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排序方式: 共有766条查询结果,搜索用时 31 毫秒
1.
Robert A. Goldstein Steven A. Gherini Charles T. Driscoll Richard April Carl L. Schofield Carl W. Chen 《Biogeochemistry》1987,3(1-3):5-20
An integrated analysis of a terrestrial-aquatic ecosystem, the North Branch of the Moose River in the Adirondack region of New York, was conducted. This basin contains a large number of interconnected surface waters that exhibit marked gradients in pH and acid neutralizing capacity (ANC). As a result, the basin has been the focus of research activity, including the Regional Integrated Lake-Watershed Acidification Study (RILWAS). The objective of the current analysis was to use the North Branch of the Moose River as a case study to:
- Evaluate processes regulating the acid-base chemistry of surface waters.
- To assess the effects of surface water acidification on fish populations.
2.
Elizabeth A. Grimm William L. Crump III April Durett Jeane P. Hester Sandhya Lagoo-Deenadalayan Laurie B. Owen-Schaub 《Cancer immunology, immunotherapy : CII》1988,27(1):53-58
Summary Employing serum-free media, human peripheral blood mononuclear cells, and purified recombinant interleukin-2 (IL-2), conditions were observed in which the development of IL-2-driven cytotoxic activity was suppressed. The cytotoxic activity of such IL-2-generated lymphokine activated killing (LAK) was tested against natural killer-resistant cultured tumor cells (Daudi, Raji, and a glioma). LAK generation was inhibited by addition of some normal sera, normal platelets, or some tumor cells. Because recent reports have indicated that transforming growth factor-beta (TGF-beta)-like factors are often secreted by tumors and the acidic alpha granules of platelets and can be present in sera, we tested the effect of purified human TGF-beta on the activation of LAK. Our results indicated that TGF-beta is very suppressive for LAK induction, and can completely prevent both the IL-2-driven proliferation and cytotoxicity at concentrations as low as 5 ng/ml. Titrations of IL-2 and of TGF-beta indicated that the suppression is dose-dependent and can be avoided by employing higher levels of IL-2. It was also found that the suppressive effect of TGF-beta can be overcome by washing suppressed cell populations and further culture in low levels of IL-2. Collectively, these data indicate that TGF-beta can be a potent inhibitor of LAK generation under standard activation conditions, but that this effect is regulated by the relative level of IL-2 and may be overcome and/or reversed in vitro. 相似文献
3.
Donnan potentials from A-bands and I-bands were measured as a function of sarcomere length in skinned long-tonic muscle fibers of the crayfish. These measurements were made using standard electrophysiological technique. Simultaneously, the relative cross-sectional area of the fibers was determined. Lattice plane spacings and hence unit-cell volumes were determined by low-angle x-ray diffraction. At a sarcomere length at which the myosin filaments and actin filaments nominally do not overlap, measurements of potential, relative cross-sectional area, and unit-cell volume were used in conjunction with Donnan equilibrium theory to calculate the effective linear charge densities along the myosin filament (6.6 X 10(4) e-/mu) and actin filament (6.8 X 10(3) e-/mu). Using these linear charge densities, unit-cell volumes and Donnan equilibrium theory, an algorithm was developed to predict A-band and I-band potentials at any sarcomere length. Over the range of sarcomere lengths investigated, the predicted values coincide with the experimental data. The ability of the model to predict the data demonstrates the applicability of Donnan equilibrium theory to measurements of electrochemical potential from liquid-crystalline systems. 相似文献
4.
Clara W. Hall April R. Robbins Sharon S. Krag 《Molecular and cellular biochemistry》1986,72(1-2):35-45
A novel screening procedure was developed for isolating Chinese hamster ovary cell mutants altered in the early steps of the biosynthesis of asparagine-linked glycoproteins. This procedure identifies cells with low intracellular levels of two lysosomal hydrolases, beta-glucuronidase and alpha-iduronidase. One mutant cell line isolated in this way, CHB 11-1-3, has low intracellular levels of seven lysosomal enzymes as compared to wild-type cells. Although CHB 11-1-3 synthesizes mannosylphosphoryldolichol and [Man]5[NAcG1cNH2]2-P-P-lipid, it fails to utilize these lipid intermediates to make normal amounts of [Glc]3[Man]9[NAcG1cNH2]2P-P-lipid. As a consequence of this glycosylation defect, this mutant transfers oligosaccharides of a different structure than wild type to the lysosomal enzyme beta-hexosaminidase. In addition, it underglycosylates its proteins. 相似文献
5.
