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1.
2.
In two mountain ecosystems at the Alptal research site in central Switzerland, pulses of 15NO3 and 15NH4 were separately applied to trace deposited inorganic N. One forested and one litter meadow catchment, each approximately
1600 m2, were delimited by trenches in the Gleysols. K15NO3 was applied weekly or fortnightly over one year with a backpack sprayer, thus labelling the atmospheric nitrate deposition.
After the sampling and a one-year break, 15NH4Cl was applied as a second one-year pulse, followed by a second sampling campaign. Trees (needles, branches and bole wood),
ground vegetation, litter layer and soil (LF, A and B horizon) were sampled at the end of each labelling period. Extractable
inorganic N, microbial N, and immobilised soil N were analysed in the LF and A horizons. During the whole labelling period,
the runoff water was sampled as well. Most of the added tracer remained in both ecosystems. More NO3− than NH4+ tracer was retained, especially in the forest. The highest recovery was in the soil, mainly in the organic horizon, and in
the ground vegetation, especially in the mosses. Event-based runoff analyses showed an immediate response of 15NO3− in runoff, with sharp 15N peaks corresponding to discharge peaks. NO3− leaching showed a clear seasonal pattern, being highest in spring during snowmelt. The high capacity of N retention in these
ecosystems leads to the assumption that deposited N accumulates in the soil organic matter, causing a progressive decline
of its C:N ratio. 相似文献
3.
Ab initio (RHF, MP2) and Density Functional Theory (DFT) methods have been used to examine six isomers of the N15m cluster with the 6-31+G* basis set. Different from the known odd-numbered anionic N7m, N9m, and N11m clusters, in which the open-chain structures are the most stable species, the most stable N15m isomer is structure 1 (C1), which may be considered as a complex between the fragments cyclic N5m (D5h) and staggered N10 (D2d). The decomposition pathways of structure 2 (CS), containing two aromatic N5 rings connected by a N5 chain, and the open-chain structure 3 (C2v) were studied at the B3LYP/6-31+G* level of theory. Relative energies were refined at the level of B3LYP/6-311+G(3df,2p)//B3LYP/6-31+G*+ZPE (B3LYP/6-31+G*). The barriers for N2 and N5m (D5h) fission reactions for structure 2 are predicted to be 18.2 and 14.2 kcal x mol(-1), respectively. The corresponding N2+N3m fission barrier for structure 3 is predicted to be 11.2 kcal x mol(-1). Supplementary material is available for this article if you access the article at http://dx.doi.org/10.1007/s00894-003-0118-0. A link in the frame on the left on that page takes you directly to the supplementary material. Figure Structure 1 of the N15m cluster, showing bond distances in A and bond angles in degrees 相似文献
4.
Arginine side-chains are often key for enzyme catalysis, protein–ligand and protein–protein interactions. The importance of arginine stems from the ability of the terminal guanidinium group to form many key interactions, such as hydrogen bonds and salt bridges, as well as its perpetual positive charge. We present here an arginine 13Cζ-detected NMR experiment in which a double-quantum coherence involving the two 15Nη nuclei is evolved during the indirect chemical shift evolution period. As the precession frequency of the double-quantum coherence is insensitive to exchange of the two 15Nη; this new approach is shown to eliminate the previously deleterious line broadenings of 15Nη resonances caused by the partially restricted rotation about the Cζ–Nε bond. Consequently, sharp and well-resolved 15Nη resonances can be observed. The utility of the presented method is demonstrated on the L99A mutant of the 19 kDa protein T4 lysozyme, where the measurement of small chemical shift perturbations, such as one-bond deuterium isotope shifts, of the arginine amine 15Nη nuclei becomes possible using the double-quantum experiment. 相似文献
5.
Growing concentrations of N2O within the atmosphere have been accompanied by decreasing δ15N values, provoking the hypothesis of a global decline in the rate of N2O reduction relative to its production in soil. We estimate that the ratio of N2O produced to N2O reduced within the soil profile has declined by about 10–25% relative to its pre-industrial value. To a smaller extent,
a reduction in the uptake of atmospheric N2O at the soil surface relative to its emission could also have contributed to the reported isotopic signal. This calls for
a greater consideration of the process of N2O reduction in soil and its role in the global turnover of N2O. 相似文献
6.
