Regulation of the activity of mung bean (Phaseolus aureus) glutamine synthetase by amino acids and nucleotides

The activity of glutamine synthetase isolated from the germinated seedlings of Phaseolus aureus was regulated by feedback inhibition by alanine, glycine, histidine, AMP, and ADP. When glutamate was the varied substrate, alanine, histidine, and glycine were partial noncompetitive, competitive, and mixed-type inhibitors, respectively. The type of inhibition by these amino acids was confirmed by fractional inhibition analysis. The adenine nucleotides, AMP and ADP, completely inhibited the enzyme activity and were competitive with respect to ATP. Multiple inhibition analyses revealed the presence of separate and nonexclusive binding sites for the amino acids and mutually exclusive sites for adenine nucleotides. Cumulative inhibition was observed with these end products.