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901.
Jo Nelissen Koen Nuyts Marta De Zotti Rob Lavigne Chris Lamberigts Wim M. De Borggraeve 《PloS one》2012,7(12)
The total synthesis is reported of the peptaibol Septocylindrin B which is related to the well documented channel forming peptaibol antibiotic Alamethicin. Several analogues were synthesized with a modified C-terminus, to investigate the SAR of the terminal residue Phaol. All these peptides were tested for their membrane perturbation properties by fluorescent dye leakage assay and for their antibacterial activity. 相似文献
902.
Production of official statistics frequently requires expert judgement to evaluate and reconcile data of unknown and varying quality from multiple and potentially conflicting sources. Moreover, exceptional events may be difficult to incorporate in modelled estimates. Computational logic provides a methodology and tools for incorporating analyst''s judgement, integrating multiple data sources and modelling methods, ensuring transparency and replicability, and making documentation computationally accessible. Representations using computational logic can be implemented in a variety of computer-based languages for automated production. Computational logic complements standard mathematical and statistical techniques and extends the flexibility of mathematical and statistical modelling. A basic overview of computational logic is presented and its application to official statistics is illustrated with the WHO & UNICEF estimates of national immunization coverage. 相似文献
903.
Matera I Ferraroni M Bürger S Scozzafava A Stolz A Briganti F 《Journal of molecular biology》2008,380(5):856-868
The crystallographic structure of salicylate 1,2-dioxygenase (SDO), a new ring fission dioxygenase from the naphthalenesulfonate-degrading strain Pseudaminobacter salicylatoxidans BN12, which oxidizes salicylate to 2-oxohepta-3,5-dienedioic acid by a novel ring fission mechanism, has been solved by molecular replacement techniques and refined at 2.9 Å resolution (Rfree 26.1%; R-factor 19.3%). SDO is a homo-tetramer member of type III extradiol-type dioxygenases with a subunit topology characteristic of the bicupin β-barrel folds. The catalytic center contains a mononuclear iron(II) ion coordinated to three histidine residues (His119, His121, and His160), located within the N-terminal domain in a solvent-accessible pocket. SDO is markedly different from the known gentisate 1,2-dioxygenases (GDO) or 1-hydroxy-2-naphthoate dioxygenase because of its unique ability to oxidatively cleave numerous salicylates, gentisates and 1-hydroxy-2-naphthoate with high catalytic efficiency. The comparison of the structure and substrate specificity for a series of different substrates with the corresponding data for several GDOs and the docking of salicylates/gentisates in the active site of SDO, allowed the identification of several active site residues responsible for differences of substrate specificity. In particular, a more defined electron density of the N-terminal region allowed the discovery of a novel structure fragment in SDO previously unobserved in GDO. This region contributes several residues to the active site that influence substrate specificity for both of these enzymes. Implications on the catalytic mechanism are discussed. 相似文献
904.
Králová-Hromadová I Spakulová M Horácková E Turceková L Novobilský A Beck R Koudela B Marinculić A Rajský D Pybus M 《The Journal of parasitology》2008,94(1):58-67
Complete sequences of ribosomal and mitochondrial genes of the giant liver fluke Fascioloides magna are presented. In particular, small subunit (18S) and internal transcribed spacers (ITS1 and ITS2) of the ribosomal gene (rDNA), as well as cytochrome c oxidase subunit I (cox1) and nicotinamide dehydrogenase subunit I (nad1) of the mitochondrial DNA (mtDNA), were analyzed. The 18S and ITS sequences were compared with previously published sequences of the liver fluke Fasciola hepatica. Fixed interspecific genetic differences were determined that allow molecular differentiation of F. magna and F. hepatica using either the PCR-RFLP method or PCR amplification of species-specific DNA regions. Additionally, intraspecific sequence polymorphism of the complete cox1 and nad1 mitochondrial genes in geographically distinct F. magna populations was determined. Based on the sequence divergences, short (< 500 bp) variable regions suitable for broader biogeographical studies of giant liver fluke were designed. 相似文献
905.
Morten S. Frederiksen Marta Pérez Juan Manuel Ruiz 《Journal of experimental marine biology and ecology》2008,358(1):98-109
The effect of increased sediment sulfide concentrations on the sulfur isotopic composition (δ34S), total sulfur (TS) and elemental sulfur (S0) concentrations in plant tissues was studied for the two seagrasses Zostera marina (3 weeks in laboratory) and Posidonia oceanica (4 months in situ). Porewater sulfide concentrations were experimentally regulated and plants exposed to high sediment sulfide concentrations had δ34S signals closer to the δ34S of sulfide, whereas plants exposed to no / low sulfide concentrations had δ34S signals closer to the δ34S of seawater sulfate, indicating a higher sulfide invasion in plants exposed to high sulfide concentrations. The δ34S varied between the plant tissues in both species with the leaves having more positive δ34S signals than roots and rhizomes, indicating that sulfide was invading into the roots and moved to the other tissues through the lacunae. TS and S0 concentrations were higher in plants exposed to sulfide in both experiments suggesting that sulfur derived from sediment sulfide accumulated in the plants. The δ34S signal in S0 was similar to sediment sulfide verifying that S0 found in the seagrasses originated from sediment sulfide. Direct comparisons of δ34S in the two different seagrasses and across the treatments were not possible due to large differences in δ34S of the sulfur sources. Fsulfide adjusted for these differences and may be a useful alternative, when δ34S of the sulfur sources varies between study sites. There were no significant effects of sulfide exposure on plant growth and mortality in Z. marina and P. oceanica after 3 weeks and 8 weeks exposure, respectively, but P. oceanica showed indications of reduced growth and higher mortality after 16 weeks of sulfide exposure probably due to sulfide invasion/toxicity. 相似文献
906.
