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排序方式: 共有589条查询结果,搜索用时 15 毫秒
581.
Weyand S Shimamura T Yajima S Suzuki S Mirza O Krusong K Carpenter EP Rutherford NG Hadden JM O'Reilly J Ma P Saidijam M Patching SG Hope RJ Norbertczak HT Roach PC Iwata S Henderson PJ Cameron AD 《Science (New York, N.Y.)》2008,322(5902):709-713
The nucleobase-cation-symport-1 (NCS1) transporters are essential components of salvage pathways for nucleobases and related metabolites. Here, we report the 2.85-angstrom resolution structure of the NCS1 benzyl-hydantoin transporter, Mhp1, from Microbacterium liquefaciens. Mhp1 contains 12 transmembrane helices, 10 of which are arranged in two inverted repeats of five helices. The structures of the outward-facing open and substrate-bound occluded conformations were solved, showing how the outward-facing cavity closes upon binding of substrate. Comparisons with the leucine transporter LeuT(Aa) and the galactose transporter vSGLT reveal that the outward- and inward-facing cavities are symmetrically arranged on opposite sides of the membrane. The reciprocal opening and closing of these cavities is synchronized by the inverted repeat helices 3 and 8, providing the structural basis of the alternating access model for membrane transport. 相似文献
582.
Alvarez JI Dodelet-Devillers A Kebir H Ifergan I Fabre PJ Terouz S Sabbagh M Wosik K Bourbonnière L Bernard M van Horssen J de Vries HE Charron F Prat A 《Science (New York, N.Y.)》2011,334(6063):1727-1731
The blood-brain barrier (BBB) is composed of tightly bound endothelial cells (ECs) and perivascular astrocytes that regulate central nervous system (CNS) homeostasis. We showed that astrocytes secrete Sonic hedgehog and that BBB ECs express Hedgehog (Hh) receptors, which together promote BBB formation and integrity during embryonic development and adulthood. Using pharmacological inhibition and genetic inactivation of the Hh signaling pathway in ECs, we also demonstrated a critical role of the Hh pathway in promoting the immune quiescence of BBB ECs by decreasing the expression of proinflammatory mediators and the adhesion and migration of leukocytes, in vivo and in vitro. Overall, the Hh pathway provides a barrier-promoting effect and an endogenous anti-inflammatory balance to CNS-directed immune attacks, as occurs in multiple sclerosis. 相似文献
583.
Simmons G Glynn SA Komaroff AL Mikovits JA Tobler LH Hackett J Tang N Switzer WM Heneine W Hewlett IK Zhao J Lo SC Alter HJ Linnen JM Gao K Coffin JM Kearney MF Ruscetti FW Pfost MA Bethel J Kleinman S Holmberg JA Busch MP;Blood XMRV Scientific Research Working Group 《Science (New York, N.Y.)》2011,334(6057):814-817
Murine leukemia viruses (MLVs), including xenotropic-MLV-related virus (XMRV), have been controversially linked to chronic fatigue syndrome (CFS). To explore this issue in greater depth, we compiled coded replicate samples of blood from 15 subjects previously reported to be XMRV/MLV-positive (14 with CFS) and from 15 healthy donors previously determined to be negative for the viruses. These samples were distributed in a blinded fashion to nine laboratories, which performed assays designed to detect XMRV/MLV nucleic acid, virus replication, and antibody. Only two laboratories reported evidence of XMRV/MLVs; however, replicate sample results showed disagreement, and reactivity was similar among CFS subjects and negative controls. These results indicate that current assays do not reproducibly detect XMRV/MLV in blood samples and that blood donor screening is not warranted. 相似文献
584.
Immunoblotting was used to check the antigenic profiling of 27 Mycoplasma meleagridis strains isolated in different countries. Hyperimmune polyclonal rabbit antiserum as well as monoclonal antibodies (MAbs) raised against M. meleagridis (MM) showed antigen heterogeneity among strains. Five anti-MM MAbs were selected for lack of reaction against heterologous avian mycoplasma. Three of these five Mabs did not cross-react with 63 mycoplasma strains from six species affecting turkeys other than M. meleagridis. The five Mabs used to analyse the epitopes of 30 M. meleagridis strains indicated that some epitopes were not expressed in all strains. Moreover, other epitopes were located on proteins which differed according to number or molecular mass from strain to strain. The five Mabs therefore, recognised variable surface proteins, among which two were amphiphilic membrane proteins.Three of the selected Mabs recognised 29 or 30 of the 30 tested strains. The in vitro expression of surface epitopes in M. meleagridis ATCC 25284 was investigated by colony immunobinding and allowed demonstration of a variable antigenic system. 相似文献
585.
