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  • 1
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    Accretion of pristine gas and dilution during the formation of multiple-population globular clusters (2016)
    Oxford University Press
    Details
    Publication Date: 2016-07-29
    Description: We study the interaction of the early spherical GC wind powered by Type II supernovae (SNe II) with the surrounding ambient medium consisting of the gaseous disc of a star-forming galaxy at redshift z 2. The bubble formed by the wind eventually breaks out of the disc, and most of the wind moves directly out of the galaxy and is definitively lost. The fraction of the wind moving nearly parallel to the galactic plane carves a hole in the disc which will contract after the end of the SN activity. During the interval of time between the end of the SN explosions and the ‘closure’ of the hole, very O-poor stars (the Extreme population) can form out of the super-AGB (asymptotic giant branch) ejecta collected in the GC centre. Once the hole contracts, the AGB ejecta mix with the pristine gas, allowing the formation of stars with an oxygen abundance intermediate between that of the very O-poor stars and that of the pristine gas. We show that this mechanism may explain why Extreme populations are present only in massive clusters, and can also produce a correlation between the spread in helium and the cluster mass. Finally, we also explore the possibility that our proposed mechanism can be extended to the case of multiple populations showing bimodality in the iron content, with the presence of two populations characterized by a small difference in [Fe/H]. Such a result can be obtained taking into account the contribution of delayed SN II.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 2
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    The structural basis of agonist-induced activation in constitutively active rhodopsin (2011)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2011-03-11
    Description: G-protein-coupled receptors (GPCRs) comprise the largest family of membrane proteins in the human genome and mediate cellular responses to an extensive array of hormones, neurotransmitters and sensory stimuli. Although some crystal structures have been determined for GPCRs, most are for modified forms, showing little basal activity, and are bound to inverse agonists or antagonists. Consequently, these structures correspond to receptors in their inactive states. The visual pigment rhodopsin is the only GPCR for which structures exist that are thought to be in the active state. However, these structures are for the apoprotein, or opsin, form that does not contain the agonist all-trans retinal. Here we present a crystal structure at a resolution of 3 A for the constitutively active rhodopsin mutant Glu 113 Gln in complex with a peptide derived from the carboxy terminus of the alpha-subunit of the G protein transducin. The protein is in an active conformation that retains retinal in the binding pocket after photoactivation. Comparison with the structure of ground-state rhodopsin suggests how translocation of the retinal beta-ionone ring leads to a rotation of transmembrane helix 6, which is the critical conformational change on activation. A key feature of this conformational change is a reorganization of water-mediated hydrogen-bond networks between the retinal-binding pocket and three of the most conserved GPCR sequence motifs. We thus show how an agonist ligand can activate its GPCR.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3715716/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3715716/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Standfuss, Jorg -- Edwards, Patricia C -- D'Antona, Aaron -- Fransen, Maikel -- Xie, Guifu -- Oprian, Daniel D -- Schertler, Gebhard F X -- EY007965/EY/NEI NIH HHS/ -- MC_U105178937/Medical Research Council/United Kingdom -- MC_U105197215/Medical Research Council/United Kingdom -- R01 EY007965/EY/NEI NIH HHS/ -- England -- Nature. 2011 Mar 31;471(7340):656-60. doi: 10.1038/nature09795. Epub 2011 Mar 9.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21389983" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acid Motifs ; Binding Sites ; Crystallization ; Crystallography, X-Ray ; HEK293 Cells ; Humans ; Hydrogen Bonding/drug effects ; Ligands ; Models, Molecular ; Peptide Fragments/chemistry/metabolism ; Protein Conformation/drug effects ; Retinaldehyde/chemistry/metabolism/pharmacology ; Rhodopsin/*agonists/*chemistry/genetics/metabolism ; Rotation ; Transducin/chemistry/metabolism ; Water/chemistry/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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  • 3
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    The Hubble Space TelescopeUV Legacy Survey of Galactic Globular Clusters - V. Constraints on formation scenarios (2015)
    Oxford University Press
    Details
    Publication Date: 2015-10-30
    Description: We build on the evidence provided by our Legacy Survey of Galactic globular clusters (GC) to submit to a crucial test four scenarios currently entertained for the formation of multiple stellar generations in GCs. The observational constraints on multiple generations to be fulfilled are manifold, including GC specificity, ubiquity, variety, predominance, discreteness, supernova avoidance, p -capture processing, helium enrichment and mass budget. We argue that scenarios appealing to supermassive stars, fast rotating massive stars and massive interactive binaries violate in an irreparable fashion two or more among such constraints. Also the scenario appealing to asymptotic giant branch (AGB) stars as producers of the material for next generation stars encounters severe difficulties, specifically concerning the mass budget problem and the detailed chemical composition of second-generation stars. We qualitatively explore ways possibly allowing one to save the AGB scenario, specifically appealing to a possible revision of the cross-section of a critical reaction rate destroying sodium, or alternatively by a more extensive exploration of the vast parameter space controlling the evolutionary behaviour of AGB stellar models. Still, we cannot ensure success for these efforts and totally new scenarios may have to be invented to understand how GCs formed in the early Universe.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
    Electronic Resource
    Electronic Resource
    Fractionation and determination of the lipid and steroid constituents of the adrenal glands of rats by means of thin-layer chromatography
    Amsterdam : Elsevier
    Journal of Chromatography A 18 (1965), S. 57-68 
    Details
    ISSN: 0021-9673
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/S0021-9673(01)80320-4
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    Paper (German National Licenses)
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