Summary: A higher activity of glutamine synthetase (EC was found in when NH was limiting as nitrogen source than when glutamate was limiting. When glutamate, glutamine or NH were in excess, a lower activity was found. Immunological titration and sucrose gradient sedimentation of the enzyme established that under all these conditions enzyme activity corresponded to enzyme concentration and that the octamer was the predominant oligomeric form. When was shifted from nitrogen-limiting substrates to excess product as nitrogen source, the concentration of glutamine synthetase was adjusted with kinetics that closely followed dilution by growth. When grown on limiting amounts of glutamate, a lower oligomer was present in addition to the octameric form of the enzyme. When the culture was shifted to excess NH , glutamine accumulated at a high rate; nevertheless, there was only a slow decrease in enzyme activity and no modification of the oligomeric pattern.


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