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  • 1
    Electronic Resource
    Electronic Resource
    Purification and molecular properties of ferredoxin-glutamate synthase from Chlamydomonas reinhardii (1984)
    Springer
    Planta 162 (1984), S. 180-187 
    Details
    ISSN: 1432-2048
    Keywords: Chlamydomonas (ferredoxin-glutamate synthase) ; Ferredoxin-glutamate synthase ; Glutamate synthase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Ferredoxin-glutamate synthase (EC 1.4.7.1) from Chlamydomonas reinhardii has been purified to electrophoretic homogeneity, with a specific activity of 10.4 units mg-1 protein, by a method which included chromatography on diethylaminoethyl sephacel and hydroxylapatite, and ferredoxin-sepharose affinity treatment. The enzyme is a single polypeptide chain of M r 146000 dalton which shows an absorption spectrum with maxima at 278, 377 and 437 nm, and an A276/A437 absorptivity ratio of 7.0. The anaerobic addition of dithionite results in the loss of the absorption peak at 437 nm, which is restored upon reoxidation of the enzyme with an excess of 2-oxoglutarate, alone or in the presence of glutamine. This indicates the presence in the enzyme of a flavin prosthetic group, which is functional during the catalysis. The ferredoxin-glutamate synthase can be assayed with methyl viologen, chemically reduced with dithionite, but it is unable to use reduced pyridine nucleotide. Azaserine, 6-diazo-5-oxo-norleucine, bromocresol green and p-hydroxymercuribenzoate are potent inhibitors of this activity, which, on the other hand, is stable upon heating at 45°C for 10 min.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00410216
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  • 2
    Electronic Resource
    Electronic Resource
    Regulation of the expression of ferredoxin-glutamate synthase in barley (1997)
    Springer
    Planta 203 (1997), S. 517-525 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Glutamate synthase ; Hordeum (glutamate synthase) ; Light (N assimilation) ; Nitrogen assimilation ; Plant development ; Senescence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. We have investigated the regulation of ferredoxin–glutamate synthase (Fd-GOGAT) in leaves of barley (Hordeum vulgare L. cv. Maris Mink) at the mRNA, protein and enzyme activity levels. Studies of the changes in Fd-GOGAT during plant development showed that the activity in shoots increases rapidly after germination to reach a maximum (on a fresh-weight basis) at day 10 and then declines markedly to less than 50% of the maximal activity by day 30, this decline being correlated with an equivalent loss of Fd-GOGAT protein. Growing the plants in darkness reduced the maximum activity attained in the shoots, but did not affect the overall pattern of the changes or their timing. The activity of Fd-GOGAT increased two- to three-fold within 48 h when etiolated leaves were exposed to light, and Northern blots indicated that the induction occurred at the mRNA level. However, whilst a carbon source could at least partially substitute for light in the induction of nitrate reductase activity, no induction of Fd-GOGAT activity was seen when etiolated leaves were treated with either sucrose or glucose. Interestingly, the levels of Fd-GOGAT mRNA and activity remained high up to a period of 16 h or 72 h darkness, respectively. Compared with plants grown in N-free medium, light-grown plants supplied with nitrate had almost two-fold higher Fd-GOGAT activities and increased Fd-GOGAT mRNA levels, but nitrate had no effect on the abundance of the enzyme or its mRNA in etiolated plants, indicating that light is required for nitrate induction of barley Fd-GOGAT.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050221
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  • 3
    Electronic Resource
    Electronic Resource
    Immunological studies of ferredoxin-nitrite reductases and ferredoxin-glutamate synthases from photosynthetic organisms (1990)
    Springer
    Archives of microbiology 153 (1990), S. 230-234 
    Details
    ISSN: 1432-072X
    Keywords: Photosynthetic organisms ; Chlamydomonas reinhardii ; Ferredoxin-glutamate synthase ; Ferredoxin-nitrite reductase ; Common antigenic determinants ; Ferredoxin-binding domain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Polyclonal antiserum specific for ferredoxin-nitrite reductase (EC 1.7.7.1) from the green alga Chlamydomonas reinhardii recognized the nitrite reductase from other green algae, but did not cross-react with the corresponding enzyme from different cyanobacteria or higher plant leaves. An analogous situation was also found for ferredoxin-glutamate synthase (EC 1.4.7.1), using its specific antiserum. Besides, the antibodies raised against C. reinhardii ferredoxin-glutamate synthase were able to inactivate the ferredoxin-dependent activity of nitrite reductase from green algae. These results suggest that there exist similar domains in ferredoxin-nitrite reductases and ferredoxin-glutamate synthases from green algae. In addition, both types of enzymes share common antigenic determinants, probably located at the ferredoxin-binding domain. In spite of their physicochemical resemblances, no apparent antigenic correlation exists between the corresponding enzymes from green algae and those from higher plant leaves or cyanobacteria.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00249073
