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. 1975 Jun;55(6):968–974. doi: 10.1104/pp.55.6.968

Pea Leaf Glutamine Synthetase

Regulatory Properties 1

Thomas Denny O'Neal a, Kenneth W Joy a,2
PMCID: PMC541748  PMID: 16659228

Abstract

Of a variety of purine and pyrimidine nucleotides tested, only ADP and 5′AMP significantly inhibited the Mg2+-dependent activity of pea leaf glutamine synthetase. They were less effective inhibitors where Mn2+ replaced Mg2+. They were competitive inhibitors with respect to ATP, with inhibition constant (Ki) values of 1.2 and 1.8 mm, respectively. The energy charge significantly affects the activity of glutamine synthetase, especially with Mg2+. Of a variety of amino acids tested, l-histidine and l-ornithine were the most inhibitory, but significant inhibition was seen only where Mn2+ was present. Both amino acids appeared to compete with l-glutamate, and the Ki values were 1.9 mm for l-histidine (pH 6.2) and 7.8 mm for l-ornithine (pH 6.2). l-Alanine, glycine, and l-serine caused slight inhibition (Mn2+-dependent activity) and were not competitive with ATP or l-glutamate.

Carbamyl phosphate was an effective inhibitor only when Mn2+ was present, and did not compete with substrates. Inorganic phosphate and pyrophosphate caused significant inhibition of the Mg2+-dependent activity.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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