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991.
992.
Axonal transport of neurofilaments in normal and disease states 总被引:5,自引:0,他引:5
Miller CC Ackerley S Brownlees J Grierson AJ Jacobsen NJ Thornhill P 《Cellular and molecular life sciences : CMLS》2002,59(2):323-330
Neurofilaments are among the most abundant organelles in neurones. They are synthesised in cell bodies and then transported
into and through axons by a process termed 'slow axonal transport' at a rate that is distinct from that driven by conventional
fast motors. Several recent studies have now demonstrated that this slow rate of transport is actually the consequence of
conventional fast rates of movement that are interrupted by extended pausing. At any one time, most neurofilaments are thus
stationary. Accumulations of neurofilaments are a pathological feature of several human neurodegenerative diseases suggesting
that neurofilament transport is disrupted in disease states. Here, we review recent advances in our understanding of neurofilament
transport in both normal and disease states. Increasing evidence suggests that phosphorylation of neurofilaments is a mechanism
for regulating their transport properties, possibly by promoting their detachment from the motor(s). In some neurodegenerative
diseases, signal transduction mechanisms involving neurofilament kinases and phosphatases may be perturbed leading to disruption
of transport.
Received 11 July 2001; received after revision 30 August 2001; accepted 31 August 2001 相似文献
993.
Chemical investigation of hassium (element 108) 总被引:5,自引:0,他引:5
Düllmann ChE Brüchle W Dressler R Eberhardt K Eichler B Eichler R Gäggeler HW Ginter TN Glaus F Gregorich KE Hoffman DC Jäger E Jost DT Kirbach UW Lee DM Nitsche H Patin JB Pershina V Piguet D Qin Z Schädel M Schausten B Schimpf E Schött HJ Soverna S Sudowe R Thörle P Timokhin SN Trautmann N Türler A Vahle A Wirth G Yakushev AB Zielinski PM 《Nature》2002,418(6900):859-862
The periodic table provides a classification of the chemical properties of the elements. But for the heaviest elements, the transactinides, this role of the periodic table reaches its limits because increasingly strong relativistic effects on the valence electron shells can induce deviations from known trends in chemical properties. In the case of the first two transactinides, elements 104 and 105, relativistic effects do indeed influence their chemical properties, whereas elements 106 and 107 both behave as expected from their position within the periodic table. Here we report the chemical separation and characterization of only seven detected atoms of element 108 (hassium, Hs), which were generated as isotopes (269)Hs (refs 8, 9) and (270)Hs (ref. 10) in the fusion reaction between (26)Mg and (248)Cm. The hassium atoms are immediately oxidized to a highly volatile oxide, presumably HsO(4), for which we determine an enthalpy of adsorption on our detector surface that is comparable to the adsorption enthalpy determined under identical conditions for the osmium oxide OsO(4). These results provide evidence that the chemical properties of hassium and its lighter homologue osmium are similar, thus confirming that hassium exhibits properties as expected from its position in group 8 of the periodic table. 相似文献
994.
The energy efficiency of formation of photons, radicals and ions during single-bubble cavitation 总被引:6,自引:0,他引:6
It is extremely difficult to perform a quantitative analysis of the chemistry associated with multibubble cavitation: unknown parameters include the number of active bubbles, the acoustic pressure acting on each bubble and the bubble size distribution. Single-bubble sonoluminescence (characterized by the emission of picosecond flashes of light) results from nonlinear pulsations of an isolated vapour-gas bubble in an acoustic field. Although the latter offers a much simpler environment in which to study the chemical activity of cavitation, quantitative measurements have been hindered by the tiny amount of reacting gas within a single bubble (typically <10(-13) mol). Here we demonstrate the existence of chemical reactions within a single cavitating bubble, and quantify the sources of energy dissipation during bubble collapse. We measure the yields of nitrite ions, hydroxyl radicals and photons. The energy efficiency of hydroxyl radical formation is comparable to that in multibubble cavitation, but the energy efficiency of light emission is much higher. The observed rate of nitrite formation is in good agreement with the calculated diffusion rate of nitrogen into the bubble. We note that the temperatures attained in single-bubble cavitation in liquids with significant vapour pressures will be substantially limited by the endothermic chemical reactions of the polyatomic species inside the collapsing bubble. 相似文献
995.