Shawn Thatcher April Leonard Marianna Lauer Gayathri Panangipalli Bret Norman Zhenglin Hou Victor Llaca Wang-Nan Hu Xiuli Qi Jennifer Jaqueth Dina Severns David Whitaker Bill Wilson Girma Tabor Bailin Li 《Molecular Plant Pathology》2023,24(7):758-767
Northern corn leaf blight, caused by the fungal pathogen Exserohilum turcicum, is a major disease of maize. The first major locus conferring resistance to E. turcicum race 0, Ht1, was identified over 50 years ago, but the underlying gene has remained unknown. We employed a map-based cloning strategy to identify the Ht1 causal gene, which was found to be a coiled-coil nucleotide-binding, leucine-rich repeat (NLR) gene, which we named PH4GP-Ht1. Transgenic testing confirmed that introducing the native PH4GP-Ht1 sequence to a susceptible maize variety resulted in resistance to E. turcicum race 0. A survey of the maize nested association mapping genomes revealed that susceptible Ht1 alleles had very low to no expression of the gene. Overexpression of the susceptible B73 allele, however, did not result in resistant plants, indicating that sequence variations may underlie the difference between resistant and susceptible phenotypes. Modelling of the PH4GP-Ht1 protein indicated that it has structural homology to the Arabidopsis NLR resistance gene ZAR1, and probably forms a similar homopentamer structure following activation. RNA sequencing data from an infection time course revealed that 1 week after inoculation there was a threefold reduction in fungal biomass in the PH4GP-Ht1 transgenic plants compared to wild-type plants. Furthermore, PH4GP-Ht1 transgenics had significantly more inoculation-responsive differentially expressed genes than wild-type plants, with enrichment seen in genes associated with both defence and photosynthesis. These results demonstrate that the NLR PH4GP-Ht1 is the causal gene underlying Ht1, which represents a different mode of action compared to the previously reported wall-associated kinase northern corn leaf blight resistance gene Htn1/Ht2/Ht3. 相似文献
6.
7.
Goupille Ronald E.; Smith April E.; Toida Toshihiko; Linhardt Robert J. 《Glycobiology》1997,7(2):231-239
Porcine intestinal mucosal heparan sulfate was exhaustivelydepolymerized on a large scale using beparin lyase II (heparinaseII) or heparin lyase III (heparitinase, EC 4.2.2.8
[EC]
). The oligosaccharidemixtures formed with each enzyme were fractionated by low pressuregel permeation chromatography. Size-uniform mixtures of disaccharides,tetrasaccharides, and hexasaccharides were obtained. Each size-fractionatedmixture was then purified on the basis of charge by repetitivesemipreparative strong-anion-exchange high-performance liquidchromatography. This approach has led to the isolation of 13homogenous oligosaccharides. The purity of each oligosaccharidewas demonstrated by the presence of a single peak on analyticalstrong-anion-exchange high-performance liquid chromatographyand reversed polarity capillary electrophoresis. The structuresof these oligosaccharides were established using 500 MHz one-and two-dimensional nuclear magnetic resonance spectroscopy.Three of the thirteen structures that were solved were novelwhile the remaining 10 have been previously described. All ofthe structures obtained using heparin lyase III contained a 相似文献
8.
9.
