1,720,987 research outputs found
Discovery of novel pathways of microbial arginine biosynthesis
No full textThe amino acid L-arginine is an essential component of all living organisms. Its importance resides in the variety of functions that arginine itself, along with some intermediary metabolites involved in its de novo synthesis in the cell.
In many prokaryotes, fungi, and plants the de novo biosynthesis of arginine proceeds from glutamate in eight enzymatic steps (Figure 2). The first committed step of this pathway is the N-acetylation of glutamate. Acetylation of the early precursors of arginine distinguishes them from the analogous intermediates in the biosynthesis of proline.
Although each and every step of the pathway is essential for its completion, transcarbamylation of ornithine to produce citrulline is one of the crucial steps in the pathway. This reaction is catalyzed by the enzyme ornithine transcarbamylase (OTC).
The transcarbamylases family of enzymes belongs to the carboxyl- and carbamoyltransferases group, EC 2.1.3, a family that comprises enzymes that catalyze the transfer of a carbamoyl group from carbamylphosphate (CP) to an amino or oxygen group of a second substrate. Members of the transcarbamylase family can be identified based on sequence identities in the N-terminal or CP-binding domain as all the members of this family share common residues involved in the binding of CP to the enzyme.
All the evolutionary conserved motifs present in the transcarbamylase family have led to the erroneous annotation of a large, yet increasing, number of genes as OTCases without experimental confirmation of such activity. The case of the transcarbamylase-like gene found in B. fragilis illustrates this statement.
The present thesis work is focused in the case of two families of misannotated microbial transcarbamylases that have been identified as essential for arginine biosynthesis, but which lacked the ability to catalyze the conversion of ornithine into citrulline.
The objectives of the present thesis work are the biochemical and molecular characterization of the N-acetylornithine transcarbamylase (AOTC) activity of XcArgF’ as well as the elucidation of the enzymatic activity of BfArgF’ and its biochemical and molecular characterization.
We show that Xanthomonads and Bacteroidetes use novel pathways for the de novo arginine biosynthesis mediated by acetyl- and succinyl-ornithine transcarbamylases, we identify a recognition motif for these enzymes and we provide evidence supporting the view that the existence of succinyl-ornithine transcarbamylase requires that the first five steps of the arginine biosynthesis pathway use succinylated rather than acetylated intermediates
Biochemical characterization of cytidine triphosphate synthase (CTPase) from Toxoplasma gondii
No full textToxoplasma gondii is a ubiquitous intracellular parasite with worldwide distribution. New antiparasitic drugs with greater effectiveness in controlling T. gondii are necessary. The enzymes of de novo pyrimidine biosynthetic pathway are considered potential drug targets, because they are required for the parasite' s virulence and survival. Cytidine triphosphate synthase (CTPase) catalyzes the conversion of UTP to CTP, the final step in the production of cytidine nucleotides, and the first step in the formation of phospholipid intermediates. In many organisms, CTPase also plays a structural role in vivo, forming filaments together with other proteins. The function of these filaments is unknown, and identification of their protein components could aid in elucidating function. Our goal was the biochemical characterization of cytidine triphosphate synthase of T. gondii (TgCTPase), and generated tools to study protein-protein interactions, in order to begin to determine its importance as a potential antiparasitic targetMagíster en BiologíaMaestrí
Biochemical characterization of cytidine triphosphate synthase (CTPase) from Toxoplasma gondii
No full textToxoplasma gondii is a ubiquitous intracellular parasite with worldwide distribution. New antiparasitic drugs with greater effectiveness in controlling T. gondii are necessary. The enzymes of de novo pyrimidine biosynthetic pathway are considered potential drug targets, because they are required for the parasite' s virulence and survival. Cytidine triphosphate synthase (CTPase) catalyzes the conversion of UTP to CTP, the final step in the production of cytidine nucleotides, and the first step in the formation of phospholipid intermediates. In many organisms, CTPase also plays a structural role in vivo, forming filaments together with other proteins. The function of these filaments is unknown, and identification of their protein components could aid in elucidating function. Our goal was the biochemical characterization of cytidine triphosphate synthase of T. gondii (TgCTPase), and generated tools to study protein-protein interactions, in order to begin to determine its importance as a potential antiparasitic targetMagíster en BiologíaMaestrí
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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
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