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1.
Selenoprotein W gene regulation by selenium in L8 cells 总被引:3,自引:0,他引:3
2.
This paper deals with the spatio-temporal dynamics of a pollinator–plant–herbivore mathematical model. The full model consists
of three nonlinear reaction–diffusion–advection equations defined on a rectangular region. In view of analyzing the full model,
we firstly consider the temporal dynamics of three homogeneous cases. The first one is a model for a mutualistic interaction
(pollinator–plant), later on a sort of predator–prey (plant–herbivore) interaction model is studied. In both cases, the interaction
term is described by a Holling response of type II. Finally, by considering that the plant population is the unique feeding
source for the herbivores, a mathematical model for the three interacting populations is considered. By incorporating a constant
diffusion term into the equations for the pollinators and herbivores, we numerically study the spatiotemporal dynamics of
the first two mentioned models. For the full model, a constant diffusion and advection terms are included in the equation
for the pollinators. For the resulting model, we sketch the proof of the existence, positiveness, and boundedness of solution
for an initial and boundary values problem. In order to see the separated effect of the diffusion and advection terms on the
final population distributions, a set of numerical simulations are included. We used homogeneous Dirichlet and Neumann boundary
conditions. 相似文献
3.
4.
《Laboratory Automation and Information Management》1999,34(2):159-165
The analytical performance of an on-line focused microwave digestion method for the determination of selenium in enriched yeast by hydride generation–atomic absorption spectrometry (HG–AAS) is evaluated. The method is based on the direct injection of slurried samples into a carrier stream of water. Microwave-assisted digestion in the presence of 1% K2S2O8 permits the quantitative extraction of selenium species from the solid samples and their transformation with HCl acid to selenite. Based on a sample injection volume of 100 μl, limits of detection (L.D.) of about 1 ng Se and relative standard deviation (R.S.D.) of 4.5% were obtained. The results of comparison with traditional digestion procedures are reported. 相似文献
5.
Sarah Jackson-Rosario Darin Cowart Andrew Myers Rebecca Tarrien Rodney L. Levine Robert A. Scott William Thomas Self 《Journal of biological inorganic chemistry》2009,14(4):507-519
Clostridium difficile is a nosocomial pathogen whose incidence and importance are on the rise. Previous work in our laboratory characterized the
central role of selenoenzyme-dependent Stickland reactions in C. difficile metabolism. In this work we have identified, using mass spectrometry, a stable complex formed upon reaction of auranofin
(a gold-containing drug) with selenide in vitro. X-ray absorption spectroscopy supports the structure that we proposed on
the basis of mass-spectrometric data. Auranofin potently inhibits the growth of C. difficile but does not similarly affect other clostridia that do not utilize selenoproteins to obtain energy. Moreover, auranofin inhibits
the incorporation of radioisotope selenium (75Se) in selenoproteins in both Escherichia coli, the prokaryotic model for selenoprotein synthesis, and C. difficile without impacting total protein synthesis. Auranofin blocks the uptake of selenium and results in the accumulation of the
auranofin–selenide adduct in the culture medium. Addition of selenium in the form of selenite or l-selenocysteine to the growth medium significantly reduces the inhibitory action of auranofin on the growth of C. difficile. On the basis of these results, we propose that formation of this complex and the subsequent deficiency in available selenium
for selenoprotein synthesis is the mechanism by which auranofin inhibits C. difficile growth. This study demonstrates that targeting selenium metabolism provides a new avenue for antimicrobial development against
C. difficile and other selenium-dependent pathogens.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
6.
Selenium has been increasingly recognized as an important element in biological systems, which participates in numerous biochemical processes in organisms, notably in enzyme reactions. Selenium can substitute sulfur of cysteine and methionine to form their selenium analogues, selenocysteine (Sec) and selenomethionine (SeM). The nature of amino acid pockets in proteins is dependent on their composition and thus different non-covalent forces determine the interactions between selenium of Sec or SeM and other functional groups, resulting in specific biophysical behavior. The discrimination of selenium toward sulfur has been reported. In order to elucidate the difference between the nature of S-π and Se-π interactions, we performed extensive DFT calculations of dispersive and electrostatic contributions of Se-π interactions in substituted benzenes/hydrogen selenide (H2Se) complexes. The results are compared with our earlier reported S-π calculations, as well as with available experimental data. Our results show a larger contribution of dispersive interactions in Se-π systems than in S-π ones, which mainly originate from the attraction between Se and substituent groups. We found that selenium exhibits a strong interaction with aromatic systems and may thus play a significant role in stabilizing protein folds and protein–inhibitor complexes. Our findings can also provide molecular insights for understanding enzymatic specificity discrimination between single selenium versus a sulfur atom, notwithstanding their very similar chemical properties. 相似文献
7.
