1,720,960 research outputs found
Chemo-enzymatic synthesis of antiviral prodrugs
Get PDFLipases have been widely applied in the manufacture of food products and in some areas of the industry, nowadays they are used in synthetic organic chemistry catalyzing the hydrolytic/esterification reactions under very mild conditions in the field of protecting groups or enantiomer resolution. In this study, the commercial lipase from bacterium Pseudomonas fluorescens was immobilized using the sol-gel process into organosilicate materials with propyl, octyl or phenyl substituents. The highest hydrolytic activity was found in the enzyme on the octyl-derived carrier. The immobilized enzymes differ in their hydrolytic activities on 4-nitrophenyl esters of various lengths. Subsequent experiments revealed quite good pH stability of the enzymes in a buffer (incubations in pH 3 through pH 11), as well as good temperature stability in isooctane (incubations at up to 100 řC). The majority of organic solvents seem to have no substantial effect on the lipase activity. The biocatalytic properties were studied on a model compound from the group of the acyclic nucleoside analogues - 9-(2',3'-dihydroxypropyl)adenine (DHPA). It was found for example that the best acyl donors are vinyl esters, that the lipase shows a preference towards longer vinyl esters, that the reaction proceeds faster in non-polar solvents or that it..
Funkční analýza hmyzích reduktáz a desaturáz mastných acylkoenzymů A
Get PDFLipidy odvozené od mastných kyselin představují důležité biomolekuly. Kromě své hlavní role při stavbě buněk, ukládání energie a signalizaci, slouží celé řadě dalších funkcí, např. jako izolační či nesmáčivé povrchy, obranné látky a feromony. Na úpravách intermediátů vznikajících při biosyn- téze mastných kyselin se podílí celá řada enzymů, mezi něž se řadí např. i desaturázy, které syn- tetizují nenasycené mastné kyseliny, a reduktázy, jež syntetizují mastné alkoholy. Funkčně vysoce diverzifikované desaturázy a reduktázy z hmyzu, jakožto jedněch z nejhojněji zastoupených zvířat na světe, představují podstatný zdroj pro moderní biotechnologii buněčných továren. Tato práce shrnuje dostupné informace o reduktázách a desaturázách a popisuje výsledky, které jsme při jejich studiu získali. U čmeláků jsme identifikovali několik reduktázových transkriptů, jež jsou hojně zastoupeny v samčí feromonové žláze. Příslušné enzymy jsme následně funkčně charakterizovali v kvasinkách a odhadli jejich zapojení do biosyntézy mastných alkoholů v tkáni produkující značkovací feromon. Studované enzymy redukují širokou řadu substrátů, od krátkých mastných acylů (C14) až po velmi dlouhé (C26), od nasycených mastných acylů po polynenasycené. Dále jsme poukázali na to, že na expanzi a následném funkčním rozrůznění čmeláčích...Fatty acid-derived lipids are an important class of biomolecules. In addition to their primary role in cellular architecture, energy storage and signaling, they function in many other ways, e.g. as isolating or waterproof coatings, defense compounds and pheromones. Multiple enzymes mod- ify intermediates originating from fatty acid biosynthetic pathway, including desaturases (FADs) which synthesize unsaturated fatty acids, and reductases (FARs) which synthesize fatty alcohols. Functionally highly diversified fatty acyl-modifying enzymes from insects, one of the most abun- dant animals in the world, present a significant source for modern biotechnology of cell factories. This thesis summarizes available information on the FADs and FARs and describes the results which we have obtained while studying them. In bumblebees, we identified several FAR transcripts which are abundantly expressed in male pheromone-producing tissue. We then functionally characterized the corresponding enzymes in yeasts, and estimated their participation in the biosynthesis of fatty alcohols observed in the mark- ing pheromone-producing tissue. The studied enzymes reduce broad range of substrates, from short fatty acyls (e.g. C14) to very long ones (e.g. C26), from saturated fatty acyls to polyunsatu- rated ones. We also found...Katedra biochemieDepartment of BiochemistryPřírodovědecká fakultaFaculty of Scienc
Functional analysis of insect fatty acyl-coenzyme A reductases and desaturases
No full textFatty acid-derived lipids are an important class of biomolecules. In addition to their primary role in cellular architecture, energy storage and signaling, they function in many other ways, e.g. as isolating or waterproof coatings, defense compounds and pheromones. Multiple enzymes mod- ify intermediates originating from fatty acid biosynthetic pathway, including desaturases (FADs) which synthesize unsaturated fatty acids, and reductases (FARs) which synthesize fatty alcohols. Functionally highly diversified fatty acyl-modifying enzymes from insects, one of the most abun- dant animals in the world, present a significant source for modern biotechnology of cell factories. This thesis summarizes available information on the FADs and FARs and describes the results which we have obtained while studying them. In bumblebees, we identified several FAR transcripts which are abundantly expressed in male pheromone-producing tissue. We then functionally characterized the corresponding enzymes in yeasts, and estimated their participation in the biosynthesis of fatty alcohols observed in the mark- ing pheromone-producing tissue. The studied enzymes reduce broad range of substrates, from short fatty acyls (e.g. C14) to very long ones (e.g. C26), from saturated fatty acyls to polyunsatu- rated ones. We also found..
Antioxidant properties of medicinal plants
Get PDFDuring the evolution plants have developed rather efficient mechanisms for the re- moval of harmful compounds, which include e. g. the reactive oxygen species (ROS). These mechanisms are mainly based on the antioxidant effects of ascorbic acid, gluta- thione in intimate cooperation with superoxide dismutase, catalase and various perox- idases - the reduced coenzymes, NADH and NADPH, play a major role in the ROS elimination, too. However, in recent times, the attention has turned from these key compounds of primary metabolism to secondary metabolites. Interestingly, the phenolic com- pounds together with some terpenes and alkaloids exhibit antioxidant effects, too, and apparently they play an irreplaceable role in the life of a plant - besides their antiox- idant action they are also important in the fight against pathogens and herbivores, in attracting the pollinators or in the moderation of UV light effects. Natural products are also studied in their relation to man - a broad variety of effects is known including the antioxidant, anti-inflammatory and anticancer effects for the most part. In this work, extracts comprising mainly of low-molecular-weight compounds were obtained from 32 plants with either hot water, 80 %w aqueous methanol or just by plain juicing. The extracts were then examined by three..
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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