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1.
Maria Saline Vladislav Orekhov Karin Lindkvist-Petersson B. Göran Karlsson 《Biomolecular NMR assignments》2010,4(1):1-4
The staphylococcal enterotoxin H (SEH; 217 aa, 25 kD) belongs to a family of superantigens that cause a massive immune response upon simultaneous binding to the T cell receptor (TCR) and the major histocompatibility complex class II. The SEH-TCR interaction is weak and amenable to studies using NMR methodology. Essentially, 2 mg of U{2H, 13C,15N}-labeled SEH was used for the complete sequential backbone assignment of SEH at 900 MHz. The protein secondary structure inferred from the chemical shift index (Cα and Cβ) is in very good agreement with the secondary structure elements of the X-ray structure. 相似文献
2.
Effect of Water Activity on Enterotoxin B Production and Growth of Staphylococcus aureus 总被引:7,自引:5,他引:2
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John A. Troller 《Applied microbiology》1971,21(3):435-439
Staphylococcus aureus C-243, an enterotoxin B-producing strain, was cultured on media adjusted to various water activity (aw) levels by means of two different solute systems. Total numbers and rate of growth were diminished at low aw levels, and enterotoxin synthesis was extremely sensitive to reduction in aw. A reduction of aw from 0.99 to 0.98 in one medium and from 0.99 to 0.97 in the other medium resulted in extremely low levels of enterotoxin in spent culture media despite the attainment of high numbers of staphylococci. 相似文献
3.
B. Rihn J.M. Scheftel R. Girardot H. Monteil 《Biochemical and biophysical research communications》1984,124(3):690-695
produces two toxins, an enterotoxin and a cytotoxin. The enterotoxin was purified using fast methods (tangential flow filtration, fast protein liquid chromatography). The purified enterotoxin is composed of two subunits (A1 = 41,500, A2 = 16,000) and its pI is 3.5. 相似文献
4.
C4 photosynthesis and water stress 总被引:1,自引:0,他引:1
Ghannoum O 《Annals of botany》2009,103(4):635-644
Background
In contrast to C3 photosynthesis, the response of C4 photosynthesis to water stress has been less-well studied in spite of the significant contribution of C4 plants to the global carbon budget and food security. The key feature of C4 photosynthesis is the operation of a CO2-concentrating mechanism in the leaves, which serves to saturate photosynthesis and suppress photorespiration in normal air. This article reviews the current state of understanding about the response of C4 photosynthesis to water stress, including the interaction with elevated CO2 concentration. Major gaps in our knowledge in this area are identified and further required research is suggested.Scope
Evidence indicates that C4 photosynthesis is highly sensitive to water stress. With declining leaf water status, CO2 assimilation rate and stomatal conductance decrease rapidly and photosynthesis goes through three successive phases. The initial, mainly stomatal phase, may or may not be detected as a decline in assimilation rates depending on environmental conditions. This is because the CO2-concentrating mechanism is capable of saturating C4 photosynthesis under relatively low intercellular CO2 concentrations. In addition, photorespired CO2 is likely to be refixed before escaping the bundle sheath. This is followed by a mixed stomatal and non-stomatal phase and, finally, a mainly non-stomatal phase. The main non-stomatal factors include reduced activity of photosynthetic enzymes; inhibition of nitrate assimilation, induction of early senescence, and changes to the leaf anatomy and ultrastructure. Results from the literature about CO2 enrichment indicate that when C4 plants experience drought in their natural environment, elevated CO2 concentration alleviates the effect of water stress on plant productivity indirectly via improved soil moisture and plant water status as a result of decreased stomatal conductance and reduced leaf transpiration.Conclusions
It is suggested that there is a limited capacity for photorespiration or the Mehler reaction to act as significant alternative electron sinks under water stress in C4 photosynthesis. This may explain why C4 photosynthesis is equally or even more sensitive to water stress than its C3 counterpart in spite of the greater capacity and water use efficiency of the C4 photosynthetic pathway.Key words: C3 and C4 photosynthesis, stomatal and non-stomatal limitation, high CO2, water stress 相似文献5.
