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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;glutamine synthetase;chloroplastic;isozymes|
|IPC Code:||C12N 9|
|Abstract:||Two isozymes of glutamine synthetase GS1 and GS2 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. Mg2+ was the most effective cation for activity of both the isozymes; however, it could be efficiently replaced by Co 2+.The pH optima for GS1 and GS2 were 7.0 and 8.0, respectively. GS1 exhibited maximum activity at 42ºC, with activation energy of 18 KJ mol-1 and a Q10 of 3.0, whereas GS2 showed maximum activity at 50ºC, with activation energy of 40 KJ mol-1 and Q10 of 2.25. GS1 was more thermostable than GS2. The Km value for Mg2+ of GS1 was 2-fold higher than GS2; however, these isozymes did not differ much in their affinity for other substrates. Alanine, serine and glycine lowered GS1 and GS2 activities, whereas cysteine enhanced their activities with a more pronounced effect on GS2. 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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