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891.
In mitochondria and many aerobic bacteria cytochrome c oxidase is the terminal enzyme of the respiratory chain where it catalyses the reduction of oxygen to water. The free energy released in this process is used to translocate (pump) protons across the membrane such that each electron transfer to the catalytic site is accompanied by proton pumping. To investigate the mechanism of electron-proton coupling in cytochrome c oxidase we have studied the pH-dependence of the kinetic deuterium isotope effect of specific reaction steps associated with proton transfer in wild-type and structural variants of cytochrome c oxidases in which amino-acid residues in proton-transfer pathways have been modified. In addition, we have solved the structure of one of these mutant enzymes, where a key component of the proton-transfer machinery, Glu286, was modified to an Asp. The results indicate that the P3-->F3 transition rate is determined by a direct proton-transfer event to the catalytic site. In contrast, the rate of the F3-->O4 transition, which involves simultaneous electron transfer to the catalytic site and is characteristic of any transition during CytcO turnover, is determined by two events with similar rates and different kinetic isotope effects. These reaction steps involve transfer of protons, that are pumped, via a segment of the protein including Glu286 and Arg481. 相似文献
892.
Changes in the decomposer community when converting spruce monocultures to mixed spruce/beech stands
The impact of the admixture of beech in spruce monocultures on structure and function of the decomposer community was studies in the Ore mountains (Saxony, Germany) on Dystric Cambisols between 2000 and 2002. The study sites represented four stages of forest conversion from a mature spruce stand to a mature spruce/beech stand. There, the functional profile of the nematodes, enchytraeids, lumbricids, and dipterans was analysed on the basis of ecological guilds, and their metabolic equivalences were calculated to characterize the decomposition potential of the invertebrate decomposer community. Because of the acidic parent soil the coenoses at all study sites were dominated by the enchytraeids with increasing importance of lumbricids and dipterans in progress of forest conversion. Gradual changes with rising coverage of beech culminated in intense differences of entire biomasses and metabolic equivalences between the mature stands, indicating a higher decomposition potential of the invertebrate decomposer community by the admixture of beeches in spruce forests. The quality of the beech litter is likely to be the important factors for these changes. To prove this assumption further investigations of the saprovore food chain are necessary, taking microbial parameters into account. 相似文献
893.
Gisela Richardson Yemin Sun Maud Langton Anne-Marie Hermansson 《Carbohydrate polymers》2004,57(4):369-377
The interaction of lignosulfonates with starches was examined by microscopy and viscosity measurements. 8% starch dispersions with Ca- or Na-lignosulfonate, or with only Ca2+ or Na+, were heated to 97 °C and cooled to 50 °C in a Brabender Viscograph, the gelatinization was followed by light microscopy and image analysis, and the gel network formed after cooling to 4 °C was studied under the transmission electron microscope.
The lignosulfonates (2%) delayed the initial granule swelling in all starches (native maize, waxy maize and waxy barley). The presence of ions enhanced amylose leakage resulting in lower peak viscosity. The viscosity during cooling increased more with Ca-LS than with Na-LS. With a low lignosulfonate concentration the network formed after cooling was homogeneous with fine strands. With Na-lignosulfonate, as well as with Na+, the network connectivity deteriorated and spherical aggregates formed. Ca-lignosulfonate induced a network with thick strands, but with Ca2+ the strands became thinner. 相似文献
894.
895.
Summary Extensive tidal areas of the Recent coast of southern Tunisia are overgrown by microbial mats. Different mat types of which
each are dominated by distinct and well adapted cyanobacterial species develop. Ecological response of the mat-forming microorganisms
to climatological hydrological and sedimentological factors produce characteristic sedimentary structures (=microbially induced
sedimentary structures).
A suecession of Pleistocene rocks crops out near the lagoon El Bibane, southern Tunisia. The stratigraphic section comprises
structures that we regard as fossil equivalents to those microbially induced structures we observe in the Recent coastal area.
Preservation of the structures is result of lithification of the microbial mats. This we conclude from fossil filaments of
cyanobacteria visible within the rock matrix.
The Recent microbially induced sedimentary structures indicate facies zones within the modern tidal environment. Comparison
of the Recent structures with the fossil analogues recorded in the stratigraphic section aids to identify the same distinct
facies zones within the Pleistocene coastal environment also.
Erosion by water currents forms step-like cliffs, and the microbial mat is undermined and ripped off piece by piece. shallows
within the supratidal area are overgrown by copious microbial mats comprising structures like biolaminites and—varvites, as
well as polygons of cracks. The features originate from effects triggered by seasonal variations of climate. Tufts and reticulate
pattern of bulges indicate supernatant water films covering the mat surfaces. Morphologically higher parts of the Recent tidal
area are overgrown by single-layered mats forming petees, induced by microbial mat growth and evaporitive pumping.
The study demonstrates that microbially induced sedimentary structures can be used to reconstruct small-scaled facies zones
within coastal environments. The also include hints on paleoclimatological, hydrological and sedimentological conditions. 相似文献
896.
