1,720,976 research outputs found
Isocitrate dehydrogenase from extremophiles; Molecular adaptations to high temperatures
Get PDFLife on earth has adapted to a wide variety of environmental conditions, many of which are extreme to us humans. Temperature is one of the most important factors limiting biological activity and survival, but so far, biological activity has been observed in a wide temperature range; from -20 to + 121 °C. The organisms living at different temperature ranges are classified according to their optimal growth temperature; psychrophiles below 15 °C, mesophiles 15-45 °C, thermophiles 45-80 °C and hyperthermophiles above 80 °C. The forces governing the high thermal stability of enzymes from (hyper)thermophiles are of great interest due to their possible applications in different industries. Although several comparative structural studies on homologous enzymes from mesophilic and (hyper)thermophilic organisms have been performed no universal feature responsible for the high thermal stability of (hyper)thermophilic enzymes have been observed. In order to understand more closely the molecular mechanisms underlaying protein stability, heat-adaptive features of isocitrate dehydrogenase (IDH) from two hyperthermophiles, Aeropyrum pernix (ApIDH) and Archaeoglobus fulgidus (AfIDH), have been analysed based on their 3D-structures and comparisons to mesophilic homologs, in particular to IDH from E. coli (EcIDH). Isocitrate dehydrogenase, a key enzyme in the tricarboxylic acid cycle (TCA), catalyzes the oxidative decarboxylation of isocitrate to α-ketoglutarate using NAD(P)+ as cofactor. A previous study revealed ApIDH as a hyperstable IDH with an apparent melting temperature (Tm) of 109.9 °C, whereas AfIDH was less stable with a Tm of 98.5 °C. In the present work, Tms of the thermophilic Thermoplasma acidophilum IDH (TaIDH), Methylococcus capsulatus IDH (McIDH) and the mesophilic EcIDH were determined to 80.0, 70.3 and 52.6 °C, respectively. Each of the (hyper)thermophilic enzymes showed significantly higher Tm than EcIDH. To investigate the importance of certain structural traits for the thermal stability of the hyperthermophilic ApIDH and AfIDH, a mutational analysis and a domain-swapping experiment was performed, respectively. The hyperthermophilic IDHs showed additional stabilization of their N-terminus; ApIDH by a disulfide bond, and AfIDH through an aromatic cluster. The size and positioning of ionic networks differed among the hyperthermophilic ApIDH and AfIDH and the mesophilic EcIDH. ApIDH possessed a higher number of intra-and inter-subunit ion pairs and the ionic networks were larger than observed in AfIDH and EcIDH. Mutational disruption of a 7-membered inter-domain network demonstrated the importance of this ionic network in the thermal stability of the former enzyme. The hyperthermophilic AfIDH was, however, strikingly similar to EcIDH and possessed almost the same number of ion pairs and ionic networks. However, a unique inter-subunit 4-membered ionic network between the claspdomain and the small domain was found in the former enzyme. To investigate the contribution of the clasp-domain to the thermal stability of AfIDH, chimeras of the two enzymes were constructed by domain-swapping. An aromatic cluster which is believed to further strengthen the subunit interaction was also identified in ApDIH and AfIDH. This cluster also seems to be conserved conserved in the moderately thermostable TaIDH. The biochemical characterization of McIDH identified the first homotetrameric NAD+- dependent form of a bacterial IDH with a high sequence similarity to homoisocitrate dehydrogenase and isopropylmalate dehydrogenase. In conclusion, the work presented in this thesis has increased our knowledge on how enzymes from (hyper)thermophiles can adapt to and resist thermal denaturation at high temperatures
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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