1,720,972 research outputs found
Analytical and preparative isoelectric focusing of peptides in immobilized pH gradients
No full textA new method for peptide analysis and purification is described, based on isoelectric focusing in immobilized pH gradients. On the analytical scale, the peptide zones can now be revealed by an stain for primary and secondary amino group (e.g. ninydrin, fluorescamine, dansyl chloride) since the buffering species, unlike conventional carrier ampholytes, contain only carboxyl and tertiary amino groups. For preparative purposes, conditions have been described to remove most contaminants (e.g. unreacted monomers, non-cross-linked, short polyacrylamide chains) from the gel matrix before the electrophoretic run. However, ca. 2% of the gel dry mass is still present as extractable material. The focused peptides can be recovered in higly yields (ca. 90%) with a fairly high degree of purity (75%), the contaminants being mostly components eluted from the polyacrylamide gel
Isoelectric focusing of oligopeptides: Detections by specific stains
No full textBy using ultrathin (350 μm) polyacrylamide gels, which at the end of the fractionation are pasted to filter paper and dried in an oven at 110°C, and after isoelectric focusing it has been possible to detect oligopeptides in the di- to tetradecapeptide range, which could not be detected by protein staining techniques. This is achieved by developing a series of specific stains for the following amino acid: Arg, Tyr, His, Trp, Met and Cys. Except for Met and Cys, the detection limits appear to be in the order of 0.2-2 μg of free amino acid loaded in the gel. The Pauli reaction for His and Tyr and the Sakaguchi stain for Arg can be developed sequentially in the same gel, thus allowing the detection of four different amino acids since, under these conditions, also Trp reacts. Unfortunately, more general reactions, such as the permanganage, the "Lowry" and the ninhydrin stains, cannot be utilized since the carrier ampholytes react very strongly with all these reagents
Angiosuppressive and angiostimulatory effects exerted by synthetic partial sequences of endostatin
No full textPurpose: Endostatin, a peptide derived from proteolysis
of collagen XVIII, is an endogenous inhibitor of angiogenesis
and tumor growth. We have synthesized five peptide fragments
designed to cover the whole length of the endostatin
molecule (containing 40–50 amino acids each) with the aim
of exploring the possibility that a specific sequence within
the molecule might be responsible for its antiangiogenic
effects.
Experimental Design: The five peptide sequences,
termed fragments I, II, III, IV, and IVox, the latter bearing
the original disulfide bond Cys135-Cys165, were investigated
for their effects on cultured endothelial cells, on enzyme
activities related to angiogenesis, on tube formation in threedimensional
gel matrices, in vivo in the avascular rabbit
cornea assay, and in an experimental tumor burden paradigm.
Results: Both the fragment covering the COOH-terminal
endostatin region, fragment IV, and particularly fragment
IVox, retained the angioinhibitory effects of endostatin.
Fragment IVox strongly inhibited endothelial cell
migration and proliferation, in vitro tube formation, and in
vivo angiogenesis, displaying a potency comparable with
that of endostatin. When tested in vivo on tumor growth,
fragment IVox demonstrated to be more effective than fulllength
endostatin. Unexpectedly, fragment III exhibited
proangiogenic activity, increasing endothelial cell migration,
producing neovascularization to an extent similar to that of
vascular endothelial growth factor, and enhancing the angiogenic
response to vascular endothelial growth factor in
the cornea assay. Peptides encompassing the NH2-terminal
region of endostatin (fragments I and II) had negligible
effects on angiogenesis.
Conclusions: In view of these results, which show strikingly
distinct profiles of endostatin fragments, we propose
that the amino acid sequence of endostatin contains both
angiosuppressive and angiostimulatory domains
Human endostatin-derived synthetic peptides possess potent antiangiogenic properties in vitro and in vivo
No full textPharmacological control of the angiogenic process (i.e., the neovascularization necessary for the growth and progression of tumors and metastases) is considered to be one of the most promising approaches to antineoplastic therapy. Endostatin, a 20-kDa protein derived from collagen XVIII, is one of the first recently discovered endogeneous antiangiogenic substances, but its cell targets and mechanism(s) of action are still unknown. We thought it would be interesting to test whether shorter peptides derived from endostatin might preserve its antiangiogenic activity. Four synthetic peptides corresponding to the sequences 6-49 (I), 50-92 (II), 93-133 (III), and 134-178 (IV) of human endostatin were tested for their ability to inhibit endothelial cell proliferation, migration, and both in vitro and in vivo angiogenesis. Fragment I (and fragment IV in the tests performed) was found to be fully biologically active in all of the angiogenesis assays, and sometimes showed even greater potency and efficacy than full-length human endostatin itself
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
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