V. A. Belyaev D. A. Kozlov A. A. Terent’ev A. E. Trenin 《Plasma Physics Reports》2017,43(10):1039-1041
A method for determining the lifetime of unstable ions is described. The method is based on measuring the decrease in the ion beam current onto a fixed detector with increasing path length of the ion beam from the ion source to the detector. The measurements performed for D? 2 and HD? molecular ions have shown that their lifetimes are 3.5 ± 0.1 and 4.4 ± 0.1 μs, respectively. 相似文献
7.
Massive anthropogenic acceleration of the global nitrogen (N) cycle has stimulated interest in understanding the fate of excess
N loading to aquatic ecosystems. Nitrate (NO3
−) is traditionally thought to be removed mainly by microbial respiratory denitrification coupled to carbon (C) oxidation,
or through biomass assimilation. Alternatively, chemolithoautotrophic bacterial metabolism may remove NO3
− by coupling its reduction with the oxidation of sulfide to sulfate (SO4
2−). The NO3
− may be reduced to N2 or to NH4
+, a form of dissimilatory nitrate reduction to ammonium (DNRA). The objectives of this study were to investigate the importance
of S oxidation as a NO3
− removal process across diverse freshwater streams, lakes, and wetlands in southwestern Michigan (USA). Simultaneous NO3
− removal and SO4
2− production were observed in situ using modified “push-pull” methods in nine streams, nine wetlands, and three lakes. The
measured SO4
2− production can account for a significant fraction (25–40%) of the overall NO3
− removal. Addition of 15NO3
− and measurement of 15NH4
+ production using the push–pull method revealed that DNRA was a potentially important process of NO3
− removal, particularly in wetland sediments. Enrichment cultures suggest that Thiomicrospira denitrificans may be one of the organisms responsible for this metabolism. These results indicate that NO3
−-driven SO4
2− production could be widespread and biogeochemically important in freshwater sediments. Removal of NO3
− by DNRA may not ameliorate problems such as eutrophication because the N remains bio-available. Additionally, if sulfur (S)
pollution enhances NO3
− removal in freshwaters, then controls on N processing in landscapes subject to S and N pollution are more complex than previously
appreciated.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
8.
Tessari F Bortolami S Zoccarato F Alexandre A Cavallini L 《Journal of bioenergetics and biomembranes》2011,43(3):267-274
Sodium Nitroprusside (SNP) and S-Nitrosoglutathione (GSNO) differently affect mitochondrial H2O2 release at Complex-I. mM SNP increases while GSNO decreases the release induced by succinate alone or added on top of NAD-linked
substrates. Stimulation likely depends on Nitric Oxide (
.
NO) (released by SNP but not by GSNO) inhibiting cytochrome oxidase and mitochondrial respiration. Preincubations with SNP
or high GSNO (10 mM plus DTE to increases its
.
NO release) induces an inhibition of the succinate dependent H2O2 production consistent with a
.
NO dependent covalent modification. However maximal inhibition of the succinate dependent H2O2 release is obtained in the presence of low GSNO (20–100 μM), but not with SNP. This inhibition appears independent of
.
NO release since μM GSNO does not affect mitochondrial respiration, or the H2O2 detection systems and its effect is very rapid. Inhibition may be partly due to an increased removal of O2.− since GSNO chemically competes with NBT and cytochrome C in O2.− detection. 相似文献
9.
