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排序方式: 共有333条查询结果,搜索用时 78 毫秒
1.
Separation of neutral reducing oligosaccharides derived from glycoproteins by HPLC on a hydroxylated polymeric support 总被引:1,自引:0,他引:1
A prototype hydroxylated polymeric support, Glyco-PAK N, was employed to separate a number of neutral reducing oligosaccharides derived from various glycoproteins by the hydrazinolysis/re-N-acetylation/mild acid hydrolysis procedure. General features of the separation properties of the matrix are described. A major advantage of the packing over silica-based supports is its stability, a property which is advantageous both in repetitive analytical chromatography and in the preparative isolation and spectroscopic identification of pure compounds, free of column breakdown products. 相似文献
2.
Ascorbic acid induces alkaline phosphatase, type X collagen, and calcium deposition in cultured chick chondrocytes 总被引:10,自引:0,他引:10
P S Leboy L Vaias B Uschmann E Golub S L Adams M Pacifici 《The Journal of biological chemistry》1989,264(29):17281-17286
During the process of endochondral bone formation, proliferating chondrocytes give rise to hypertrophic chondrocytes, which then deposit a mineralized matrix to form calcified cartilage. Chondrocyte hypertrophy and matrix mineralization are associated with expression of type X collagen and the induction of high levels of the bone/liver/kidney isozyme of alkaline phosphatase. To determine what role vitamin C plays in these processes, chondrocytes derived from the cephalic portion of 14-day chick embryo sternae were grown in the absence or presence of exogenous ascorbic acid. Control untreated cells displayed low levels of type X collagen and alkaline phosphatase activity throughout the culture period. However, cells grown in the presence of ascorbic acid produced increasing levels of alkaline phosphatase activity and type X collagen mRNA and protein. Both alkaline phosphatase activity and type X collagen mRNA levels began to increase within 24 h of ascorbate treatment; by 9 days, the levels of both alkaline phosphatase activity and type X collagen mRNA were 15-20-fold higher than in non-ascorbate-treated cells. Ascorbate treatment also increased calcium deposition in the cell layer and decreased the levels of types II and IX collagen mRNAs; these effects lagged significantly behind the elevation of alkaline phosphatase and type X collagen. Addition of beta-glycerophosphate to the medium increased calcium deposition in the presence of ascorbate but had no effect on levels of collagen mRNAs or alkaline phosphatase. The results suggest that vitamin C may play an important role in endochondral bone formation by modulating gene expression in hypertrophic chondrocytes. 相似文献
3.
4.
Stimulation of soluble ribonucleic acid methylase activity by polyamines 总被引:10,自引:0,他引:10
P S Leboy 《Biochemistry》1970,9(7):1577-1584
5.
Nina K. Lany Phoebe L. Zarnetske Andrew O. Finley Deborah G. McCullough 《Ecography》2020,43(3):456-466
Species distribution models (SDMs) project the outcome of community assembly processes – dispersal, the abiotic environment and biotic interactions – onto geographic space. Recent advances in SDMs account for these processes by simultaneously modeling the species that comprise a community in a multivariate statistical framework or by incorporating residual spatial autocorrelation in SDMs. However, the effects of combining both multivariate and spatially-explicit model structures on the ecological inferences and the predictive abilities of a model are largely unknown. We used data on eastern hemlock Tsuga canadensis and five additional co-occurring overstory tree species in 35 569 forest stands across Michigan, USA to evaluate how the choice of model structure, including spatial and non-spatial forms of univariate and multivariate models, affects ecological inference about the processes that shape community composition as well as model predictive ability. Incorporating residual spatial autocorrelation via spatial random effects did not improve out-of-sample prediction for the six tree species, although in-sample model fit was higher in the spatial models. Spatial models attributed less variation in occurrence probability to environmental covariates than the non-spatial models for all six tree species, and estimated higher (more positive) residual co-occurrence values for most species pairs. The non-spatial multivariate model was better suited for evaluating habitat suitability and hypotheses about the processes that shape community composition. Environmental correlations and residual correlations among species pairs were positively related, perhaps indicating that residual correlations were due to shared responses to unmeasured environmental covariates. This work highlights the importance of choosing a non-spatial model formulation to address research questions about the species–environment relationship or residual co-occurrence patterns, and a spatial model formulation when within-sample prediction accuracy is the main goal. 相似文献
6.
Lyme disease is the most frequently reported vector borne illness in the United States, and incidences are increasing steadily year after year. This study explores the influence of landscape (e.g., land use pattern and landscape fragmentation) and climatic factors (e.g., temperature and precipitation) at a regional scale on Lyme disease incidence. The study area includes thirteen states in the Northeastern United States. Lyme disease incidence at county level for the period of 2002–2006 was linked with several key landscape and climatic variables in a negative binomial regression model. Results show that Lyme disease incidence has a relatively clear connection with regional landscape fragmentation and temperature. For example, more fragmentation between forests and residential areas results in higher local Lyme disease incidence. This study also indicates that, for the same landscape, some landscape variables derived at a particular scale show a clearer connection to Lyme disease than do others. In general, the study sheds more light on connections between Lyme disease incidence and climate and landscape patterns at the regional scale. Integrating findings of this regional study with studies at a local scale will further refine understanding of the pattern of Lyme disease as well as increase our ability to predict, prevent, and respond to disease. 相似文献
7.
