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991.
Two distinct types of cell growth of suspension-cultured Mentha were formed when the cells maintained in the medium containing 1000 micrograms l-1 2,4-D were subcultured into different 2,4-D concentrations. Few cell elongation of Mentha (average cell length: 34-40 microns) was observed after division in the medium containing 1-200 micrograms l-1 2,4-D; and significant cell elongation (average cell length: 95-130 microns) was observed after cell division in the medium containing 500-2000 micrograms l-1 2,4-D. A close correlation between culture medium and water content in the cells indicated that 2,4-D promoted cell elongation by water uptake. Amounts of phenolic acid in cell walls were much higher in unelongated cell walls than in elongated ones during the cultivation, and there was a close correlation between the amounts and the level of PAL activity in elongated and unelongated cells. However, there was no significant difference in cell wall components and its neutral sugar composition between elongated and unelongated cells. 相似文献
992.
R. M. Davydov Joanne Smieja S. A. Dikanov Y. Zang Lawrence Que Jr. M. K. Bowman 《Journal of biological inorganic chemistry》1999,4(3):292-301
Radiolytic reduction at 77 K of oxo-/hydroxo-bridged dinuclear iron(III) complexes in frozen solutions forms kinetically
stabilized, mixed-valent species in high yields that model the mixed-valent sites of non-heme, diiron proteins. The mixed-valent
species trapped at 77 K retain ligation geometry similar to the initial diferric clusters. The shapes of the mixed-valent
EPR signals depend strongly on the bridging ligands. Spectra of the Fe(II)OFe(III) species reveal an S=1/2 ground state with small g-anisotropy as characterized by the uniaxial component (g
z
–g
av /2<0.03) observable at temperatures as high as ∼100 K. In contrast, hydroxo-bridged mixed-valent species are characterized
by large g-anisotropy (g
z
–g
av /2>0.03) and are observable only below 30 K. Annealing at higher temperatures causes structural relaxation and changes in
the EPR characteristics. EPR spectral properties allow the oxo- and hydroxo-bridged, mixed-valent diiron centers to be distinguished
from each other and can help characterize the structure of mixed-valent centers in proteins.
Received: 27 June 1998 / Accepted: 25 February 1999 相似文献
993.
Tiffany M. Tsang Jeffrey S. Wiese Suleyman Felek Malte Kronshage Eric S. Krukonis 《PloS one》2013,8(12)
The Yersinia pestis adhesin Ail mediates host cell binding and facilitates delivery of cytotoxic Yop proteins. Ail from Y. pestis and Y. pseudotuberculosis is identical except for one or two amino acids at positions 43 and 126 depending on the Y. pseudotuberculosis strain. Ail from Y. pseudotuberculosis strain YPIII has been reported to lack host cell binding ability, thus we sought to determine which amino acid difference(s) are responsible for the difference in cell adhesion. Y. pseudotuberculosis YPIII Ail expressed in Escherichia coli bound host cells, albeit at ∼50% the capacity of Y. pestis Ail. Y. pestis Ail single mutants, Ail-E43D and Ail-F126V, both have decreased adhesion and invasion in E. coli when compared to wild-type Y. pestis Ail. Y. pseudotuberculosis YPIII Ail also had decreased binding to the Ail substrate fibronectin, relative to Y. pestis Ail in E. coli. When expressed in Y. pestis, there was a 30–50% decrease in adhesion and invasion depending on the substitution. Ail-mediated Yop delivery by both Y. pestis Ail and Y. pseudotuberculosis Ail were similar when expressed in Y. pestis, with only Ail-F126V giving a statistically significant reduction in Yop delivery of 25%. In contrast to results in E. coli and Y. pestis, expression of Ail in Y. pseudotuberculosis led to no measurable adhesion or invasion, suggesting the longer LPS of Y. pseudotuberculosis interferes with Ail cell-binding activity. Thus, host context affects the binding activities of Ail and both Y. pestis and Y. pseudotuberculosis Ail can mediate cell binding, cell invasion and facilitate Yop delivery. 相似文献
994.
995.
In the photosynthetic green filamentous bacterium Chloroflexus aurantiacus, excitation energy is transferred from a large bacteriochlorophyll (BChl) c antenna via smaller BChl a antennas to the reaction center. The effects of substituted 1,4-naphthoquinones on BChl c and BChl a fluorescence and on flash-induced cytochrome c oxidation were studied in whole cells under aerobic conditions. BChl c fluorescence in a cell suspension with 5.4 microM BChl c was quenched to 50% by addition of 0.6 microM shikonin ((R)-2-(1-hydroxy-4-methyl-3-pentenyl)-5,8-dihydroxy-1, 4-naphthoquinone), 0.9 microM 5-hydroxy-1,4-naphthoquinone, or 4 microM 2-acetyl-3-methyl-1,4-naphthoquinone. Between 25 and 100 times higher quinone concentrations were needed to quench BChl a fluorescence to a similar extent. These quinones also efficiently inhibited flash-induced cytochrome c oxidation when BChl c was excited, but not when BChl a was excited. The quenching of BChl c fluorescence induced by these quinones correlated with the inhibition of flash-induced cytochrome c oxidation. We concluded that the quinones inhibited electron transfer in the reaction center by specifically quenching the excitation energy in the BChl c antenna. Our results provide a model system for studying the redox-dependent antenna quenching in green sulfur bacteria because the antennas in these bacteria inherently exhibit a sensitivity to O(2) similar to the quinone-supplemented cells of Cfx. aurantiacus. 相似文献
996.
