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排序方式: 共有139条查询结果,搜索用时 15 毫秒
1.
Addition of ATP (100 microM) to hepatocytes from starved rats incubated with 5 mM [1-14C]glutamine caused a stimulation of glucose formation; the magnitude of the concomitant increases in 14CO2 production and glutamine consumption indicate that flux from glutamine to glucose was increased. ATP also caused a simultaneous decrease in the cell content of oxoglutarate; together with the increased flux this is consistent with an activation of oxoglutarate dehydrogenase. In corroboration of this, a stimulation by ATP of gluconeogenesis and a decrease in oxoglutarate was also observed with 5 mM proline as substrate. ATP caused an increase in hepatocyte cytoplasmic free Ca2+ concentration, [Ca2+]c, as indicated by the increase in the fluorescence of cytoplasmically trapped quin2, from a resting value of about 0.2 microM to greater than 1 microM. The mechanism of oxoglutarate dehydrogenase activation may be via an increase in mitochondrial Ca2+ content as a consequence of the increase in [Ca2+]c. The effects of 100 microM adenosine were also investigated. An increase in flux from glutamine to glucose was observed together with a decrease in the cell oxoglutarate, thus indicating that adenosine addition to hepatocytes could also activate oxoglutarate dehydrogenase. The activation by adenosine was less than that produced by ATP. Adenosine caused a small apparent increase in [Ca2+]c to 0.3-0.4 microM; it remains to be established if this effect, which is small relative to that of ATP, is sufficient to elicit the activation of oxoglutarate dehydrogenase: alternative mechanisms may exist. 相似文献
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Detecting non-neutral heterogeneity across a region of DNA sequence in the ratio of polymorphism to divergence 总被引:11,自引:4,他引:7
Natural selection, in the form of balancing selection or selective sweeps,
can result in a decoupling of the amounts of molecular polymorphism and
divergence. Thus natural selection can cause some areas of DNA sequence to
have greater silent polymorphism, relative to divergence between species,
than other areas. It would be useful to have a statistical test for
heterogeneity in the polymorphism to divergence ratio across a region of
DNA sequence, one that could identify heterogeneity greater than that
expected from the neutral processes of mutation, drift, and recombination.
The only currently available test requires that a region be arbitrarily
divided into sections that are compared with each other, and the
subjectivity of this division could be problematic. Here a test is proposed
in which runs of polymorphic and fixed sites are counted, where a "run" is
a set of one or more sites of one type preceded and followed by the other
type. The number of runs is smaller than otherwise expected if
polymorphisms are clumped together. By simulating neutral evolution and
comparing the observed number of runs to the simulations, a statistical
test is possible which does not require any a priori decisions about
subdivision.
相似文献
4.
Pasteurella multocida toxin, a potent mitogen, increases inositol 1,4,5-trisphosphate and mobilizes Ca2+ in Swiss 3T3 cells 总被引:4,自引:0,他引:4
J M Staddon C J Barker A C Murphy N Chanter A J Lax R H Michell E Rozengurt 《The Journal of biological chemistry》1991,266(8):4840-4847
Pasteurella multocida toxin, both native and recombinant, is an extremely potent mitogen for Swiss 3T3 cells and acts to enhance the formation of total inositol phosphates (Rozengurt, E., Higgins, T., Changer, N., Lax, A.J., and Staddon, J.M. (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 123-127). P. multocida toxin also stimulates diacylglycerol production and activates protein kinase C (Staddon, J.M., Chanter, N., Lax, A.J., Higgins, T.E., and Rozengurt, E. (1990) J. Biol. Chem. 265, 11841-11848). Here we analyze, by [3H]inositol labeling and high performance liquid chromatography, the inositol phosphates in recombinant P. multocida toxin-treated cells. Recombinant P. multocida toxin stimulated increases in [3H]inositol 1,4,5-trisphosphate ([3H]Ins(1,4,5)P3) and its metabolic products, including Ins(1,3,4,5)P4, Ins(1,3,4)P3, Ins(1,4)P2, Ins(4/5)P, and Ins(1/3)P. The profile of the increase in the cellular content of these distinct inositol phosphates was very similar to that elicited by bombesin. Furthermore, recombinant P. multocida toxin, like bombesin, mobilizes an intracellular pool of Ca2+. Recombinant P. multocida toxin pretreatment greatly reduces the Ca2(+)-mobilizing action of bombesin, consistent with Ca2+ mobilization from a common pool by the two agents. The enhancement of inositol phosphates and mobilization of Ca2+ by recombinant P. multocida toxin were blocked by the lysosomotrophic agents methylamine, ammonium chloride, and chloroquine and occurred after a dose-dependent lag period. The stimulation of inositol phosphate production by recombinant P. multocida toxin persisted after removal of extracellular toxin, in contrast to the reversibility of the action of bombesin. Recombinant P. multocida toxin, unlike bombesin and guanosine 5'-O-(gamma-thiotriphosphate), did not cause the release of inositol phosphates in permeabilized cells. These data demonstrate that recombinant P. multocida toxin, acting intracellularly, stimulates the phospholipase C-mediated hydrolysis of phosphatidylinositol 4,5-bisphosphate. 相似文献
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7.
