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1Author    Remigius Manderscheid, Aloysius WildRequires cookie*
 Title    Characterization of Glutamine Synthetase of Roots, Etiolated Cotyledons and Green Leaves from Sinapis alba (L.)  
 Abstract    Glutamine synthetase of roots, etiolated cotyledons and green leaves from mustard plants cannot all clearly be separated by DEAE-Sephacel chromatography. However, the enzyme of the roots, etiolated cotyledons and green leaves, respectively, differed in the kinetic properties deter­ mined in the crude extract. The root enzyme showed a pH-optimum of about 6.9, a K m value of 3 m M for glutamate and a temperature optimum at 48 °C. Glutamine synthetase of etiolated cotyledons possessed a Km for glutamate of 6 or 12 m M , depending on the dithioerythritol con­ centration in the homogenisation buffer and a temperature optimum at 46 °C. The enzyme of green leaves was characterized by a temperature optimum at 40 °C, a pH-optimum at about 7.4 and a low glutamate affinity with positive cooperative substrate binding. Based on isolation of chloroplasts and identification of glutamine synthetase the enzyme of green leaves seems to be the chloroplastic form. This enzyme was purified by DEAE-Sephacel, hydroxylapatite and Sephacryl S-300 chromatography. Affinity for glutamate and M g S04 of the purified enzyme differed from that found in the crude extract. The function of the different isoenzymes is discussed. Intro du ction 
  Reference    Z. Naturforsch. 41c, 712 (1986); received March 17 1986 
  Published    1986 
  Keywords    Enzyme Purification, Glutamine Synthetase, Isoenzymes, Photorespiration, Sinapis alba 
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 TEI-XML for    default:Reihe_C/41/ZNC-1986-41c-0712.pdf 
 Identifier    ZNC-1986-41c-0712 
 Volume    41 
2Author    Matthias Höpfner, Georg Reifferscheid, Aloysius WildRequires cookie*
 Title    Molecular Composition of Glutamine Synthetase of Sinapis alba L  
 Abstract    Chloroplastic glutamine synthetase of Sinapis alba, purified to homogeneity by a simple three step procedure, revealed a molecular weight of about 395 kDa. The native enzyme is composed of eight subunits of identical molecular weight (about 50 kDa (each), although isoelectrofocusing yielded six distinct bands in the pH 5.6 region of the gel. Labelling of the enzyme with the glutamate analogue herbicide [ 14 C]phosphinothricin and with [y-32 P]ATP indicated that glutamine synthetase has eight reactive centers per molecule. The native enzyme dissociated into two enzymatically active subaggregates of about 195 kDa after Mg 2+ deprivation. 
  Reference    Z. Naturforsch. 43c, 194—198 (1988); received November 26 1987 
  Published    1988 
  Keywords    Active Centers, Enzyme Purification, Enzyme Structure, Glufosinate, Glutamine Synthetase, Phosphinothricin 
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 TEI-XML for    default:Reihe_C/43/ZNC-1988-43c-0194.pdf 
 Identifier    ZNC-1988-43c-0194 
 Volume    43 
3Author    Kassem Alef, Hans-Joachim Burkardt, Hans-Joachim Horstmann, WalterG. ZumftRequires cookie*
 Title    Molecular Characterization of Glutamine Synthetase from the Nitrogen-Fixing Phototrophic Bacterium Rhodopseudomonas palustris1  
 Abstract    The phototrophic bacterium Rhodopseudomonas palustris assimilated ammonium via glutamine synthetase and glutamate synthase. Diazotrophic and ammonium-grown cells had high levels of both enzymes, whereas enzymes o f alternative assimilatory pathways were absent or had only low activities. Glutamine synthetase was purified to electrophoretic homogeneity within three steps by dye-ligand and ion exchange chromatography. Electron microscopy revealed a dodecameric molecular entity which was in accordance with parameters derived from electrophoretic techniques. The molecular weight of the enzyme monomer was 55800; that o f the dodecamer 670000. The amino acid composition o f R. palustris glutamine synthetase was determined and compared by a statistical method with other known enzyme compositions from prokaryotic and eukaryotic origins. 
