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71.
Bennett IM Farfano HM Bogani F Primak A Liddell PA Otero L Sereno L Silber JJ Moore AL Moore TA Gust D 《Nature》2002,420(6914):398-401
Transport of calcium ions across membranes and against a thermodynamic gradient is essential to many biological processes, including muscle contraction, the citric acid cycle, glycogen metabolism, release of neurotransmitters, vision, biological signal transduction and immune response. Synthetic systems that transport metal ions across lipid or liquid membranes are well known, and in some cases light has been used to facilitate transport. Typically, a carrier molecule located in a symmetric membrane binds the ion from aqueous solution on one side and releases it on the other. The thermodynamic driving force is provided by an ion concentration difference between the two aqueous solutions, coupling to such a gradient in an auxiliary species, or photomodulation of the carrier by an asymmetric photon flux. Here we report a different approach, in which active transport is driven not by concentration gradients, but by light-induced electron transfer in a photoactive molecule that is asymmetrically disposed across a lipid bilayer. The system comprises a synthetic, light-driven transmembrane Ca2+ pump based on a redox-sensitive, lipophilic Ca2+-binding shuttle molecule whose function is powered by an intramembrane artificial photosynthetic reaction centre. The resulting structure transports calcium ions across the bilayer of a liposome to develop both a calcium ion concentration gradient and a membrane potential, expanding Mitchell's concept of a redox loop mechanism for protons to include divalent cations. Although the quantum yield is relatively low (approximately 1 per cent), the Ca2+ electrochemical potential developed is significant. 相似文献
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Three variable-gene pools common to IgM, IgG and IgA immunoglobulins 总被引:12,自引:0,他引:12
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Résumé Chez le Chien, le Chat, le Cobaye et le Rat, le chlorothiazide est antagoniste de lad-tubocurarine. Chez le Lapin, le chlorothiazide potentialise la paralysied-tubocurarinique, mais exerce une action antagoniste vis-à-vis d'autres curarimimétiques. L'administration préalable de phénylbutazone transforme en antagonisme la synergie entre le chlorothiazide et lad-tubocurarine. 相似文献
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Sand flies are the exclusive vectors of the protozoan parasite Leishmania, but the mechanism of transmission by fly bite has not been determined nor incorporated into experimental models of infection. In sand flies with mature Leishmania infections the anterior midgut is blocked by a gel of parasite origin, the promastigote secretory gel. Here we analyse the inocula from Leishmania mexicana-infected Lutzomyia longipalpis sand flies. Analysis revealed the size of the infectious dose, the underlying mechanism of parasite delivery by regurgitation, and the novel contribution made to infection by filamentous proteophosphoglycan (fPPG), a component of promastigote secretory gel found to accompany the parasites during transmission. Collectively these results have important implications for understanding the relationship between the parasite and its vector, the pathology of cutaneous leishmaniasis in humans and also the development of effective vaccines and drugs. These findings emphasize that to fully understand transmission of vector-borne diseases the interaction between the parasite, its vector and the mammalian host must be considered together. 相似文献