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51.
The beta-lactamase-inhibiting activity of 6m-ethyl-pyrid-2-yl-ammine palladium-dichloride (Pd 25681) and cis-dichloro-diammine-platinum(II) was studied and compared with the enzyme inhibitory action of potassium clavulanate and the penicillanic acid sulfone CP 45899. Using the nitrocefin test method and the Titertek/Microtiter equipment CP 45899 and potassium clavulanate were the strongest inhibitors of the Bacillus cereus beta-lactamase. Cis-dichloro-diammine-platinum(II) was fourfold less active than the palladium complex PD 25681 in ?quimolar concentration. The following ID50 values were found: CP 45899: 0.0281 microgram; K-clavulanate: 0.1274 microgram; Pd 25681: 3.8603 microgram; cis-dichlorodiammine-platinum(II): 12.5120 microgram/100 microliter. 相似文献
52.
The proportions of the different bibionid genera are used to estimate the temperature changes between the Late Eocene and the Late Miocene in Western Europe. The genus Plecia is a good indicator of the warm Cenozoic palaeoclimates. We propose a new approach for the estimation of the value of the palaeoclimatic information that could be obtained by actualistic inferences using extinct taxa. Other taxa (i.e. Mastotermitidae) that could appear a priori better palaeoclimatic indicators result to be less sensitive than bibionids to temperature changes. Intraspecific and intrageneric morphological diversity is explored for the genera Bibio, Penthetria and Plecia, showing the difficulties to characterize the fossil bibionid species. 相似文献
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Herbivores can be associated with distinct ontogenetic stages of their host in a nonseasonal, directional, and continuous pattern of colonization and extinction of species populations called ontogenetic succession, but the processes behind this pattern are still largely unknown. We used plants of Cryptocarya aschersoniana Mez (Lauraceae) belonging to different ontogenetic stages, to examine how the density of different gall‐inducing insects varies along the ontogeny of the host, and how gall density is influenced by mechanisms associated with host quality (plant height, plant shape, leaf area, specific leaf area, and hypersensitivity), and by mechanisms associated with their natural enemies (parasitoids, pathogens, and predators). In a remnant of Araucaria Forest, located in the São Francisco de Paula National Forest (Brazil), gall density (ind./100 g of leaf ) was obtained for 42 plants of C. aschersoniana divided into three height classes. Two galling species were recorded, showing quite distinct density patterns among height classes of C. aschersoniana. While Hymenoptera gall density decreased almost 50 times from small plants to canopy trees, Hemiptera gall density increased almost 10 times. Path analyses showed that Hymenoptera density was higher in smaller plants, independent of other host traits, while Hemiptera density was higher in plants exhibiting smaller leaves. Natural enemies were not detected in the Hemiptera population, and mortality rates due to predators, parasitoids, and pathogens did not affect Hymenoptera density. Processes associated with plant quality play the main role in generating the observed ontogenetic succession pattern. 相似文献
57.
The melanocortin-4 receptor (MC4R) is involved in regulating energy homeostasis and is a potential therapeutic target for obesity and cachexia. Molecular interactions between peptide ligands and MC4R have been studied in detail. Less is known regarding the role of these interactions in the mechanism of MC4R activation. The aim of this study was to investigate the molecular mechanism of human MC4R activation by [Nle4, d-Phe7]alpha-melanocyte-stimulating hormone (NDP-MSH), by first defining the role of the His6-d-Phe7-Arg8-Trp9 residues in receptor activation (Emax for stimulation of cAMP accumulation) using modified peptides, then understanding how their interaction with the receptor modulates activation using site-directed mutagenesis and a molecular model of NDP-MSH bound to the active state of the receptor. Alanine substitution indicated that the d-Phe7, Arg8, and Trp9 side chains contribute binding energy but are not essential for the receptor activation event. Conversely, His6 to Ala6 substitution reduced receptor activation but did not affect affinity. Chlorine substitutions on the d-Phe7 side chain also inhibited receptor activation. F261(6.51)A and F284(7.35)A receptor mutations acted as gain-of-function mutations, restoring efficacy to the His6 and d-Phe7 substituted peptides that had lost efficacy at the wild-type receptor. Based on a model of NDP-MSH and MC4R interaction, the antagonist behavior of these peptides is consistent with the prevention of transmembrane 6 (TM6) rotation. This data supports the hypothesis that increasing the size of d-Phe7 directly interferes with TM6 rotation, preventing receptor activation. We further propose that removing the interaction with the His6 side chain reorients the peptide within the binding pocket, indirectly impeding TM6 rotation by strengthening peptide interaction with F261(6.51) and F284(7.35). These findings refine the molecular basis for the mechanism of ligand-stimulated hMC4R activation and will be useful for the development of hMC4R agonists and antagonists. 相似文献
58.