Frank O Blumberg S Kunert C Zehentbauer G Hofmann T 《Journal of agricultural and food chemistry》2007,55(5):1945-1954
Aimed at elucidating intense bitter-tasting molecules in coffee, various bean ingredients were thermally treated in model experiments and evaluated for their potential to produce bitter compounds. As caffeic acid was found to generate intense bitterness reminiscent of the bitter taste of a strongly roasted espresso-type coffee, the reaction products formed were screened for bitter compounds by means of taste dilution analysis, and the most bitter tastants were isolated and purified. LC-MS/MS as well as 1-D/2-D NMR experiments enabled the identification of 10 bitter compounds with rather low recognition threshold concentrations ranging between 23 and 178 micromol/L. These bitter compounds are the previously unreported 1,3-bis(3',4'-dihydroxyphenyl) butane, trans-1,3-bis(3',4'-dihydroxyphenyl)-1-butene, and eight multiply hydroxylated phenylindanes, among which five derivatives are reported for the first time. In addition, the occurrence of each of these bitter compounds in a coffee brew was verified by means of LC-MS/MS (ESI-) operating in the multiple reaction monitoring (MRM) mode. The structures of these bitter compounds show strong evidence that they are generated by oligomerization of 4-vinylcatechol released from caffeic acid moieties upon roasting. 相似文献
586.
Silvana M. Caramalac Simone M. Caramalac Veronica J. Babo-Terra Carlos A. N. Ramos Mariana I. P. Palumbo 《Journal of veterinary diagnostic investigation》2021,33(5):984
Color dilution alopecia (CDA) is a dermatopathy observed exclusively in animals having a diluted coat color. In dogs, color dilution occurs as a result of a single-nucleotide variation (SNV) c.-22G > A in the melanophilin gene. We standardized a PCR–restriction-fragment length polymorphism (PCR-RFLP) technique to identify this mutation and determine its frequency in dogs in Brazil. The standardized PCR-RFLP technique could efficiently identify the SNV c.-22G > A in the melanophilin gene, with mutated allele frequencies of 0.1, 0.1, and 0.0875 in Dachshund, Miniature Pinscher, and Yorkshire Terrier breeds, respectively, with no statistical difference among the breeds (p = 0.252). The mutation was identified in 2 homozygous Dachshund dogs with alopecia, confirming the clinical characteristic of CDA. The standardization of a simpler and more accessible molecular technique for recognition of the SNV c.-22G > A in the melanophilin gene allows identification of heterozygous (phenotypically normal) dogs that can be excluded from reproduction, to avoid the birth of dogs with diluted coat color and consequently CDA. 相似文献
587.
Simone Savoia Andrea Albera Alberto Brugiapaglia Liliana Di Stasio Alessio Cecchinato Giovanni Bittante 《畜牧与生物技术杂志(英文版)》2021,(3):1214-1225
Background:The possibility of assessing meat quality traits over the meat chain is strongly limited, especially in the context of selective breeding which requi... 相似文献
588.
Abdo AA Ackermann M Ajello M Allafort A Baldini L Ballet J Barbiellini G Bastieri D Bechtol K Bellazzini R Berenji B Blandford RD Bloom ED Bonamente E Borgland AW Bouvier A Brandt TJ Bregeon J Brez A Brigida M Bruel P Buehler R Buson S Caliandro GA Cameron RA Cannon A Caraveo PA Casandjian JM Çelik Ö Charles E Chekhtman A Cheung CC Chiang J Ciprini S Claus R Cohen-Tanugi J Costamante L Cutini S D'Ammando F Dermer CD de Angelis A de Luca A de Palma F Digel SW do Couto e Silva E Drell PS 《Science (New York, N.Y.)》2011,331(6018):739-742
A young and energetic pulsar powers the well-known Crab Nebula. Here, we describe two separate gamma-ray (photon energy greater than 100 mega-electron volts) flares from this source detected by the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. The first flare occurred in February 2009 and lasted approximately 16 days. The second flare was detected in September 2010 and lasted approximately 4 days. During these outbursts, the gamma-ray flux from the nebula increased by factors of four and six, respectively. The brevity of the flares implies that the gamma rays were emitted via synchrotron radiation from peta-electron-volt (10(15) electron volts) electrons in a region smaller than 1.4 × 10(-2) parsecs. These are the highest-energy particles that can be associated with a discrete astronomical source, and they pose challenges to particle acceleration theory. 相似文献
589.