1,720,959 research outputs found
Regulation of vitamin B6 metabolism in Escherichia coli
Full text linkThe catalytically active form of vitamin B6, pyridoxal 5'-phosphate (PLP), acts as a coenzyme in a variety of different enzymatic reactions. PLP is essential for the normal growth and development of all the organisms, but only plants and microorganisms can synthetise it de novo, while the other organisms must recycle it from nutrients.
The PLP is a very reactive molecule thanks to its aldehyde group and its intracellular concentration must be kept low to avoid undesired toxic reaction in the organism. The regulation of the free PLP concentration in cells occurs through a variety of mechanism, such as its dephosphorylation to PL or, as recently discovered, through the binding to PLP Binding Protein. In Escherichia coli an important candidate for this role has recently been discovered: YggS is a non-catalytic protein able to bind PLP. It belongs to the COG0325 family, a class of protein sharing structure homology with PLP-dependent enzymes, such as alanine racemase and some decarboxylases that have the same Fold-type III.
The metabolism of PLP in E. coli has been studied for years. In this work, our group have deepened the regulation of the PLP metabolism, studying and elaborating the state of the art, and crossing the available literature data with those produced in our lab about the regulation of the expression of the genes involved in PLP homeostasis and focusing the analysis on the most important genes. Our studies have also analysed in vivo the phenotypes linked to the genes involved in PLP homeostasis when E. coli is grown in different media and in presence of vitamers, in order to better understand the role of the analysed genes. The study has also considered the expression of the genes involved in PLP homeostasis in presence of vitamin B6 vitamers and during different growth phases.
Finally, given the importance of the gene yggS in E. coli, the attention was focused on the characterization of the protein YggS, whose role has not yet been discovered. This protein is hypothesised to be both a PLP binding protein and a carrier of this important cofactor to the apo PLP-dependent enzymes. Our studies were focused on YggS capacity to bind PLP and, using mutant forms of this protein, we have verified and studied the transfer mechanism of PLP to the apo PLP-dependent enzymes
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
Purification from Deinococcus radiodurans of a 66 kDa ABC transporter acting on peptides containing at least 3 amino acids
No full textDeinococcus radiodurans is a Gram positive bacterium the capability of which to withstand high doses of ionizing radiations is well known. Physiologically speaking, D. radiodurans is a proteolytic prokaryote able to express and secrete quite a number of proteases, and to use amino acids as an energy source. When considering this, it is surprising that little information is available on the biochemical components responsible for the uptake of peptides in D. radiodurans. Here we report on the purification and characterization of an ABC peptide transporter, isolated from D. radiodurans cells grown in tryptone-glucose-yeast extract (TGY) medium. In particular, we show here that the action of this transporter (denoted DR1571, SwissProt data bank accession number Q9RU24 UF71_DEIRA) is exerted on peptides containing at least 3 amino acids. Further, using tetra-peptides as model systems, we were able to observe that the DR1571 protein does not bind to peptides containing phenylalanine or valine, but associates with high efficiency to tetra-glycine, and with moderate affinity to tetra-peptides containing arginine or aspartate
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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