A confined aquifer in the Malm Karst of the Franconian Alb, South Germany was investigated in order to understand the role of the vadose zone in denitrifiaction processes. The concentrations of chemical tracers Sr2+ and Cl– and concentrations of stable isotope 18O were measured in spring water and precipitation during storm events. Based on these measurements a conceptual model for runoff was constructed. The results indicate that pre-event water, already stored in the system at the beginning of the event, flows downslope on vertical and lateral preferential flow paths. Chemical tracers used in a mixing model for hydrograph separation have shown that the pre-event water contribution is up to 30%. Applying this information to a conceptual runoff generation model, the values of 15N and 18O in nitrate could be calculated. Field observations showed the occurence of significant microbial denitrification processes above the soil/bedrock interface before nitrate percolates through to the deeper horizon of the vadose zone. The source of nitrate could be determined and denitrification processes were calculated. Assuming that the nitrate reduction follows a Rayleigh process one could approximate a nitrate input concentration of about 170 mg/l and a residual nitrate concentration of only about 15%. The results of the chemical and isotopic tracers postulate fertilizers as nitrate source with some influence of atmospheric nitrate. The combined application of hydrograph separation and determination of isotope values in 15N and 18O of nitrate lead to an improved understanding of microbial processes (nitrification, denitrification) in dynamic systems. 相似文献
10.
An experiment is presented to determine 3JHNHα coupling constants, with significant advantages for applications to unfolded proteins. The determination of coupling constants
for the peptide chain using 1D 1H, or 2D and 3D 1H-15N correlation spectroscopy is often hampered by extensive resonance overlap when dealing with flexible, disordered proteins.
In the experiment detailed here, the overlap problem is largely circumvented by recording 1H-13C′ correlation spectra, which demonstrate superior resolution for unfolded proteins. J-coupling constants are extracted from
the peak intensities in a pair of 2D spin-echo difference experiments, affording rapid acquisition of the coupling data. In
an application to the cytoplasmic domain of human neuroligin-3 (hNlg3cyt) data were obtained for 78 residues, compared to 54 coupling constants obtained from a 3D HNHA experiment. The coupling constants
suggest that hNlg3cyt is intrinsically disordered, with little propensity for structure. 相似文献
11.
Marie Franҫoise Seck-Mbengue Anja Müller Benard Ngwene Elke Neumann Eckhard George 《Symbiosis (Philadelphia, Pa.)》2017,73(3):191-200
We investigated the effect of mineral nitrogen forms on transfer of nitrogen (N) and zinc (Zn) from attached compartments to rhodes grass (Chloris gayana) colonised with arbuscular mycorrhizal fungi (AMF). After being pre-cultivated in substrates with adequate nutrient supply and either AMF inoculated (+AM) or left non-inoculated (?AM), rhodes grass was positioned adjacent to an outer compartment holding a similar substrate but applied with labelled nitrogen (15N) either as ammonium (NH4 +) or nitrate (NO3 ?), and a high supply of Zn (150 mg kg?1 DS). Plant roots together with fungal mycelium were either allowed to explore the outer compartment (with root access) or only mycorrhizal hyphae were allowed (without root access). Within each access treatment, biomasses of rhodes grass were not significantly affected by AMF inoculation or N form. AMF contribution to plant 15N uptake was about double in NH4 + compared with NO3 ?-supplied treatments while the mycorrhizal influence on plant Zn uptake was insignificant. Without root access, the shoot 15N/Zn concentration ratio was up to ten-fold higher in +AM than –AM treatments and this ratio increase was clearly more pronounced in NH4 + than NO3 ?-supplied treatments. In conclusion, rhodes grass in symbiosis with the tested AMF acquired more N when supplied with ammonium. Moreover, there is clear indication that although the AMF have transported both nutrients (N and Zn), N was preferentially transferred as compared to Zn. We confirmed that, while rhodes grass is not able to prevent excessive Zn uptake via roots under conditions of high Zn, mycorrhiza is able to avoid excessive Zn supply to the host plant when the fungus alone has access to contaminated patches. 相似文献
12.
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14.
V. A. Belyaev M. M. Dubrovin D. A. Kozlov A. A. Terent’ev A. E. Trenin G. V. Sholin 《Plasma Physics Reports》2010,36(11):964-968
D2− ions produced in collisions of D− ions with relative energies of 2.5–9.2 eV were detected for the first time. It is shown that the effective cross section
for this reaction is no less than 1.5 × 10−14 cm2. Along with the theoretically predicted short-lived state of negative molecular deuterium ions, a state existing for more
than 1 μs was observed. 相似文献
15.
