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排序方式: 共有453条查询结果,搜索用时 46 毫秒
441.
Parsons DW Li M Zhang X Jones S Leary RJ Lin JC Boca SM Carter H Samayoa J Bettegowda C Gallia GL Jallo GI Binder ZA Nikolsky Y Hartigan J Smith DR Gerhard DS Fults DW VandenBerg S Berger MS Marie SK Shinjo SM Clara C Phillips PC Minturn JE Biegel JA Judkins AR Resnick AC Storm PB Curran T He Y Rasheed BA Friedman HS Keir ST McLendon R Northcott PA Taylor MD Burger PC Riggins GJ Karchin R Parmigiani G Bigner DD Yan H Papadopoulos N Vogelstein B Kinzler KW Velculescu VE 《Science (New York, N.Y.)》2011,331(6016):435-439
Medulloblastoma (MB) is the most common malignant brain tumor of children. To identify the genetic alterations in this tumor type, we searched for copy number alterations using high-density microarrays and sequenced all known protein-coding genes and microRNA genes using Sanger sequencing in a set of 22 MBs. We found that, on average, each tumor had 11 gene alterations, fewer by a factor of 5 to 10 than in the adult solid tumors that have been sequenced to date. In addition to alterations in the Hedgehog and Wnt pathways, our analysis led to the discovery of genes not previously known to be altered in MBs. Most notably, inactivating mutations of the histone-lysine N-methyltransferase genes MLL2 or MLL3 were identified in 16% of MB patients. These results demonstrate key differences between the genetic landscapes of adult and childhood cancers, highlight dysregulation of developmental pathways as an important mechanism underlying MBs, and identify a role for a specific type of histone methylation in human tumorigenesis. 相似文献
442.
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
443.
Herbrand K Hammerschmidt FJ Brennecke S Liebig M Lösing G Schmidt CO Gatfield I Krammer G Bertram HJ 《Journal of agricultural and food chemistry》2007,55(19):7874-7878
This study describes the identification of six allyl esters in a garlic cheese preparation and in a commercial cream cheese. The extracts were prepared by liquid/liquid extraction and concentrated by the SAFE process. The identification of the allyl esters of acetic, butyric, hexanoic, heptanoic, octanoic, and decanoic acids is based on the correlation of their mass spectrometric data and chromatographic retention time data obtained from the extracts with those of authentic standards. In addition to the gas chromatography (GC)/mass spectrometry analysis, the flavor ingredients were characterized by GC sniffing by a trained flavorist. Some of the esters were isolated by preparative GC. 相似文献
444.
Large-scale biotechnological production of the antileukemic marine natural product sorbicillactone A
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Bringmann G Gulder TA Lang G Schmitt S Stöhr R Wiese J Nagel K Imhoff JF 《Marine drugs》2007,5(2):23-30
In the search for novel bioactive compounds from sponge-derived microorganisms, we have recently identified two structurally and biosynthetically unprecedented fungal metabolites, the novel-type alkaloids sorbicillactone A and sorbicillactone B. Sorbicillactone A is active against leukemia cells without showing notable cytotoxicity. Therefore, we have developed an efficient process for its biotechnological production and isolation on a large scale supplying sufficient material for the ongoing preclinical investigations and structure-activity relationship (SAR) studies. 相似文献
445.
Substantial amounts of low molecular weight organic compounds (LMWs) such as sugars and amino acids are transferred from plant roots into soil. These substances are released due to decomposition processes or leaching (exudation). Afterwards they can be metabolized by soil microorganisms into different compounds, or they can be partially re‐absorbed by the plants. The aim of this study was to clarify the influence of five wild plant species on the composition and pool sizes of LMWs extractable from three different soils. Four of the five species caused significant changes in soil LMW pools. In Chernozem, the sugar concentrations of soil with plants were up to 60 % higher than those of the bulk reference soil, and amino acids increased by as much as 207 %. The relative abundance of free amino acids in roots did not correlate with the relative abundance of amino acids in soil after six weeks of plant growth. The relative abundance of soil amino acids, that increased after plant growth, was strongly dependent on the type of soil and on the plant species present. We suggest that rather than rhizodeposition being dependent on soil type, it reflects differential microbial metabolization of amino acids in the respective soils. 相似文献
446.
W. Gerhard 《European Journal of Forest Research》1932,54(14):465-479
447.
448.
449.
Gerhard Michael 《植物养料与土壤学杂志》2001,164(2):111-119
Little is known about the physiological regulation of root hair development. Though the literature on the topic is fragmentary, with many gaps, it has been used to put forward some proposals for a central regulatory mechanism, taking note especially of the strong physiological influence of environmental factors on root hair formation. A hypothesis which implicates ethylene (ET) in this mechanism is proposed. This hypothesis is supported by numerous indications and observations in the literature about the effect of ET on cell wall formation and cell wall properties during the phase of root expansion and hair formation. It is assumed that environmental conditions control the effective ET concentration in epidermal hair-forming cells; they influence root development and ET production, while, through affecting the rhizosphere, they modify gas exchange at the root surface, accelerating removal of ET thereby limiting its function in hair formation. In such a way the effects of various specific factors (e.g. soil temperature, bulk density, gas exchange at the root surface or the effect of nutrients) might be manifestations of a central regulatory mechanism. The hope is that this hypothesis will stimulate further research and some suggestions are made as to the direction such research might take. 相似文献
450.
DHPLC scoring of a SNP between promoter sequences of HMW glutenin x-type alleles at the Glu-D1 locus in wheat 总被引:2,自引:0,他引:2
Schwarz G Sift A Wenzel G Mohler V 《Journal of agricultural and food chemistry》2003,51(15):4263-4267
The promoter regions of HMW glutenin x-type genes at the Glu-D1 locus were surveyed for SNPs within a subpopulation of German bread wheat cultivars. On the basis of the promoter sequences of HMW glutenin subunit genes Glu-A1-x1, Glu-A1-x2, Glu-B1-x1, Glu-B1-x7, Glu-D1-x2, and Glu-D1-x5, an amplification refractory mutation system assay was designed to selectively amplify Dx-specific PCR fragments. Comparative sequence analysis among seven Glu-D1-x2 and seven Glu-D1-x5 wheat cultivars only confirmed a G-A transition in the promoter sequence to be a true polymorphism. SNP scoring by DHPLC of 95 German bread wheat cultivars, with the exception of cv. Anemos, showed that the transition completely agreed with the presence of HMW glutenin subunits 1Dx5 + 1Dy10 in SDS-PAGE. Therefore, the developed DHPLC assay is suitable for high-throughput genotyping to assist the selection of HMW glutenin genes in wheat quality breeding programs. 相似文献