Journal Article

Gln49 and Ser174 Residues Play Critical Roles in Determining the Catalytic Efficiencies of Plant Glutamine Synthetase

Keiki Ishiyama, Eri Inoue, Tomoyuki Yamaya and Hideki Takahashi

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 47, issue 2, pages 299-303
Published in print February 2006 | ISSN: 0032-0781
Published online February 2006 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pci238
Gln49 and Ser174 Residues Play Critical Roles in Determining the Catalytic Efficiencies of Plant Glutamine Synthetase

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Two essential residues playing critical roles in determining the substrate specificities of cytosolic glutamine synthetase (GS1) have been identified from the alignment of high-affinity (GLN1;1 and GLN1;4) and low-affinity (GLN1;2 and GLN1;3) GS1 isoenzymes in Arabidopsis, and confirmed by site-directed mutagenesis. The results indicated that either K49Q or A174S mutation is sufficient to increase the catalytic efficiencies of GLN1;3 by decreasing its K m values for ammonium. In contrast, replacement of Gln49 and Ser174 by lysine and alanine, respectively, was detrimental to glutamine synthetic activities in GLN1;4. The results suggested that Gln49 and Ser174 in the high-affinity GS1 isoenzymes are interchangeable with Lys49 and Ala174 in the low-affinity variants at the corresponding positions.

Keywords: Ammonium assimilation; Arabidopsis thaliana; Catalytic efficiency; Glutamine synthetase; Nitrogen metabolism; Site-directed mutagenesis; GS, glutamine synthetase; GS1, cytosolic glutamine synthetase; GS2, plastidic/chloroplastic glutamine synthetase

Journal Article.  3137 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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