Liqun Zhang Brian Button Sherif E. Gabriel Susan Burkett Yu Yan Mario H. Skiadopoulos Yan Li Dang Leatrice N. Vogel Tristan McKay April Mengos Richard C. Boucher Peter L. Collins Raymond J. Pickles 《PLoS biology》2009,7(7)
Dysfunction of CFTR in cystic fibrosis (CF) airway epithelium perturbs the normal regulation of ion transport, leading to a reduced volume of airway surface liquid (ASL), mucus dehydration, decreased mucus transport, and mucus plugging of the airways. CFTR is normally expressed in ciliated epithelial cells of the surface and submucosal gland ductal epithelium and submucosal gland acinar cells. Critical questions for the development of gene transfer strategies for CF airway disease are what airway regions require CFTR function and how many epithelial cells require CFTR expression to restore normal ASL volume regulation and mucus transport to CF airway epithelium? An in vitro model of human CF ciliated surface airway epithelium (CF HAE) was used to test whether a human parainfluenza virus (PIV) vector engineered to express CFTR (PIVCFTR) could deliver sufficient CFTR to CF HAE to restore mucus transport, thus correcting the CF phenotype. PIVCFTR delivered CFTR to >60% of airway surface epithelial cells and expressed CFTR protein in CF HAE approximately 100-fold over endogenous levels in non-CF HAE. This efficiency of CFTR delivery fully corrected the basic bioelectric defects of Cl− and Na+ epithelial ion transport and restored ASL volume regulation and mucus transport to levels approaching those of non-CF HAE. To determine the numbers of CF HAE surface epithelial cells required to express CFTR for restoration of mucus transport to normal levels, different amounts of PIVCFTR were used to express CFTR in 3%–65% of the surface epithelial cells of CF HAE and correlated to increasing ASL volumes and mucus transport rates. These data demonstrate for the first time, to our knowledge, that restoration of normal mucus transport rates in CF HAE was achieved after CFTR delivery to 25% of surface epithelial cells. In vivo experimentation in appropriate models will be required to determine what level of mucus transport will afford clinical benefit to CF patients, but we predict that a future goal for corrective gene transfer to the CF human airways in vivo would attempt to target at least 25% of surface epithelial cells to achieve mucus transport rates comparable to those in non-CF airways. 相似文献
10.
Hill M Allenby A Ramsby B Schönberg C Hill A 《Molecular phylogenetics and evolution》2011,59(1):81-88
Among the Porifera, symbiosis with Symbiodinium spp. (i.e., zooxanthellae) is largely restricted to members of the family Clionaidae. We surveyed the diversity of zooxanthellae associated with sponges from the Caribbean and greater Indo-Pacific regions using chloroplast large subunit (cp23S) domain V sequences. We provide the first report of Clade C Symbiodinium harbored by a sponge (Cliona caesia), and the first report of Clade A Symbiodinium from an Indo-Pacific sponge (C. jullieni). Clade A zooxanthellae were also identified in sponges from the Caribbean, which has been reported previously. Sponges that we examined from the Florida Keys all harbored Clade G Symbiodinium as did C. orientalis from the Indo-Pacific, which also supports earlier work with sponges. Two distinct Clade G lineages were identified in our phylogenetic analysis; Symbiodinium extracted from clionaid sponges formed a monophyletic group sister to Symbiodinium found in foraminiferans. Truncated and 'normal' length variants of 23S rDNA sequences were detected simultaneously in all three morphotypes of C. varians providing the first evidence of chloroplast-based heteroplasmy in a sponge. None of the other sponge species examined showed evidence of heteroplasmy. As in previous work, length variation in cp23S domain V sequences was found to correspond in a highly precise manner to finer resolution of phylogenetic topology among Symbiodinium clades. On a global scale, existing data indicate that members of the family Clionaidae that host zooxanthellae can form symbiotic associations with at least four Symbiodinium clades. The majority of sponge hosts appear to harbor only one cladal type of symbiont, but some species can harbor more than one clade of zooxanthellae concurrently. The observed differences in the number of partners harbored by sponges raise important questions about the degree of coevolutionary integration and specificity of these symbioses. Although our sample sizes are small, we propose that one of the Clade G lineages identified in this study is comprised of sponge-specialist zooxanthellae. These zooxanthellae are common in Caribbean sponges, but additional work in other geographic regions is necessary to test this idea. Sponges from the Indo-Pacific region harbor zooxanthellae from Clades A, C, and G, but more sponges from this region should be examined. 相似文献