1,720,965 research outputs found
Influence of human gut microbiota on the metabolic fate of glucosinolates
Get PDFGlucosinolates (GSLs) are secondary metabolites predominantly found in cruciferous vegetables such
as broccoli, brussel sprout, cabbage and cauliflower which upon chopping and chewing will release
the indigenous plant myrosinase enzyme that catalyzes the hydrolysis of GSLs. This hydrolysis
releases a range of breakdown products including isothiocyanates (ITCs), which have been implicated
in the cancer-protective effects of cruciferous vegetables. Certain human gut bacteria are able to
metabolize GSLs and produce ITCs for human health benefits. In this work, six GSL-metabolizing
bacterial strains were isolated from human faecal sample and identified. Most bacteria were capable
of producing both nitriles (NITs) and ITCs from the metabolism of GSLs however Enterococcus sp.
C213 and Enterococcus faecium KT4S13 produced only NITs. Enterococcus casseliflavus NCCP-53,
Escherichia coli O83:H1 NRG 857C and Lactobacillus agilis R16 were able to metabolize different
types (allyl, aromatic, methylthioalkyl, methylsulfinylalkyl and indolyl) of GSLs differently over
24 h of in vitro anaerobic fermentations. For all GSLs, ITC production seemed to peak between 4 and
8 h of incubation and then declined due to the inherent instability of ITCs in culture broths and
buffers. In contrast, NIT productions gradually increased over time and remained relatively
constant. The total percentage products from each GSL metabolism in all three bacteria never
reached 100%. Interestingly, E. coli O83:H1 NRG 857C produced methylthioalkyl ITCs and NITs from
methylsulfinylalkyl GSLs while E. casseliflavus NCCP-53 produced only methylsulfinylalkyl ITCs from
the same GSLs. This difference was due to reductase activity in E. coli O83:H1 NRG 857C intact
cells and cell-free extracts that biotransforms the sulfoxide groups of methylsulfinylalkyl GSLs to
the sulfide groups. The reductase enzyme is yet to be identified at the gene and protein level,
however it has been characterized using
cell-free extracts in this work. This reductase is inducible by GSLs, oxygen-independent and
requires Mg2+ ion and NADP(H) as co-factors for its activity with optimum pH and temperature at pH
7.0 and 37˚C, respectively. Arylsulfatase activity was also detected in this bacterium. The
corresponding recombinant SUL2 enzyme (57 kDa) of E. coli O83:H1 NRG 857C expressed in BL21(DE3)
exhibited arylsulfatase activity by desulfating synthetic p-nitrocatachol sulfate substrate with
optimum pH and temperature at pH 6.0 and 30˚C,
respectively. In addition, GSL-sulfatase activity was detected in crude extracts by being able to desulfate different intact GSLs to produce desulfo-glucosinolates (DS-GSLs) with less
efficiency in comparison with the commercially available snail sulfatase from Helix pomatia. The
catalytic efficiency of recombinant SUL2 enzyme for GSLs in descending order is as follows;
sinigrin > glucoerucin > gluconasturtiin > glucoiberin. The DS-GSLs (except DS-glucoraphanin) then
act as substrates for the recombinant GH3 enzyme defived from E. casseliflavus NCCP-53 to produce
the corresponding NIT products in NB broths and the buffer with the presence of 5 mM Fe2+ ions.
This enzyme (79 kDa) showed β-O-glucosidase activity for p-nitrophenyl β-D-glucopyranoside with
optimum pH and temperature at pH 7.0 and 37˚C, respectively. NIT productions only occurred from the
metabolism of intact GSLs in bacterial culture broths, but not in the buffers unless 5 mM Fe2+ ions
are present as co-factors. Putative bacterial GSL-degrading enzymes responsible for ITC and NIT
productions from GSL metabolisms are inducible by GSL in resting cells experiments. By using
two-dimensional gel electrophoresis (2-DE) and liquid chromatography mass spectrometry (LC-MS/MS)
for the comparative analysis between proteins obtained from cultures of L. agilis R16 and E. coli
O83:H1 NRG 857C with and without GSL supplementation, upregulated/distinct proteins that may be involved in the metabolism of GSLs by these bacteria were identified. These proteins belong to
(sugar) transport system, carbohydrate metabolism especially kinases and oxidoreduction process. To date, bacterial GSL-degrading enzyme is yet to be identified.Open Acces
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
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