Identification and characterization of a heat-labile type I glutamine synthetase from Streptomyces cinnamonensis

Streptomycetes have two distinct glutamine synthetases (GS): a heat-stable dodecameric GSI and a heat-labile octameric GSII. A heat-inactivated GS activity was detected in crude extracts of Streptomyces cinnamonensis cells grown with nitrate or glutamate as the nitrogen source. The purified enzyme o...

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Bibliographic Details
Published in:Folia microbiologica 1997, Vol.42 (5), p.431-440
Main Authors: NGUYEN, K. T, NGUYEN, L. T, BENADA, O, BEHAL, V
Format: Article
Language:English
Subjects:
Bacteriology
Biological and medical sciences
Biology of microorganisms of confirmed or potential industrial interest
Biotechnology
Fundamental and applied biological sciences. Psychology
Metabolism. Enzymes
Microbiology
Mission oriented research
Physiology and metabolism
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Summary:Streptomycetes have two distinct glutamine synthetases (GS): a heat-stable dodecameric GSI and a heat-labile octameric GSII. A heat-inactivated GS activity was detected in crude extracts of Streptomyces cinnamonensis cells grown with nitrate or glutamate as the nitrogen source. The purified enzyme obtained from crude extracts of the nitrate-grown cells after affinity and anion-exchange chromatography was also heat-labile; it was inactivated by 80% when incubated at 50 degree C for 1 h. However, the enzyme has properties typical of GSI and similar with those of the heat-stable GSI purified from S. aureofaciens: It is composed of twelve subunits, each of M 55 kDa, and has a native molar mass of 625 kDa and an isoelectric point at pH 4.2. In addition, its activity is regulated by reversible adenylytation. Mg super(2+) and NaCl but not Mn super(2+) protected the purified enzyme from thermal inactivation, and both NaCl and Mn super(2+) or Mg super(2+) stabilized its activity at 4-8 degree C. As compared with GSI from S. aureofaciens, the S. cinnamonensis enzyme was cleaved more extensively during SDS-PAGE, was less sensitive to feedback inhibitors, similarly affected by divalent cations. The K sub(m) values were 12.5 mmol/L for L-glutamate, 0.1 for NH sub(4) super(+), 1.25 for ATP, 18.5 for L-glutamine, 3.3 for hydroxylamine and 0.087 for ADP. To our best knowledge, this is the first report of a heat-labile GSI from any source.
ISSN:0015-5632
1874-9356
DOI:10.1007/BF02826549