RNA viruses exist in large intra-host populations which display great genotypic and phenotypic diversity. We analyze a model
of viral competition between two viruses infecting a constantly replenished cell pool. We assume a trade-off between the ability
of the virus to colonize new cells (cell killing rate or virulence) and its local competitiveness (replicative success within
coinfected cells). We characterize the conditions that allow for viral spread by means of the basic reproductive number and
show that a local coexistence equilibrium exists, which is asymptotically stable. At this equilibrium, the less virulent competitor
has a reproductive advantage over the more virulent colonizer reflected by a larger equilibrium population size of the competitor.
The equilibria at which one virus outcompetes the other one are unstable, i.e., a second virus is always able to permanently
invade. We generalize the two-virus model to multiple viral strains, each displaying a different virulence. To account for
the large phenotypic diversity in viral populations, we consider a continuous spectrum of virulences and present a continuum
limit of this multiple viral strains model that describes the time evolution of an initial continuous distribution of virulence
without mutations. We provide a proof of the existence of solutions of the model equations, analytically assess the properties
of stationary solutions, and present numerical approximations of solutions for different initial distributions. Our simulations
suggest that initial continuous distributions of virulence evolve toward a distribution that is extremely skewed in favor
of competitors. At equilibrium, only the least virulent part of the population survives. The discrepancy of this finding in
the continuum limit with the two-virus model is attributed to the skewed equilibrium subpopulation sizes and to the transition
to a continuum. Consequently, in viral quasispecies with high virulence diversity, the model predicts collective virulence
attenuation. This result may contribute to understanding virulence attenuation, which has been reported in several experimental
studies. 相似文献
8.
Thomas von Rintelen Ristiyanti M. Marwoto G. Douglas Haffner Fabian Herder 《Hydrobiologia》2014,723(1):1-6
The fifth conference of the European Pond Conservation Network (Luxembourg, June 2012) brought together researchers, environmental managers, and other stakeholders with the aim to share state-of-the-art knowledge on the ecology, management, and conservation of ponds in the context of the many challenges facing the wider water environment. Although well-known ecological patterns apply to most ponds in Europe and elsewhere, recent data highlight that part of the environmental variables governing pond biodiversity remain specific to climatic/biogeographic regions and to elevation ranges, suggesting that, in addition to common practice, management plans should include range-specific measures. Beyond the contribution of individual ponds to the aquatic and terrestrial life, connected networks of ponds are vital in the provision of new climate space as a response to global climate change, by allowing the observed northward and/or upward movements of species. In terms of services, ponds offer sustainable solutions to key issues of water management and climate change such as nutrient retention, rainfall interception, or carbon sequestration. While the ecological role of ponds is now well-established, authoritative research-based advice remains needed to inform future direction in the conservation of small water bodies and to further bridge the gap between science and practice. 相似文献
9.
Recent experiments show that vascular endothelial growth factor (VEGF) is the crucial mediator of downstream events that ultimately
lead to enhanced endothelial cell survival and increased vascular density within many tumors. The newly discovered pathway
involves up-regulation of the anti-apoptotic protein Bcl-2, which in turn leads to increased production of interleukin-8 (CXCL8).
The VEGF–Bcl-2–CXCL8 pathway suggests new targets for the development of anti-angiogenic strategies including short interfering
RNA (siRNA) that silence the CXCL8 gene and small molecule inhibitors of Bcl-2. In this paper, we present and validate a mathematical
model designed to predict the effect of the therapeutic blockage of VEGF, CXCL8, and Bcl-2 at different stages of tumor progression.