John G. Day Erica E. Benson Roland A. Fleck 《In vitro cellular & developmental biology. Plant》1999,35(2):127-136
Summary Microalgae are a highly diverse group of unicellular organisms comprising the eukaryotic protists and the prokaryotic cyanobacteria
or blue-green algae. The microalgae have a unique environmental status; being virtually ubiquitous in euphotic aquatic niches,
they can occupy extreme habitats ranging from tropical coral reefs to the polar regions, and they contribute to half of the
globe’s photosynthetic activity. Furthermore, they form the basis of the food chain for more than 70% of the world’s biomass.
Microalgae are a valuable environmental and biotechnological resource, and the aim of this review is to explore the use of
in vitro technologies in the conservation and sustainable exploitation of this remarkable group of organisms. The first part
of the review evaluates the importance of in vitro methods in the maintenance and conservation of microalgae and describes
the central role of culture collections in applied algal research. The second part explores the application of microalgal
in vitro technologies, particularly in the context of the aquaculture and biotechnology industries. Emphasis is placed upon
the exploitation of economically important algal products including aquaculture feed, biomass production for the health care
sector, green fertilizers, pigments, vitamins, antioxidants, and antimicrobial agents. The contribution that microalgae can
make to environmental research is also appraised; for example, they have an important role as indicator organisms in environmental
impact assessments. Similarly, designated culture collection strains of microalgae are used for ecotoxicity testing. Throughout
the review, emphasis is placed on the application of in vitro techniques for the continued advancement of microalgal research.
The paper concludes by assessing future perspectives for the novel application of microalgae and their products. 相似文献
59.
Bouyer D Geier F Kragler F Schnittger A Pesch M Wester K Balkunde R Timmer J Fleck C Hülskamp M 《PLoS biology》2008,6(6):e141
Trichome patterning in Arabidopsis serves as a model system to study how single cells are selected within a field of initially equivalent cells. Current models explain this pattern by an activator–inhibitor feedback loop. Here, we report that also a newly discovered mechanism is involved by which patterning is governed by the removal of the trichome-promoting factor TRANSPARENT TESTA GLABRA1 (TTG1) from non-trichome cells. We demonstrate by clonal analysis and misexpression studies that Arabidopsis TTG1 can act non-cell-autonomously and by microinjection experiments that TTG1 protein moves between cells. While TTG1 is expressed ubiquitously, TTG1–YFP protein accumulates in trichomes and is depleted in the surrounding cells. TTG1–YFP depletion depends on GLABRA3 (GL3), suggesting that the depletion is governed by a trapping mechanism. To study the potential of the observed trapping/depletion mechanism, we formulated a mathematical model enabling us to evaluate the relevance of each parameter and to identify parameters explaining the paradoxical genetic finding that strong ttg1 alleles are glabrous, while weak alleles exhibit trichome clusters. 相似文献
60.
Daniel Urban Usan Thanabalasingam Dietger Stibenz Jan Kaufmann Heike Meyborg Eckart Fleck Michael Gräfe Philipp Stawowy 《Biochemical and biophysical research communications》2011,404(1):448