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排序方式: 共有999条查询结果,搜索用时 562 毫秒
981.
Lee SJ Evers S Roeder D Parlow AF Risteli J Risteli L Lee YC Feizi T Langen H Nussenzweig MC 《Science (New York, N.Y.)》2002,295(5561):1898-1901
Carbohydrates are thought to function as tags that mark circulatory glycoproteins for rapid clearance. To examine the role of the mannose receptor (MR) in glycoprotein clearance, we generated mice genetically deficient in MR. MR-/- mice were defective in clearing proteins bearing accessible mannose and N-acetylglucosamine residues and had elevated levels of eight different lysosomal hydrolases. Proteomic analysis of MR-/- and control mouse sera showed that an additional 4 out of 52 proteins identified were elevated in MR-/- serum. Each of these is up-regulated during inflammation and wound healing. Thus, MR appears to operate as an essential regulator of serum glycoprotein homeostasis. 相似文献
982.
Amplification of an esterase gene is responsible for insecticide resistance in a California Culex mosquito 总被引:21,自引:0,他引:21
C Mouchès N Pasteur J B Bergé O Hyrien M Raymond B R de Saint Vincent M de Silvestri G P Georghiou 《Science (New York, N.Y.)》1986,233(4765):778-780
An esterase gene from the mosquito Culex quinquefasciatus that is responsible for resistance to a variety of organophosphorus (OP) insecticides was cloned in lambda gt11 phage. This gene was used to investigate the genetic mechanism of the high production of the esterase B1 it encodes in OP-resistant Culex quinquefasciatus Say (Tem-R strain) from California. Adults of the Tem-R strain were found to possess at least 250 times more copies of the gene than adults of a susceptible strain (S-Lab). The finding that selection by pesticides may result in the amplification of genes encoding detoxifying enzymes in whole, normally developed, reproducing insects emphasizes the biological importance of this mechanism and opens new areas of investigation in pesticide resistance management. 相似文献
983.
A critical role is traditionally assigned to transition states (TSs) and minimum energy pathways, or intrinsic reaction coordinates (IRCs), in interpreting organic reactivity. Such an interpretation, however, ignores vibrational and kinetic energy effects of finite temperature. Recently it has been shown that reactions do not necessarily follow the intermediates along the IRC. We report here molecular dynamics (MD) simulations that show that dynamics effects may alter chemical reactions even more. In the heterolysis rearrangement of protonated pinacolyl alcohol Me3C-CHMe-OH2+ (Me, methyl), the MD pathway involves a stepwise route with C-O bond cleavage followed by methyl group migration, whereas the IRC pathway suggests a concerted mechanism. Dynamics effects may lead to new interpretations of organic reactivity. 相似文献
984.
Dudziak D Kamphorst AO Heidkamp GF Buchholz VR Trumpfheller C Yamazaki S Cheong C Liu K Lee HW Park CG Steinman RM Nussenzweig MC 《Science (New York, N.Y.)》2007,315(5808):107-111
Dendritic cells (DCs) process and present self and foreign antigens to induce tolerance or immunity. In vitro models suggest that induction of immunity is controlled by regulating the presentation of antigen, but little is known about how DCs control antigen presentation in vivo. To examine antigen processing and presentation in vivo, we specifically targeted antigens to two major subsets of DCs by using chimeric monoclonal antibodies. Unlike CD8+ DCs that express the cell surface protein CD205, CD8- DCs, which are positive for the 33D1 antigen, are specialized for presentation on major histocompatibility complex (MHC) class II. This difference in antigen processing is intrinsic to the DC subsets and is associated with increased expression of proteins involved in MHC processing. 相似文献
985.