H. Shen 《Molecular simulation》2013,39(1):59-64
By the quantum-molecular dynamics (QMD) technique based on the Roothaan–Hall equation and the Newton motion law, geometrical deformation and failure behavior of C60 fullerene dimer (2C60) as well as single C60 fullerene under applied external electric field are simulated. Further, the effects of the electric field direction on the electric field-induced deformation, polarization-charge distribution and dipole moment of the fullerene molecules are discussed systemically. It is found that the geometrical configuration and failure behavior of the 2C60 molecule are sensitive to the electric field direction, that when the electric field direction is parallel to the bridging C–C bonds of the 2C60 molecule the 2C60 fails easily, and that when the electric field direction is perpendicular to the 2C60 fails difficultly and has the same polarization and failure mechanism as the single C60. 相似文献
6.
It is of great significance to develop an effective method for methyl parathion (MP) detection. Herein, a novel nitrogen-doped titanium carbide quantum dots (N-Ti3C2 QDs) was prepared and used to construct a simple and sensitive fluorescence sensing platform of MP by making use of inner filter effect (IFE). The prepared N-Ti3C2 QDs can exhibit strong blue fluorescence at 434 nm. Meanwhile, MP could hydrolyze to produce p-nitrophenol (p-NP) under alkaline conditions, which showed a characteristic ultraviolet-visible (UV-visible) absorption peak at 405 nm, resulting in the fluorescence of N-Ti3C2 QDs is effectively quenched by p-NP. In addition, the investigation of time-resolved fluorescence decays indicated that the corresponding quenching mechanism of p-NP on N-Ti3C2 QDs is due to the IFE. After optimizing the conditions, the as-developed fluorescence sensing platform displayed wide detection range (0.1–30 μg mL−1) and low detection limit (0.036 μg mL−1) for MP, and it was also successfully applied for MP analysis in real water samples, thus it is expected that this simple, sensitive and enzyme-free sensing platform shows great applications. 相似文献
7.
Stomatal sensitivity to carbon dioxide and humidity: a comparison of two c(3) and two c(4) grass species 总被引:10,自引:3,他引:7
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The sensitivity of stomatal conductance to changes of CO2 concentration and leaf-air vapor pressure difference (VPD) was compared between two C3 and two C4 grass species. There was no evidence that stomata of the C4 species were more sensitive to CO2 than stomata of the C3 species. The sensitivity of stomatal conductance to CO2 change was linearly proportional to the magnitude of stomatal conductance, as determined by the VPD, the same slope fitting the data for all four species. Similarly, the sensitivity of stomatal conductance to VPD was linearly proportional to the magnitude of stomatal conductance. At small VPD, the ratio of intercellular to ambient CO2 concentration, Ci/Ca, was similar in all species (0.8-0.9) but declined with increasing VPD, so that, at large VPD, Ci/Ca was 0.7 and 0.5 (approximately) in C3 and C4 species, respectively. Transpiration efficiency (net CO2 assimilation rate/transpiration rate) was larger in the C4 species than in the C3 species at current atmospheric CO2 concentrations, but the relative increase due to high CO2 was larger in the C3 than in the C4 species. 相似文献
8.
Summary The photosynthetic processes of two ecologically-matched, herbaceous Atriplex species differed in their response to SO2 fumigations. Atriplex triangularis, a C3 species, was more sensitive than the C4 species, A. sabulosa. This difference in sensitivity can be attributed in part to the higher conductance of the C3 species in normal air and saturating light as well as greater stimulation of stomatal opening following exposure to SO2. In addition, photosynthetic mechanisms of the C3 species had higher intrinsic SO2 sensitivity than the C4 species. Differences between photosynthetic responses of these two species may also reflect differences in morphological configuration of mesophyll tissues and greater SO2 sensitivity of the initial photosynthetic carboxlating enzyme of the C3 species. It is likely that certain of the differences in photosynthetic SO2 sensitivity of these contrasting C3 and C4
Atriplex species are characteristic of C3 and C4 plants in general.Abbreviations PEP carboxylase
phosphoenolpyruvate carboxylase
- RuBP carboxylase
ribulose-1,5-bisphosphate carboxylase 相似文献
9.
10.
