Abstract
Glutamine synthetase (EC 6.3.1.2) has been purified from Rhizobium japonicum strains CC705 and CC723 respectively. The purified enzyme, which had a molecular weight of 720,000 (both strains) contained 12 subunits each of 60,000. The enzyme assayed by the γ-glutamyltransferase method had Km values for l-glutamine and hydroxylamine of 7.7 and 1.2 mM respectively. The inhibition of γ-glutamyltransferase by l-glutamate and ammonia was competitive for l-glutamine and non-competitive for hydroxylamine. The transferase activity was markedly (>65%) inhibited by l-methionine-d-sulfoximine and alanine and to a lesser extent (<45%) by glycine, arginine, aspartate, asparagine, lysine and serine. Different pairs of amino acids in various combinations resulted in a cumulative inhibition of enzyme activity. The enzyme was also inhibited by the following di- and tri-phosphate nucleotides — IDP, CDP, UDP, ATP, ITP, CTP and UTP. Malate, pyruvate, oxalate, succinate and α-ketoglutarate each at 10 mM depressed enzyme activity.
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