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|Title:||Partial purification, characterization and properties of two isoforms of glutamine synthetase from Pennisetum glaucum L. leaves|
|Keywords:||Pennisetum glaucum leaves|
|Series/Report no.:||C12N 9|
|Abstract:||Two isozymes of glutamine synthetase GS<sub>1</sub> and GS<sub>2</sub> were partially purified from Pennisetum glaucum leaves by ion-exchange and gel filtration chromatography and their kinetic and regulatory properties were studied using semisynthetase assay of GS. Mg<sup>2+</sup> was the most effective cation for activity of both the isozymes; however, it could be efficiently replaced by Co <sup>2+</sup>.The pH optima for GS<sub>1</sub> and GS<sub>2</sub> were 7.0 and 8.0, respectively. GS<sub>1</sub> exhibited maximum activity at 42ºC, with activation energy of 18 KJ mol<sup>-1</sup> and a Q<sub>10</sub> of 3.0, whereas GS<sub>2</sub> showed maximum activity at 50ºC, with activation energy of 40 KJ mol<sup>-1</sup> and Q<sub>10</sub> of 2.25. GS<sub>1</sub> was more thermostable than GS<sub>2</sub>. The K<sub>m</sub> value for Mg<sup>2+</sup> of GS<sub>1</sub> was 2-fold higher than GS<sub>2</sub>; however, these isozymes did not differ much in their affinity for other substrates. Alanine, serine and glycine lowered GS<sub>1</sub> and GS<sub>2</sub> activities, whereas cysteine enhanced their activities with a more pronounced effect on GS<sub>2</sub>. Serine inhibited the activity of both the isoforms in a competitive-manner, whereas alanine was a non-competitive inhibitor, with respect to glutamate. AMP and ADP were competitive inhibitor with respect to ATP for both the isozymes.|
|Appears in Collections:||IJBB Vol.41(6) [December 2004]|
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