In agreement with experimental observations, the model predicts that curtailing the production of CXCL8 early in development
can result in a delay in tumor growth and vascular development; however, it has little effect when applied at late stages
of tumor progression. Numerical simulations also show that blocking Bcl-2 up-regulation, either at early stages or after the
tumor has fully developed, ensures that both microvascular and tumor cell density stabilize at low values representing growth
control. These results provide insight into those aspects of the VEGF–Bcl-2–CXCL8 pathway, which independently and in combination,
are crucial mediators of tumor growth and vascular development. Continued quantitative modeling in this direction may have
profound implications for the development of novel therapies directed against specific proteins and chemokines to alter tumor
progression. 相似文献
10.
Ali F. El Mehdawi Stormy D. Lindblom Jennifer J. Cappa Sirine C. Fakra 《International journal of phytoremediation》2015,17(8):753-765
Neighbors of Se hyperaccumulators Stanleya pinnata and Astragalus bisulcatus were found earlier to have elevated Se levels. Here we investigate whether Se hyperaccumulators affect Se localization and speciation in surrounding soil and neighboring plants. X-ray fluorescence mapping and X-ray absorption near-edge structure spectroscopy were used to analyze Se localization and speciation in leaves of Artemisia ludoviciana, Symphyotrichum ericoides and Chenopodium album growing next to Se hyperaccumulators or non-accumulators at a seleniferous site. Regardless of neighbors, A. ludoviciana, S. ericoides and C. album accumulated predominantly (73–92%) reduced selenocompounds with XANES spectra similar to the C-Se-C compounds selenomethionine and methyl-selenocysteine. Preliminary data indicate that the largest Se fraction (65–75%), both in soil next to hyperaccumulator S. pinnata and next to nonaccumulator species was reduced Se with spectra similar to C-Se-C standards. These same C-Se-C forms are found in hyperaccumulators. Thus, hyperaccumulator litter may be a source of organic soil Se, but soil microorganisms may also contribute. These findings are relevant for phytoremediation and biofortification since organic Se is more readily accumulated by plants, and more effective for dietary Se supplementation. 相似文献
11.
The Wilson–Cowan model of interacting neurons (1973) is one of the most influential papers published in Biological Cybernetics (Kybernetik). This paper and a companion paper published in 1972 have been cited over 1000 times. Rather than focus on the microscopic
properties of neurons, Wilson and Cowan analyzed the collective properties of large numbers of neurons using methods from
statistical mechanics, based on the mean-field approach. New experimental techniques to measure neuronal activity at the level of large populations are now available to
test these models, including optical recording of brain activity with intrinsic signals and voltage sensitive dyes, and new
methods for analyzing EEG and MEG. These measurement techniques have revealed patterns of coherent activity that span centimetres
of tissue in the cerebral cortex. Here the underlying ideas are reviewed in a historic context.
This note was written by Alain Destexhe and Terry Sejnowski, the Editors-in-Chief of the Journal of Computational Neuroscience and Neural Computation, on the occasion of the appearance of Volume 100 of Biological Cybernetics. 相似文献
12.
E. I. Vanguelova Y. Hirano T. D. Eldhuset L. Sas-Paszt M. R. Bakker Ü. Püttsepp 《Plant biosystems》2013,147(3):460-480
Many Aloe species are exploited as natural products. Generally, the leaves are unsustainably picked from wild plants to meet the market demand. Basic scientific information on seed biology and the ways of increasing levels of secondary metabolites in seedlings is still lacking for Aloe species. This study investigated seed germination requirements and evaluated levels of secondary metabolites in seedlings of Aloe arborescens, an important species in traditional medicine. The highest percentage germination (78%) and the fastest germination rate (GR) (10% d? 1) with a mean germination time (MGT) of 9 days were achieved at 20°C under a 16-h photoperiod. At 25°C, maximum percentage germination (67%) (P < 0.05), higher GR (13% d? 1) and shorter MGT (6 days) were obtained under constant light. These results indicate that temperature and light play a significant role in germination of A. arborescens seeds. Increasing osmotic pressure on seeds decreased percentage germination, whereas buffering the solution to a range of pH values (4–10) did not significantly affect germination. Smoke–water (1:500 v/v), smoke-isolated karrikinolide (10? 8 and 10? 9 M) and potassium nitrate (10? 3 and 10? 4 M) significantly promoted germination compared with the control at 25°C (supra-optimal temperature) under a 16-h photoperiod. These treatments were also effective in increasing secondary metabolite levels (flavonoids and phenolics) in A. arborescens seedlings. 相似文献
13.
