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Abstract In the Universe, oxygen is the third most widespread element, while on Earth it is the most abundant one. Moreover, oxygen is a major constituent of all biopolymers fundamental to living organisms. Besides O(2), reactive oxygen species (ROS), among them hydrogen peroxide (H(2)O(2)), are also important reactants in the present aerobic metabolism. According to a widely accepted hypothesis, aerobic metabolism and many other reactions/pathways involving O(2) appeared after the evolution of oxygenic photosynthesis. In this study, the hypothesis was formulated that the Last Universal Common Ancestor (LUCA) was at least able to tolerate O(2) and detoxify ROS in a primordial environment. A comparative analysis was carried out of a number of the O(2)-and H(2)O(2)-involving metabolic reactions that occur in strict anaerobes, facultative anaerobes, and aerobes. The results indicate that the most likely LUCA possessed O(2)-and H(2)O(2)-involving pathways, mainly reactions to remove ROS, and had, at least in part, the components of aerobic respiration. Based on this, the presence of a low, but significant, quantity of H(2)O(2) and O(2) should be taken into account in theoretical models of the early Archean atmosphere and oceans and the evolution of life. It is suggested that the early metabolism involving O(2)/H(2)O(2) was a key adaptation of LUCA to already existing weakly oxic zones in Earth's primordial environment. Key Words: Hydrogen peroxide-Oxygen-Origin of life-Photosynthesis-Superoxide dismutase-Superoxide reductase. Astrobiology 12, 775-784. 相似文献
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V. V. Akimov V. G. Afanassyev I. D. Blokhintsev N. G. Leikov V. E. Nesterov A. M. Galper Y. V. Ozerov V. A. Rugki V. M. Zemskov M. I. Fradkin N. P. Topchiev E. I. Chuiken E. Barouch I. Grenier M. Gros A. R.Bazer-Bachi J. -M. Lavigne J. -F. Olive A. Buczkowska J. Grygorczuk J. Juchniewicz P. McCulloch 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1993,13(12):657-664
Two observations of the Vela Pulsar in the energy range 50–5000 MeV performed with the GAMMA-1 telescope in 1990 and 1991 allowed us to study time variability of the pulsar light curve and energy spectra. The light curve for Eγ > 50 MeV shows definite variations in the first interpeak phase interval. The energy spectra of the two main peaks and first interpeak in the lightcurve vary significantly below 200 MeV. 相似文献
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Jerzy Kostrowicki 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(8):209-215
The scope and degree of land transformation depends on the system of land use by man. Therefore research on land use systems is of considerable importance, both for better knowledge of resulting processes as well as for more rational land management. To start such research a classification of land use systems is necessary. The paper presents an attempt at such a classification, preceded by an information on the studies carried on in the past as well as an explanation of reasons why such an attempt has been made, followed by the discussion of possible criteria, methods and techniques of land use systems identification. 相似文献
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Tilman Spohn Karsten Seiferlin Axel Hagermann Jörg Knollenberg Andrew J. Ball Marek Banaszkiewicz Johannes Benkhoff Stanislaw Gadomski Wojciech Gregorczyk Jerzy Grygorczuk Marek Hlond Günter Kargl Ekkehard Kührt Norbert Kömle Jacek Krasowski Wojciech Marczewski John C. Zarnecki 《Space Science Reviews》2007,128(1-4):339-362
MUPUS, the multi purpose sensor package onboard the Rosetta lander Philae, will measure the energy balance and the physical parameters in the near-surface layers – up to about 30 cm depth- of the
nucleus of Rosetta’s target comet Churyumov-Gerasimenko. Moreover it will monitor changes in these parameters over time as
the comet approaches the sun. Among the parameters studied are the density, the porosity, cohesion, the thermal diffusivity
and conductivity, and temperature. The data should increase our knowledge of how comets work, and how the coma gases form.
The data may also be used to constrain the microstructure of the nucleus material. Changes with time of physical properties
will reveal timescales and possibly the nature of processes that modify the material close to the surface. Thereby, the data
will indicate how pristine cometary matter sampled and analysed by other experiments on Philae really is. 相似文献
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