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排序方式: 共有279条查询结果,搜索用时 15 毫秒
101.
In Saccharomyces cerevisiae a short amino acid sequence facilitates excretion in the growth medium of periplasmic proteins 总被引:1,自引:0,他引:1
Marina Venturini rea Morrione Patrizia Pisarra Enzo Martegani & Marco Vanoni 《Molecular microbiology》1997,23(5):997-1007
In Saccharomyces cerevisiae the cell wall is a barrier to excretion of proteins in the growth medium. Although small proteins are more easily released than bigger ones, other factors besides molecular sieving may play a role in partitioning of periplasmic proteins. By using several complementary approaches including enzyme-activity assays, quantitative immunoblotting on subcellular fractions and growth media, as well as a novel approach involving the use of flow cytometry and specific antibodies, we show that residues 1–8 of mature glucoamylase greatly enhance excretion of both glucoamylase and β-galactosidase in vivo and facilitate extraction of periplasmic proteins in vitro . Immunological data obtained by flow cytometry on whole cells indicate that this amino acid sequence increases the fraction of enzyme reaching the outer cell-wall layers. This amino acid sequence may define a novel type of topogenic sequence, facilitating the crossing of the yeast cell wall in vivo and facilitating extraction of periplasmic proteins by non-disruptive means in vitro . 相似文献
102.
Molecular Cloning and Differential Expression Patterns of Avian Glutamate Receptor mRNAs 总被引:2,自引:0,他引:2
Hans-Peter Ottiger rea Gerfin-Moser Franco Del Principe Fabrizio Dutly Peter Streit 《Journal of neurochemistry》1995,64(6):2413-2426
Abstract: We have identified and studied potential ionotropic glutamate receptor genes in pigeon brain. Three cDNA clones exhibit significant amino acid sequence identity to members of a rodent ligand-gated ion channel family. One of them, GluP-II, encodes a full-length AMPA-sensitive glutamate receptor GluR2 (GluR-B) homologue, whereas the other two partial clones, designated as GluP-III and -IV, are nearly identical to rodent GluR3 (GluR-C) and GluR4 (GluR-D) receptor subunits. Northern analysis demonstrated that the avian genes are widely expressed in the brain. Within the brain regions analyzed by in situ hybridization histochemistry, the three avian GluR subunits showed distinct and regionally specific mRNA expression patterns in the adult. Most of the differences in their expression were observed in cell types of the telencephalon, certain thalamic nuclei, the optic tectum, and the cerebellar cortex. A particularly striking finding was the expression of GluP-II in Golgi epithelial/Bergmann glial cells. In contrast, Bergmann glial cells in rat cerebellum do not express GluR2 (GluR-B) subunit genes. Immunoreactivity for a monoclonal sequence-specific antipeptide antibody was widespread and most prominent in Purkinje cell perikarya and their dendrites, neuronal cell bodies of the ectostriatum, and the deep optic tectum. These results demonstrate the existence of multiple subunits of the ionotropic glutamate receptor channel family in avians. Excitatory amino acid receptor genes appear to be highly conserved during evolution. 相似文献
103.
Applications of ecological stoichiometry for sustainable acquisition of ecosystem services 总被引:4,自引:0,他引:4
Robert Ptacnik G. Darrel Jenerette Antonie M. Verschoor rea F. Huberty Angelo G. Solimini Justin D. Brookes 《Oikos》2005,109(1):52-62
Human activities have differentially altered biogeochemical cycling at local, regional and global scales. We propose that a stoichiometric approach, examining the fluxes of multiple elements and the ratio between them, may be a useful tool for better understanding human effects on ecosystem processes and services. The different scale of impacts of the elements carbon, nitrogen and phosphorus and the different nature of their biogeochemical cycles, imply a large variation of their stoichiometric ratios in space and time and thus divergent impacts on biota.
