Fatty acids in eleven species of blue-green algae: geochemical significance     

Parker PL  Van Baalen C  Maurer L 《Science (New York, N.Y.)》1967,155(3763):707-708

Analyses of the total lipids of 11 species of blue-green algae showed a simple but qualitatively variable fatty acid composition. The species can be grouped in three categories on the basis of their oleic, linoleic, and linolenic acid content. One species was unusual in that the ten-carbon acid accounts for one-half of its total fatty acid. Branched chain acids are absent in the algae, but are major components of marine bacteria. The geochemical significance of the data is discussed.  相似文献   

Crystal structure of the carboxyltransferase domain of acetyl-coenzyme A carboxylase     

Zhang H  Yang Z  Shen Y  Tong L 《Science (New York, N.Y.)》2003,299(5615):2064-2067

Acetyl-coenzyme A carboxylases (ACCs) are required for the biosynthesis and oxidation of long-chain fatty acids. They are targets for therapeutics against obesity and diabetes, and several herbicides function by inhibiting their carboxyltransferase (CT) domain. We determined the crystal structure of the free enzyme and the coenzyme A complex of yeast CT at 2.7 angstrom resolution and found that it comprises two domains, both belonging to the crotonase/ClpP superfamily. The active site is at the interface of a dimer. Mutagenesis and kinetic studies reveal the functional roles of conserved residues here. The herbicides target the active site of CT, providing a lead for inhibitor development against human ACCs.  相似文献   

Long-term satellite record reveals likely recent aerosol trend     

Mishchenko MI  Geogdzhayev IV  Rossow WB  Cairns B  Carlson BE  Lacis AA  Liu L  Travis LD 《Science (New York, N.Y.)》2007,315(5818):1543

Analysis of the long-term Global Aerosol Climatology Project data set reveals a likely decrease of the global optical thickness of tropospheric aerosols by as much as 0.03 during the period from 1991 to 2005. This recent trend mirrors the concurrent global increase in solar radiation fluxes at Earth's surface and may have contributed to recent changes in surface climate.  相似文献   

Intersubband electroluminescence from silicon-based quantum cascade structures     

Dehlinger G  Diehl L  Gennser U  Sigg H  Faist J  Ensslin K  Grutzmacher D  Muller E 《Science (New York, N.Y.)》2000,290(5500):2277-2280

The quantum cascade laser, which uses electronic transitions within a single band of a semiconductor, constitutes a possible way to integrate active optical components into silicon-based technology. This concept necessitates a transition with a narrow linewidth and an upper state with a sufficiently long lifetime. We report the observation of intersubband electroluminescence from a p-type silicon/silicon-germanium quantum cascade structure, centered at 130 millielectron volts with a width of 22 millielectron volts, with the expected polarization, and discernible up to 180 kelvin. The nonradiative lifetime is found to depend strongly on the design of the quantum well structure, and is shown to reach values comparable to that of an equivalent GaInAs/AlInAs laser structure.  相似文献   

National character does not reflect mean personality trait levels in 49 cultures     

Terracciano A  Abdel-Khalek AM  Adám N  Adamovová L  Ahn CK  Ahn HN  Alansari BM  Alcalay L  Allik J  Angleitner A  Avia MD  Ayearst LE  Barbaranelli C  Beer A  Borg-Cunen MA  Bratko D  Brunner-Sciarra M  Budzinski L  Camart N  Dahourou D  De Fruyt F  de Lima MP  del Pilar GE  Diener E  Falzon R  Fernando K  Ficková E  Fischer R  Flores-Mendoza C  Ghayur MA  Gülgöz S  Hagberg B  Halberstadt J  Halim MS  Hrebícková M  Humrichouse J  Jensen HH  Jocic DD  Jónsson FH  Khoury B  Klinkosz W  Knezević G  Lauri MA  Leibovich N  Martin TA 《Science (New York, N.Y.)》2005,310(5745):96-100

Most people hold beliefs about personality characteristics typical of members of their own and others' cultures. These perceptions of national character may be generalizations from personal experience, stereotypes with a "kernel of truth," or inaccurate stereotypes. We obtained national character ratings of 3989 people from 49 cultures and compared them with the average personality scores of culture members assessed by observer ratings and self-reports. National character ratings were reliable but did not converge with assessed traits. Perceptions of national character thus appear to be unfounded stereotypes that may serve the function of maintaining a national identity.  相似文献   

A small molecule Smac mimic potentiates TRAIL- and TNFalpha-mediated cell death     

Li L  Thomas RM  Suzuki H  De Brabander JK  Wang X  Harran PG 《Science (New York, N.Y.)》2004,305(5689):1471-1474

We describe the synthesis and properties of a small molecule mimic of Smac, a pro-apoptotic protein that functions by relieving inhibitor-of-apoptosis protein (IAP)-mediated suppression of caspase activity. The compound binds to X chromosome- encoded IAP (XIAP), cellular IAP 1 (cIAP-1), and cellular IAP 2 (cIAP-2) and synergizes with both tumor necrosis factor alpha (TNFalpha) and TNF-related apoptosis-inducing ligand (TRAIL) to potently induce caspase activation and apoptosis in human cancer cells. The molecule has allowed a temporal, unbiased evaluation of the roles that IAP proteins play during signaling from TRAIL and TNF receptors. The compound is also a lead structure for the development of IAP antagonists potentially useful as therapy for cancer and inflammatory diseases.  相似文献   

Deep human genealogies reveal a selective advantage to be on an expanding wave front     

Moreau C  Bhérer C  Vézina H  Jomphe M  Labuda D  Excoffier L 《Science (New York, N.Y.)》2011,334(6059):1148-1150

Since their origin, human populations have colonized the whole planet, but the demographic processes governing range expansions are mostly unknown. We analyzed the genealogy of more than one million individuals resulting from a range expansion in Quebec between 1686 and 1960 and reconstructed the spatial dynamics of the expansion. We find that a majority of the present Saguenay Lac-Saint-Jean population can be traced back to ancestors having lived directly on or close to the wave front. Ancestors located on the front contributed significantly more to the current gene pool than those from the range core, likely due to a 20% larger effective fertility of women on the wave front. This fitness component is heritable on the wave front and not in the core, implying that this life-history trait evolves during range expansions.  相似文献   

Catastrophic volcanic collapse: relation to hydrothermal processes     

López DL  Williams SN 《Science (New York, N.Y.)》1993,260(5115):1794-1796

Catastrophic volcanic collapse, without precursory magmatic activity, is characteristic of many volcanic disasters. The extent and locations of hydrothermal discharges at Nevado del Ruiz volcano, Colombia, suggest that at many volcanoes collapse may result from the interactions between hydrothermal fluids and the volcanic edifice. Rock dissolution and hydrothermal mineral alteration, combined with physical triggers such as earth-quakes, can produce volcanic collapse. Hot spring water compositions, residence times, and flow paths through faults were used to model potential collapse at Ruiz. Caldera dimensions, deposits, and alteration mineral volumes are consistent with parameters observed at other volcanoes.  相似文献   

The historical roots of our ecologic crisis   总被引：1，自引：0，他引：1  

White L 《Science (New York, N.Y.)》1967,155(3767):1203-1207

  相似文献   

Carbutamide and plasma insulin activity     

VON HOLT C  VON HOLT L  KRACHT J  KRONER B  KUHNAU J 《Science (New York, N.Y.)》1957,125(3251):735-736

  相似文献