S. A. Menzikov O. V. Menzikova 《Journal of Evolutionary Biochemistry and Physiology》2007,43(3):295-304
Action of Cl? + HCO3 ?1 ions on Mg2+-ATPase from brain plasma membranes of fish and rats has been studied. Maximal effect of the anions on the “basal” Mg2+-ATPase activity is revealed in the presence of 10 mM Cl? and 3 mM HCO3 ?1 at physiological values of pH of incubation medium. The studied Cl?, HCO3 ?-activated Mg2+-ATPases of both animal species, by their sensitivity to SH-reagents (5,5-dithio-bis-nitrobenzoic acid, N-ethylmaleimide), oligomycin, and orthovanadate, are similar to transport ATPase of the P-type, but differ from them by molecular properties and by sensitivity to ligands of GABAA-receptors. It has been established that the sensitive to GABAA-ergic ligands, Cl?, HCO3 ?-activated Mg2+-ATPase from brain of the both animal species is protein of molecular mass around 300 kDa and of Stock’s radius 5.4 nm. In fish the enzyme is composed of one major unit of molecular mass approximately 56 kDa, while in rats-of three subunits of molecular masses about 57, 53, and 45 kDa. A functional and structural coupling of the ATP-hydrolyzing areas of the studied enzyme to sites of binding of GABAA-receptor ligands is suggested. 相似文献
16.
We present two NMR experiments, (3,2)D HNHA and (3,2)D HNHB, for rapid and accurate measurement of 3J(H N-H alpha) and 3J(N-H beta) coupling constants in polypeptides based on the principle of G-matrix Fourier transform NMR spectroscopy and quantitative J-correlation. These experiments, which facilitate fast acquisition of three-dimensional data with high spectral/digital resolution and chemical shift dispersion, will provide renewed opportunities to utilize them for sequence specific resonance assignments, estimation/characterization of secondary structure with/without prior knowledge of resonance assignments, stereospecific assignment of prochiral groups and 3D structure determination, refinement and validation. Taken together, these experiments have a wide range of applications from structural genomics projects to studying structure and folding in polypeptides. 相似文献
17.
The molecular weight and subunit composition of Cl-,HCO3(-)- and picrotoxin-stimulated Mg2+-ATPase from rat brain plasma membrane solubilized in sodium deoxycholate were studied by gel filtration chromatography. The enzyme activity eluted from a Sephacryl S-300 column in a single peak associated with a protein of molecular weight approximately 300 kD and a Stokes radius of 5.4 nm. The enzyme-enriched fraction, concentrated and denatured by SDS, migrated through a Sephacryl S-200 column as three peaks with molecular weights of approximately 57, 53, and 45 kD. SDS-PAGE also showed three major protein bands with molecular weights of about 57, 53, and 48 kD. The molecular weight and subunit composition of the Cl- and HCO3(-)-stimulated Mg2+-ATPase from neuronal membrane of rat brain are similar with the molecular properties of GABA(A)-benzodiazepine receptor complex from mammalian brain but are different from those of P-type transport ATPases. 相似文献
18.
We report on the transformation and expression in sugar beet (Beta vulgaris) hairy roots of a Nicotiana alata NaPI gene encoding a serine proteinase inhibitor (PI) that has been shown to effectively reduce the population of a number of
insect pests. Using in-gel analysis, two PI protein activities were detected at approximately 24- and/or 28-kDa in hairy roots
generated via Agrobacterium rhizogenes-mediated gene transfer. Immunoblot analysis revealed the presence of the expected ~40 kDa precursor, and in some transformants,
a ~20 kDa processing intermediate and the mature 6-kDa PIs. In general, processing of the precursor in the clonal lines was
reduced or not detected. The reduced efficiency of post-translational processing of the N. alata PI precursor may be attributed to modification and/or altered folding of the recombinant protein or distinct post-translational
machinery functioning in sugar beet hairy roots and Nicotiana.