Some Characteristics of the System Converting 1-Aminocyclopropane-1-carboxylic Acid to Ethylene 总被引:18,自引:13,他引:5
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The rate of C2H4 production in plant tissue appears to be limited by the level of endogenous 1-aminocyclopropane-1-carboxylic acid (ACC). Exogenous ACC stimulated C2H4 production considerably in plant tissues, but this required 10 to 100 times the endogenous concentrations of ACC before significant increases in C2H4 production were observed. This was partially due to poor penetration of ACC into the tissues. Conversion of ACC to C2H4 was inhibited by free radical scavengers, reducing agents, and copper chelators, but not by inhibitors of pyridoxal phosphate-mediated reactions. The system for converting ACC to C2H4 may be membrane-associated, for it did not survive treatment with surface-active agents and cold or osmotic shock reduced the capacity of the system to convert ACC to C2H4. The reaction rate was sensitive to temperatures above 29 and below 12 C, which suggests that the system may be associated with membrane-bound lipoproteins. The data presented support the possibility that the conversion of exogenous ACC to C2H4 proceeds via the natural physiological pathway. 相似文献
11.
Summary Six early successional plant species with differing photosynthetic pathways (3 C3 species and 3 C4 species) were grown at either 300, 600, or 1,200 ppm CO2 and at either 0.0 or 0.25 ppm SO2. Total plant growth increased with CO2 concentration for the C3 species and varied only slightly with CO2 for the C4 species. Fumigation with SO2 caused reduced growth of the C3 species at 300 ppm CO2 but not at the higher concentrations of CO2. Fumigation with SO2 reduced growth of the C4 species at high CO2 and increased growth at 300 ppm CO2. Leaf area increased with increasing CO2 for all plant species. Fumigation with SO2 reduced leaf area of C3 plants more at low CO2 than at high CO2 while leaf area of C4 plants was reduced more at high CO2 than at low CO2. These results support the notion that C3 species are more sensitive to SO2 fumigation than are C4 species at concentrations of CO2 equal to that found in normal ambient air. However, the difference in sensitivity to SO2 between C3 and C4 species was found to be reversed at higher concentrations of CO2. A possible explanation for this reversal based upon differences in stomatal response to elevated CO2 between C3 and C4 species is discussed. 相似文献
12.
Environmental Responses of the Post-lower Illumination CO(2) Burst as Related to Leaf Photorespiration
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As leaf irradiance is decreased in increments, a single transient CO2 burst is exhibited by C3 plant leaves. This post-lower illumination CO2 burst (PLIB) is sensitive to changes in irradiance, to changes in the concentrations of O2 and CO2, and to temperature. Increasing O2 concentrations above ambient produces a progressively larger PLIB while increasing CO2 concentrations above ambient produces a progressively smaller PLIB. The PLIB, which exhibits many responses to environment common with other methods for measuring photorespiration and photosynthesis, is proposed as a measure of photorespiration in illuminated leaves of C3 plants. Although the PLIB cannot be used as a quantitative measurement of photorespiration, we propose that the PLIB is a rapid, easy, relatively inexpensive, nondestructive method for evaluating photorespiration in intact illuminated C3 leaves in air. 相似文献
13.
Background and Aims
The success of C4 plants lies in their ability to attain greater efficiencies of light, water and nitrogen use under high temperature, providing an advantage in arid, hot environments. However, C4 grasses are not necessarily less sensitive to drought than C3 grasses and are proposed to respond with greater metabolic limitations, while the C3 response is predominantly stomatal. The aims of this study were to compare the drought and recovery responses of co-occurring C3 and C4 NADP-ME grasses from the subfamily Panicoideae and to determine stomatal and metabolic contributions to the observed response.Methods
Six species of locally co-occurring grasses, C3 species Alloteropsis semialata subsp. eckloniana, Panicum aequinerve and Panicum ecklonii, and C4 (NADP-ME) species Heteropogon contortus, Themeda triandra and Tristachya leucothrix, were established in pots then subjected to a controlled drought followed by re-watering. Water potentials, leaf gas exchange and the response of photosynthetic rate to internal CO2 concentrations were determined on selected occasions during the drought and re-watering treatments and compared between species and photosynthetic types.Key Results
Leaves of C4 species of grasses maintained their photosynthetic advantage until water deficits became severe, but lost their water-use advantage even under conditions of mild drought. Declining C4 photosynthesis with water deficit was mainly a consequence of metabolic limitations to CO2 assimilation, whereas, in the C3 species, stomatal limitations had a prevailing role in the drought-induced decrease in photosynthesis. The drought-sensitive metabolism of the C4 plants could explain the observed slower recovery of photosynthesis on re-watering, in comparison with C3 plants which recovered a greater proportion of photosynthesis through increased stomatal conductance.Conclusions
Within the Panicoid grasses, C4 (NADP-ME) species are metabolically more sensitive to drought than C3 species and recover more slowly from drought. 相似文献14.