《Phytomedicine》2014,21(1):75-81
The aim of this double-blind, placebo controlled clinical trial was to assess the effects of a combination of selenium and silymarin in men with lower urinary tract symptoms, benign prostatic hyperplasia and a prostate specific antigen (PSA) ≤2.5 ng/ml. The volunteers were randomized to two groups: the first one (n = 26) received 240 μg selenium (in the form of yeast l-selenomethionine) plus 570 mg silymarin daily for 6 months and the second (n = 29) received placebo. Outcome measures were changes in the International Prostate Symptom Score (IPSS), bladder volume (V), urinary flow rate, ultrasound estimated postvoid residual urine volume (RV), serum PSA, testosterone and selenium levels, safety clinical biochemistry, hematology and oxidative stress parameters at baseline and on day 180. The results showed statistically significant differences (p < 0.05) between treatment and control groups for the following parameters: IPSS score, urodynamic parameters: maximal rate of urine flow (Qmax), average flow (Qave), V and RV, total PSA value and serum selenium levels. There was a significant reduction in PSA in the selenium–silymarin group but no effect on blood testosterone level. Overall the treatment was well-tolerated with no adverse effects. 相似文献
14.
Serological identification and molecular characterization of B (A) 02 subtype
in patients and blood donors from Eastern China 下载免费PDF全文
Wen Wu Yecui Zhang Xingying Guo Peng Wu Zhibo Zhang Xiangyan Huang 《Asia-Pacific Journal of Blood Types and Genes》2017,1(1):55-59
This study was designed to identify the rare?type?ABO?blood?groups, B(A) 02, from Eastern China. Three samples with discordant serological results during routine blood type identification and four samples from one sample’ family were selected. All of them were detected by serological method. The exon 6 and 7 of the ABO genes were amplified by PCR and sequenced. They were typed as AsubB by serology and as BO by genotype. In AsubB samples, nt 700C>G mutation was detected in B gene, which was previously defined as B(A)02 alleles. In these seven samples, six showed B(A)02/O01 and one showed B(A)02/O02.B(A)02 allele was found to be more common in this study than B(A)04 which is considered to be more frequent than B(A)02. The careful identification of rare blood types is important for the safety of clinical blood transfusion. 相似文献
15.
Nostoc sphaeroides Kützing was cultivated in paddlewheel-driven raceway ponds and the growth kinetics of 1-2 mm and 3-4 mm colonies of N. sphaeroides was studied. The biomass productivities in 2.5 m(2) raceway ponds inoculated with 1-2 mm and 3-4 mm colonies were 5.2 and 0.25 g dry wt m(-2) d(-1), respectively. Furthermore, differently sized colonies showed different relative water content, total soluble carbohydrates, chlorophyll a content and density of filaments. This is the first report on mass culture of N. sphaeroides under outdoor conditions. 相似文献
16.
State I-State II transitions were monitored in vivo and in vitro in the Antarctic, psychrophillic, green alga, Chlamydomonas subcaudata, as changes in the low-temperature (77 K) chlorophyll fluorescence emission maxima at 722 nm (F722) relative to 699 nm (F699). As expected, the control mesophillic species, Chlamydomonas reinhardtii, was able to modulate the light energy distribution between photosystem II and photosystem I in response to exposure to four different conditions: (i) dark/anaerobic conditions, (ii) a change in Mg2+ concentration, (iii) red light, and (iv) increased incubation temperature. This was correlated with the ability to phosphorylate both of its major light-harvesting polypeptides. In contrast, exposure of C. subcaudata to the same four conditions induced minimum alterations in the 77 K fluorescence emission spectra, which was correlated with the ability to phosphorylate only one of its major light-harvesting polypeptides. Thus, C. subcaudata appears to be deficient in the ability to undergo a State I-State II transition. Functionally, this is associated with alterations in the apparent redox status of the intersystem electron transport chain and with higher rates of photosystem I cyclic electron transport in the psychrophile than in the mesophile, based on in vivo P700 measurements. Structurally, this deficiency is associated with reduced levels of Psa A/B relative to D1, the absence of specific photosystem I light-harvesting polypeptides [R.M. Morgan et al. (1998) Photosynth Res 56:303-314] and a cytochrome b6/f complex that exhibits a form of cytochrome f that is approximately 7 kDa smaller than that observed in C. reinhardtii. We conclude that the Antarctic psychrophile, C. subcaudata, is an example of a natural variant deficient in State I-State II transitions. 相似文献
17.