Hydrogenated amorphous and nanocrystalline silicon films manufactured by plasma deposition techniques are used widely in electronic and optoelectronic devices. The crystalline fraction and grain size of these films determines electronic and optical properties; the nanocrystal nucleation mechanism, which dictates the final film structure, is governed by the interactions between the hydrogen atoms of the plasma and the solid silicon matrix. Fundamental understanding of these interactions is important for optimizing the film structure and properties. Here we report the mechanism of hydrogen-induced crystallization of hydrogenated amorphous silicon films during post-deposition treatment with an H(2) (or D(2)) plasma. Using molecular-dynamics simulations and infrared spectroscopy, we show that crystallization is mediated by the insertion of H atoms into strained Si-Si bonds as the atoms diffuse through the film. This chemically driven mechanism may be operative in other covalently bonded materials, where the presence of hydrogen leads to disorder-to-order transitions. 相似文献
996.
Germline mutations in FH predispose to dominantly inherited uterine fibroids, skin leiomyomata and papillary renal cell cancer 总被引:26,自引:0,他引:26
Tomlinson IP Alam NA Rowan AJ Barclay E Jaeger EE Kelsell D Leigh I Gorman P Lamlum H Rahman S Roylance RR Olpin S Bevan S Barker K Hearle N Houlston RS Kiuru M Lehtonen R Karhu A Vilkki S Laiho P Eklund C Vierimaa O Aittomäki K Hietala M Sistonen P Paetau A Salovaara R Herva R Launonen V Aaltonen LA;Multiple Leiomyoma Consortium 《Nature genetics》2002,30(4):406-410
997.
Thyroid hormone controls carnitine status through modifications of γ-butyrobetaine hydroxylase activity and gene expression 总被引:1,自引:0,他引:1
Galland S Georges B Le Borgne F Conductier G Dias JV Demarquoy J 《Cellular and molecular life sciences : CMLS》2002,59(3):540-545
The carnitine system plays a key role in β-oxidation of long-chain fatty acids by permitting their transport into the mitochondrial
matrix. The effects of hypothyroidism and hyperthyroidism were studied on γ-butyrobetaine hydroxylase (BBH), the enzyme responsible
for carnitine biosynthesis in the rat. In rat liver, BBH activity was decreased in the hypothyroid state and increased in
hyperthyroid animals. The modifications in BBH activity correlated with changes in the enzyme Vmax values. These changes were
shown to be related to hepatic BBH mRNA abundance. Thyroid hormones are known to interact with lipid metabolism, in particular
by increasing long-chain fatty acid oxidation through activation of carnitine-dependent fatty acid import into mitochondria.
Our study showed that thyroid hormones also increased carnitine bioavailability.
Received 23 October 2001; received after revision 11 January 2002; accepted 15 January 2002 相似文献
998.
Immunomodulatory properties of cystatins 总被引:8,自引:0,他引:8
Cystatins are natural tight-binding reversible inhibitors of cysteine proteases. Because these cysteine proteases exist in
all living organisms and because they are involved in various biological and pathological processes, the control of these
protease functions by cystatins is of cardinal importance. Cystatins are found in mammals but cystatin-like molecules are
also present in mammals and parasites. In the immune system, cystatins modulate cathepsin activities and antigen presentation.
They also induce tumor necrosis factor α and interleukin 10 synthesis, and they stimulate nitric oxide production by interferon
γ-activated murine macrophages. In turn, nitric oxide has inhibitory activity on cysteine proteases, especially those from
parasitic protozoa. Cystatins isolated from parasitic nematodes also have immunomodulatory activities that are distinguishable
from those induced by lipopolysacharide-like molecules from endosymbiotic bacteria. On the whole, cystatins and cystatin-like
molecules belong to a new category of immunomodulatory molecules. Doubtless increasing data will improve our knowledge of
this property, leading to practical applications in immunotherapy.
Received 11 April 2002; accepted 18 April 2002
RID="*"
ID="*"Corresponding author. 相似文献
999.
1000.