1,720,978 research outputs found
Enzyme-iron nanoparticle direct interactions: complex formation and application for a coulometric biosensor for aminoaldehydes
No full textRecombinant aminoaldehyde dehydrogenase from tomato (LeAMADH1) was used as a model protein for studying the intimate interaction at the interface between proteins and surface active maghemite nanoparticles (SAMNs). SAMNs represent a new class of maghemite nanoparticles, displaying great colloidal behavior and specific surface chemical properties, as well as, peculiar electrochemical characteristics and specificity toward protein binding [1-2]. A potential anchor zone was individuated in a carboxylic rich surface area of the protein structure by molecular modeling. LeAMADH1 was successfully bound to the surface of bare SAMNs and its enzymatic activity was preserved, leading to a magnetic drivable enzymatic hybrid (SAMN@LeAMADH1). The catalytic parameters of SAMN@LeAMADH1 were determined, and exploited for the construction of a coulometric biosensor for the determination of aminoaldehydes in alcoholic beverages. A suspension of SAMN@LeAMADH1, used inside a low volume (1 μL) electrochemical flow cell, fabricated in-house, led to the complete oxidation of aminoaldehydes, producing a correspondent amount of NADH. The hybrid nanomaterial was magnetically removed after the enzymatic reaction allowing its reutilization. At the same time, a SAMN modified carbon paste electrode, inserted in the microcell was used for the direct electro-oxidation of NADH, leading to the coulometric determination of NADH produced during the enzymatic process. The novel biosensor showed a series of peculiarities: a) SAMN modified carbon paste electrode was used for NADH electro-oxidation; b) the complete enzymatic oxidation of sample aminoaldehydes, producing NADH, was carried out in a colloidal suspension, inside a low volume electrochemical flow cell, optimizing reactant diffusion; c) NADH, produced during the complete enzymatic oxidation of aminoaldehydes, was coulometrically determined at the SAMN modified lectrode; d) the capture of the hybrid, by the application of an external magnet, makes it reusable. 1)Baratella et al., Biosensors and Bioelectronics, 2013, 45, 13–18. 2)Magro et al., Biosensors and Bioelectronics, 2014, 52, 159–165
Coulometric biosensor for aminoaldehydes based on the direct electro-oxidation of NADH on iron oxide nanoparticle modified electrode
No full text
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
FAD-containing polyamine oxidases: a timely challenge for researchers in biochemistry and physiology of plants
No full textRecent investigations on plant polyamine oxidase (PAO) are reviewed. The enzyme belongs to a new class of flavoenzymes with similar structural features including, among others, monoamine oxidase. Plant PAOs catalyse the oxidation of the polyamine substrates spermidine and spermine. The reaction products are propane-1,3-diamine and 1-pyrroline or 1-(3-aminopropyl)pyrrolinium, respectively, along with hydrogen peroxide. Plant PAOs are predominantly localised in the cell wall. Purification procedures and molecular properties of several plant PAOs are compared. A special attention is being paid to the recently solved crystal structure of the maize enzyme and its implications for the substrate binding and catalytic mechanism. Substrate specificity and inhibitors of plant PAOs are also described. The potential roles for PAO-generated H(2)O(2) in lignin biosynthesis and cell wall cross-linking reactions, which may regulate growth and contribute to cell defence, are discussed
Analysis of the glycosylation pattern of plant copper amine oxidases by MALDI-TOF/TOF MS coupled to a manual chromatographic separation of glycans and glycopeptide
No full textThe N-glycosylation in pea seedling amine oxidase and lentil seedling amine oxidase was analyzed in the present work. For that purpose, the enzymes were purified as native proteins from their natural sources. An enzymatic deglycosylation of pea seedling amine oxidase by endoglycosidase H under denaturing conditions combined with its proteolytic digestion by trypsin was carried out in order to analyze both N-glycans and "trimmed" N-glycopeptides with a residual N-acetylglucosamine attached at the originally occupied N-glycosylation sites. The released N-glycans were subjected to a manual chromatographic purification followed by MALDI-TOF/TOF MS. MS and MS/MS analyses were also performed directly on peptides and N-glycopeptides generated by proteolytic digestion of the studied enzymes. Sequencing of glycopeptides by MALDI-TOF/TOF MS/MS after their separation on a RP using a microgradient chromatographic device clearly demonstrated binding of paucimannose and hybrid N-glycan structures at Asn558. Such carbohydrates have been reported to exist in many plant N-glycoproteins, e.g. in peroxidases. Although high-mannose glycan structures were identified after the enzymatic deglycosylation, they could not be assigned to a particular N-glycosylation site. The presence of unoccupied glycosylation sites in several peptides was also confirmed from MS/MS results
Reactions of plant copper/topaquinone amine oxidases with N6–aminoalkyl derivatives of adenine
No full textPlant copper/topaquinone-containing amine oxidases (CAOs, EC 1.4.3.6) are enzymes oxidising various amines. Here we
report a study on the reactions of CAOs from grass pea (Lathyrus sativus), lentil (Lens esculenta) and Euphorbia characias, a
Mediterranean shrub, with N6-aminoalkyl adenines representing combined analogues of cytokinins and polyamines. The
following compounds were synthesised: N6-(3-aminopropyl)adenine, N6-(4-aminobutyl)adenine, N6-(4-amino-trans-but-2-
enyl)adenine, N6-(4-amino-cis-but-2-enyl)adenine and N6-(4-aminobut-2-ynyl)adenine. From these, N 6-(4-aminobutyl)
adenine and N6-(4-amino-trans-but-2-enyl)adenine were found to be substrates for all three enzymes ðKm , 1024MÞ:
Absorption spectroscopy demonstrated such an interaction with the cofactor topaquinone, which is typical for common
diamine substrates. However, only the former compound provided a regular reaction stoichiometry. Anaerobic absorption
spectra of N6-(3-aminopropyl)adenine, N6-(4-amino-cis-but-2-enyl)adenine and N6-(4-aminobut-2-ynyl)adenine reactions
revealed a similar kind of initial interaction, although the compounds finally inhibited the enzymes. Kinetic measurements
allowed the determination of both inhibition type and strength; N 6-(3-aminopropyl)adenine and N6-(4-amino-cis-but-2-
enyl)adenine produced reversible inhibition ðKi , 1025 –1024MÞ whereas, N 6-(4-aminobut-2-ynyl)adenine could be considered a powerful inactivator
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
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