Physiological regulation of plant-atmosphere ammonia exchange 总被引:10,自引:0,他引:10
Schjoerring Jan K. Husted Søren Mäck Gisela Nielsen Kent Høier Finnemann Jørgen Mattsson Marie 《Plant and Soil》2000,221(1):95-102
Plants have a compensation point for NH3 which ranges from 0.1 to 20 nmol mol-1, and may be several-fold higher or lower than naturally occurring atmospheric NH3 concentrations. This implies that NH3 fluxes over vegetated surfaces are bi-directional and that ammonia exchange with the atmosphere in many cases contributes
significantly to the nitrogen economy of vegetation. Physiological regulation of plant–atmosphere NH3 fluxes is mediated via processes involved in nitrogen uptake, transport and metabolism. A rapid turnover of NH3
+ in plant leaves leads to the establishment of a finite NH3
+ concentration in the leaf apoplastic solution. This concentration determines, together with that of H+, the size of the NH3 compensation point. Barley and oilseed rape plants with access to NH3
+ in the root medium have higher apoplastic NH3
+ concentrations than plants absorbing NO3
-. Furthermore, the apoplastic NH3
+ concentration increases with the external NH3
+ concentration. Inhibition of GS leads to a rapid and substantial increase in apoplastic NH3
+ and barley mutants with reduced GS activity have higher apoplastic NH3
+ than wild-type plants. Increasing rates of photorespiration do not affect the steady-state NH3
+ or H+ concentration in tissue or apoplast of oilseed rape, indicating that the NH3
+ produced is assimilated efficiently. Nevertheless, NH3 emission increases due to a temperature-mediated displacement of the chemical equilibrium between gaseous and aqueous NH3 in the apoplast. Sugarbeet plants grown with NO3
- seem to be temporarily C-limited in the light due to a repression of respiration. As a consequence, the activity of chloroplastic
GS declines during the day causing a major part of NH3
+ liberated in photorespiration to be assimilated during darkness when 2-oxoglutarate is supplied in high rates by respiration.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
897.
Marcelo J. Kogan Gisela Kristoff María P. Benavides María L. Tomaro 《Plant Growth Regulation》2000,30(1):87-94
The accumulation of compatible solutes is one of the strategies that plants have developed to tolerate salt stress. Proline and betaine are the main metabolites that accumulate in various species of higher plants in response to salt stress. In Helianthus annuus L., pre-treatment of seeds with ethanolamine led to enhanced seedling tolerance to conditions of saline stress during germination, as evidenced by the greater growth of pretreated seedlings (EAS group) versus untreated seedlings (S group), evaluated through such parameters as length, water and chlorophyll content. During the germination period, a considerable increase was observed in proline levels (up to 300%) in seedlings subjected to saline stress, whereas in the EAS group, the proline increment was much smaller (20%). Starting from the fourth day of germination, betaine levels in seedlings pretreated with ethanolamine and then with water (EAW group) and in EAS showed a significant increase versus C (control) and S seedlings, possibly because such a precursor promotes betaine biosynthesis. This could be responsible for the enhanced growth observed in EAS versus S seedlings, as well as for preventing the decrease in chlorophyll content in the EAS group. The accumulation of betaine seems to correlate with the greater tolerance of these seedlings against stress induced by sodium chloride. 相似文献
898.
Diverse endophytic bacteria isolated from a leguminous tree Conzattia multiflora grown in Mexico 总被引:1,自引:0,他引:1
Wang ET Tan ZY Guo XW Rodríguez-Duran R Boll G Martínez-Romero E 《Archives of microbiology》2006,186(4):251-259
Conzattia multiflora is a leguminous tree present only in Mexico and Guatemala. There is no record about its symbiotic or pathogenic microbes. In this study, we found that numerous bacteria with 104–106 individuals per gram of fresh epidermis were distributed in the tissue of this plant. All the bacteria isolated from the Conzattia epidermis were Gram-negative, facultative anaerobic rods and formed yellow or colorless colonies. They were identified as endophytes by inoculation tests. Some of the bacteria could significantly promote the growth of Conzattia seedlings. Nine different groups were defined by PCR-based RFLP, which were classified as Pantoea, Erwinia, Salmonella, Enterobacter, Citrobacter and Klebsiella by the phylogenetic analysis of 16S rRNA genes. The existence of plant-borne lineages of Salmonella indicates that the unexplored plants may harbor some unknown microbes. 相似文献
899.
Are animals autistic savants 总被引:1,自引:0,他引:1
900.
Seitz W Geneste H Backfisch G Delzer J Graef C Hornberger W Kling A Subkowski T Zimmermann N 《Bioorganic & medicinal chemistry letters》2008,18(2):527-531
An unexpected ring contraction of benzazepinone based alpha(nu)beta(3) antagonists led to the design of quinolinone-type derivatives. Novel and efficient synthetic routes to isoquinolinone, benzoxazinone, and quinazolinone acetates were established. Nanomolar alpha(nu)beta(3) antagonists based on these new scaffolds were prepared. Moreover, benzoxazinones 15a and 15b exhibited high microsomal stability and good permeability. 相似文献