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1.
During February and August 2016 (winter and summer season), 192 samples of raw bulk tank milk have been collected from small dairy farms in five different regions of Kosova (Prishtina, Prizren, Peja, Mitrovica, and Gjilan). These samples were analyzed for aflatoxin M1 (AFM1) contamination level by ultra-high performance liquid chromatography coupled with electrospray ionization triple quadrupole tandem mass spectrometry (UHPLC–ESI–MS/MS). The limit of quantification for AFM1 was 0.02 μg/L and recovery at 0.1–0.5 μg/L was 90–95% (coefficient of variation 15–25%). A total of 74 milk samples (38%) were found to be contaminated with AFM1 and 11 samples (5.7%) slightly exceeded the European Union maximum level of 0.05 μg/L. The maximum AFM1 level was at 0.082 μg/L. There was no relevant difference between summer and winter with regard to AFM1 frequency and levels. Although the frequency of AFM1-positive samples varied between regions, from 7% (Prishtina) to 53% (Prizren), only minor regional differences were observed with regard to average and maximum toxin levels. The high percentage of milk samples which were non-compliant with AFM1 maximum levels indicates that efforts to reduce the contamination levels of aflatoxin B1 in cows feed in Kosovo are necessary.  相似文献   

2.
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   

3.
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   

4.
Seasonal oscillations in the carbon (δ13C) and nitrogen (δ15N) isotope signatures of aquatic algae can cause seasonal enrichment–depletion cycles in the isotopic composition of planktonic invertebrates (e.g., copepods). Yet, there is growing evidence that seasonal enrichment–depletion cycles also occur in the isotope signatures of larger invertebrate consumers, taxa used to define reference points in isotope-based trophic models (e.g., trophic baselines). To evaluate the general assumption of temporal stability in non-zooplankton aquatic invertebrates, δ13C and δ15N time series data from the literature were analyzed for seasonality and the influence of biotic (feeding group) and abiotic (trophic state, climate regime) factors on isotope temporal patterns. The amplitude of δ13C and δ15N enrichment–depletion cycles was negatively related to body size, although all size-classes of invertebrates displayed a winter-to-summer enrichment in δ13C and depletion in δ15N. Among feeding groups, periphytic grazers were more variable and displayed larger temporal changes in δ13C than detritivores. For nitrogen, temporal variability and magnitude of directional change of δ15N was most strongly related to ecosystem trophic state (eutrophic > mesotrophic, oligotrophic). This study provides evidence of seasonality in the isotopic composition of aquatic invertebrates across very broad geographical and ecological gradients as well as identifying factors that are likely to modulate the strength and variability of seasonality. These results emphasize the need for researchers to recognize the likelihood of temporal changes in non-zooplankton aquatic invertebrate consumers at time scales relevant to seasonal studies and, if present, to account for temporal dynamics in isotope trophic models.  相似文献   

5.
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   

6.
We studied the possibility of K+ and Cl efflux from tobacco pollen grains during their activation in vitro or on the stigma of a pistil. For this purpose the X-ray microanalysis and spectrofluorometry were applied. We found that the relative content of potassium and chlorine in the microvolume of pollen grain decreases during its hydration and activation on stigma. Efflux of these ions was found both in vivo and in vitro. In model in vitro experiments anion channel inhibitor NPPB ((5-nitro-2-(3-phenylpropylamino) benzoic acid) in the concentration that was blocking pollen germination, reduced Cl efflux; potassium channel inhibitor TEA (tetraethylammonium chloride) partially reduced K+ efflux and lowered the percent of activated cells. Another blocker of potassium channels Ba2+ caused severe decrease in cell volume and blocked the activation. In general, the obtained data demonstrates that the initiation of pollen germination both in vivo and in vitro involves the activation of K+ and Cl release. An important role in these processes is played by NPPB-, TEA- and Ba2+-sensitive plasmalemma ion channels.  相似文献   

7.
The structures and stabilities of eleven N13 + and N13 isomers have been investigated with second-order Møller–Plesset (MP2) and density functional theory (DFT) methods. Five N13 + isomers and six N13 isomers are all reasonable local minima on their potential energy hypersurfaces. The most stable N13 + cation is structure C-2 with C2v symmetry, which contains a pentazole ring and two N4 open chains. It is different from those of the N7 + and N9 + clusters, but similar to the N11 + cluster. Meanwhile, the most stable N13 structure A-2 is composed of a pentazole ring and a six-membered ring connected by two nitrogen atoms. It is not only different from those of the N7 and N9 clusters, but also from the N11 cluster. The decomposition pathways of structures C-2 and A-2 were investigated at the B3LYP/(aug)-cc-pVDZ level. From the barrier heights of the structures C-2 and A-2 decomposition processes, it is suggested that C-2 is difficult to observe experimentally and A-2 may be observed as a short-lived species. Figure Optimized geometrical parameters of N13 + isomer C-2   相似文献   