In this paper, we examine the effects of anthropogenic perturbations on nutrient ratios in ecosystems in two examples and one case study. Altered stoichiometry in agricultural systems (example 1) can affect not only crop yield and quality but also the interactions between plants and their pollinators, pests and pathogens. Human activities have also altered stoichiometry in coastal ecosystems (example 2). Increased N loading has especially lead to increased N:P and reduced Si:N ratios, with detrimental effects on ecosystem services derived from coastal pelagic food webs, such as fish yield and water quality. The terrestrial–aquatic linkage in stoichiometric alterations is illustrated with a case study, the Mississippi River watershed, where anthropogenic activities have caused stoichiometric changes that have propagated through the watershed into the northern Gulf of Mexico.
Coupled with altered stoichiometric nutrient inputs are the inherent differences in variation and sensitivity of different ecosystems to anthropogenic disturbance. Furthermore, the connections among the components of a watershed may result in downstream cascades of disrupted functioning. Applying a multiple element perspective to understanding and addressing societal needs is a new direction for both ecological stoichiometry and sustainability. 相似文献
In this paper, we examine the effects of anthropogenic perturbations on nutrient ratios in ecosystems in two examples and one case study. Altered stoichiometry in agricultural systems (example 1) can affect not only crop yield and quality but also the interactions between plants and their pollinators, pests and pathogens. Human activities have also altered stoichiometry in coastal ecosystems (example 2). Increased N loading has especially lead to increased N:P and reduced Si:N ratios, with detrimental effects on ecosystem services derived from coastal pelagic food webs, such as fish yield and water quality. The terrestrial–aquatic linkage in stoichiometric alterations is illustrated with a case study, the Mississippi River watershed, where anthropogenic activities have caused stoichiometric changes that have propagated through the watershed into the northern Gulf of Mexico.
Coupled with altered stoichiometric nutrient inputs are the inherent differences in variation and sensitivity of different ecosystems to anthropogenic disturbance. Furthermore, the connections among the components of a watershed may result in downstream cascades of disrupted functioning. Applying a multiple element perspective to understanding and addressing societal needs is a new direction for both ecological stoichiometry and sustainability. 相似文献
104.
In Adrenal Medulla Synaptophysin (Protein p38) Is Present in Chromaffin Granules and in a Special Vesicle Population 总被引:9,自引:4,他引:5
Dieter Obendorf Ulrike Schwarzenbrunner Reiner Fischer-Colbrie rea Laslop Hans Winkler 《Journal of neurochemistry》1988,51(5):1573-1580
We have analyzed the properties and subcellular localization of synaptophysin (protein p38) in bovine adrenal medulla. In one-dimensional immunoblotting the adrenal antigen appears identical to synaptophysin of rat synaptic vesicles. In two-dimensional immunoblotting it migrates as a heterogeneous band varying in pI from 4.5 to 5.8. Subcellular fractionation by various sucrose gradients revealed that synaptophysin was present in two different cell particles. More than half of the antigens present in adrenal medulla were confined to special membranes that sedimented both with the "large granules" and with microsomal elements. These membranes could be removed from the large granule sediment by washing. In gradients it equilibrated in regions of low sucrose density. These membranes did not contain any markers for chromaffin granules. Less than half of the amount of synaptophysin present in adrenal medulla copurified with chromaffin granules. Despite several variations in the fractionation scheme synaptophysin could not be removed from chromaffin granules. After washing of granule membranes with alkaline solution synaptophysin still cosedimented in gradients with typical granule markers. The concentration of synaptophysin in membranes of chromaffin granules is low (less than 10%) when compared with synaptic vesicles. It is concluded that in adrenal medulla synaptophysin is present in special membranes, probably in high concentration, and in membranes of chromaffin granules, either in a low concentration in all or in a higher concentration in some of them. 相似文献
105.
