1,721,003 research outputs found
An improved microbial synthesis of purine nucleosides
Get PDFE. coli BL21 synthesized purine nucleosides from pyrimidine ones. A 94% yield of adenosine from uridine was reached within 1 h.Fil: Lewkowicz, Elizabeth Sandra. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes; ArgentinaFil: Martínez, Natalia. Universidad Nacional de Quilmes; ArgentinaFil: Rogert, María C.. Universidad Nacional de Quilmes; ArgentinaFil: Porro, Silvia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes; ArgentinaFil: Iribarren, Adolfo Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; Argentin
Nucleoside Phosphorylases
Get PDFNucleoside phosphorylases (NPs) are transferases that catalyse the reversible cleavage of the glycosidic bond of ribo- or deoxyribo nucleosides, in the presence of inorganic phosphate, to generate the base and ribose- or deoxyribose- 1-phosphate. Since pyrimidine as well as purine nucleoside phosphorylases exist, the combination of both enzymes makes possible the generation of purine nucleosides from pyrimidine ones. As a consequence, NPs from different sources, mainly bacterial, have been exploited as tools for the enzymatic synthesis of nucleoside analogues. These molecules are extensively used as antiviral and anticancer agents because of their ability to act as reverse transcriptase inhibitors or chain terminators in RNA or DNA synthesis. This review covers literature reports from 2000 on, focused mainly on the synthesis of nucleosides by free and immobilised microbial whole cells, along with some examples of modified nucleosides obtained by coupling transglycosylation to other enzymatic reactions. The biological aspects of NPs are also discussed since they became an interesting target for clinical applications due to their key role in nucleotide metabolism. Finally, brief comments about their structures and catalytic mechanisms are included.Fil: Lewkowicz, Elizabeth Sandra. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología; ArgentinaFil: Iribarren, Adolfo Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigación en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres". Grupo Vinculado al INGEBI- Laboratorio de Biocatálisis y Biotransformaciones - LBB - UNQUI; Argentin
Expanding the toolbox for enantioselective sulfide oxidations: Streptomyces strains as biocatalysts
Get PDFSulfide oxidase activity ofStreptomyces genus is reported here for the first time. Three Streptomyces strains were selected as new tools to access to enantioenriched R- and S-dialkyl sulfoxides. The bacterial screening was carried out using cyclohexyl methyl sulfide as model substrate.Both sulfoxide antipodes were obtained in a one-pot, time-dependent biotransformation employing S. phaeochromogenes NCIMB 11741 as biocatalyst. S. flavogriseus ATCC 33331produced mainly the S-enantiomer, while S. hiroshimensis ATCC 27429 yielded enantiopure R-cyclohexyl methyl sulfoxide.Fil: Mascotti, María Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto de Investigaciones en Tecnología Química; ArgentinaFil: Palazzolo, Martín Alejandro. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Area Química. Laboratorio de Biotransformaciones; ArgentinaFil: Lewkowicz, Elizabeth Sandra. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Area Química. Laboratorio de Biotransformaciones; ArgentinaFil: Kurina Sanz, Marcela Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto de Investigaciones en Tecnología Química; Argentin
Screening of Catalytically Active Microorganisms for the Synthesis of 6-Modified Purine Nucleosides
No full textModified nucleosides can be prepared by microbial transglycosylation from cheaper nucleoside precursors using free or immobilised whole cells. An efficient screening method to find transglycosylation activity in microorganisms was developed for the synthesis of 6-modified purine nucleosides, such as 6-chloro-, 6-methoxy-, 6-iodo- and 6-mercaptopurine ribonucleoside. Out of 100 microorganisms screened, Bacillus stearothermophilus (ATCC 12980) was found to be the best strain for this purpose.Fil: Trelles, Jorge Abel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes; ArgentinaFil: Valino, Ana Laura. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes; ArgentinaFil: Runza, V.. Universidad Nacional de Quilmes; ArgentinaFil: Lewkowicz, Elizabeth Sandra. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes; ArgentinaFil: Iribarren, Adolfo Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; Argentina. Universidad Nacional de Quilmes; Argentin
Aldolases : useful enzymes for the synthesis of anticholesterolemic products