8.
The contributions of Ca2+, H+, and Cl in generation of variation potentials (VP) in 3- to 4-week-old pumpkin (Cucurbita pepo L., cv. Mozoleevskaya) plants were assessed. During VP generation, transient alkalinization of the medium around the stem was recorded with a potentiometric method. The pH changes were kinetically similar to the electric potential changes and were apparently due to temporal suppression of the plasma-membrane electrogenic H+ pump. These data and the observed inhibition of VP in the stem zone treated locally with a metabolic inhibitor (NaN3) indicate that the VP generation is related to the reversible suppression of the H+-pump. The anion channel blocker (ethacrynic acid) decelerated significantly the front slope of VP and reduced the VP amplitude. A short-term increase in external Cl concentration around the stem was observed during potential transients representing the VP front slope and the pulses integrated into VP. The removal of Ca2+ from extracellular medium inhibited the VP generation. It is proposed that Ca2+ plays a role in activation of anion channels and in the H+-pump inactivation. The VP generation is probably determined by a complex mechanism, with contributions from passive ion fluxes (Ca2+, Cl) moving along the electrochemical gradients and from changes in the electrogenic pump activity.  相似文献   

9.
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   

10.
11.
Using vesicles of symbiosome membrane (SM), it was shown that the Ca2+-ATPase can function as an ATP-energized Ca2+/H+ antiporter. The initial rate of the acidic shift inside the vesicles, as well as the rate of the ITP-dependent alkalization of the medium inside them markedly increased in the presence of valinomycin. This process was rapidly stopped by eosin Y, a known inhibitor of the type IIB Ca2+-ATPase. ITP-dependent uptake of Ca2+ was blocked after the addition to the reaction mixture of nigericin in the presence of K+. Under these conditions, the alkaline shift of pH inside the vesicles occurred, leading to the inhibition of operation of the calcium pump in SM. Evaluation of the pH shifts inside the vesicles by using pH-indicator pyranine confirmed the ion-exchange mechanism of the Ca2+-ATPase functioning in the SM.  相似文献   

12.
Based on the difference in the CD14 and CD16 expression, two subsets of monocytes were identified in human and other mammalian blood. These subsets have different patterns of adhesion molecules and chemokine receptors that suggests the different mode of their interaction with endothelium and tissue traffic. Here, we investigated the ability of CD14+CD16+ and CD14++CD16 monocytes to adhere to endothelial cell monolayer in presence or absence of pro- and anti-inflammatory cytokines. We demonstrated that CD14+CD16+ monocytes had a higher level of adhesion to intact monolayer of endothelial cells than CD14++CD16 monocytes. Adhesion of CD14++CD16 and CD14+CD16+ monocytes significantly increased in the presence of TNFα or its combination with other cytokines. IFNγ and IL-4 alone did not affect the adhesion of monocytes. These results show that CD14++CD16 and CD14+CD16+ monocytes can be recruited to the inflamed endothelium, but CD14+CD16+ monocytes adhere to endothelial cells without inflammations twice as strongly as CD14++CD16 monocytes.  相似文献   

13.
The peptide RHDSGY, a fragment of the human β-amyloid Zn-binding site, and its isomers RH(D-Asp)SGY and RH(β-Asp)SGY have been obtained as amides by means of solid-phase synthesis and analyzed by HPLC and various mass spectrometric methods. The problem of low yield of the RHDSGY peptide and its isomers attributed to 9-fluorenylmethoxycarbonyl (Fmoc)-amino acids and/or formation of such side-products as RH(β-Asp)SGY (or RHDSGY during synthesis of RH(β-Asp)SGY) and RH(Asp-imide) SGY was solved via selection of individual reagents for removal of Fmoc groups from α-amino groups of the growing peptide chain.  相似文献   

14.
Imino 1H–15N residual dipolar couplings (RDCs) provide additional structural information that complements standard 1H–1H NOEs leading to improvements in both the local and global structure of RNAs. Here, we report measurement of imino 1H–1H RDCs for the Iron Responsive Element (IRE) RNA and native E. coli tRNAVal using a BEST-Jcomp-HMQC2 experiment. 1H–1H RDCs are observed between the imino protons in G–U wobble base pairs and between imino protons on neighboring base pairs in both RNAs. These imino 1H–1H RDCs complement standard 1H–15N RDCs because the 1H–1H vectors generally point along the helical axis, roughly perpendicular to 1H–15N RDCs. The use of longitudinal relaxation enhancement increased the signal-to-noise of the spectra by ~3.5-fold over the standard experiment. The ability to measure imino 1H–1H RDCs offers a new restraint, which can be used in NMR domain orientation and structural studies of RNAs. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

