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  • 1
    Electronic Resource
    Electronic Resource
    Chemical modification ofStaphylococcus aureus α-toxin by diethylpyrocarbonate: Role of histidines in its membrane-damaging properties (1991)
    Springer
    The journal of membrane biology 119 (1991), S. 41-52 
    Details
    ISSN: 1432-1424
    Keywords: α-toxin ; membrane damage ; hemolysis ; histidine modification ; diethylpyrocarbonate ; Staphylococcus aureus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Staphylococcus aureus α-toxin causes cell damage by forming an amphiphilic hexamer that inserts into the cell membrane and generates a hydrophilic pore. To investigate the role of the three histidine residues of this toxin we modified them with diethylpyrocarbonate, obtaining N-carbethoxy-histidine whose appearance may be followed spectrophotometrically. Despite the statistical nature of random chemical modification, it was possible to establish that modification of any one of the three histidines was enough to impair α-toxin activity on red blood cells and platelets. Two out of three histidines were essential for the interaction of the toxin with model membranes such as lipid vesicles and planar bilayers. Loss of lytic activity in both natural and model membranes was due both to defective binding and to defective oligomerization. When α-toxin hexamers inserted into lipid vesicles were assayed for chemical modifiability two histidines per monomer were found to be protected from diethylpyrocarbonate modification, whereas only one was protected after delipidation of the oligomer with a detergent. A possible model for the role of each histidine in the monomer is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868539
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  • 2
    Electronic Resource
    Electronic Resource
    Modification of lysine residues ofStaphylococcus aureus α-toxin: Effects on its channel-forming properties (1991)
    Springer
    The journal of membrane biology 119 (1991), S. 53-64 
    Details
    ISSN: 1432-1424
    Keywords: α-toxin ; pore formation ; ion selectivity ; lysine modification ; diethylpyrocarbonate ; trinitrobenzenesulfonic acid ; Staphylococcus aureus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Staphylococcus aureaus α-toxin opens an ion channel in planar phospholipid bilayers which is selective for anions over cations, supposedly because of the presence of positively charged groups along the ion pathway. To remove some positive charges of this protein toxin, we chemically modified part of its lysine residues either with diethylpyrocarbonate, followed by histidine regeneration with hydroxylamine, or with trinitrobenzenesulfonic acid. The extent of chemical modification can be followed accurately by native polyacrylamide gel electrophoresis and isoelectric focusing. Ethoxyformilation of two to three lysine residues per toxin monomer does not impair hemolysis of rabbit red blood cells nor formation of pores in model membranes. It reduces the conductance and the anion selectivity of the channel and changes the shape of its current-voltage characteristic. This indicates that positively charged lysine residues are actually important in determining the electrical properties of the pore. Ethoxyformilation of channels preassembled in planar bilayers produces the same changes as modification of toxin monomers before channel formation. Furthermore, it can be performed by adding diethylpyrocarbonate on either side of the bilayer. This suggests that the lysine residues relevant for the electrical properties of the pore are located inside its lumen where they can be reached by diethylpyrocarbonate diffusing from either entrance of the channel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868540
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  • 3
    Electronic Resource
    Electronic Resource
    Pore formation by Staphylococcus aureus alpha-toxin in lipid bilayers (1987)
    Springer
    European biophysics journal 14 (1987), S. 349-358 
    Details
    ISSN: 1432-1017
    Keywords: Staphylococcus aureus ; α-toxin ; ionic channel ; activation energy ; oligomerization ; fluorescence ; lipid vesicles ; planar lipid membranes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Staphylococcus aureus α-toxin forms ionic channels of large size in lipid bilayer membranes. We have developed two methods for studying the mechanism of pore formation. One is based on measurement of the ionic current flowing through a planar lipid membrane after exposure to the toxin; the other is based on measuring the release of the fluorescent complex Tb-Dipicolinic acid from large unilamellar vesicles under similar conditions. Both methods indicate that the pore formation process is complex, showing an initial delay followed by non-linear kinetics. The power dependence of the pore formation rate on the toxin concentration in planar bilayers indicates that an aggregation mechanism underlies the channel assembly. Arrhenius plots, obtained with both techniques, show no deviation from linearity up to 50°C and the derived activation energies are found to be comparable to those for the binding and the lysis of rabbit erythrocytes by the same toxin. The temperature dependence of the conductance induced in planar bilayers by a large number of toxin channels indicates that the pores are filled with aqueous solution. The analysis of single conductance events shows that a heterogeneous population of pores exist and that smaller channels are preferred at low temperature. We attribute this heterogeneity to the existence of pores resulting from the aggregation of different numbers of monomers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00262320
