1,720,985 research outputs found
Substrate specificity of lentil seedling amine oxidase
No full textCopper diamine oxidase from lentil (Lens culinaris) seedlings was shown to be able to catalyze the oxidative deamination of a wide range of aliphatic and aromatic monoamine compounds, including some amino acids. Although the catalytic efficiencies were only 1-3% of that measured with the diamine substrate putrescine, they were still comparable to those of specialized monoamine oxidases. In particular, the lentil enzyme oxidized benzylamine and histamine with K(m) and Vmax values similar to those found for the mammalian enzymes benzylamine oxidase and histaminase. Cysteamine was found to be a substrate of the enzyme, whereas hypotaurine and taurine were found to be neither substrates nor inhibitors of the enzyme. Quite unexpectedly the amino acids L-ornithine and L-lysine were oxidized by lentil enzyme, and beta-alanine and gamma-aminobutyric acid were oxidized only at high concentrations of enzyme. These results suggest that enzymes normally classified as diamine oxidases could in fact have a more diversified role in metabolism than recognized so far
Oxidation of benzylamine Br-derivatives by lentil seedling copper-amine oxidase
No full textCopper amine oxidase was shown to be able to catalyse the oxidative deamination of 2-, 3- and 4-Br-derivatives of benzylamine to the corresponding aldehydes, that all absorb at 250 nm. This change in the absorption spectrum made it possible to follow the enzyme reaction. 2-Br-benzylamine, 3-Br-benzylamine, and 4-Br-benzylamine showed K-m values similar to benzylamine, but 3-Br-benzylamine showed a slower k(C), which allows it to be a catalytically more efficient substrate. Under anaerobic conditions the native enzyme oxidised 1 equivalent of all Br-derivatives and released 1 equivalent of aldehyde per enzyme subunit. These findings demonstrate that, in anaerobic conditions, the enzyme can oxidise substrates with a single incomplete turnover. The possible involvement of the cofactor 6-hydroxydopa quinone and of a negatively charged residue in the oxidation of Br-benzylamines is discussed
Substrate specificity of lentil seedling amine oxidase
No full textCopper diamine oxidase from lentil (Lens culinaris) seedlings was shown to be able to catalyze the oxidative deamination of a wide range of aliphatic and aromatic monoamine compounds, including some amino acids. Although the catalytic efficiencies were only 1-3% of that measured with the diamine substrate putrescine, they were still comparable to those of specialized monoamine oxidases. In particular, the lentil enzyme oxidized benzylamine and histamine with K-m and V-max values similar to those found for the mammalian enzymes benzylamine oxidase and histaminase. Cysteamine was found to be a substrate of the enzyme, whereas hypotaurine and taurine were found to be neither substrates nor inhibitors of the enzyme. Quite unexpectedly the aminoacids L-ornithine and L-lysine were oxidized by lentil enzyme, and beta-alanine and gamma-aminobutyric acid were oxidized only at high concentrations of enzyme. These results suggest that enzymes normally classified as diamine oxidases could in fact have a more diversified role in metabolism than recognized so far
Purification and properties of Oryza sativa Cu-Zn superoxide dismutase
No full textSuperoxide dismutase has been purified to homogeneity from Oryza sativa germinated seeds growth in the dark. The purified enzyme contained two electrophoretically distinct bands on continuous gel electrophoresis or analytical gel electrofocusing. SDS-PAGE showed a single band of an M(r) 15 000 while gel chromatography on Sephadex G 100 showed a single peak of an M(r) 32 000. It contained two Cu and two Zn ions. The spectra of ultraviolet and visible regions were similar to those of Cu-Zn mammalian and plant superoxide dismutases. The activation energy was estimated at 16 Kcal mol(-1)
Aminoglycosides as substrates and inhibitors of peroxidases: a possible role of these antibiotics against myeloperoxidase-dependent cytotoxicity
No full textThe kinetics of the catalytic cycle of myeloperoxidase and of horseradish peroxidase reacting with aminoglycosides have been studied by conventional and stopped-flow spectrophotometry. Aminoglycosides acted as one-electron reducing substrates converting compound I, formed when stoichiometric amounts of hydrogen peroxide were added to the enzyme, to compound II, and compound II to the resting, ferric enzyme. The latter gradually decayed into a further spectroscopic derivative (lambda(max) = 540 and 403 nm) tentatively identified as a complex of ferric heme with the antibiotic oxidation product(s), and the resulting enzyme was fully inactivated. Since myeloperoxidase is the only human enzyme known to convert chloride ions into the cytotoxic hypochlorous acid, the data presented in this paper bear relevance to the pharmacological effects of aminoglycoside antibiotics, which, while inhibiting bacterial growth, also prevent oxidative cellular damage caused by hypochlorous acid aging as substrates and inhibitors of myeloperoxidase
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
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