Elongation factor Tu: a molecular switch in protein biosynthesis 总被引:5,自引:0,他引:5
Albert Weijland Kim Harmark Robbert H. Cool † Pieter H. Anborgh rea Parmeggiani 《Molecular microbiology》1992,6(6):683-688
Elongation factor Tu (EF-Tu), the most abundant protein in Escherichia coli, is a guanine nucleotide-binding protein that in the 'on' state acts as a carrier of amino acyl-tRNA to the ribosome. Our knowledge of this essential component of translation has brought substantial progress in the past decade thanks to the co-ordinated application of biochemical, physico-chemical and genetic methods. Crystallographic analysis at 2.6 A resolution and site-directed mutagenesis have revealed structural and functional similarities between the guanine nucleotide-binding domains of EF-Tu and human H-ras p21 protein. The regulation of the expression of the two EF-Tu-encoding genes in E. coli, particularly that of tufB, has been shown to involve diverse mechanisms. Several aspects of the functions of EF-Tu in the elongation cycle have been reinvestigated, leading to new insights. These studies have emphasized the manifold aspects of the mechanisms regulating the activity of EF-Tu in the bacterial cell. 相似文献
106.
Stochastic and deterministic processes jointly structure tropical arthropod communities 总被引:1,自引:0,他引:1
The question of whether ecological assemblages are structured by stochastic and deterministic (e.g. interspecific competition) processes is controversial, but it is difficult to design sampling regimes and experiments that can dissect the relative importance of stochastic and deterministic processes in natural assemblages. Using null models, we tested communities of arthropod decomposers in tropical epiphytes for patterns of species co-occurrence, while controlling for habitat gradients, seasonal variations and ecological succession. When environmental conditions were controlled, our analysis showed that the communities were structured stochastically. However, analysing mixed sets of communities that were deliberately created either from two distinct heights or two successional stages revealed that communities were structured deterministically. These results confirm that habitat gradients and dispersal/competition trade-offs are capable of generating non-random patterns within decomposer arthropod communities, but reveal that when such effects are accounted for, species co-occurrence is fundamentally random. 相似文献
107.
Associate Professor Frances Trix Associate Professor rea Sankar 《American anthropologist》1998,100(1):32-40
As activist research, this study of women's experiences of the Hill-Thomas hearings was conducted within three weeks of the Senate Judiciary Committee hearings on Anita Hill's charges of sexual harassment by Supreme Court nominee Clarence Thomas. Unlike polls at the time, interviews of 100 Detroit-area women (65 percent white, 35 percent African American) revealed a msyority of strong support for Hill, a default category of support for Thomas, age rather than race as predictor of strong support for Hill or Thomas, and responses of anger and pain from women across the board. The study brings out strengths and challenges of activist research. 相似文献
108.
109.
Serena Ammendola Angelo Lembo rea Battistoni Pietro Tagliatesta Carlo Ghisalberti & Alessandro Desideri 《FEMS microbiology letters》2009,294(1):61-67
Undecanoic acid (UDA) is a fatty acid with significant antimycotic activity. In this work we have synthesized 10-undecanhydroxamic acid, a hydroxamate derivative of the UDA, and tested its antimicrobial activity on different microorganisms. Our results demonstrate that this compound has higher efficacy than UDA against a variety of fungi and bacteria. Analysis of the intracellular concentration of protein involved in iron transport in Salmonella enterica serovar Typhimurium suggests that its antimicrobial effect actually relies on the ability to chelate iron ions, providing an efficient mechanism to interfere with microbial growth. 相似文献
110.
G Faccioli G Lalatta Costerbosa M L Lucchi R Bortolami 《Archives italiennes de biologie》1985,123(1):43-62
The mesencephalic trigeminal nucleus (MTN) cells of both young and adult ducks as well as of rabbits were investigated by scanning electron microscope. The rabbit showed only ovoid unipolar cells, while the duck also presented polyhedral cells. Few of these latter revealed processes originating from their surface and were recognized as multipolar cells. Some differences between the MTN cell surface of young and adult ducks were noticed. Synaptic bulbs were observed on the MTN cells in both duck and rabbit. 相似文献