  Reference    Z. Naturforsch. 36c, 246—254 (1981); received December 231980 
  Published    1981 
  Keywords    Rhodopseudomonas palustris, Glutamine Synthetase, Dye-Ligand Chromatography, Nitrogen Fixation, Ammonium Assimilation 
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 TEI-XML for    default:Reihe_C/36/ZNC-1981-36c-0246.pdf 
 Identifier    ZNC-1981-36c-0246 
 Volume    36 
4Author    F. L. FigueroaRequires cookie*
 Title    Photoregulation of Nitrogen Metabolism and Protein Accumulation in the Red Alga Corallina elongata Ellis et Soland  
 Abstract    Reductase Red and blue light pulses of 5 min applied together with 45 (aM K N 0 3 stimulated the nitrate uptake and reduction and the assimilation of ammonium in darkness in the red alga Corallina elongata. N itrate reductase and glutamine synthetase activities were increased in darkness after the application of both red and blue light pulses. Red light produced a dram atic increase in enzyme activities after the first hour in darkness but after 4 h the effect of blue light pulses was greater. The photostim ulation of nitrogen metabolism was correlated with light-regulated accumulation of soluble proteins. Nitrogen incorporation, assimilation of am monium, accu­ m ulation of total proteins and the increment in total intracellular nitrogen was greater in N-limited algae (C :N = 17.3) than in N-sufficient algae (C :N = 10.3) after the application of light pulses and nitrate. Because the stimulant effects o f red and blue light on N-metabolism were partially reversed by far-red light, the possible involvement o f the photoreversible red/ far-red photoreceptor, phytochrom e, is proposed. In addition, the blue-light effect seems to be mediated by a specific B-light photoreceptor besides phytochrome due to the different time course of the response and the extent of the stimulation after blue compared to red light pulses. 
  Reference    Z. Naturforsch. 48c, 788—794 (1993); received June 15/ 
  Published    1993 
  Keywords    Blue-Light Photoreceptor, Corallina elongata, Glutamine Synthetase, Light Quality, N itrate 
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 TEI-XML for    default:Reihe_C/48/ZNC-1993-48c-0788.pdf 
 Identifier    ZNC-1993-48c-0788 
 Volume    48 
5Author    Gottfried Martin, Peter BögerRequires cookie*
 Title    Two Ways of Hydrogen Peroxide Formation in the Oxidative Inactivation of Cyanobacterial Glutamine Synthetase  
 Abstract    Using crude extracts from the cyanobacterium Anabaena variabilis glutamine synthetase (GS) activity was rapidly irreversibly reduced to about 60% during dark incubation ("sponta­ neous GS inactivation"). An additional decrease was observed by the addition of ammonia in the light ("ammonia-m ediated inactivation"). Both effects were prevented by EDTA, MnCl2 or catalase indicative of the involvement of H 20 2. This is a key interm ediate in oxida­ tive enzyme inactivation. In both spontaneous and am monia-mediated GS inactivation H 20 2 is produced in different ways. Spontaneous inactivation is prevented by depletion of reduced pyridine nucleotides which apparently donate electrons to produce H 20 2. Fractionation of the crude extract showed that the light-enhanced GS inactivation by ammonia required the presence of thylakoid membranes. The photosynthesis inhibitor DCM U decreased GS inacti­ vation by ammonia. For the inactivation in the light apparently H 20 2 is produced from super­ oxide during photosynthetic electron transport. 
  Reference    Z. Naturforsch. 52c, 812—816 (1997); received August 12 1997 
  Published    1997 
  Keywords    Glutamine Synthetase, Protein Oxidation Ammonia Effect, Photosynthetic Hydrogen Peroxide Production, Cyanobacterium, Anabaena variabilis 
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 TEI-XML for    default:Reihe_C/52/ZNC-1997-52c-0812.pdf 
 Identifier    ZNC-1997-52c-0812 
 Volume    52