Ethoxyzolamide Inhibition of CO(2)-Dependent Photosynthesis in the Cyanobacterium Synechococcus PCC7942 总被引:5,自引:4,他引:1
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Cells of the cyanobacterium, Synechococcus PCC7942, grown under high inorganic carbon (Ci) conditions (1% CO2; pH 8) were found to be photosynthetically dependent on exogenous CO2. This was judged by the fact that they had a similar photosynthetic affinity for CO2 (K0.5[CO2] of 3.4-5.4 micromolar) over the pH range 7 to 9 and that the low photosynthetic affinity for Ci measured in dense cell suspensions was improved by the addition of exogenous carbonic anhydrase (CA). The CA inhibitor, ethoxyzolamide (EZ), was shown to reduce photosynthetic affinity for CO2 in high Ci cells. The addition of 200 micromolar EZ to high Ci cells increased K0.5(CO2) from 4.6 micromolar to more than 155 micromolar at pH 8.0, whereas low Ci cells (grown at 30 microliters CO2 per liter of air) were less sensitive to EZ. EZ inhibition in high and low Ci cells was largely relieved by increasing exogenous Ci up to 100 millimolar. Lipid soluble CA inhibitors such as EZ and chlorazolamide were shown to be the most effective inhibitors of CO2 usage, whereas water soluble CA inhibitors such as methazolamide and acetazolamide had little or no effect. EZ was found to cause a small drop in photosystem II activity, but this level of inhibition was not sufficient to explain the large effect that EZ had on CO2 usage. High Ci cells of Anabaena variabilis M3 and Synechocystis PCC6803 were also found to be sensitive to 200 micromolar EZ. We discuss the possibility that the inhibitory effect of EZ on CO2 usage in high Ci cells of Synechococcus PCC7942 may be due to inhibition of a `CA-like' function associated with the CO2 utilizing Ci pump or due to inhibition of an internal CA activity, thus affecting CO2 supply to ribulose bisphosphate carboxylase-oxygenase. 相似文献
15.
Alterations in plasma membrane permeability induced by Clostridium perfringens enterotoxin were studied using Vero (African green monkey kidney) cells which were radioactively labeled with four markers of different molecular size. The markers were α-amino[14C]isobutyric acid (Mr 103), 3H-labeled nucleotide (Mr approx. 300), 51Cr label (Mr approx. 3000) and [3H]RNA (Mr > 25 000). Over a 2 h period, enterotoxin caused significant release of aminoisobutyric acid, nucleotides and 51Cr label but not RNA. The effects of enterotoxin on label release were dose- and time-dependent. The rate of release of markers was dependent upon their size. Permeability alterations could be detected within 15 min with a high dose of enterotoxin. Gel chromatography of released material was used to determine that markers of Mr 3000 but not 25 000 leaked from permeabilized cells. It was concluded that enterotoxin is producing functional ‘holes’ of limited size in the membrane. Permeability changes due to enterotoxin treatment differed between confluent and non-confluent (growing) cells. We propose that the primary action of the enterotoxin is to interact with the plasma membrane and produce functional ‘holes’ of defined size. The resultant alterations in membrane permeability cause the loss of essential cellular substances which inhibits processes such as macromolecular synthesis and eventually leads to cell deterioration and death. 相似文献
16.
O. Ghannoum K. Siebke S. Von Caemmerer & J. P. Conroy 《Plant, cell & environment》1998,21(11):1123-1131
Evidence is presented contrary to the suggestion that C4 plants grow larger at elevated CO2 because the C4 pathway of young C4 leaves has C3-like characteristics, making their photosynthesis O2 sensitive and responsive to high CO2. We combined PAM fluorescence with gas exchange measurements to examine the O2 dependence of photosynthesis in young and mature leaves of Panicum antidotale (C4, NADP-ME) and P. coloratum (C4, NAD-ME), at an intercellular CO2 concentration of 5 Pa. P. laxum (C3) was used for comparison. The young C4 leaves had CO2 and light response curves typical of C4 photosynthesis. When the O2 concentration was gradually increased between 2 and 40%, CO2 assimilation rates (A) of both mature and young C4 leaves were little affected, while the ratio of the quantum yield of photosystem II to that of CO2 assimilation (ΦPSII/ΦCO2) increased more in young (up to 31%) than mature (up to 10%) C4 leaves. A of C3 leaves decreased by 1·3 and ΦPSII/ΦCO2 increased by 9-fold, over the same range of O2 concentrations. Larger increases in electron transport requirements in young, relative to mature, C4 leaves at low CO2 are indicative of greater O2 sensitivity of photorespiration. Photosynthesis modelling showed that young C4 leaves have lower bundle sheath CO2 concentration, brought about by higher bundle sheath conductance relative to the activity of the C4 and C3 cycles and/or lower ratio of activities of the C4 to C3 cycles. 相似文献
17.