15.
Samples of raw or pasteurized cow’s milk and infant formula were assayed for glutathione peroxidase (GSH-Px) activity, selenium (Se), and total protein. GSH-Px activity was detected in raw milk, but not in market-pasteurized milk or infant formula. The correlation between GSH-Px activity and Se levels was significant, even when the influence of protein level was removed. This result implies a role of GSH-Px as one of biologically active forms of Se in raw milk. Absence of GSH-Px activity in pasteurized milk and infant formula result from the heating process in these productions, because the heating of raw milk gave an irreversible inactivation of GSH-Px. Both GSH-Px activity and Se levels had significant correlation with protein level, but not so when the respective influences of Se and GSH-Px levels were removed. In raw cow’s milk, Se content was 23 ng/mL and GSH-Px activity was 20 U/mL. About 12% of Se was bound to GSH-Px, and 0.003% of protein was GSH-Px. Raw milk obtained in July contained higher levels of Se, GSH-Px, and protein than that in November. Data for cow’s milk were discussed in relation to those for human milk and those in New Zealand.  相似文献   

16.
17.
Since its introduction approximately seven years ago, selamectin (Stronghold®/Revolution®, Pfizer Inc.) has been used off-label to treat a number of ecto- and endoparasite conditions in dogs and cats. It has been used as a successful prophylactic against Dirofilaria repens and as a treatment for Aelurostrongylus abstrusus in cats. It has also been used to treat notoedric mange, infestation with the nasal mite Pneumonyssoides caninum, Cheyletiella spp. and Neotrombicula autumnalis infestations and larval Cordylobia anthropophaga infection. However, to date attempts to treat generalised canine demodicosis have not been successful. In all cases, treatment was apparently well tolerated by the host.  相似文献   

18.
γS-crystallin is a major structural component of the human eye lens, which maintains its stability over the lifetime of an organism with negligible turnover. The G57W mutant of human γS-crystallin (abbreviated hereafter as γS-G57W) is associated with dominant congenital cataracts. In order to provide a structural basis for the ability of γS-G57W causing cataract, we have cloned, overexpressed, isolated and purified the protein. The 2D [15N–1H]-HSQC spectrum recorded with uniformly 13C/15N-labelled γS-G57W was highly dispersed indicating the protein to adopt an ordered conformation. In this paper, we report almost complete sequence-specific 1H, 13C and 15N resonance assignments of γS-G57W using a suite of heteronuclear 3D NMR experiments.  相似文献   

19.
New 3D HCN quantitative J (QJ) pulse schemes are presented for the precise and accurate measurement of one-bond 15N1/913C1, 15N1/913C6/8, and 15N1/913C2/4 residual dipolar couplings (RDCs) in weakly aligned nucleic acids. The methods employ 1H–13C multiple quantum (MQ) coherence or TROSY-type pulse sequences for optimal resolution and sensitivity. RDCs are obtained from the intensity ratio of H1–C1–N1/9 (MQ-HCN-QJ) or H6/8–C6/8–N1/9 (TROSY-HCN-QJ) correlations in two interleaved 3D NMR spectra, with dephasing intervals of zero (reference spectrum) and 1/(2JNC) (attenuated spectrum). The different types of 15N–13C couplings can be obtained by using either the 3D MQ-HCN-QJ or TROSY-HCN-QJ pulse scheme, with the appropriate setting of the duration of the constant-time 15N evolution period and the offset of two frequency-selective 13C pulses. The methods are demonstrated for a uniformly 13C, 15N-enriched 24-nucleotide stem-loop RNA sequence, helix-35, aligned in the magnetic field using phage Pf1. For measurements of RDCs systematic errors are found to be negligible, and experiments performed on a 1.5 mM helix-35 sample result in an estimated precision of ca. 0.07 Hz for 1DNC, indicating the utility of the measured RDCs in structure validation and refinement. Indeed, for a complete set of 15N1/913C1, 15N1/913C6/8, and 15N1/913C2/4 dipolar couplings obtained for the stem nucleotides, the measured RDCs are in excellent agreement with those predicted for an NMR structure of helix-35, refined using independently measured observables, including 13C–1H, 13C–13C and 1H–1H dipolar couplings.Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1007/s10858-005-0646-2.  相似文献   

20.
The limits of resolution that can be obtained in 1H–15N 2D NMR spectroscopy of isotopically enriched nanocrystalline proteins are explored. Combinations of frequency switched Lee–Goldburg (FSLG) decoupling, fast magic angle sample spinning (MAS), and isotopic dilution via deuteration are investigated as methods for narrowing the amide 1H resonances. Heteronuclear decoupling of 15N from the 1H resonances is also studied. Using human ubiquitin as a model system, the best resolution is most easily obtained with uniformly 2H and 15N enriched protein where the amides have been exchanged in normal water, MAS at 20 kHz, and WALTZ-16 decoupling of the 15N nuclei. The combination of these techniques results in average 1H lines of only 0.26 ppm full width at half maximum. Techniques for optimizing instrument stability and 15N decoupling are described for achieving the best possible performance in these experiments.  相似文献   

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