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71.
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Marleen TJ van Ampting Arjan J Schonewille Carolien Vink Robert Jan M Brummer van der Roelof Meer Ingeborg MJ Bovee-Oudenhoven 《BMC physiology》2009,9(1):6-9
Background
Glutathione, the main antioxidant of intestinal epithelial cells, is suggested to play an important role in gut barrier function and prevention of inflammation-related oxidative damage as induced by acute bacterial infection. Most studies on intestinal glutathione focus on oxidative stress reduction without considering functional disease outcome. Our aim was to determine whether depletion or maintenance of intestinal glutathione changes susceptibility of rats to Salmonella infection and associated inflammation. 相似文献73.
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Uniform sampling from graphical realizations of a given degree sequence is a fundamental component in simulation-based measurements of network observables, with applications ranging from epidemics, through social networks to Internet modeling. Existing graph sampling methods are either link-swap based (Markov-Chain Monte Carlo algorithms) or stub-matching based (the Configuration Model). Both types are ill-controlled, with typically unknown mixing times for link-swap methods and uncontrolled rejections for the Configuration Model. Here we propose an efficient, polynomial time algorithm that generates statistically independent graph samples with a given, arbitrary, degree sequence. The algorithm provides a weight associated with each sample, allowing the observable to be measured either uniformly over the graph ensemble, or, alternatively, with a desired distribution. Unlike other algorithms, this method always produces a sample, without back-tracking or rejections. Using a central limit theorem-based reasoning, we argue, that for large , and for degree sequences admitting many realizations, the sample weights are expected to have a lognormal distribution. As examples, we apply our algorithm to generate networks with degree sequences drawn from power-law distributions and from binomial distributions. 相似文献
76.
Niels Bassler 《Radiation and environmental biophysics》2010,49(3):373-378
Due to their high sensitivity and signal-to-noise ratio, charge-coupled devices (CCDs) have been the preferred optical photon
detectors of astronomers for several decades. CCDs are flown in space as the main detection instrument on several well-known
missions, such as the Hubble Space Telescope, XMM-Newton or the Cassini Probe. Also, CCDs are frequently used in satellite
star trackers which provide attitude information to the satellite orientation system. However, one major drawback is their
extreme vulnerability to radiation, which is readily abundant in space. Here, we shall give a brief overview of the radiation
effects on CCDs, and mention ways how to mitigate the effects in other ways than merely increase shielding, such as cooling
and annealing. As an example, we have investigated the radiation hardness of a particular CCD, the so-called CCD47-20 from
Marconi Applied Technologies (now E2V), by exposing it to radiation fields representing the radiation environment found in
a highly elliptic orbit crossing the Van-Allen radiation belts. Two engineering-grade CCDs were irradiated with proton beams
and photons, and effects of increased bulk dark current, surface dark current and inversion threshold voltage shifts were
observed and are quantified. 相似文献
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Quorum sensing is a process of bacterial cell-cell communication that enables populations of cells to carry out behaviours in unison. Quorum sensing involves detection of the density-dependent accumulation of extracellular signal molecules called autoinducers that elicit population-wide changes in gene expression. In Vibrio species, CqsS is a membrane-bound histidine kinase that acts as the receptor for the CAI-1 autoinducer which is produced by the CqsA synthase. In Vibrio cholerae, CAI-1 is (S)-3-hydroxytridecan-4-one. The C170 residue of V. cholerae CqsS specifies a preference for a ligand with a 10-carbon tail length. However, a phenylalanine is present at this position in Vibrio harveyi CqsS and other homologues, suggesting that a shorter CAI-1-like molecule functions as the signal. To investigate this, we purified the V. harveyi CqsS ligand, and determined that it is (Z)-3-aminoundec-2-en-4-one (Ea-C8-CAI-1) carrying an 8-carbon tail. The V. harveyi CqsA/CqsS system is exquisitely selective for production and detection of this ligand, while the V. cholerae CqsA/CqsS counterparts show relaxed specificity in both production and detection. We isolated CqsS mutants in each species that display reversed specificity for ligands. Our analysis provides insight into how fidelity is maintained in signal transduction systems. 相似文献
79.
Kimberly C Tu Wenyun Lu N P Ong Bonnie L Bassler Ned S Wingreen 《Molecular systems biology》2011,7(1)
Quorum sensing is a chemical signaling mechanism used by bacteria to communicate and orchestrate group behaviors. Multiple feedback loops exist in the quorum‐sensing circuit of the model bacterium Vibrio harveyi. Using fluorescence microscopy of individual cells, we assayed the activity of the quorum‐sensing circuit, with a focus on defining the functions of the feedback loops. We quantitatively investigated the signaling input–output relation both in cells with all feedback loops present as well as in mutants with specific feedback loops disrupted. We found that one of the feedback loops regulates receptor ratios to control the integration of multiple signals. Together, the feedback loops affect the input–output dynamic range of signal transmission and the noise in the output. We conclude that V. harveyi employs multiple feedback loops to simultaneously control quorum‐sensing signal integration and to ensure signal transmission fidelity. 相似文献
80.
Hu H Armstrong PC Khalil E Chen YC Straub A Li M Soosairajah J Hagemeyer CE Bassler N Huang D Ahrens I Krippner G Gardiner E Peter K 《PloS one》2011,6(4):e19190