1,720,975 research outputs found
Kinetic properties of native and mutagenized isoforms of mitochondrial alcohol dehydrogenase III purified from Kluyveromyces lactis
No full textBy computer modelling and protein engineering we have investigated changes in two amino acid residues located in the coenzyme pocket of the yeast Kluyveromyces lactis mitochondrial alcohol dehydrogenase III. These two residues, Gly 225 and Ala 274, were hypothesized to be involved in the enzyme discrimination between NAD(H) and NADP(H). Upon changing Gly 225 to Ala we produced an enzyme (mutant G225A) showing very little difference from the wild-type. On the contrary, change at position 274 of Phe instead of Ala (mutantA274F) caused a significant increase of K, values for NAD(P) and for NADPH and even a more marked decrease in catalytic activity. The k(cat)/K-m rates for NADP(H) were also decreased in this mutant. Enzymes with the double changes at 225 and 274 (mutant G225A-A274F) showed, apart the substantial low K, value for NADPH and its high catalytic efficiency, kinetic parameters relative to coenzymes which were not additive over the single substitutions. Surprisingly, enzymes with changes at the two positions reduced efficiently acetaldehyde, displaying a K, value 10-fold lower and a catalytic efficiency sevenfold higher with respect to parent or singularly mutated enzymes. None of the engineered enzymes would convert formaldehyde, glutaraldehyde or aromatic aldehydes but all enzymes reduced propionaldehyde and butyraldehyde at relative reaction rates approximately half of that exhibited by acetaldehyde. Interestingly only mutant A274F was able to oxidize methanol almost as well as ethanol. In addition, this mutant was capable to convert secondary and cyclic alcohols, at a rate not detected in the other isoforms. These results are in general agreement with the prediction that increasing the size of amino acids in the proximity of the coenzyme pocket would hamper the accommodation of NADP but discord the increased affinity for NADPH as well as for alcoholic or aldehydic substrates with high steric hindrance. (C) 2004 Elsevier SAS. All rights reserved
Folding propensity and biological activity of peptides: The effect of a single stereochemical isomerization on the conformational properties of bombinins in aqueous solution
No full textFolding propensities of bombinins H2 and H4, two members of amphibian bombinins H, a family of 17–20 residue a-helical peptides, have been investigated by means of circular dichroism (CD) measurements and molecular dynamics (MD) simulations. The two peptides, with primary structure IIGPVLGLVGSALGGLLKKI- NH2 and differing only for the configuration of the second aminoacid (an L-isoleucine in H2 and a D-alloisoleucine in H4) behave rather differently in solution. In particular both CD measurements and MD simulations indicate that bombinin H2 shows a markedly higher tendency to fold. From a careful inspection of MD trajectories it emerges that the stereochemical isomerization mutation of residue 2 to D-alloisoleucine in H4 peptide, drastically decreases its ability to form intrapeptide contacts. MD simulations also indicate that the conformational sampling in both systems derives from a subtle combination of energetic and entropic effects both involving the peptide itself and the solvent. The present results have been finally paralleled with preliminary information on bombinins H2 and H4 biological activity, i.e. interaction with membrane, supporting the hypothesis of an ‘‘already folded’’ conformation in water rather than interfacial folding tenet
Multiple unfolded states of alcohol dehydrogenase I from Kluyveromyces lactis by guanidinium chloride
No full textInactivation, dissociation, and unfolding of tetrameric alcohol dehydrogenase I from Kluyverpmyces lactis (KIADH I) were investigated using guanidinium chloride (GdmCl) as denaturant. Protein transitions were monitored by enzyme activity, intrinsic fluorescence and gel filtration chromatography. At low denaturant concentrations (less than 0.3 M), reversible transformation of enzyme into tetrameric inactive form occurs. At denaturant concentrations between 0.3 and 0.5 M, the enzyme progressively dissociates into structured monomers through an irreversible reaction. At higher denaturant concentrations, the monomers unfold completely. Refolding studies indicate that a total reactivation occurs only with the enzyme denatured between 0 and 0.3 M GdmCl concentrations. The enzyme denatured at GdmC1 concentrations higher than 0.3 M refolds only partially. All together, our results indicate that unfolding of the KIADH I is a multistep process, i.e., inactivation of the structured tetramer, dissociation into partially structured monomers, followed by complete unfolding. (C) 2001 Elsevier Science B.V. All rights reserved
The P-113 peptide: new experimental evidences on its biological activity and conformational insights from Molecular Dynamics simulations
No full textIn this article, we report novel and additional results, both experimental and computational, obtained in our laboratories on the peptide P-113. In particular, our experimental results indicate that this peptide is endowed with a high target-cell selectivity towards yeast species, suggesting its potential development as a new drug against oral microbial infections. To provide additional structural insights, we performed several Molecular Dynamics simulations in different conditions. Results suggest that P-113 is a rather compact species presumably because of its highly charged state as emerged from the dramatic increase of internal fluctuation occurring upon point-mutation. The peptide turns out to adopt, in water, a beta-hairpin-like conformation and, in a more hydrophobic environment, is found to be in a (probably slow) equilibrium between α-helix and hairpin conformations. Complexation with Zn(2+) induces a drastic mechanical stabilization, which prevents any conformational organization of the peptide into a biologically active state.In this article, we report novel and additional results, both experimental and computational, obtained in our laboratories on the peptide P-113. In particular, our experimental results indicate that this peptide is endowed with a high target-cell selectivity towards yeast species, suggesting its potential development as a new drug against oral microbial infections. To provide additional structural insights, we performed several Molecular Dynamics simulations in different conditions. Results suggest that P-113 is a rather compact species presumably because of its highly charged state as emerged from the dramatic increase of internal fluctuation occurring upon point-mutation. The peptide turns out to adopt, in water, a beta-hairpin-like conformation and, in a more hydrophobic environment, is found to be in a (probably slow) equilibrium between α-helix and hairpin conformations. Complexation with Zn(2+) induces a drastic mechanical stabilization, which prevents any conformational organiz
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
Temporin L: antimicrobial, haemolytic and cytotoxic activities, and effects on membrane permeabilization in lipid vesicles
No full textThe temporins are a family of small, linear antibiotic peptides with intriguing biological properties. We investigated the antibacterial, haemolytic and cytotoxic activities of temporin L (FVQWFSKFLGRIL-NH2), isolated from the skin of the European red frog Rana temporaria. The peptide displayed the highest activity of temporins studied to date, against both human erythrocytes and bacterial and fungal strains. At variance with other known temporins, which are mainly active against Gram-positive bacteria, temporin L was also active against Gram-negative strains such as Pseudomonas aeruginosa A.T.C.C. 15692 and Escherichia coli D21 at concentrations comparable with those that are microbiocidal to Gram-positive bacteria. In addition, temporin L was cytotoxic to three different human tumour cell lines (Hut-78, K-562 and U-937), causing a necrosis-like cell death, although sensitivity to the peptide varied markedly with the specific cell line tested. A study of the interaction of temporin L with liposomes of different lipid compositions revealed that the peptide causes perturbation of bilayer integrity of both neutral and negatively charged membranes, as revealed by the release of a vesicle-encapsulated fluorescent marker, and that the action of the peptide is modulated to some extent by membrane lipid composition. In particular, the presence of negatively charged lipids, in the model bilayer inhibits the lytic power of temporin L. We also show that the release of fluorescent markers caused by temporin L is size-dependent and that the peptide does not have a detergent-like effect on the membrane, suggesting that perturbation of bilayer organization takes place on a local scale, i.e. through the formation of pore-like openings
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
- …
