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排序方式: 共有104条查询结果,搜索用时 15 毫秒
1.
Inhibition of early steps of de novo fatty-acid biosynthesis by different xenobiotica 总被引:1,自引:0,他引:1
The importance of the early steps of de novo fatty-acid biosynthesis is discussed in terms of rate-limiting enzymic reactions with respect to their inhibition by xenobiotics. The inhibitory spectra of allicin as an inhibitor of the acetyl-CoA-synthase, two classes of graminicides (cyclohexane-1,3-diones and aryloxyphenoxypropionic acids) as inhibitors of acetyl-CoA-carboxylase, and the two antibiotics cerulenin and thiolactomycin, which affect the condensing step in fatty-acid biosynthesis, are compared. 相似文献
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3.
In 160 women large but variable amounts of intravenous oxytocin were needed to induce labour within a reasonable time interval to 5 cm cervical dilatation. Thereafter 7 mU of oxytocin/min would maintain progress. Since large maintenance doses may cause obstetric problems it is recommended that a maintenance regimen should be used once labour has progressed to this stage. 相似文献
4.
We have tested the effect of dithiothreitol (DTT) treatment on the initial spreading of human fibroblasts in serum-free medium in tissue culture dishes. Cell spreading was inhibited following treatment of these cells with 10 mM DTT. Inhibition occurred when the cells were treated at 37°C but not at 4° and was reversible metabolically but not by the addition of sulfhydryl oxidizing reagents. The inhibition was overcome when DTT-treated human fibroblasts were plated on cold insoluble globulin (plasma fibronectin)—coated dishes. Under these conditions spreading appeared to be completely normal, including the formation of focal adhesions. Analysis of the fibronectin concentrations in the human fibroblasts following DTT treatment indicated that there was little decrease in the absolute level of activity as determined in a biological assay for BHK cell spreading on culture dishes. Analysis of the fibronectin distribution on the DTT-treated human fibroblasts by indirect immunofluorescence using a specific anti-CIG antiserum revealed that fibronectin was no longer deposited onto the culture dish surfaces. Even when the DTT-treated human fibroblasts spread in the presence of fetal calf serum, the cell fibronectin remained for the most part in a perinuclear location. These results indicate that DTT treatment of human fibroblasts prevents the normal translocation of fibronectin from a perinuclear location to the surface of the culture dish. This study further supports our hypothesis that the initial spreading in serum-free medium of fibroblasts from cell strains depends upon secretion of fibronectin onto the culture dish surface. 相似文献
5.
Tomographic phase microscopy 总被引:1,自引:0,他引:1
We report a technique for quantitative three-dimensional (3D) mapping of refractive index in live cells and tissues using a phase-shifting laser interferometric microscope with variable illumination angle. We demonstrate tomographic imaging of cells and multicellular organisms, and time-dependent changes in cell structure. Our results will permit quantitative characterization of specimen-induced aberrations in high-resolution microscopy and have multiple applications in tissue light scattering. 相似文献
6.
Weibel DB Oldham NJ Feld B Glombitza G Dettner K Boland W 《Insect biochemistry and molecular biology》2001,31(6-7):583-591
The biosynthesis of chrysomelidial and plagiodial was studied in the rove beetle subtribe Philonthina (Staphylinidae). Glandular homogenates were found to convert synthetic (2E,6E)-[trideuteromethyl-5,5-(2)H(5)]octa-2,6-diene-1,8-diol (10) into nor-chrysomelidial (14) and nor-plagiodial (13). The overall transformation requires; i) oxidation of the substrate at C(1) and C(8), ii) cyclization of the resulting dialdehyde to nor-plagiodial followed by iii) isomerization to give nor-chrysomelidial. The oxidase requires molecular oxygen as a cofactor and operates with removal of the pro-R hydrogen from C(1) and C(8) of synthetic (1R,8R,2E,6E)-[1,8-(2)H(2)]-2,6-dimethyl-octa-2,6-diene-1,8-diol (15), producing a dialdehyde along with H(2)O(2). Unlike enzymes from iridoid-producing leaf beetle larvae, the Philonthus enzyme is able to oxidize saturated substrates such as citronellol. Crude protein extracts prepared from Philonthus glands by ammonium sulfate precipitation, were found to produce hydrogen peroxide at a rate of 0.085+/-0.003 ng H(2)O(2) (ng protein)(-1) hr(-1) with nerol as an oxidase substrate. The cyclase operates with opposite stereochemistry to the enzyme(s) from Phaedon cochleariae and other herbivorous leaf beetles, specifically removing the C(5)-H(R) hydrogen atom from (4R,5S,2E,6E)-[4,5-(2)H(2)]-2-methyl-octa-2,6-diene-1,8-diol (17). These findings have enabled us to construct a detailed account of iridoid biosynthesis in rove beetles, which resembles the biosynthetic route in leaf beetle larvae, but exhibits distinct stereochemical differences. 相似文献
7.