The effect that an increase in the activity of an enzyme has on its flux normally decreases with activity increase. To achieve a large increase in flux by manipulating a single step would therefore require a high initial effect that maintains or increases when the activity is increased, what has been called sustained or paradoxical control. Using metabolic control analysis for large responses, we derive conditions for sustained or paradoxical control in terms of elasticity coefficients. These are used to characterise types of rate laws contributing to this behaviour. The result that simple pathways, with normal kinetics, subject to large activity changes can lead to paradoxical control behaviour suggests that this type of pattern may be much more ubiquitous than could have, in principle, been suspected. 相似文献
907.
Pellizzari EH Barontini M Figuerola Mde L Cigorraga SB Levin G 《Life sciences》2008,83(11-12):413-420
AIMS: Pheochromocytomas are catecholamine-secreting tumors that also synthesize and secrete several neuropeptides, including opioids. A negative regulation of catecholamine secretion by opioids has been postulated in chromaffin cells. However, results obtained so far are contradictory when referred to human pheochromocytomas. The aim of this study was to define the role of locally produced enkephalins on catecholamine release in human pheochromocytoma cells. MAIN METHODS: Cells obtained from eleven human pheochromocytomas of different genetic origins were cultured for 5 days. Cultures were maintained under basal condition or under enkephalin, dexamethasone and naloxone alone or in combination with enkephalin or dexamethasone-stimulated conditions. Catecholamine and enkephalin levels in the culture medium were measured by HPLC-ED and RIA respectively. KEY FINDINGS: Enkephalin induced a decrease in norepinephrine levels in all tumor cultures. Dexamethasone treatment, which increased enkephalin levels, also decreased catecholamine levels. On the other hand, the addition of naloxone to the cultures reverted to normal the inhibitory action exerted by enkephalin and dexamethasone treatments. SIGNIFICANCE: These results suggest the existence of an autocrine negative regulatory loop exerted by enkephalin on norepinephrine release in human pheochromocytoma cells. 相似文献
908.
Costa PM Lobo J Caeiro S Martins M Ferreira AM Caetano M Vale C Delvalls TA Costa MH 《Mutation research》2008,654(1):29-37
Juvenile Solea senegalensis (Senegalese sole) were exposed to freshly collected sediments from three sites of the Sado Estuary (West-Portuguese coast) in 28-day laboratory assays in order to assess the ecological risk from sediment contaminants, by measuring two genotoxicity biomarkers in peripheral blood: the percentage of Erythrocyte Nuclear Abnormalities (ENA) by use of an adaptation of the micronucleus test, and the percentage of DNA strand-breakage (DNA-SB) with the Comet assay. Sediments were surveyed for metallic (Cr, Ni, Cu, Zn, As, Cd and Pb) and organic (PAHs (polycyclic aromatic hydrocarbons), PCBs (polychlorinated biphenyls) and DDTs (dichloro-diphenyl-trichloroethane)) contaminants. Sediments from site A (farthest from hotspots of contamination) were found to be the least contaminated and weaker inducers of genotoxic damage, whereas sediments from sites B (urban influence) and C (affected by industrial effluents and agricultural runoffs) were responsible for a very significant increase in both ENA and DNA-SB, site B being most contaminated with metals and site C mainly with organic pollutants, especially PAHs and PCBs . Analysis of genotoxic effects showed a strong correlation between the concentrations of PAHs and PCBs and both biomarkers at sampling times T(14) and T(28), while the amounts of Cu, As, Cd and Pb were less strongly correlated, and at T(28) only, with ENA and DNA-SB. These results show that organic contaminants in sediment are stronger and faster acting genotoxic stressors. The results also suggest that metals may have an inhibitory effect on genotoxicity when interacting with organic contaminants, at least during early exposure. ENA and DNA-SB do not show a linear relationship, but a strong correlation exists between the overall increase in genotoxicity caused by exposure to sediment, confirming that they are different, and possibly non-linked effects that respond similarly to exposure. Although the Comet assay showed enhanced sensitivity, the two analyses are complementary and suitable for the biomonitoring of sediment contaminants in a benthic species like S. senegalensis. 相似文献
909.
Herbivory can induce changes in plant traits that may involve both tolerance mechanisms that compensate for biomass loss and
resistance traits that reduce herbivore preference. Seagrasses are marine vascular plants that possess many attributes that
may favour tolerance and compensatory growth, and they are also defended with mechanisms of resistance such as toughness and
secondary metabolites. We quantified phenotypic changes induced by herbivore damage on the temperate seagrass Posidonia oceanica in order to identify specific compensatory and resistance mechanisms in this plant, and to assess any potential trade-offs
between these two strategies of defence. We simulated three natural levels of fish herbivory by repeatedly clipping seagrass
leaves during the summer period of maximum herbivory. Compensatory responses were determined by measuring shoot-specific growth,
photosynthetic rate, and the concentration of nitrogen and carbon resources in leaves and rhizomes. Induced resistance was
determined by measuring the concentration of phenolic secondary metabolites and by assessing the long-term effects of continued
clipping on herbivore feeding preferences using bioassays. Plants showed a significant ability to compensate for low and moderate
losses of leaf biomass by increasing aboveground growth of damaged shoots, but this was not supported by an increase in photosynthetic
capacity. Low levels of herbivory induced compensatory growth without any measurable effects on stored resources. In contrast,
nitrogen reserves in the rhizomes played a crucial role in the plant’s ability to compensate and survive herbivore damage
under moderate and high levels of herbivory, respectively. We found no evidence of inducibility of long-term resistance traits
in response to herbivory. The concentration of phenolics decreased with increasing compensatory growth despite all treatments
having similar carbon leaf content, suggesting reallocation of these compounds towards primary functions such as cell-wall
construction. 相似文献
910.