1,721,036 research outputs found
Capillary isoelectric focusing and isoelectric buffers: an evolving scenario.
No full textThe present review offers a new look at capillary isoelectric focusing (cIEF) by centering on the most troublesome aspects of the technique, namely: 1) how to modulate the slope of the pH gradient, for increasing resolution (equivalent to pH gradient engineering, as easily available in immobilized pH gradients); and 2) how to keep proteins in solution at (and in the proximity of) the pl value. A simple solution is offered in the first case: addition, to the standard 2-pH-units interval, of separators or spacers, i.e., of amphoteric molecules (either single or in combination) able to locally flatten the pH and increment resolution. Examples of the separation of fetal and glycated hemoglobins are provided. In the second case, a unique solubilization power (while maintaining full protein integrity and enzyme activity) is obtained if class I solubilizers are used. They consist of mixtures of sugars (e.g., sucrose and sorbitol) at ca. 1 M concentration, with zwitterions (up to 1 M) such as the class of nondetergent sulfobetaines, but also taurine and some of the Good's buffers (e.g., CAPS). In these solvents, the protein exists in a state of superhydration and its solubility is greatly augmented. The review ends with an excursus on the use of isoelectric buffers in zone electrophoretic separations. Such isoelectric buffers offer unique advantages: They permit very-high-voltage gradients (up to 1000 V/cm) and thus minimize analysis times (down to a few min in 30-35 cm long capillaries). This results in a marked increase in resolution, due to minimal diffusion-driven peak spreading. Such buffers are finding unique applications for generating peptide maps of tryptic digests of proteins and also in the analysis of oligonucleotides
Isoelectric focusing of histones in extremely alkaline immobilized pH gradients: comparison with capillary electrophoresis.
No full textVarious classes of calf thymus histones (fractions II-AS, VI-S, VII-S and VIII-S) were separated to the steady state in an extremely alkaline immobilized pH gradient, covering non-linearly the pH 10-12 interval. Successful separations were obtained in 5%T, 4%C polyacrylamide matrices, reswollen in 8 M urea, 1.5% Tween 20, 1.5% Nonidet P-40 and 0.5% Ampholine pH 9-11. Additionally, in order to quench the very high conductivity of the gel region on the cathodic side, the reswelling solution contained a 0-10% (anode to cathode) sorbitol gradient. The best focusing was obtained by running the gel at 17 degrees C, instead of the customary 10 degrees C. All major histone components had pi values between pH 11 and 12 and only minor components (possibly acetylated and phosphorylated forms) focused below pH 11. By summing up all bands in Arg- and Lys-rich fractions, eight to ten major components and at least twelve minor zones are clearly resolved. In contrast, capillary zone electrophoresis (in a coated capillary, 7 M urea, 50 mM Tris-acetate buffer, pH 8.0) can only resolve six major fractions and two minor, broad zones
Toward a mitochondrial therapy of collagen VI muscular dystrophies (TELETHON GRANT GGPO8107)
No full textMuscular dystrophies are genetic, progressive diseases for which no therapy is currently available. We have
discovered why muscle fibers degenerate in two human muscular dystrophies caused by abnormalities of
Collagen VI, Ullrich Congenital Muscular Dystrophy (UCMD) and Bethlem Myopathy (BM). The absence
of Collagen VI has a major impact inside the fibers by triggering a short circuit in the cell’s energy
generators, the mitochondria. This short circuit is caused by opening of a channel called the “Permeability
Transition Pore” (PTP), which can be inhibited by the drug cyclosporin A (CsA). We have blocked the
short circuit and cured the disease in a mouse lacking Collagen VI; and we have shown that cells from
patients affected by UCMD and BM also respond to CsA. A short−term pilot trial with CsA in patients
affected by UCMD and BM has provided encouraging results, but long−term use of CsA may expose the
patients to the risks of immunosuppression. To overcome this hurdle we will test the efficacy of a derivative
of CsA that inhibits the PTP but does not cause immunosuppression, and which we have already shown to
be effective in curing the patients’ cells in vitro. We will also identify further potential targets for
pharmacological intervention, with the goal of providing an effective treatment for human Collagen VI
muscular dystrophies
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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