Indicators for biodiversity and ecosystem services: towards an improved framework for ecosystems assessment 总被引:1,自引:0,他引:1
Christian K. Feld José Paulo Sousa Pedro Martins da Silva Terence P. Dawson 《Biodiversity and Conservation》2010,19(10):2895-2919
Ecosystem assessment and monitoring requires the development and application of suitable indicators, i.e. they need to be
(i) reliable and capable of simplifying complex relationships, (ii) quantifiable and transparent in order to enable an easy
communication, and (iii) fit for the purpose of indication. These requirements are scarcely fulfilled in current ecosystem
assessment and monitoring efforts to address the requirements of international biodiversity conventions. Here we present and
test a set of seven criteria towards an improved framework for ecosystems indication with particular emphasis on the indication
of biodiversity and ecosystem services: purpose of indication, indicator type according to the EEA’s Driver-Pressure-State-Impact-Response
scheme, direct/indirect linkages to biodiversity and ecosystem services, spatial scale and scalability across scales, applicability
of benchmarks/reference values, availability of data and protocols, and applicability of remote sensing. The criteria are
tested using 24 indicators of ecosystem assessment and monitoring at the global, continental and regional scale. Based on
the general trends revealed by our evaluation, we present recommendations to streamline and improve ecosystem indication with
respect to international biodiversity conventions. The implementation of our recommendations does require concerted international
effort, comparable, for instance, to the implementation of the Water Framework Directive in Europe. 相似文献
8.
9.
This article comprises a literature analysis of 41 river rehabilitation projects to assess the short-term (5 years) ability
of indicator groups to demonstrate progress towards river rehabilitation goals. Positive indications were compared to land-use,
river size, rehabilitation intervention and time. A questionnaire was developed to investigate river manager’s interpretation
of rehabilitation success and to assess their level of adherence to recommendations in the literature with regard to rehabilitation
assessment on a conceptual level. A total of 54 responses were received from respondents based in Germany, The Netherlands
and the United Kingdom. The results indicate that macroinvertebrate indicators, while widely used in assessing river rehabilitation
efforts, exhibited a lower frequency of positive responses than most other indicator types in the short term. Conversely,
terrestrial floodplain indicators exhibited the most frequent level of positive response for all ecological type indicators
leading to recommendations for further investigations into their use for short-term monitoring. Assessment procedures recommended
in literature are largely followed, illustrating the advances that have been made with regard to assessment planning. Indicator
responses are influenced by scale factors, for example, land-use and river size, that are often not considered by rehabilitation
managers. While an emphasis is placed on ecological, hydrological and morphological indicators in monitoring schemes, the
socioeconomic perspective (emphasized in the literature as forming an integral part of the river system) is neglected. 相似文献
10.
Seismic and auditory tuning curves from bullfrog saccular and amphibian papular axons 总被引:1,自引:0,他引:1
Xiaolong Yu Edwin R. Lewis David Feld 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1991,169(2):241-248
We present seismic and auditory frequency tuning curves of individual bullfrog, Rana catesbeiana, saccular and amphibian papilla axons that responded to both seismic and auditory stimuli. In this study we found: 1) most saccular axons respond well to auditory stimuli with moderate signal strength (50-70 dB SPL) as well as to seismic stimuli; 2) most amphibian papilla axons respond well to seismic stimuli as well as to auditory stimuli, and their seismic sensitivities are comparable to those of saccular axons (responding to sinusoidal stimuli with peak accelerations in the range 0.001 to 0.1 cm/S2); 3) the responses to both seismic and auditory stimuli from both saccule and amphibian papilla are tuned, i.e. the strength of the response varies with the frequency of the stimulus; and this tuning is clearly not the result of second order resonance; 4) in individual axons the tuning properties for seismic stimuli often are not the same as those for auditory stimuli, a fact that may provide clues about how the stimulus signal energy is transferred to the hair cells in each case. 相似文献