Subha Kalyaanamoorthy Yi-Ping Phoebe Chen 《Biochimica et Biophysica Acta - Proteins and Proteomics》2013,1834(1):317-328
Histone deacetylases (HDACs) are important class of enzymes that deacetylate the ε-amino group of the lysine residues in the histone tails to form a closed chromatin configuration resulting in the regulation of gene expression. Inhibition of these HDACs enzymes have been identified as one of the promising approaches for cancer treatment. The type-specific inhibition of class I HDAC enzymes is known to elicit improved therapeutic effects and thus, the search for promising type-specific HDAC inhibitors compounds remains an ongoing research interest in cancer drug discovery. Several different strategies are employed to identify the features that could identify the isoform specificity factors in these HDAC enzymes. This study combines the insilico docking and energy-optimized pharmacophore (e-pharmacophore) mapping of several known HDACi's to identify the structural variants that are significant for the interactions against each of the four class I HDAC enzymes. Our hybrid approach shows that all the inhibitors with at least one aromatic ring in their linker regions hold higher affinities against the target enzymes, while those without any aromatic rings remain as poor binders. We hypothesize the e-pharmacophore models for the HDACi's against all the four Class I HDAC enzymes which are not reported elsewhere. The results from this work will be useful in the rational design and virtual screening of more isoform specific HDACi's against the class I HDAC family of proteins. 相似文献
8.
Phoebe Rapando Ann Wangai Rose Ramkat 《Archives Of Phytopathology And Plant Protection》2013,46(6):579-586
Abstract Tomato spotted wilt virus (TSWV) vectored by thrips is one of the major diseases affecting cucumber yield. Control of thrips is an underlying factor in its management. A study was conducted to determine the effect of time of inoculation, variety and mulch on disease incidence. Four varieties were inoculated with TSWV at cotyledon, 3 – 4 leaf and flower bud stages in a RCBD experiment replicated four times in a greenhouse. In the field, a 2×8 factorial design where two cucumber varieties were raised on seven types of mulches (red, yellow, silver, clear, black, white, and straw) with unmulched plots as controls was used. Variety Marketer was more tolerant to the disease compared to other varieties. Most varieties were generally tolerant to TSWV at cotyledonous but susceptible at 3 – 4 leaf and flower bud stages. Silver and clear mulches significantly suppressed thrip populations, yield and quality under field conditions. 相似文献
9.
Eric E. Irons Justin W. Flatt Konstantin Doronin Tara L. Fox Mauro Acchione Phoebe L. Stewart Dmitry M. Shayakhmetov 《Journal of virology》2013,87(17):9610-9619
Adenoviruses (Ads) are promising vectors for therapeutic interventions in humans. When injected into the bloodstream, Ad vectors can bind several vitamin K-dependent blood coagulation factors, which contributes to virus sequestration in the liver by facilitating transduction of hepatocytes. Although both coagulation factors FVII and FX bind the hexon protein of human Ad serotype 5 (HAdv5) with a very high affinity, only FX appears to play a role in mediating Ad-hepatocyte transduction in vivo. To understand the discrepancy between efficacy of FVII binding to hexon and its apparently poor capacity for supporting virus cell entry, we analyzed the HAdv5-FVII complex by using high-resolution cryo-electron microscopy (cryo-EM) followed by molecular dynamic flexible fitting (MDFF) simulations. The results indicate that although hexon amino acids T423, E424, and T425, identified earlier as critical for FX binding, are also involved in mediating binding of FVII, the FVII GLA domain sits within the surface-exposed hexon trimer depression in a different orientation from that found for FX. Furthermore, we found that when bound to hexon, two proximal FVII molecules interact via their serine protease (SP) domains and bury potential heparan sulfate proteoglycan (HSPG) receptor binding residues within the dimer interface. In contrast, earlier cryo-EM studies of the Ad-FX interaction showed no evidence of dimer formation. Dimerization of FVII bound to Ad may be a contributing mechanistic factor for the differential infectivity of Ad-FX and Ad-FVII complexes, despite high-affinity binding of both these coagulation factors to the virus. 相似文献
10.
Agnieszka Misiura Ying Z. Pigli Susan Boyle‐Vavra Robert S. Daum Martin R. Boocock Phoebe A. Rice 《Molecular microbiology》2013,88(6):1218-1229
Methicillin‐resistant Staphylococcus aureus (MRSA) emerged via acquisition of a mobile element, staphylococcal cassette chromosome mec (SCCmec). Integration and excision of SCCmec is mediated by an unusual site‐specific recombination system. Most variants of SCCmec encode two recombinases, CcrA and CcrB, that belong to the large serine family. Since CcrA and CcrB are always found together, we sought to address their specific roles. We show here that CcrA and CcrB can carry out both excisive and integrative recombination in Escherichia coli in the absence of any host‐specific or SCCmec‐encoded cofactors. CcrA and CcrB are promiscuous in their substrate choice: they act on many non‐canonical pairs of recombination sites in addition to the canonical ones, which may explain tandem insertions into the SCCmec attachment site. Moreover, CcrB is always required, but CcrA is only required if one of the four half‐sites is present. Recombinational activity correlates with DNA binding: CcrA recognizes only that half‐site, which overlaps a conserved coding frame on the host chromosome. Therefore, we propose that CcrA serves as a specificity factor that emerged through modular evolution to enable recognition of a bacterial recombination site that is not an inverted repeat. 相似文献