Barnes JW Brown RH Turtle EP McEwen AS Lorenz RD Janssen M Schaller EL Brown ME Buratti BJ Sotin C Griffith C Clark R Perry J Fussner S Barbara J West R Elachi C Bouchez AH Roe HG Baines KH Bellucci G Bibring JP Capaccioni F Cerroni P Combes M Coradini A Cruikshank DP Drossart P Formisano V Jaumann R Langevin Y Matson DL McCord TB Nicholson PD Sicardy B 《Science (New York, N.Y.)》2005,310(5745):92-95
Observations from the Cassini Visual and Infrared Mapping Spectrometer show an anomalously bright spot on Titan located at 80 degrees W and 20 degrees S. This area is bright in reflected light at all observed wavelengths, but is most noticeable at 5 microns. The spot is associated with a surface albedo feature identified in images taken by the Cassini Imaging Science Subsystem. We discuss various hypotheses about the source of the spot, reaching the conclusion that the spot is probably due to variation in surface composition, perhaps associated with recent geophysical phenomena. 相似文献
986.
Daranlot J Jorfi M Xie C Bergeat A Costes M Caubet P Xie D Guo H Honvault P Hickson KM 《Science (New York, N.Y.)》2011,334(6062):1538-1541
More than 100 reactions between stable molecules and free radicals have been shown to remain rapid at low temperatures. In contrast, reactions between two unstable radicals have received much less attention due to the added complexity of producing and measuring excess radical concentrations. We performed kinetic experiments on the barrierless N((4)S) + OH((2)Π) → H((2)S) + NO((2)Π) reaction in a supersonic flow (Laval nozzle) reactor. We used a microwave-discharge method to generate atomic nitrogen and a relative-rate method to follow the reaction kinetics. The measured rates agreed well with the results of exact and approximate quantum mechanical calculations. These results also provide insight into the gas-phase formation mechanisms of molecular nitrogen in interstellar clouds. 相似文献
987.
Bouatia-Naji N Rocheleau G Van Lommel L Lemaire K Schuit F Cavalcanti-Proença C Marchand M Hartikainen AL Sovio U De Graeve F Rung J Vaxillaire M Tichet J Marre M Balkau B Weill J Elliott P Jarvelin MR Meyre D Polychronakos C Dina C Sladek R Froguel P 《Science (New York, N.Y.)》2008,320(5879):1085-1088
Several studies have shown that healthy individuals with fasting plasma glucose (FPG) levels at the high end of the normal range have an increased risk of mortality. To identify genetic determinants that contribute to interindividual variation in FPG, we tested 392,935 single-nucleotide polymorphisms (SNPs) in 654 normoglycemic participants for association with FPG, and we replicated the most strongly associated SNP (rs560887, P = 4 x 10(-7)) in 9353 participants. SNP rs560887 maps to intron 3 of the G6PC2 gene, which encodes glucose-6-phosphatase catalytic subunit-related protein (also known as IGRP), a protein selectively expressed in pancreatic islets. This SNP was associated with FPG (linear regression coefficient beta = -0.06 millimoles per liter per A allele, combined P = 4 x 10(-23)) and with pancreatic beta cell function (Homa-B model, combined P = 3 x 10(-13)) in three populations; however, it was not associated with type 2 diabetes risk. We speculate that G6PC2 regulates FPG by modulating the set point for glucose-stimulated insulin secretion in pancreatic beta cells. 相似文献
988.
989.
K E Michel 《Journal of Feline Medicine and Surgery》2001,3(1):3-8
One of the most frequent motivations for seeking veterinary attention for a cat is when the owner recognises a loss of normal appetite in his pet. The medical term for a lack of appetite for food is 'anorexia', and it may be partial or complete. While anorexia is a common manifestation of disease, the mechanisms underlying decreased food intake are complex and not completely understood. The regulation of appetite involves interaction of external stimuli with signals from the gastrointestinal tract and central nervous system. Aberrations in any of the internal control systems for hunger and satiety, or changes in external factors such as diet or feeding environment, can result in partial or total anorexia. The challenge for the practitioner is not only to diagnose and treat the underlying condition, but to recognise at what point inadequate food intake has or will impinge on the patient's nutritional status to the extent that it might deleteriously affect clinical outcome. It is also important to bear in mind the significance that the patient's appetite and food intake has for the cat owner in his overall perception of his pet's condition and quality of life. 相似文献
990.
Nongma Zongo Juliane Dao Désiré Jean-Pascal Lompo Kathrin Stenchly Christoph Steiner Delphine Manka'abusi Michel Papaoba Sedogo Andreas Buerkert Rainer Georg Joergensen 《植物养料与土壤学杂志》2023,186(2):188-195