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排序方式: 共有705条查询结果,搜索用时 31 毫秒
691.
C A Gotelli E Astolfi C Cox E Cernichiari T W Clarkson 《Science (New York, N.Y.)》1985,227(4687):638-640
Phenylmercury absorbed through the skin from contaminated diapers affected urinary excretion in infants in Buenos Aires. The effects were reversible and quantitatively related to the concentration of urinary mercury. Excretion of gamma-glutamyl transpeptidase, an enzyme in the brush borders of renal tubular cells, increased in a dose-dependent manner when mercury excretion exceeded a "threshold" value. Urine volume also increased but at a higher threshold with respect to mercury. The results support the threshold concept of the systemic toxicity of metals. gamma-Glutamyl transpeptidase is a useful and sensitive marker for preclinical effects of toxic metals. 相似文献
692.
Spiess FN Macdonald KC Atwater T Ballard R Carranza A Cordoba D Cox C Garcia VM Francheteau J Guerrero J Hawkins J Haymon R Hessler R Juteau T Kastner M Larson R Luyendyk B Macdougall JD Miller S Normark W Orcutt J Rangin C 《Science (New York, N.Y.)》1980,207(4438):1421-1433
Hydrothermal vents jetting out water at 380 degrees +/- 30 degrees C have been discovered on the axis of the East Pacific Rise. The hottest waters issue from mineralized chimneys and are blackened by sulfide precipitates. These hydrothermal springs are the sites of actively forming massive sulfide mineral deposits. Cooler springs are clear to milky and support exotic benthic communities of giant tube worms, clams, and crabs similar to those found at the Galápagos spreading center. Four prototype geophysical experiments were successfully conducted in and near the vent area: seismic refraction measurements with both source (thumper) and receivers on the sea floor, on-bottom gravity measurements, in situ magnetic gradiometer measurements from the submersible Alvin over a sea-floor magnetic reversal boundary, and an active electrical sounding experiment. These high-resolution determinations of crustal properties along the spreading center were made to gain knowledge of the source of new oceanic crust and marine magnetic anomalies, the nature of the axial magma chamber, and the depth of hydrothermal circulation. 相似文献
693.
Antigen presentation requires transport of MHC class I molecules from the endoplasmic reticulum 总被引:15,自引:0,他引:15
J H Cox J W Yewdell L C Eisenlohr P R Johnson J R Bennink 《Science (New York, N.Y.)》1990,247(4943):715-718
The role of exocytosis of major histocompatibility complex (MHC) class I molecules in the presentation of antigens to mouse cytotoxic T lymphocytes (CTLs) was examined by use of a recombinant vaccinia virus that expresses the E19 glycoprotein from adenovirus. E19 blocked the presentation of vaccinia and influenza virus proteins to CTLs in a MHC class I allele-specific manner identical to its inhibition of MHC class I transport from the endoplasmic reticulum. This finding indicates that (i) the relevant parameter for antigen presentation is the rate of MHC class I molecule exocytosis, not the level of class I cell surface expression, and (ii) association of class I molecules with antigen is likely to occur within the endoplasmic reticulum. 相似文献
694.
Receptor-coupled activation of phosphoinositide-specific phospholipase C by an N protein 总被引:26,自引:0,他引:26
Cleavage of phosphatidylinositol 4,5-bisphosphate by phospholipase C results in the production of two important second messengers: inositol-1,4,5-trisphosphate and 1,2-diacylglycerol. Although several receptors promote this cleavage, the molecular details of phospholipase C activation have remained unresolved. In this study, occupancy of a Ca2+-mobilizing receptor, the oligopeptide chemoattractant receptor on human polymorphonuclear leukocyte plasma membranes, was found to lead to the activation of a guanine nucleotide regulatory (N) protein by guanosine 5'-triphosphate. The activated N protein then stimulated a polyphosphoinositide-specific phospholipase C by reducing the Ca2+ requirement for expression of this activity from superphysiological to normal intracellular concentrations. Therefore, the N protein-mediated activation of phospholipase C may be a key step in the pathway of cellular activation by chemoattractants and certain other hormones. 相似文献
695.
696.