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  • 4
    Electronic Resource
    Electronic Resource
    Molecular analysis of barley mutants deficient in chloroplast glutamine synthetase (1990)
    Springer
    Plant molecular biology 14 (1990), S. 297-311 
    Details
    ISSN: 1573-5028
    Keywords: cDNA sequence ; chloroplast protein ; glutamine synthetase ; Hordeum vulgare L. ; mRNA ; mutants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A barley leaf cDNA library has been screened with two oligonucleotide probes designed to hybridize to conserved sequences in glutamine synthetase (GS) genes from higher plants. Two GS cDNA clones were identified as hybridizing strongly to one or both probes. The larger clone (pcHvGS6) contained a 1.6 kb insert which was shown by primer extension analysis to be an almost full-length cDNA. Both clones were more closely related to cDNAs for the chloroplast form of GS (GS2) from pea and Phaseolus vulgaris than to cDNAs for the cytosolic form (GS1). A sequence identicalto an N-terminal sequence determined from a purified preparation of the mature GS2 polypeptide (NH2-XLGPETTGVIQRMQQ) was found in the pcHvGS6-encoded polypeptide at residues 46–61, indicating a pre-sequence of at least 45 amino acids. The pre-sequence has only limited sequence homology to the pre-sequences of pea and P. vulgaris GS2 subunits, but is similarly rich in basic residues and possesses some of the structural features common to the targeting sequences of other chloroplast proteins. The molecular lesions responsible for the GS2-deficient phenotypes of eight photorespiratory mutants of barley were investigated using a gene-specific probe from pcHvGS6 to assay for GS2 mRNA, and an anti-GS antiserum to assay for GS2 protein. Three classes of mutants were identified: class I, in which absence of cross-reacting material was correlated with low or undetectable levels of GS2 mRNA; class II, which had normal or increased levels of GS2 mRNA but very little GS2 protein; and class III, which had significant amounts of GS2 protein but little or no GS2 activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00028767
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  • 5
    Electronic Resource
    Electronic Resource
    Cloning and sequence analysis of a cDNA for barley ferredoxin-dependent glutamate synthase and molecular analysis of photorespiratory mutants deficient in the enzyme (1993)
    Springer
    Planta 189 (1993), S. 475-483 
    Details
    ISSN: 1432-2048
    Keywords: Amidotransferase ; Amino-terminal sequences ; Chromosomal assignment ; Glutamate synthase ; Hordeum (mutants) ; Photorespiration mutants (barley) ; Polymerase chain reaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The NH2-terminal sequences of ferredoxin-dependent glutamate synthase (Fd-GOGAT; EC 1.4.7.1) purified from barley (Hordeum vulgare L.) and Chlamydomonas reinhardtii (Dangeard), and of a barley peptide, were determined and the barley sequences were used to design oligonucleotide primers for the polymerase chain reaction. A specific 1.3-kilobase (kb) cDNA fragment specifying the NH2-terminal one-third of the mature barley polypeptide, was amplified, cloned and sequenced. The NH2-terminus of plant Fd-GOGAT is highly conserved and homologous to the NH2-terminus of the heavy subunit of Escherichia coli NADPH-GOGAT. Based on sequence homologies, we tentatively identified the NH2-terminal region of Fd-GOGAT as the glutamine-amidotransferase domain, which is related to the corresponding domain of the purF-type amidotransferases. The Fd-GOGAT cDNA clone, and polyclonal antibodies raised against the barley enzyme, were used to analyse four Fd-GOGAT-deficient photorespiratory mutants. Three mutants (RPr 82/1, RPr 82/9 and RPr 84/82) had no detectable Fd-GOGAT protein in leaves, while the fourth (RPr 84/42) had a small amount of cross-reacting material. Hybridization to Northern blots of total leaf RNA revealed that both RPr 82/9 and RPr 84/82 were indistinguishable from the parental line (Maris Mink), having normal amounts of a 5.7-kb mRNA species. On the other hand, RPr 82/2 and RPr 84/42 each contained two distinct hybridizing RNA species, one of which was larger than 5.7 kb, the other smaller. Using a set of wheat-barley telosomic addition lines we have assigned the Fd-GOGAT structural locus to the short arm of chromosome 2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00198209