Cells resistant to enterotoxin were selected from cultures of highly sensitive Vero (African green monkey kidney) cells. Studies were done with the sensitive and resistant cells to determine the relationship between binding and biological activity. Binding studies using 125I-enterotoxin revealed the apparent existence of high and low affinity binding sites for the enterotoxin on both cell types. The binding site density on resistant cells was found to be that of sensitive cells. It was found that, even with high doses of enterotoxin, only partial affect upon DNA synthesis, membrane permeability, and plating efficiency was noted in resistant cells. It is concluded that without specific binding there is little or no ability of the enterotoxin to effect biological activity in cells. 相似文献
18.
The photosynthetic linear electron transport rate in excess of that used for CO2 reduction was evaluated in Sorghum bicolor Moench. [NADP-malic enzyme (ME)-type C4 plant], Amaranthus cruentus L. (NAD-ME-type C4 plant) and Helianthus annuus L. (C3 plant) leaves at different CO2 and O2 concentrations. The electron transport rate (J
F) was calculated from fluorescence using the light partitioning factor (relative PSII cross-section) determined under conditions
where excess electron transport was assumed to be negligible: low light intensities, 500 μmol CO2 · mol−1 and 2% O2. Under high light intensities there was a large excess of J
F/4 at 10–100% O2 in the C3 plant due to photorespiration, but very little in sorghum and somewhat more in amaranth, showing that photorespiration is
suppressed, more in the NADP-ME- and less in the NAD-ME-type species. It is concluded that when C4 photosynthesis is limited by supply of atmospheric CO2 to the C4 cycle, the C3 cycle becomes limited by regeneration of ribulose 1,5-bisphosphate (RuBP) which in turn limits RuBP oxygenase activity and
photorespiration. The rate of excess electron transport over that consumed for CO2 fixation in C4 plants was very sensitive to the presence of O2 in the gas phase, rapidly increasing between 0.01 and 0.1% O2, and at 2% O2 it was about two-thirds of that at 21% O2. This shows the importance of the Mehler O2 reduction as an electron sink, compared with photorespiration in C4 plants. However, the rate of the Mehler reaction is still too low to fully account for the extra ATP which is needed in C4 photosynthesis.
Received: 8 November 1997 / Accepted: 26 December 1997 相似文献
19.
《FEBS letters》1986,199(1):75-79
Photosynthetic O2 evolution in the green alga, Scenedesmus obliquus, was shown to be more sensitive to the uncoupler FCCP when assayed in a low Ci medium than in a high Ci medium, indicating the action of an energy-dependent mechanism for Ci uptake. Low Ci adapted algae exhibited characteristic luminescence decay kinetics with a transient peak 20–60 s after excitation. This peak was abolished by addition of FCCP and HCO−3. The effect caused by HCO−3 was partially reversed by methyl viologen. In view of the results obtained, a model is presented in order to discuss the origin of the transient luminescence peak. 相似文献
20.
D. Mansuy J.-Y. Lallemand J.-C. Chottard B. Cendrier G. Gacon H. Wajcman 《Biochemical and biophysical research communications》1976,70(2):595-599
The addition of an excess of C2H5N13C to myoglobin and human adult and fetal hemoglobins, gives three characteristic NMR spectra with new 13C resonances respectively at δ = ?10,56 ppm, δ = ?7,03 and ?7,95 ppm and δ = ?6,28 and ?7,95 ppm (CH3CO2Na as external standard). These signals correspond to the C2H5N13C bound to the Fe(II) of the different heme units, according to CO exchange experiments. Characteristic resonances can be assigned to C2H5N13C bound to α, β and γ subunits. C2H5N13C appears as a more sensitive probe than 13CO for hemoprotein NMR studies. 相似文献