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101.
Klekociuk AR Brown PG Pack DW ReVelle DO Edwards WN Spalding RE Tagliaferri E Yoo BB Zagari J 《Nature》2005,436(7054):1132-1135
Much of the mass of most meteoroids entering the Earth's atmosphere is consumed in the process of ablation. Larger meteoroids (> 10 cm), which in some cases reach the ground as meteorites, typically have survival fractions near 1-25 per cent of their initial mass. The fate of the remaining ablated material is unclear, but theory suggests that much of it should recondense through coagulation as nanometre-sized particles. No direct measurements of such meteoric 'smoke' have hitherto been made. Here we report the disintegration of one of the largest meteoroids to have entered the Earth's atmosphere during the past decade, and show that the dominant contribution to the mass of the residual atmospheric aerosol was in the form of micrometre-sized particles. This result is contrary to the usual view that most of the material in large meteoroids is efficiently converted to particles of much smaller size through ablation. Assuming that our observations are of a typical event, we suggest that large meteoroids provide the dominant source of micrometre-sized meteoritic dust at the Earth's surface over long timescales. 相似文献
102.
Loftus B Anderson I Davies R Alsmark UC Samuelson J Amedeo P Roncaglia P Berriman M Hirt RP Mann BJ Nozaki T Suh B Pop M Duchene M Ackers J Tannich E Leippe M Hofer M Bruchhaus I Willhoeft U Bhattacharya A Chillingworth T Churcher C Hance Z Harris B Harris D Jagels K Moule S Mungall K Ormond D Squares R Whitehead S Quail MA Rabbinowitsch E Norbertczak H Price C Wang Z Guillén N Gilchrist C Stroup SE Bhattacharya S Lohia A Foster PG Sicheritz-Ponten T Weber C Singh U Mukherjee C El-Sayed NM 《Nature》2005,433(7028):865-868
Entamoeba histolytica is an intestinal parasite and the causative agent of amoebiasis, which is a significant source of morbidity and mortality in developing countries. Here we present the genome of E. histolytica, which reveals a variety of metabolic adaptations shared with two other amitochondrial protist pathogens: Giardia lamblia and Trichomonas vaginalis. These adaptations include reduction or elimination of most mitochondrial metabolic pathways and the use of oxidative stress enzymes generally associated with anaerobic prokaryotes. Phylogenomic analysis identifies evidence for lateral gene transfer of bacterial genes into the E. histolytica genome, the effects of which centre on expanding aspects of E. histolytica's metabolic repertoire. The presence of these genes and the potential for novel metabolic pathways in E. histolytica may allow for the development of new chemotherapeutic agents. The genome encodes a large number of novel receptor kinases and contains expansions of a variety of gene families, including those associated with virulence. Additional genome features include an abundance of tandemly repeated transfer-RNA-containing arrays, which may have a structural function in the genome. Analysis of the genome provides new insights into the workings and genome evolution of a major human pathogen. 相似文献
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P Bernard F Couraud 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1979,289(3):315-318
Embryonic Chick hearts aged less than 4 days are not always sensitive to tetrodotoxin, an inhibitor of fast sodium channel. It is shown that in the most frequent cases, in which tetrodotoxin sensitivity is apparently absent, this sensitivity can be demonstrated after previous treatment by veratridine or by toxin II of androctonus australis Hector Scorpion venom. It is concluded that the fast tetrodotoxin-sensitive sodium channel is regularly present in the heart of Chick embryos aged 2 and 3 days, but most often in a permanently inactivated state. 相似文献
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A David J Bernard N Thiernesse G Nicolas J C Cerottini D Zagury 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1979,288(4):441-444
In this paper, we formulate the hypothesis that in the process of target cell lysis a lysosomal enzyme regurgitation, performed by killer cells at the level of the target effector junction, accounts for the target lesion which precedes the lysis (lethal hit). This process of exocytosis, similar to the one described previously in polymorphonuclear neutrophils is supported by cytological studies performed directly on identified killers isolated by micromanipulation. Light and electron microscopy observations confirm a previous report which describes the effector cells rich in lysosomal bodies. In addition, when a killer cell is associated with a target cell to form a conjugate, lysosomes are concentrated near the cell junction and, after incubation at 37 degrees C, acid phosphatases may be detected at the junction. Lysosomal enzyme exocytosis explains why target lysis needs an effector target binding to occur and also the other conditions required for any exocytosis process such as Ca++ in the medium, integrity of the microtubular apparatus, a low level of cyclic AMP and energy dependancy. 相似文献
107.
R. Dixon S. East M. Buckley A. Darragh 《Cellular and molecular life sciences : CMLS》1973,29(4):483-484
Zusammenfassung Nach i. v. Verabreichung von Thyrotrophin-releasing Hormonen an Versuchspersonen ergibt sich eine biphasische Kurve für den Abfall der Tritiumaktivität im Plasma mit einer Exkretions-Halbwertszeit von 3 h.
Acknowledgements. The authors wish to express their gratitude to Hoffmann-La Roche and Co. AG, Basel for the research funds which supported this work. We are indebted to Dr.C. Metzler, Upjohn Co., Kalamazoo for a gift of the NON-LIN computer programme. 相似文献
Acknowledgements. The authors wish to express their gratitude to Hoffmann-La Roche and Co. AG, Basel for the research funds which supported this work. We are indebted to Dr.C. Metzler, Upjohn Co., Kalamazoo for a gift of the NON-LIN computer programme. 相似文献
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