Disclaimer: Mention and/or use of a commercial or proprietary product to the exclusion of others does not constitute endorsement
by the USDA. 相似文献
19.
This study investigated the relationship between 13C of ecosystem components, soluble plant carbohydrates and the isotopic signature of ecosystem respired CO2 (13CR) during seasonal changes in soil and atmospheric moisture in a beech (Fagus sylvatica L.) forest in the central Apennine mountains, Italy. Decrease in soil moisture and increase in air vapour pressure deficit during summer correlated with substantial increase in 13C of leaf and phloem sap soluble sugars. Increases in 13C of ecosystem respired CO2 were linearly related to increases in phloem sugar 13C (r2=0.99, P0.001) and leaf sugar 13C (r2=0.981, P0.01), indicating that a major proportion of ecosystem respired CO2 was derived from recent assimilates. The slopes of the best-fit lines differed significantly (P0.05), however, and were about 0.86 (SE=0.04) for phloem sugars and about 1.63 (SE=0.16) for leaf sugars. Hence, changes in isotopic signature in phloem sugars were transferred to ecosystem respiration in the beech forest, while leaf sugars, with relatively small seasonal changes in 13C, must have a slower turnover rate or a significant storage component. No significant variation in 13C was observed in bulk dry matter of various plant and ecosystem components (including leaves, bark, wood, litter and soil organics). The apparent coupling between the 13C of soluble sugars and ecosystem respiration was associated with large apparent isotopic disequilibria. Values of 13CR were consistently more depleted by about 4 relative to phloem sugars, and by about 2 compared to leaf sugars. Since no combination of the measured pools could produce the observed 13CR signal over the entire season, a significant isotopic discrimination against 13C might be associated with short-term ecosystem respiration. However, these differences might also be explained by substantial contributions of other not measured carbon pools (e.g., lipids) to ecosystem respiration or contributions linked to differences in footprint area between Keeling plots and carbohydrate sampling. Linking the seasonal and inter-annual variations in carbon isotope composition of carbohydrates and respiratory CO2 should be applicable in carbon cycle models and help the understanding of inter-annual variation in biospheric sink strength. 相似文献
20.
Jennifer L. Bankers-Fulbright Kathleen R. Bartemes Gail M. Kephart Hirohito Kita Scott M. O’Grady 《The Journal of membrane biology》2009,228(2):99-109
Human eosinophils spontaneously adhere to various substrates in the absence of exogenously added activators. In the present
study a method was developed for characterizing eosinophil adhesion by measuring changes in impedance. Impedance measurements
were performed in HCO3-buffered HybriCare medium maintained in a humidified 5% CO2 incubator at 37°C. Impedance increased by more than 1 kΩ within minutes after eosinophils made contact with the substrate,
reaching a peak within 20 min. Blocking mobilization of intracellular [Ca2+] that precedes adhesion with BAPTA-AM (10 μM) completely inhibited the rise in impedance as well as the changes in cell shape
typically observed in adherent cells. However, lowering the extracellular [Ca2+] with 2.5 mM EGTA did not inhibit the increase in impedance. Pretreatment with anti-CD18 antibody to block substrate interactions
with β2-integrins, or jasplakinolide (2 μM) to block actin reorganization, abolished the increase in impedance and adherent morphology
of the cells. Exposure of eosinophils to the phosphatidylinositol 3 kinase inhibitor LY294002 (5 μM) or treatment with protein
kinase C zeta pseudosubstrate to competitively inhibit activity of the enzyme significantly reduced the increase in impedance
and inhibited the cell spreading associated with adhesion. These results demonstrate a novel method for measuring eosinophil
adhesion and showed that, following formation of a tethered attachment, a rapid increase in intracellular [Ca2+] precedes the cytoskeletal rearrangements required for cell shape changes and plasma membrane-substrate interactions associated
with adhesion. 相似文献