No full textFil: Fernández Varela, Romina. Universidad Nacional de Quilmes; Argentina.Fil: Iribarren, Adolfo. Universidad Nacional de Quilmes; Argentina.Fil: Lewkowicz, Elizabeth. Universidad Nacional de Quilmes; Argentina.Las aldolasas – enzimas pertenecientes al grupo de las liasas – son biocatalizadores efectivos para realizar reacciones de adición aldólica en medios acuosos, con elevado rendimiento y alta estereoselectividad. Según el sustrato que utilice la enzima, las aldolasas se clasifican en cinco tipos. En particular, 2-desoxy-D-ribosa-5-fosfato aldolasa (DERA) es la única aldolasa capaz de aceptar acetaldehído como sustrato dador nucleofílico. A la vez, se ha comprobado que DERA es capaz de catalizar una doble adición empleando tres moléculas de acetaldehído cuando éste es el único sustrato. Esta particularidad ha hecho que, en los últimos años, DERA sea utilizada en la síntesis de estatinas, drogas empleadas para el control del nivel de colesterol en sangre. Constantemente se invierten esfuerzos para lograr estructuras análogas que reduzcan efectos secundarios adversos y que resulten más potentes médicamente. En nuestro laboratorio se están desarrollando nuevos análogos de estatinas empleando DERA de Pectobacterium atrosepticum.Aldolases, enzymes that belong to the group of lyases, are useful biocatalysts to perform aldol addition reactions in aqueous media, in high yields and stereo selectively. According to the donor substrate, aldolases are classified into five types. In particular, 2-deoxy-D-ribose-5-phosphate aldolase (DERA) is the only aldolase capable of accepting acetaldehyde as donor substrate. In addition, it has been shown that when acetaldehyde is the only availabre substrate, DERA is able to catalyze a double aldol addition using three acetaldehyde molecules.. As a result, in recent years, DERA has been employed for the synthesis of statins, drugs used to control cholesterol level in blood. Efforts are constantly being made to achieve new structures with fewer adverse side effects and improved medicinal efficiency. In our laboratory we are developing new statin analogs using DERA from Pectobacterium atrosepticum
Citrobacter koseri immobilized on agarose beads for nucleoside synthesis: a potential biocatalyst for preparative applications
No full textThe biocatalyzed synthesis of purine nucleosides and their analogs is a case widely studied due to the high pharmaceutical interest of these compounds, providing the whole-cell biocatalysts, a useful tool for this purpose. Vidarabine and fludarabine are commercial examples of expensive bioactive nucleosides that can be prepared using a microbial transglycosylation approach. Citrobacter koseri whole-cells immobilized on agarose beads proved to be an interesting option to transform this biotransformation in a preparative process. The entrapment matrix provided a useful and resistant multipurpose biocatalyst regarding its stability, mechanical strength, microbial viability and reuse. Immobilized biocatalyst retained the initial activity for up to 1 year storage and after 10 years, the biocatalyst did not show cell leaking and still exhibited residual activity. In addition, the biocatalyst could be reused in batch 68 times keeping up to 50% of the initial biocatalytic activity and for at least 124 h in a continuous process.Fil: Nóbile, Matías Leonardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología; ArgentinaFil: Iribarren, Adolfo Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología; ArgentinaFil: Lewkowicz, Elizabeth Sandra. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología; Argentin
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
New biocatalysts for one pot multistep enzymatic synthesis of pyrimidine nucleoside diphosphates from readily available reagents
No full textSince the preparation of nucleoside 5′-diphosphates by classical methodologies is complex, multistep enzymatic systems were explored to synthesize pyrimidine nucleoside 5′-diphosphates starting from readily available reagents. Different strategies were combined to prepare uridine- and thymidine 5′-diphosphates as ribo- and deoxyribonucleoside models, respectively. For uridine 5′-diphosphate synthesis, conversions between 38 and 66% were achieved, using a simple methodology that involves commercial yeast extract as biocatalyst and biocatalytically in situ prepared uridine 5′-monophosphate. Corynebacterium ammoniagenes ATCC 19350 was used for the first time as biocatalyst to synthesize uridine 5′-monophosphate from uracil and orotic acid while Raoultella planticola was the selected biocatalyst for uridine 5′-monophosphate synthesis from uridine. The overall performances of all the tested approaches were similar but the use of uracil leads to a more suitable and cheaper process. Alternatively, for thymidine 5′-diphosphate synthesis two consecutive one pot multistep enzyme systems were assayed. In the first biotransformation, 2′-deoxyribose 5-phosphate was formed from glucose by Erwinia carotovora whole cells followed by the action of phosphopentomutase and thymidine phosphorylase affording thymidine in 85% conversion relative to 2′-deoxyribose 5-phosphate. Finally, in the second one pot reaction, the nucleoside was converted to thymidine 5′-diphosphate by the combined action of Escherichia coli BL21 pET22b-phoRp and Saccharomyces cerevisiae.Fil: Valino, Ana Laura. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Area Química. Laboratorio de Biotransformaciones; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Iribarren, Adolfo Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; ArgentinaFil: Lewkowicz, Elizabeth Sandra. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Area Química. Laboratorio de Biotransformaciones; Argentin
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