Force–Velocity Curves of Motor Proteins Cooperating In Vivo 总被引:1,自引:0,他引:1
Shtridelman Y Cahyuti T Townsend B DeWitt D Macosko JC 《Cell biochemistry and biophysics》2008,52(1):19-29
Motor proteins convert chemical energy into work, thereby generating persistent motion of cellular and subcellular objects.
The velocities of motor proteins as a function of opposing loads have been previously determined in vitro for single motors.
These single molecule “force–velocity curves” have been useful for elucidating motor kinetics and for estimating motor performance
under physiological loads due to, for example, the cytoplasmic drag force on transported organelles. Here we report force–velocity
curves for single and multiple motors measured in vivo. Using motion enhanced differential interference contrast (MEDIC) movies
of living NT2 (neuron-committed teratocarcinoma) cells at 37°C, three parameters were measured—velocity (v), radius (a), and effective cytoplasmic viscosity (η′)—as they applied to moving vesicles. These parameters were combined in Stokes’
equation, F = 6πaη′v, to determine the force, F, required to transport a single intracellular particle at velocity, v. In addition, the number of active motors was inferred from the multimodal pattern seen in a normalized velocity histogram.
Using this inference, the resulting in vivo force–velocity curve for a single motor agrees with previously reported in vitro
single motor force–velocity curves. Interestingly, however, the curves for two and three motors lie significantly higher in
both measured velocity and computed force, which suggests that motors can work cooperatively to attain higher transport forces
and velocities.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
18.
Simone Fattorini 《Journal of the history of biology》2017,50(3):473-496
Hewett Cottrell Watson and Edward Forbes were two naturalists of the Victorian age. They were protagonists on a dispute that generated comment and serves as an illuminating case study of misunderstanding in priority issues. Watson accused Forbes of having plagiarized his original classification of the British plants into groups on the basis of their geographical distribution. This controversy originated mostly from a so-far-ignored basic difference in Watson’s and Forbes’ ideas about biogeographical regionalization. Watson’s classification of the British flora into groups of species with similar distribution was probably the first application of the concept of “regional chorotype.” By contrast, the biogeographical classification of the British flora proposed by Forbes belongs to the concept of “element,” because it was based on assumed species history (i.e. colonization routes). The two approaches may produce similar outcomes, but remain conceptually different. Although personal reasons may have contributed to exacerbate the Watson–Forbes controversy, failure in recognizing this distinction by its actors and their contemporaries, such as Hooker and Darwin, was the most important cause. 相似文献
19.
B. Shrestha S. Lipe K. A. Johnson T. Q. Zhang W. Retzlaff Z.-Q. Lin 《Plant and Soil》2006,288(1-2):189-196
Biological volatilization of selenium (Se) in contaminated areas represents an environmentally friendly phytoremediation approach. Implementation of phytovolatilization technology for the remediation of Se-contaminated soils or sediments is oftentimes limited by its low remediation efficiency under field conditions. This greenhouse study determined the feasibility of manipulating soil organic content and hydraulic conditions in a soil–pickleweed (Salicornia bigelovii) system for the enhancement of Se volatilization. Based on annual shoot biomass production rate under field conditions (approximately 1.5 kg m−2), the addition of pickleweed shoot tissues to the soil surface resulted in 2.2-fold more biogenic volatile Se than the control, up to 251.6 ± 140.5 μg m−2 d−1. Selenium volatilization was significantly reduced at a soil water potential of −25 kPa, but substantially increased after re-irrigation to 0 kPa. In a 42-day experiment, the rate of Se volatilization was significantly correlated with soil water potential (P < 0.0001). Findings from this study demonstrate that Se volatilization be substantially enhanced by amending soil with pickleweed residues and by creating wetting and drying cycles that can be monitored with soil water potential probes in the field. 相似文献