1,721,032 research outputs found
interactions of pig brain cytosolic sialidase with gangliosides. the formation of catalytically inactive enzyme-ganglioside complexes requires homogeneous ganglioside micelles and is reversible phenomenon
No full textCytosolic sialidase A, obtained from pig brain and purified, interacts with ganglioside GT1b giving two catalytically inactive enzyme-ganglioside complexes. Treatment of these complexes with Triton X-100 under given conditions (1% detergent; 1 h at 37°C; 0.1 M acetic acid-sodium acetate buffer, pH4.8) leads to the liberation of part of the enzyme (about 47%) in a free and fully active form. Reversible inactivation of cytosolic sialidase requires the presence of homogeneous micelles of GTlb or of mixed micelles (for instance Triton X-100 and GT1b) with a high GT1b content. Triton X-100/ganglioside mixed micelles with a molar ratio above 50, as well as small unilamellar vesicles of egg yolk lecithin and GTlb (7-15 mol%), did not inactivate the enzyme at all; on the contrary these forms of ganglioside dispersion behaved as excellent substrates for the enzyme. It is to be concluded that under in vitro conditions the ability of ganglioside to interact with cytosolic sialidase, giving rise to catalytically inactive complexes or to Michaelis-Menten enzyme-substrate complexes, depends on the supramolecular organization of the ganglioside molecules. Arrangements of tightly packed molecules with strong side-side interactions facilitate the formation of complexes with the enzyme; arrangement with separated and loosely interacting molecules facilitates binding at the catalytically active site of the enzyme
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
occurrence of sialyltransferase activity in the synaptosomal membranes prepared from calf brain
No full textThe possible occurrence of sialyltransferase activity in the plasma membranes surrounding nerve endings (synaptosomal membranes) was studied, using calf brain cortex. The synaptosomal membranes were prepared by an improved procedure which provided: (a) a 'nerve ending fraction' consisting of at least 85% well-preserved nerve endings and containing only small quantities of membranes of intracellular origin; (b) a 'synaptosomal membrane fraction' carrying high amounts of authentic plasma membrane markers (Na+-K+ ATPase, 5'-nucleotidase, sialidase, gangliosides) with values of specific activity four to fivefold higher than those in the 'nerve ending fraction' and very small amounts of cerebroside sulphotransferase, marker of the Golgi apparatus, and of other markers of intracellular membranes (rotenone-insensitive NADH and NADPH: cytochrome c reductases), the specific activities of which were, respectively, 0.5- and 0.7-fold that in the 'nerve ending fraction'. Thus the preparation of synaptosomal membranes used had the characteristics of plasma membranes and carried a negligible contamination of membranes of intracellular origin. The distribution of sialyltransferase activity in the main brain subcellular fractions (microsomes; P2 fraction; nerve ending fraction; mitochondria) resembled most closely that of thiamine pyrophosphatase, the enzyme known to be linked to the Golgi apparatus and the plasma membranes and of acetylcholine esterase, the enzyme known to be linked to either intracellular or plasma membranes. The enrichment of sialyltransferase activity in the 'synaptosomal membrane fraction', referred to the 'nerve ending fraction', was practically the same as that exhibited by authentic plasma membrane markers. All this is consistent with the hypothesis that in calf brain cortex sialyltransferase has two different subcellular locations: one at the level of intracellular structures, most likely the Golgi apparatus (as described by other authors), the other in the synaptosomal plasma membranes. The basic properties (pH optimum, V/S, V/t and V/protein relationships) and detergent requirements of the synaptosomal membrane-bound sialyltransferase were established. The highest enzyme activities were recorded on exogenous acceptors, lactosylceramide and DS-fetuin. The K values for CMP-NeuNAc were different using lactosylceramide and DS-fetuin as acceptor substrates (0.57 and 0.135 mM, respectively); the thermal stability of the enzyme acting on glycolipid acceptor was higher than that on the glycoprotein acceptor; the effect of detergents was different when using glycoprotein from glycolipid acceptors; no competition was observed between lactosylceramide and DS-fetuin. Thus the synaptosomal membranes carry at least two different sialyltransferase activities; one acting on lactosylceramide (and glycolipid acceptors), the other working on DS-fetuin (and glycoprotein acceptors). Ganglioside GM3 was recognized as the product of synaptosomal membrane-bound sialyltransferase activity working on lactosylceramide as acceptor substrate
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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