropic physiological role of these enzymes and complex biologic impact of H2O2. 相似文献
15.
Hernández-Linares MG Sandoval-Ramírez J Meza-Reyes S Montiel-Smith S Guerrero-Luna G 《Steroids》2011,76(14):1521-1526
An easy and fast procedure was developed for one-pot synthesis of steroidal isoxazoles starting from 23-acetylsapogenins derivatives in presence of P2O5/SiO2 in dry media under microwaves irradiation is described. Substrates of the 25S and 25R series were used as raw materials, establishing that this new methodology is applicable to both series. 相似文献
16.
Glycolate oxidase (GO; EC 1.1.3.1) was purified from the leaves of three plant species:Amaranthus hypochondriacus L.(NAD-ME type C4 dicot),Pisum sativum L. (C3 species) andParthenium hysterophorus L. (C3–C4. intermediate). A flavin moiety was present in the enzyme from all the three species. The enzyme from the C4 plant had a low specific activity, exhibited lower KM for glycolate, and required a lower pH for maximal activity, compared to the C3 enzyme. The enzyme from the C4 species oxidized glyoxylate at <10% of the rate with glycolate, while the GO from the C3 plant oxidized glyoxylate at a rate of about 35 to 40% of that with glycolate. The sensitivity of GO from C4 plant to -hydroxypyridinemethane sulfonate, 2-hydroxy-3-butynoate and other inhibitors was less than that of the enzyme from C3 source. The properties of GO fromParthenium hysterophorus, were similar to those of the enzyme fromPisum sativum. The characteristics of glycolate oxidase from leaves of a C4 plant,Amaranthus hypochondriacus are different from those of the C3 species or the C3–C4 intermediate. 相似文献
17.
Yakov M. Milgrom 《BBA》2010,1797(10):1768-1774
The effect of inorganic phosphate (Pi) on uni-site ATP binding and hydrolysis by the nucleotide-depleted F1-ATPase from beef heart mitochondria (ndMF1) has been investigated. It is shown for the first time that Pi decreases the apparent rate constant of uni-site ATP binding by ndMF1 3-fold with the Kd of 0.38 ± 0.14 mM. During uni-site ATP hydrolysis, Pi also shifts equilibrium between bound ATP and ADP + Pi in the direction of ATP synthesis with the Kd of 0.17 ± 0.03 mM. However, 10 mM Pi does not significantly affect ATP binding during multi-site catalysis. 相似文献
18.
The capability to reassimilate CO2 originating from intracellular decarboxylating processes connected with the photorespiratory glycolate pathway and-or decarboxylation of C4 acids during C4 photosynthesis has been investigated with four species of the genus Flaveria (Asteraceae). The C3-C4 intermediate species F. pubescens and F. anomala reassimilated CO2 much more efficiently than the C3 species F. cronquistii and, with respect to this feature, behaved similarly to the C4 species F. trinervia. Therefore, under atmospheric conditions the intermediate species photorespired with rates only between 10–20% of that measured with F. cronquistii. At low oxygen concentrations (1,5%) the reassimilation potential of F. anomala approached that of F. trinervia and was distinct from that found with F. pubescens. The data are discussed with respect to a possible sequence of events during evolution of C4 photosynthesis. If compared with related data for C3-C4 intermediate species from other genera they support the hypothesis that, during evolution of C4 photosynthesis, an efficient capacity for CO2 reassimilation evolved prior to a CO2-concentrating mechanism.Abbreviations C3, C4
assimilated CO2 initially found in 3-phosphoglycerate (C3) or malate and aspartate (C4)
-
D
reassimilation coefficient
-
R
n
, R
t
net, total CO2 evolution as measured with 0.03 and 3% CO2, respectively
- RuBP
ribulose-1,5-bisphosphate
- TPS
true photosynthesis 相似文献
19.
Schäfer I Rössle M Biuković G Müller V Grüber G 《Journal of bioenergetics and biomembranes》2006,38(2):83-92
The first low-resolution shape of subunit F of the A1AO ATP synthase from the archaeon Methanosarcina mazei Gö1 in solution was determined by small angle X-ray scattering. Independent to the concentration used, the protein is monomeric and has an elongated shape, divided in a main globular part with a length of about 4.5 nm, and a hook-like domain of about 3.0 nm in length. The subunit-subunit interaction of subunit F inside the A1AO ATP synthase in the presence of 1-ethyl-3-(dimethylaminopropyl)-carbodiimide EDC was studied as a function of nucleotide binding, demonstrating movements of subunits F relative to the nucleotide-binding subunit B. Furthermore, in the intact A1AO complex, crosslinking of subunits D-E, A-H and A-B-D was obtained and the peptides, involved, were analyzed by MALDI-TOF mass spectrometry. Based on these data the surface of contact of B-F could be mapped in the high-resolution structure of subunit B of the A1AO ATP synthase. 相似文献
20.
The in-situ inter- and intracellular localization patterns of phosphoenolpyruvate (PEP) and ribulose 1,5-bisphosphate (RuBP) carboxylases in green leaves of severalPanicum species were investigated using an indirect immunofluorescence technique. Four species were examined and compared:P. miliaceum (C4),P. bisulcatum (C3), andP. decipiens andP. milioides (C3–C4 intermediates which have Kranz-like leaf anatomy and reduced photorespiration). In the C4
Panicum, PEP carboxylase was located in the cytosol of the mesophyll cells and RuBP carboxylase was restricted to the bundle-sheath chloroplasts. In contrast, in the C3
Panicum species, PEP carboxylase was found throughout the leaf chlorenchyma, in both the cytosol and chloroplasts, and RuBP carboxylase was located in the chloroplasts. For the C3–C4 intermediate plants, the patterns depended on the species examined. ForP. decipiens, the in-situ localization of both carboxylases was similar to that described forP. bisulcatum and other C3 plants. However, inP. milioides, PEP carboxylase was found exclusively in the cytosol of the mesophyll cells, as inP. miliaceum and other C4 species, whereas RuBP carboxylase was distributed in both the mesophyll and bundle-sheath chloroplasts.Abbreviations PEP
phosphoenolpyruvate
- RuBP
ribulose 1,5-bisphosphate 相似文献