Bruna de Cssia M. Ramos Danessa S. Boligon Gilson R. P. Moreira 《Ecological Entomology》2019,44(5):610-622
1. Larvae of tortoise beetles present exaggerated body parts in association with an abdominal shield, which is made of faeces and exuviae that are deposited on the urogomphi throughout ontogeny. Growth trajectories and scaling relationships of these functional structures associated with the shield, if any, are unknown. 2. This study of Gratiana spadicea first tested, under field conditions, whether there is adaptive value associated with the shield regarding protection against predation and sunlight. Then, under laboratory conditions, the growth trajectory and allometric relationships among body parts were investigated, including scoli, individual and apparent furcae, and shield. The influence of food deprivation on the development of these structures was also determined. 3. Findings from previous studies were confirmed, suggesting that the adaptive value assigned to the shield is related to protection against predators. The present study demonstrated for the first time that the shield acts as a parasol in cassidines, decreasing the exposure of their larval body to sunlight. The scoli and apparent furca are exaggerated structures of G. spadicea, the development of which involves allometric growth and greater energetic investment (positive allometry) during ontogeny. There was proportionally less energetic investment for somatic construction of individual furca (negative allometry) due to the accumulation of the exuviae. 4. The possible consequences, in terms of developmental costs and survivorship benefits associated with the evolution of such exaggerated structures, are discussed. 相似文献
997.
S C Lee J Y Shew F H Chang M J Chou C S Yang 《Proceedings of the National Science Council, Republic of China. Part B, Life sciences》1984,8(2):143-147
Protein kinase activity has been found in hepatitis B virions (Dane particles) purified from the plasma of hepatitis B surface antigen carriers [Albin, C., and Robinson, W.S. (1980) J. Virol. 34, 297-302]. Dane particles were purified from the pooled, HBeAg-positive plasma. When this preparation was incubated with [gamma 32P]ATP in the presence of 10mM MnCl2 and 0.5% NP-40 for 15 seconds at 30 degrees C, several phosphorylated polypeptides of 20,000, 42,000, 48,000, 50,000 and 56,000 daltons were detected in sodium dodecyl sulfate-polyacrylamide gels. When the Dane particles were incubated with [gamma 32P]ATP, 10 mM MnCl2, and 0.5% NP-40 in the presence of human hepatoma cell (J-5) particulate fraction at 30 degrees C, 15 seconds, the 42,000, 48,000 and 50,000 daltons phosphorylated polypeptides were not found. When human peripheral blood lymphocytes particulate fraction was incubated with Dane particles under the same conditions, no change of Dane particle phosphorylated polypeptides was detected. Previous publications [Albin, C., and Robinson, W.S. (1980) J. Virol. 34, 297-302; Gerlich, W.H. et al. (1982) J. Virol. 42, 761-766] showed that when hepatitis B core particles purified from hepatoma tissues contained protein kinase activity, only phosphorylated polypeptide was 20,000 daltons. Our data suggested that when Dane particles were put in an environment of hepatoma cells (or tissues), the protein kinase could only phosphorylate selected polypeptides in these particles. 相似文献
998.
S Batzri 《Biochimica et biophysica acta》1981,677(3-4):521-524
In dispersed mucosal cells from guinea-pig stomach, somatostatin inhibited in a noncompetitive fashion (Ki, 2 x 10(-8) M) the increase in cellular cyclic AMP caused by histamine but not by prostaglandin E1 or phosphodiesterase inhibitors. Somatostatin also inhibited the increase in [14C]aminopyrine uptake caused by low concentrations of histamine probably by interfering with the synthesis of cellular cyclic AMP. 相似文献
999.
As turkey erythrocytes were progressively depleted of ATP by preincubation with dinitrophenol, the (Na+ + K+ + 2Cl-)-cotransport system (assayed by the bumetanide-sensitive fraction of 86Rb+ influx) became less responsive to activation. The dependence upon intracellular ATP concentration was significantly steeper for transport activated by hypertonic shock (halfmaximal activity at 0.7 mM ATP) than for that activated by either epinephrine or cyclic AMP (halfmaximal activity at 1.7 mM ATP). Upon removal of epinephrine or cyclic AMP from cells that had been preincubated with those substances, bumetanide-sensitive transport activity declined sharply, even though the intracellular cyclic AMP concentration was still over 10-fold that required to maximally activate the transport system. These data are in agreement with the notion that the (Na+ + K+ + 2Cl-)-cotransport system in turkey erythrocytes is activated by cyclic AMP, presumably through the 'classical' pathway involving a protein kinase. They do however indicate that some other, as yet undefined aspect of cyclic AMP metabolism is important for the maintenance of transport activity. 相似文献
1000.
Piracetam produces a more pronounced effect on cerebral circulation disturbed by hemorrhagic shock as compared with intact animals. Piracetam has a depressant effect on the nervous regulation of cerebral circulation by suppressing the reflex constriction of the vessels in both arterial systems of the brain. The cerebrovascular effects of piracetam are not mediated through the GABAergic bicuculline-sensitive mechanisms, which is supported by experiments where the drug exhibits its effects under the blockade of GABA receptors. 相似文献