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  • 4
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    Reconciling the temperature dependence of respiration across timescales and ecosystem types (2012)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2012-06-23
    Description: Ecosystem respiration is the biotic conversion of organic carbon to carbon dioxide by all of the organisms in an ecosystem, including both consumers and primary producers. Respiration exhibits an exponential temperature dependence at the subcellular and individual levels, but at the ecosystem level respiration can be modified by many variables including community abundance and biomass, which vary substantially among ecosystems. Despite its importance for predicting the responses of the biosphere to climate change, it is as yet unknown whether the temperature dependence of ecosystem respiration varies systematically between aquatic and terrestrial environments. Here we use the largest database of respiratory measurements yet compiled to show that the sensitivity of ecosystem respiration to seasonal changes in temperature is remarkably similar for diverse environments encompassing lakes, rivers, estuaries, the open ocean and forested and non-forested terrestrial ecosystems, with an average activation energy similar to that of the respiratory complex (approximately 0.65 electronvolts (eV)). By contrast, annual ecosystem respiration shows a substantially greater temperature dependence across aquatic (approximately 0.65 eV) versus terrestrial ecosystems (approximately 0.32 eV) that span broad geographic gradients in temperature. Using a model derived from metabolic theory, these findings can be reconciled by similarities in the biochemical kinetics of metabolism at the subcellular level, and fundamental differences in the importance of other variables besides temperature-such as primary productivity and allochthonous carbon inputs-on the structure of aquatic and terrestrial biota at the community level.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Yvon-Durocher, Gabriel -- Caffrey, Jane M -- Cescatti, Alessandro -- Dossena, Matteo -- del Giorgio, Paul -- Gasol, Josep M -- Montoya, Jose M -- Pumpanen, Jukka -- Staehr, Peter A -- Trimmer, Mark -- Woodward, Guy -- Allen, Andrew P -- England -- Nature. 2012 Jul 26;487(7408):472-6. doi: 10.1038/nature11205.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉School of Biological & Chemical Sciences, Queen Mary University of London, London E1 4NS, UK. g.yvon-durocher@exeter.ac.uk〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22722862" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Biomass ; Biota ; Carbon/*metabolism ; Carbon Dioxide/*metabolism ; Cell Respiration ; Data Collection ; *Ecosystem ; *Global Warming ; Humans ; Kinetics ; Lakes ; Marine Biology ; *Oxygen Consumption ; Photosynthesis ; Rivers ; Seasons ; Seawater ; *Temperature ; Time Factors ; Trees/metabolism
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 5
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    Global convergence in the temperature sensitivity of respiration at ecosystem level (2010)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2010-07-07
    Description: The respiratory release of carbon dioxide (CO(2)) from the land surface is a major flux in the global carbon cycle, antipodal to photosynthetic CO(2) uptake. Understanding the sensitivity of respiratory processes to temperature is central for quantifying the climate-carbon cycle feedback. We approximated the sensitivity of terrestrial ecosystem respiration to air temperature (Q(10)) across 60 FLUXNET sites with the use of a methodology that circumvents confounding effects. Contrary to previous findings, our results suggest that Q(10) is independent of mean annual temperature, does not differ among biomes, and is confined to values around 1.4 +/- 0.1. The strong relation between photosynthesis and respiration, by contrast, is highly variable among sites. The results may partly explain a less pronounced climate-carbon cycle feedback than suggested by current carbon cycle climate models.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Mahecha, Miguel D -- Reichstein, Markus -- Carvalhais, Nuno -- Lasslop, Gitta -- Lange, Holger -- Seneviratne, Sonia I -- Vargas, Rodrigo -- Ammann, Christof -- Arain, M Altaf -- Cescatti, Alessandro -- Janssens, Ivan A -- Migliavacca, Mirco -- Montagnani, Leonardo -- Richardson, Andrew D -- New York, N.Y. -- Science. 2010 Aug 13;329(5993):838-40. doi: 10.1126/science.1189587. Epub 2010 Jul 5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Max Planck Institute for Biogeochemistry, 07745 Jena, Germany. mmahecha@bgc-jena.mpg.de〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20603495" target="_blank"〉PubMed〈/a〉
    Keywords: Carbon/metabolism ; Carbon Dioxide/*metabolism ; Cell Respiration ; *Climate ; Ecological and Environmental Processes ; *Ecosystem ; Models, Biological ; Models, Statistical ; Photosynthesis ; Plants/*metabolism ; Soil/analysis ; Soil Microbiology ; *Temperature
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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