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The public perception of selenium has changed significantly over the last decades. Originally mainly known for its high toxicity,
it was later recognized as an essential trace element and is now (despite its narrow therapeutic window) almost being marketed
as a lifestyle drug. Indeed, some clinical and preclinical studies suggest that selenium supplementation may be beneficial
in a large number of clinical conditions. However, its mode of action is unresolved in most of these cases. Selenocysteine
– identified as the 21st amino acid used in ribosome-mediated protein synthesis – is incorporated in at least 25 specific, genetically determined
human selenoproteins, many of which have only recently been discovered. Restoration of normal selenoprotein levels may be
– apart from direct supranutritional effects – one possible explanation for the effects of selenium supplements. In this review
we provide a brief but up-to-date overview of what is currently known about these 25 acknowledged human selenoproteins and
their synthesis.
Received 30 March 2005; received after revision 4 July 2005; accepted 13 July 2005 相似文献
123.
Li Q Duan L Estes JD Ma ZM Rourke T Wang Y Reilly C Carlis J Miller CJ Haase AT 《Nature》2005,434(7037):1148-1152
In early simian immunodeficiency virus (SIV) and human immunodeficiency virus-1 (HIV-1) infections, gut-associated lymphatic tissue (GALT), the largest component of the lymphoid organ system, is a principal site of both virus production and depletion of primarily lamina propria memory CD4+ T cells; that is, CD4-expressing T cells that previously encountered antigens and microbes and homed to the lamina propria of GALT. Here, we show that peak virus production in gut tissues of SIV-infected rhesus macaques coincides with peak numbers of infected memory CD4+ T cells. Surprisingly, most of the initially infected memory cells were not, as expected, activated but were instead immunophenotypically 'resting' cells that, unlike truly resting cells, but like the first cells mainly infected at other mucosal sites and peripheral lymph nodes, are capable of supporting virus production. In addition to inducing immune activation and thereby providing activated CD4+ T-cell targets to sustain infection, virus production also triggered an immunopathologically limiting Fas-Fas-ligand-mediated apoptotic pathway in lamina propria CD4+ T cells, resulting in their preferential ablation. Thus, SIV exploits a large, resident population of resting memory CD4+ T cells in GALT to produce peak levels of virus that directly (through lytic infection) and indirectly (through apoptosis of infected and uninfected cells) deplete CD4+ T cells in the effector arm of GALT. The scale of this CD4+ T-cell depletion has adverse effects on the immune system of the host, underscoring the importance of developing countermeasures to SIV that are effective before infection of GALT. 相似文献
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The nonlinear nature of friction 总被引:1,自引:0,他引:1
Tribology is the study of adhesion, friction, lubrication and wear of surfaces in relative motion. It remains as important today as it was in ancient times, arising in the fields of physics, chemistry, geology, biology and engineering. The more we learn about tribology the more complex it appears. Nevertheless, recent experiments coupled to theoretical modelling have made great advances in unifying apparently diverse phenomena and revealed many subtle and often non-intuitive aspects of matter in motion, which stem from the nonlinear nature of the problem. 相似文献
126.
Stochastic yet biased expression of multiple Dscam splice variants by individual cells 总被引:1,自引:0,他引:1
The Drosophila melanogaster gene Dscam is essential for axon guidance and has 38,016 possible alternative splice forms. This diversity can potentially be used to distinguish cells. We analyzed the Dscam mRNA isoforms expressed by different cell types and individual cells. The choice of splice variants expressed is regulated both spatially and temporally. Different subtypes of photoreceptors express broad yet distinctive spectra of Dscam isoforms. Single-cell RT-PCR documented that individual cells express several different Dscam isoforms and allowed an estimation of the diversity that is present. For example, we estimate that each R3/R4 photoreceptor cell expresses 14-50 distinct mRNAs chosen from the spectrum of thousands of splice variants distinctive of its cell type. Thus, the Dscam repertoire of each cell is different from those of its neighbors, providing a potential mechanism for generating unique cell identity in the nervous system and elsewhere. 相似文献
127.
The information carrier of today's communications, a weak pulse of light, is an intrinsically quantum object. As a consequence, complete information about the pulse cannot be perfectly recorded in a classical memory, even in principle. In the field of quantum information, this has led to the long-standing challenge of how to achieve a high-fidelity transfer of an independently prepared quantum state of light onto an atomic quantum state. Here we propose and experimentally demonstrate a protocol for such a quantum memory based on atomic ensembles. Recording of an externally provided quantum state of light onto the atomic quantum memory is achieved with 70 per cent fidelity, significantly higher than the limit for classical recording. Quantum storage of light is achieved in three steps: first, interaction of the input pulse and an entangling field with spin-polarized caesium atoms; second, subsequent measurement of the transmitted light; and third, feedback onto the atoms using a radio-frequency magnetic pulse conditioned on the measurement result. The density of recorded states is 33 per cent higher than the best classical recording of light onto atoms, with a quantum memory lifetime of up to 4 milliseconds. 相似文献
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Elevated erythrocyte calcium in sickle cell disease 总被引:19,自引:0,他引:19