Janine JH Oosterhof G Jolanda Elving Ietse Stokroos Arie van nieuw Amerongen Henny C van der Mei Henk J Busscher 《Biofouling》2013,29(6):347-353
The integrity of biofilms on voice prostheses used to rehabilitate speech in laryngectomized patients causes unwanted increases in airflow resistance, impeding speech. Biofilm integrity is ensured by extracellular polymeric substances (EPS). This study aimed to determine whether synthetic salivary peptides or mucolytics, including N-acetylcysteine and ascorbic acid, influence the integrity of voice prosthetic biofilms. Biofilms were grown on voice prostheses in an artificial throat model and exposed to synthetic salivary peptides, mucolytics and two different antiseptics (chlorhexidine and Triclosan). Synthetic salivary peptides did not reduce the air flow resistance of voice prostheses after biofilm formation. Although both chlorhexidine and Triclosan reduced microbial numbers on the prostheses, only the Triclosan-containing positive control reduced the air flow resistance. Unlike ascorbic acid, the mucolytic N-acetylcysteine removed most EPS from the biofilms and induced a decrease in air flow resistance. 相似文献
8.
Plantago lanceolata with or without the mycorrhizal
fungus Glomus mosseae were grown over a 100 d period
under ambient (38050 mol mol-1) and elevated
(600150 mol
mol-1) atmospheric CO2 conditions. To achieve
similar growth, non-mycorrhizal plants received phosphorus in solution
whereas mycorrhizal plants were supplied with bonemeal. Measures of plant
growth, photosynthesis and carbon input to the soil were obtained. Elevated
CO2 stimulated plant growth to the same extent in mycorrhizal and
non0mycorrhizal plants, but had no effect on the partitioning of carbon
between shoots and roots or on shoot tissue phosphorus concentration.
Mycorrhizal colonization was low, but unaffected by CO2 treatment. Net
photosynthesis was stimulated both by mycorrhizal colonization and elevated
CO2, and there was a more than additive effect of the two treatments on net
photosynthesis. Colonization by mycorrhizal fungi inhibited acclimation, in
terms of net carbon assimilation, or plants to elevated CO2.
13C natural abundance techniques were used to
measure carbon input into the soil, although the results were not
conclusive. Direct measurements of below-ground root biomass showed that
elevated CO2 did stimulate carbon flow below-ground and this was higher in
mycorrhizal than non-mycorrhizal plants. For the four treatment
combinations, the observed relative differences in amount of below-ground
carbon were compared with those expected from the differences in net
photosynthesis. A considerable amount of the extra carbon fixed both as a
result of mycorrhizal colonization and growth in elevated CO2 did not
reveal itself as increased plant biomass. As there was no evidence for a
substantial increase in soil organic matter, most of this extra carbon must
have been respired by the mycorrhizal fungus and the roots or by the plants
as dark-respiration. The need for detailed studies in this area is
emphasized. 相似文献
9.
Carbon isotopes in functional soil ecology 总被引:10,自引:0,他引:10
Staddon PL 《Trends in ecology & evolution》2004,19(3):148-154
Soil is an integral part of terrestrial ecosystems. Many soil ecologists interested in soil ecosystem functioning rely, to some degree, on stable isotope methodologies. The study of the natural abundance of carbon isotopes, especially (13)C but also (14)C, in the environment and the use of stable carbon isotope tracers have proved very useful in investigating the soil carbon cycle and soil trophic relationships. Recent methodological and technical advances have greatly extended the possibilities for the application of stable carbon isotopes to terrestrial ecology and have vastly improved our knowledge of belowground ecosystem functioning and will continue to do so. A better understanding of soil processes is invaluable in predicting the future impacts of global environmental change on terrestrial ecosystems. 相似文献
10.
In situ (13)C pulse labelling was used to measure the temporal and spatial carbon flow through an upland grassland. The label was delivered as (13)C-CO(2) to vegetation in three replicate plots in each of two treatments: control and lime addition. Harvests occurred over a two month period and samples were taken along transects away from the label delivery area. The (13)C concentration of shoot, root, bulk soil, and soil-respired CO(2) was measured. There was no difference in the biomass and (13)C concentration of shoot and root material for the control and lime treatments meaning that the amount of (13)C-CO(2) assimilated by the vegetation and translocated below ground was the same in both treatments. The (13)C concentration of the bulk soil was lower in the lime treatment than in the control and, conversely, the (13)C concentration of the soil-respired CO(2) was higher in the lime. Unlike the difference in bulk soil (13)C concentration between treatments, the difference in the (13)C concentration of the soil-respired CO(2) was obvious only at the delivery site and primarily within 1 d after labelling. An observed increase in the abundance of mycorrhizal fungi in the lime treatment was a possible cause for this faster carbon throughput. The potential key role of mycorrhizas in the soil carbon cycle is discussed. The importance of a better understanding of soil processes, especially biological ones, in relation to the global carbon cycle and environmental change is highlighted. 相似文献