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  • 6
    Electronic Resource
    Electronic Resource
    Site-directed mutagenesis of Glu-297 from the α-polypeptide of Phaseolus vulgaris glutamine synthetase alters kinetic and structural properties and confers resistance to L-methionine sulfoximine (1999)
    Springer
    Plant molecular biology 40 (1999), S. 835-845 
    Details
    ISSN: 1573-5028
    Keywords: glutamine synthetase ; Phaseolus vulgaris ; plant nitrogen assimilation ; recombinant protein ; site-directed mutagenesis ; structure-function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In this paper we examine the functionality of Glu-297 from the α-polypeptide of Phaseolus vulgaris glutamine synthetase (EC 6.3.1.2). For this purpose, the glnα cDNA was recombinantly expressed in Escherichia coli, and site-directed mutants constructed, in which this residue was replaced by alanine. The level of glutamine synthetase transferase catalytic activity in the mutant strain was 70-fold lower while biosynthetic activity remained practically unaffected. Kinetic parameters for both enzyme activities were not greatly altered except for the Km for ammonium in biosynthetic activity, which increased 100-fold. A similar result was reported when mutagenizing Glu-327 from E. coli glutamine synthetase, a residue shown to be present at the active site. This suggests that the Glu residue mutated in the higher-plant enzyme could develop a similar catalytic role to that of bacteria. Another characteristic feature of the mutant protein was its higher resistance to inhibition of the biosynthetic activity by L-methionine sulfoximine, a typical inhibitor of glutamine synthetase. In addition, we show that immunoreactivity of the glutamine synthetase mutant protein, both under native and denaturing conditions, is similar to the wild type, indicating that no deep conformational changes were produced as a consequence of the introduced mutation. However, structural changes in the active site can be predicted from alterations detected in the behaviour of the mutant protein towards affinity chromatography on 2′,5′-ADP-Sepharose, as compared to the wild type. Nevertheless, complementation of an E. coli glnA mutation indicated that the E297A mutant enzyme was physiologically functional.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006257323624
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  • 7
    Electronic Resource
    Electronic Resource
    Characterization of a light-dependent glutamate synthase activity in Chlamydomonas reinhardtii (1987)
    Springer
    Photosynthesis research 12 (1987), S. 73-81 
    Details
    ISSN: 1573-5079
    Keywords: Chlamydomonas ; photosynthesis ; biosynthesis of glutamate ; Fd-glutamate synthase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Photosynthetically active vesicles prepared from Chlamydomonas reinhardtii retained a light-dependent glutamate synthase activity which was highly specific for 2-oxoglutarate (Km=2.1 mM) and L-glutamine (Km=0.9 mM) as amido group acceptor and donor respectively. This activity was inhibited by azaserine, p-hydroxymercuribenzoate and 3-(p-chlorophenyl)-1,1-dimethyl urea. Light-dependent synthesis of glutamate was also obtained by coupling Chlamydomonas photosynthetic particles to purified ferredoxin-glutamate synthase, using ascorbate and 2,6-dichlorophenol-indophenol as electron donor. This system was also specific for 2-oxoglutarate (Km=1 mM) and L-glutamine (Km=0.8 mM) as substrates, and was stimulated by dithioerythritol. Azaserine and p-hydroxymercuribenzoate, but not 3-(p-chlorophenyl)-1,1-dimethyl urea, inhibited the reconstituted activity; high concentrations of 2-oxoglutarate were inhibitory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00019152
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  • 8
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    Regulation of the expression of ferredoxin-glutamate synthase in barley (1997)
    Springer
    Details
    Publication Date: 1997-11-20
    Print ISSN: 0032-0935
    Electronic ISSN: 1432-2048
    Topics: Biology
    Published by Springer
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  • 9
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    Structural analysis of K+ dependence in l-asparaginases from Lotus japonicus (2011)
    Springer
    Details
    Publication Date: 2011-03-10
    Print ISSN: 0032-0935
    Electronic ISSN: 1432-2048
    Topics: Biology
    Published by Springer
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  • 10
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    Identification of an essential cysteinyl residue for the structure of glutamine synthetase α from Phaseolus vulgaris (2010)
    Springer
    Details
    Publication Date: 2010-02-21
    Print ISSN: 0032-0935
    Electronic ISSN: 1432-2048
    Topics: Biology
    Published by Springer
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