1,721,056 research outputs found
Origin of the ribosome factors responsible for peptide chain elongation in yeast
No full textThe data reported in the present paper sugges that in yeast the genetic information for polypetide chain elongation factors is encoded in the nuclear DNA and that such information is translated on the cytoplasmic ribosome
Dihydrofolate reductase from Daucus carota cell suspension cultures: purification, molecular and kinetic characterization
No full textThe purification of dihydrofolate reductase (5, 6, 7, 8 tetrahydrofolate: NADP+ oxidoreductase, E.C.: 1.5.1.3) from Daucus carota to apparent homogeneity, is described. The enzyme is a soluble protein with a molecular weight of 183 000k +-2500, composed of identical subunits of 58 400+-1000. The enzyme is only
weakly recognized by antibodies against human DHFR. The carrot DHFR is characterized by a pH optimum of 5.9, Km values for dihydrofolate and NADPH of 3.7 μM and 2.2 μM, respectively and a turnover number of 4750 or 1500 when referring to the 183 K form or the 58 K monomer, respectively. Molecular and kinetic properties are remarkably different from those reported for the soybean enzyme. Sensitivity to methotrexate is similar to that of bacterial and mammalian enzymes while sensitivity to trimethoprim and dihydrotriazine is intermediate between the two groups of organisms
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
5-Enol-pyruvyl-shikimate-3-phosphate synthase from Zea mays cultured cells: purification and properties
No full textThe shikimate pathway enzyme 5-enol-pyruvyl-shikimate-3-phosphate (EPSP) synthase (3-phosphoshikimate-1-carboxyvinyl transferase, EC 2.5.1.19) was purified from cultured maize (Zea mays L. var Black Mexican Sweet) cells. Homogeneous enzyme preparations were obtained by a four-step procedure using ammonium sulfate fractionation, anion- and cation-exchange chromatography, and substrate elution from a cellulose phosphate column. The last step resulted in two well-separated activities of about the same molecular weight. A 2000- to 3000-fold purification, with an overall recovery of one-fourth of the initial activity, was achieved. Both EPSP synthase isoforms were characterized with respect to structural, kinetic, and biochemical properties. Only slight differences are seen in molecular mass, activation energy, and apparent affinities for the two substrates. A more pronounced difference was found between their thermal inactivation rates. Two EPSP synthase isoforms were also elucidated in crude homogenates by anion-exchange fast protein liquid chromatography. This allowed us to follow their expression during a culture growth cycle. One form was found at substantial levels throughout, whereas the other increased in exponentially growing cells and declined in late-logarithmic phase. The analysis of highly purified plastid preparations demonstrated a plastidial localization of both proteins. Possible functional roles for maize EPSP synthase isozymes, with regard to the dual-pathway hypothesis and to the recent findings on defense-related aromatic biosynthesis in higher plants, are discussed
5-enolpyruvyl-shikimate-3-phosphate synthase from Zea mays cultured cells: purification and properties.
No full textThe shikimate pathway enzyme 5-enol-pyruvyl-shikimate-3-phosphate (EPSP) synthase (3-phosphoshikimate-1-carboxyvinyl transferase, EC 2.5.1.19) was purified from cultured maize (Zea mays L. var Black Mexican Sweet) cells. Homogeneous enzyme preparations were obtained by a four-step procedure using ammonium sulfate fractionation, anion- and cation-exchange chromatography, and substrate elution from a cellulose phosphate column. The last step resulted in two well-separated activities of about the same molecular weight. A 2000- to 3000-fold purification, with an overall recovery of one-fourth of the initial activity, was achieved. Both EPSP synthase isoforms were characterized with respect to structural, kinetic, and biochemical properties. Only slight differences are seen in molecular mass, activation energy, and apparent affinities for the two substrates. A more pronounced difference was found between their thermal inactivation rates. Two EPSP synthase isoforms were also elucidated in crude homogenates by anion-exchange fast protein liquid chromatography. This allowed us to follow their expression during a culture growth cycle. One form was found at substantial levels throughout, whereas the other increased in exponentially growing cells and declined in late-logarithmic phase. The analysis of highly purified plastid preparations demonstrated a plastidial localization of both proteins. Possible functional roles for maize EPSP synthase isozymes, with regard to the dual-pathway hypothesis and to the recent findings on defense-related aromatic biosynthesis in higher plants, are discusse
Dihydrofolate reductase of plant cells: purification and characterization of the carrot enzyme
No full textDihydrofolate reductase and thymidylate synthase in plants: an open problem.
Full text linkThis review deals with recent findings in tlie purification and characterization of dihydrofolate reductase (DHFR) and thymidylate synthase (TS) in plants. The few enzymes purified, which differ remarkably in regard to their structure, kinetic and molecular properties and subcellular location are described. The response of DHFRs to antifolic agents and the analysis of resistance mechanisms in isolated cell lines is also reported. Problems opened by recent studies of the enzymes isolated from plants are outlined
Daucus carota cells contain a diydrofolate reductase:thymidylate synthase bifunctional polypeptide
No full textDihydrofolate reductase (DHFR) and thymidylate synthase (TS) activities from cell suspension cultures of Daucus carota were shown to copurify on (NH4)2S04 fractionation, DEAE Sephadex and methotrexate- Sepharose affinity chromatography and to share approximately the same M, (183 kDa and 185 kDa respectively)
as judged by gel filtration on Sephacryl S-200. The copurified protein migrated as a single band on polyacrylamide gel electrophoresis under denaturing conditions. Both activities could be eluted from the same position of the native gel.
Moreover, methotrexate-resistant cell lines which overproduce DHFR revealed to have a parallel higher level of TS. It is therefore proposed and discussed that in carrot, similarly to protozoa, TS and DHER are present on a single bifunctional polypeptide of 58 kDa
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