KINETIC AND INHIBITION STUDIES OF GLUTAMINE-SYNTHETASE FROM THE CYANOBACTERIUM ANABAENA 7120

A number of biochemical parameters of glutamine synthetase (EC 6.3.1.2) isolated from the cyanobacterium Anabaena 7120 were determined. Apparent Km for glutamate and ATP were 2.1 and 0.32 mM, respectively; that for ammonia was < 20 .mu.M, significantly lower than that reported for glutamine synthetases from other species. Serine, alanine, glycine, cysteine, aspartic acid, methionine sulfone and methionine sulfoximine inhibited the enzyme. The enzyme is controlled neither by adenylylation nor by feedback inhibition by glutamine, mechanisms found in some other prokaryotes. It must be regulated by a different mechanism, possibly a combination of feedback by alanine, serine and glycine, metabolites which are especially effective in inhibiting Anabaena glutamine synthetase.