Neotropical rivers support a diverse array of endemic taxa, including electric fishes of the order Gymnotiformes. A comprehensive survey of the main channels of the Amazon River and its major tributaries (>2000-kilometer transect) yielded 43 electric fish species. Biogeographical analyses suggest that local mainstem electric fish diversity is enhanced by tributaries. Mainstem species richness tends to increase downstream of tributary confluences, and species composition is most similar between tributaries and adjacent downstream mainstem locations. These findings support a "nodal" or heterogeneous model of riverine community organization across a particularly extensive and diverse geographical region. 相似文献
697.
Hinds DA Stuve LL Nilsen GB Halperin E Eskin E Ballinger DG Frazer KA Cox DR 《Science (New York, N.Y.)》2005,307(5712):1072-1079
Individual differences in DNA sequence are the genetic basis of human variability. We have characterized whole-genome patterns of common human DNA variation by genotyping 1,586,383 single-nucleotide polymorphisms (SNPs) in 71 Americans of European, African, and Asian ancestry. Our results indicate that these SNPs capture most common genetic variation as a result of linkage disequilibrium, the correlation among common SNP alleles. We observe a strong correlation between extended regions of linkage disequilibrium and functional genomic elements. Our data provide a tool for exploring many questions that remain regarding the causal role of common human DNA variation in complex human traits and for investigating the nature of genetic variation within and between human populations. 相似文献
698.
Howlett NG Taniguchi T Olson S Cox B Waisfisz Q De Die-Smulders C Persky N Grompe M Joenje H Pals G Ikeda H Fox EA D'Andrea AD 《Science (New York, N.Y.)》2002,297(5581):606-609
Fanconi anemia (FA) is a rare autosomal recessive cancer susceptibility disorder characterized by cellular hypersensitivity to mitomycin C (MMC). Six FA genes have been cloned, but the gene or genes corresponding to FA subtypes B and D1 remain unidentified. Here we show that cell lines derived from FA-B and FA-D1 patients have biallelic mutations in BRCA2 and express truncated BRCA2 proteins. Functional complementation of FA-D1 fibroblasts with wild-type BRCA2 complementary DNA restores MMC resistance. Our results link the six cloned FA genes with BRCA1 and BRCA2 in a common pathway. Germ-line mutation of genes in this pathway may result in cancer risks similar to those observed in families with BRCA1 or BRCA2 mutations. 相似文献
699.
Stuart SN Chanson JS Cox NA Young BE Rodrigues AS Fischman DL Waller RW 《Science (New York, N.Y.)》2004,306(5702):1783-1786
The first global assessment of amphibians provides new context for the well-publicized phenomenon of amphibian declines. Amphibians are more threatened and are declining more rapidly than either birds or mammals. Although many declines are due to habitat loss and overutilization, other, unidentified processes threaten 48% of rapidly declining species and are driving species most quickly to extinction. Declines are nonrandom in terms of species' ecological preferences, geographic ranges, and taxonomic associations and are most prevalent among Neotropical montane, stream-associated species. The lack of conservation remedies for these poorly understood declines means that hundreds of amphibian species now face extinction. 相似文献
700.
Schipper J Chanson JS Chiozza F Cox NA Hoffmann M Katariya V Lamoreux J Rodrigues AS Stuart SN Temple HJ Baillie J Boitani L Lacher TE Mittermeier RA Smith AT Absolon D Aguiar JM Amori G Bakkour N Baldi R Berridge RJ Bielby J Black PA Blanc JJ Brooks TM Burton JA Butynski TM Catullo G Chapman R Cokeliss Z Collen B Conroy J Cooke JG da Fonseca GA Derocher AE Dublin HT Duckworth JW Emmons L Emslie RH Festa-Bianchet M Foster M Foster S Garshelis DL Gates C Gimenez-Dixon M Gonzalez S 《Science (New York, N.Y.)》2008,322(5899):225-230
Knowledge of mammalian diversity is still surprisingly disparate, both regionally and taxonomically. Here, we present a comprehensive assessment of the conservation status and distribution of the world's mammals. Data, compiled by 1700+ experts, cover all 5487 species, including marine mammals. Global macroecological patterns are very different for land and marine species but suggest common mechanisms driving diversity and endemism across systems. Compared with land species, threat levels are higher among marine mammals, driven by different processes (accidental mortality and pollution, rather than habitat loss), and are spatially distinct (peaking in northern oceans, rather than in Southeast Asia). Marine mammals are also disproportionately poorly known. These data are made freely available to support further scientific developments and conservation action. 相似文献