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11.
The enzyme NADPH oxidase in phagocytes is important in the body's defence against microbes: it produces superoxide anions (O2-, precursors to bactericidal reactive oxygen species). Electrons move from intracellular NADPH, across a chain comprising FAD (flavin adenine dinucleotide) and two haems, to reduce extracellular O2 to O2-. NADPH oxidase is electrogenic, generating electron current (I(e)) that is measurable under voltage-clamp conditions. Here we report the complete current-voltage relationship of NADPH oxidase, the first such measurement of a plasma membrane electron transporter. We find that I(e) is voltage-independent from -100 mV to >0 mV, but is steeply inhibited by further depolarization, and is abolished at about +190 mV. It was proposed that H+ efflux mediated by voltage-gated proton channels compensates I(e), because Zn2+ and Cd2+ inhibit both H+ currents and O2- production. Here we show that COS-7 cells transfected with four NADPH oxidase components, but lacking H+ channels, produce O2- in the presence of Zn2+ concentrations that inhibit O2- production in neutrophils and eosinophils. Zn2+ does not inhibit NADPH oxidase directly, but through effects on H+ channels. H+ channels optimize NADPH oxidase function by preventing membrane depolarization to inhibitory voltages. 相似文献
12.
对两种商业用球形胶质纤维素和它的低孔隙的胶质改性物的吸附特性进行了研究.得到了他们的孔隙率、排斥分离尺寸和描述微粒分配平衡系数的模型.特别是,发现他们中的一种的微粒分配平衡系数可用简单的RandomPlane模型来描述. 相似文献
13.
Cross-sectional approach for clustering time varying data 总被引:2,自引:0,他引:2
Cluster analysis is to be performed on a three-mode data matrix of type: units, variables, time. A general model for calculating the distance between two units varying in time is proposed. One particular model is developed and used in an example concerned with clustering of 23 European countries according to the similarity of energy consumption in the years 1976–1982.Supported in part by the Research Council of Slovenia, Yugoslavia. 相似文献
14.
Vladimir Jankovic 《Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics》2010,41(3):201-207
The paper looks at how an early eighteenth-century climatological model of the ‘best climate’ on Earth became a platform for political, economic, and demographic action of extraordinary significance for the colonization of new commodity environments. It analyzes the science used by an early modern business adventurer to model ‘climate’ as an economic tool informing imperial governance and exploitation of local resources. Jean Pierre Purry’s construction of ‘model climate’ portrayed North Carolina’s township at Yamassee River as an ideal environment geared toward mercantilist principles of trade but also as a model community based on skilled labor and optimal climatic capital. His climatological analysis was a purposeful act of policy making based on a science of colonial expansion similar to more recent calls at economic modelling of future climate impact. 相似文献
15.
The reinforcement model of evolution argues that natural selection enhances pre-zygotic isolation between divergent populations or species by selecting against unfit hybrids or costly interspecific matings. Reinforcement is distinguished from other models that consider the formation of reproductive isolation to be a by-product of divergent evolution. Although theory has shown that reinforcement is a possible mechanism that can lead to speciation, empirical evidence has been sufficiently scarce to raise doubts about the importance of reinforcement in nature. Agrodiaetus butterflies (Lepidoptera: Lycaenidae) exhibit unusual variability in chromosome number. Whereas their genitalia and other morphological characteristics are largely uniform, different species vary considerably in male wing colour, and provide a model system to study the role of reinforcement in speciation. Using comparative phylogenetic methods, we show that the sympatric distribution of 15 relatively young sister taxa of Agrodiaetus strongly correlates with differences in male wing colour, and that this pattern is most likely the result of reinforcement. We find little evidence supporting sympatric speciation: rather, in Agrodiaetus, karyotypic changes accumulate gradually in allopatry, prompting reinforcement when karyotypically divergent races come into contact. 相似文献
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17.
Marscher AP Jorstad SG D'Arcangelo FD Smith PS Williams GG Larionov VM Oh H Olmstead AR Aller MF Aller HD McHardy IM Lähteenmäki A Tornikoski M Valtaoja E Hagen-Thorn VA Kopatskaya EN Gear WK Tosti G Kurtanidze O Nikolashvili M Sigua L Miller HR Ryle WT 《Nature》2008,452(7190):966-969
Blazars are the most extreme active galactic nuclei. They possess oppositely directed plasma jets emanating at near light speeds from accreting supermassive black holes. According to theoretical models, such jets are propelled by magnetic fields twisted by differential rotation of the black hole's accretion disk or inertial-frame-dragging ergosphere. The flow velocity increases outward along the jet in an acceleration and collimation zone containing a coiled magnetic field. Detailed observations of outbursts of electromagnetic radiation, for which blazars are famous, can potentially probe the zone. It has hitherto not been possible to either specify the location of the outbursts or verify the general picture of jet formation. Here we report sequences of high-resolution radio images and optical polarization measurements of the blazar BL Lacertae. The data reveal a bright feature in the jet that causes a double flare of radiation from optical frequencies to TeV gamma-ray energies, as well as a delayed outburst at radio wavelengths. We conclude that the event starts in a region with a helical magnetic field that we identify with the acceleration and collimation zone predicted by the theories. The feature brightens again when it crosses a standing shock wave corresponding to the bright 'core' seen on the images. 相似文献
18.
The amphioxus genome and the evolution of the chordate karyotype 总被引:2,自引:0,他引:2
Putnam NH Butts T Ferrier DE Furlong RF Hellsten U Kawashima T Robinson-Rechavi M Shoguchi E Terry A Yu JK Benito-Gutiérrez EL Dubchak I Garcia-Fernàndez J Gibson-Brown JJ Grigoriev IV Horton AC de Jong PJ Jurka J Kapitonov VV Kohara Y Kuroki Y Lindquist E Lucas S Osoegawa K Pennacchio LA Salamov AA Satou Y Sauka-Spengler T Schmutz J Shin-I T Toyoda A Bronner-Fraser M Fujiyama A Holland LZ Holland PW Satoh N Rokhsar DS 《Nature》2008,453(7198):1064-1071
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20.
The Oct4 and Nanog transcription network regulates pluripotency in mouse embryonic stem cells 总被引:45,自引:0,他引:45