Determination of cadmium, copper, and lead in sodium chloride food salts by flame atomic absorption spectroscopy   总被引：1，自引：0，他引：1  

M J Alvarez De Eulate  R Montoro  N Yba?ez  M De La Guardia 《Journal of the Association of Official Analytical Chemists》1986,69(5):871-873

A method for determination of Cd, Cu, and Pb in sodium chloride food salt samples has been developed. It consists of extraction in 4-methyl-2-pentanone of the complexes formed with ammonium pyrrolidine dithiocarbamate and further analysis of the extracts by flame atomic absorption spectroscopy. Detection limits in ng/g salt were 0.2 for Cd, 0.7 for Cu, and 10.0 for Pb. The coefficients of variation of 12 independent analyses were 13% for Cd (at a level of 0.4 ppb), 18% for Cu (1.6 ppb), and 5% for Pb (40 ppb). The recoveries were 100 +/- 0% for Cd, 115 +/- 14% for Cu, and 100 +/- 13% for Pb.  相似文献   

THE TIME TO CUT DANDELIONS     

La Rue CD 《Science (New York, N.Y.)》1935,82(2128):350-351

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Antibody Formation in Embryos     

La Via MF  Rowlands DT  Block M 《Science (New York, N.Y.)》1963,140(3572):1219-1220

The production of agglutinins to Salmonella typhi was studied in the opossum embryo in the period immediately before and after the development of thymic and lymph node lymphoid tissue. Antibody was found only in embryos older than 8 days which corresponds to an 8- to 10-week human embryo in terms of organogenesis and is the earliest stage at which antibody production has been recorded.  相似文献   

CO2 emissions: a piece of the pie     

Wigley TM 《Science (New York, N.Y.)》2007,316(5826):829-30; author reply 829-30

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加查县产业化潜力分析与开发途径   总被引：1，自引：0，他引：1  

张亚生  贡嘎  彭君  拉巴次仁  旺久  洛桑 《西藏农业科技》2005,27(3):1-13

本文全面分析了加查县生态及自然、社会等资源要素,就生产要素的合理配置、布局及区域经济发展作了全面探讨,由此,提出了以发展核桃为主导产业的可能性和必要性,找出了一条21世纪本区域内脱贫致富奔小康必由之路,对发展加查县经济有一定的指导意义和经济价值.  相似文献   

Myoglobin diffusion in bovine heart muscle   总被引：15，自引：0，他引：15  

D J Livingston  G N La Mar  W D Brown 《Science (New York, N.Y.)》1983,220(4592):71-73

The rotational mobility of myoglobin in situ was determined by proton nuclear magnetic resonance line width measurements of a characteristic myoglobin resonance observed in bovine heart muscle spectra. The protein diffuses intracellularly at nearly half the rate observed in dilute solution. This high mobility allows the oxygenated form of myoglobin to contribute significantly to the overall diffusive flux of oxygen in respiring heart muscle.  相似文献   

Eco1-dependent cohesin acetylation during establishment of sister chromatid cohesion     

Rolef Ben-Shahar T  Heeger S  Lehane C  East P  Flynn H  Skehel M  Uhlmann F 《Science (New York, N.Y.)》2008,321(5888):563-566

Replicated chromosomes are held together by the chromosomal cohesin complex from the time of their synthesis in S phase onward. This requires the replication fork-associated acetyl transferase Eco1, but Eco1's mechanism of action is not known. We identified spontaneous suppressors of the thermosensitive eco1-1 allele in budding yeast. An acetylation-mimicking mutation of a conserved lysine in cohesin's Smc3 subunit makes Eco1 dispensable for cell growth, and we show that Smc3 is acetylated in an Eco1-dependent manner during DNA replication to promote sister chromatid cohesion. A second set of eco1-1 suppressors inactivate the budding yeast ortholog of the cohesin destabilizer Wapl. Our results indicate that Eco1 modifies cohesin to stabilize sister chromatid cohesion in parallel with a cohesion establishment reaction that is in principle Eco1-independent.  相似文献   

Activation of the cellular DNA damage response in the absence of DNA lesions   总被引：1，自引：0，他引：1  

Soutoglou E  Misteli T 《Science (New York, N.Y.)》2008,320(5882):1507-1510

The cellular DNA damage response (DDR) is initiated by the rapid recruitment of repair factors to the site of DNA damage to form a multiprotein repair complex. How the repair complex senses damaged DNA and then activates the DDR is not well understood. We show that prolonged binding of DNA repair factors to chromatin can elicit the DDR in an ATM (ataxia telangiectasia mutated)- and DNAPK (DNA-dependent protein kinase)-dependent manner in the absence of DNA damage. Targeting of single repair factors to chromatin revealed a hierarchy of protein interactions within the repair complex and suggests amplification of the damage signal. We conclude that activation of the DDR does not require DNA damage and stable association of repair factors with chromatin is likely a critical step in triggering, amplifying, and maintaining the DDR signal.  相似文献   

Regular Production of Transgenic Wheat Mediated by Agrobacterium tumefaciens   总被引：4，自引：1，他引：4  

YE Xing-guo  Shirley Sato  XU Hui-jun  DU Li-Pu  Tom Clemente 《中国农业科学(英文版)》2002,1(3):239-244

Wheat is the number one crop both in acreage and total yield in the world. Therefore, it is very important to improve wheat by gene engineering techniques even though it belongs to the plants insensitive to gene transformation, especially to Agrobacterium-mediated transformation. Wheat immature embryos of 1.0-1.5mm in size, C58c1 of Agrobacterium strain harboring pPTN249, pPTN270, pPTN254, and pSIS-GFP respectively (all the vectors contain the aphA selectable gene driven by enhanced 35S promoter and a target gene controlled by ubi promoter or E35S promoter), AB medium for Agrobacterium activate culture, WCC medium for co-culture, were used in this study. The embryos with 4 days of pre-culture were transferred onto selection medium with 10mg/L geneticin, 50mg/L ticarcillin, 50mg/L vancomycin, and 50mg/L cefotaxine after 30 minutes of infection and 2 days of co-cultivation with Agrobacterium. Followed callus production,shoot regeneration on selection medium, 114 resistant plantlets were obtained from 10 transformation experiments of four genotypes. By nptⅡ ELISA (nptⅡ enzyme assay), PCR, Southern blot and leaf bleach,29 positive plants were identified from two genotypes of Bobwhite and Yanglmai 10, with an average transformation efficiency of 0.82 %. The result tested by Southern blot also showed that the transgenic plants with single- copy integration of target gene took 65.52% among total positive plants. The ELISA value of transgenic plant was also related to the copies of alien DNA integrating into wheat chromosomes, the transgenic plants with single copy integration giving higher ELISA value than the ones with 2 or 3 copies integration.  相似文献   

Crystal structure of the long-chain fatty acid transporter FadL     

van den Berg B  Black PN  Clemons WM  Rapoport TA 《Science (New York, N.Y.)》2004,304(5676):1506-1509

The mechanisms by which hydrophobic molecules, such as long-chain fatty acids, enter cells are poorly understood. In Gram-negative bacteria, the lipopolysaccharide layer in the outer membrane is an efficient barrier for fatty acids and aromatic hydrocarbons destined for biodegradation. We report crystal structures of the long-chain fatty acid transporter FadL from Escherichia coli at 2.6 and 2.8 angstrom resolution. FadL forms a 14-stranded beta barrel that is occluded by a central hatch domain. The structures suggest that hydrophobic compounds bind to multiple sites in FadL and use a transport mechanism that involves spontaneous conformational changes in the hatch.  相似文献