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991.
In addition to the two species of ferredoxin-type iron-sulfur centers (Centers S-1 and S-2), a third iron-sulfur center (Center S-3), which is paramagnetic in the oxidezed state analogous to the bacterial high potential iron-sulfur protein, has bwen detected in the reconstitutively active soluble succinate dehydrogenase preparation. Midpoint potential (at pH 7.4) of Center S-3 determined in a particulate succinate-cytochrome c reductase is +60 +/- 15 mV. In soluble form, Center S-3 becomes extremely labile towards oxygen or ferricyanide plus phenazine methosulfate similar to reconstitutive activity of the dehydrogenase. Thus, even freshly prepared reconstitutively active enzyme preparations show EPR spectra of Center S-3 which correspond approximately to 0.5 eq per flavin; in particulate preparations this component was found in a 1:1 ratio to flavin. All reconstitutively inactive dehydrogenase preparations that Center S-3 is an innate constituent of succinate dehydrogenase and plays an important role in mediating electrons from the flavoprotein subunit to most probably ubiquinone and then to the cytochrome chain. 相似文献
992.
G. Heinrich Krause Alexander W. Cheesman Klaus Winter Barbara Krause Aurelio Virgo 《Journal of plant physiology》2013
Global warming and associated increases in the frequency and amplitude of extreme weather events, such as heat waves, may adversely affect tropical rainforest plants via significantly increased tissue temperatures. In this study, the response to two temperature regimes was assessed in seedlings of the neotropical pioneer tree species, Ficus insipida. Plants were cultivated in growth chambers at strongly elevated daytime temperature (39 °C), combined with either close to natural (22 °C) or elevated (32 °C) nighttime temperatures. Under both growth regimes, the critical temperature for irreversible leaf damage, determined by changes in chlorophyll a fluorescence, was approximately 51 °C. This is comparable to values found in F. insipida growing under natural ambient conditions and indicates a limited potential for heat tolerance acclimation of this tropical forest tree species. Yet, under high nighttime temperature, growth was strongly enhanced, accompanied by increased rates of net photosynthetic CO2 uptake and diminished temperature dependence of leaf-level dark respiration, consistent with thermal acclimation of these key physiological parameters. 相似文献
993.
994.
The crystal and molecular structure of the complex of amylose with dimethyl sulfoxide has been studied by a combination of stereochemical analysis, potential energy, and X-ray diffraction methods. The complex crystallizes in a pseudotetragonal unit cell with a = b = 19.17 Å and c (fiber axis) = 24.39 Å, with two antiparallel chains per unit cell and space group P212121. The amylose chain is a left-handed 61(1.355) helix with three turns per crystallographic repeat. The O(6) rotational position is approximately gt. Dimethyl sulfoxide is located inside the helix with one DMSO molecule for every three glucose residues. An additional four DMSO molecules and eight water molecules each are located in the large interstices between chains, and it is the interaction of these molecules with the helix that results in the pseudotetragonal chain packing. The interstitial DMSO is the source of the previously reported additional layer lines, which are not consistent with the 8.13-Å amylose repeat distance. The final R factor for the layers with amylose contribution to the structure factors was 0.29, while the overall R factor was 0.35. The stereochemical packing analysis provided suitable phasing models for the subsequent X-ray refinement. 相似文献
995.
996.
997.
Rasikari HL Leach DN Waterman PG Spooner-Hart RN Basta AH Banbury LK Winter KM Forster PI 《Phytochemistry》2005,66(24):2844-2850
Three clerodane diterpenes were isolated and identified from leaf extract of Glossocarya calcicola. Compound has been characterised as (rel)-10betaH-trans-12xi-(2-methylbut-2(E)-enoyl)-1beta-(isobutanoyl)-6alpha,13xi-dihydroxyclerodan-4(20),8(18)-dien-7,15-dione-15,16-oxide, to which we have assigned the trivial name calcicolin-A. The other two compounds had the same skeletal structure and C-12 substituent but in compound, the C-1 esterifying group becomes 2-methylbut-2(E)-enoic acid and in it becomes 2-methylbutanoic acid. Although anti-insect activity was not observed for G. calcicola, cytotoxicity against insect and human carcinoma cell lines was detected. 相似文献
998.
The large subunit HoxC of the H2-sensing [NiFe] hydrogenase from Ralstonia eutropha was purified without its small subunit. Two forms of HoxC were identified. Both forms contained iron but only substoichiometric amounts of nickel. One form was a homodimer of HoxC whereas the second also contained the Ni-Fe site maturation proteins HypC and HypB. Despite the presence of the Ni-Fe active site in some of the proteins, both forms, which lack the Fe-S clusters normally present in hydrogenases, cannot activate hydrogen. The incomplete insertion of nickel into the Ni-Fe site provides direct evidence that Fe precedes Ni in the course of metal center assembly. 相似文献
999.
In the epiphytic tillandsioids, Guzmania monostachia, Werauhia sanguinolenta, and Guzmania lingulata (Bromeliaceae), juvenile plants exhibit an atmospheric habit, whereas in adult plants the leaf bases overlap and form water-holding tanks. CO2 gas-exchange measurements of the whole, intact plants and δ13C values of mature leaves demonstrated that C3 photosynthesis was the principal pathway of CO2 assimilation in juveniles and adults of all three species. Nonetheless, irrespective of plant size, all three species were able to display features of facultative CAM when exposed to drought stress. The capacity for CAM was the greatest in G. monostachia, allowing drought-stressed juvenile and adult plants to exhibit net CO2 uptake at night. CAM expression was markedly lower in W. sanguinolenta, and minimal in G. lingulata. In both species, low-level CAM merely sufficed to reduce nocturnal respiratory net loss of CO2. δ13C values were generally less negative in juveniles than in adult plants, probably indicating increased diffusional limitation of CO2 uptake in juveniles. 相似文献
1000.
Expression of Ep-CAM shifts the state of cadherin-mediated adhesions from strong to weak 总被引:9,自引:0,他引:9
Winter MJ Nagelkerken B Mertens AE Rees-Bakker HA Briaire-de Bruijn IH Litvinov SV 《Experimental cell research》2003,285(1):50-58
Various adhesion molecules play an important role in defining cell fate and maintaining tissue integrity. Therefore, cross-signaling between adhesion receptors should be a common phenomenon to support the orchestrated changes of cells' connections to the substrate and to the neighboring cells during tissue remodeling. Recently, we have demonstrated that the epithelial cell adhesion molecule Ep-CAM negatively modulates cadherin-mediated adhesions in direct relation to its expression levels. Here, we used E-cadherin/alpha-catenin chimera constructs to define the site of Ep-CAM's negative effect on cadherin-mediated adhesions. Murine L-cells transfected with either E-cadherin/alpha-catenin fusion protein, or E-cadherin fused to the carboxy-terminal half of alpha-catenin, were subsequently supertransfected with an inducible Ep-CAM construct. Introduction of Ep-CAM altered the cell's morphology, weakened the strength of cell-cell interactions, and decreased the cytoskeleton-bound fraction of the cadherin/catenin chimeras in both cell models. Furthermore, expression of Ep-CAM induced restructuring of F-actin, with changes in thickness and orientation of the actin filaments. The results showed that Ep-CAM affects E-cadherin-mediated adhesions without involvement of beta-catenin by disrupting the link between alpha-catenin and F-actin. The latter is likely achieved through remodeling of the actin cytoskeleton by Ep-CAM, possibly through pp120. 相似文献