Glutamate synthase labeling studies

The short-lived radionuclide, has been extremely useful in studies of N2 fixation and NH4 assimilation. Wolk and his collaborators have demonstrated that the glutamine synthetase/glutamate synthase pathway is the major assimilatory route for NH4 in N2-fixing cultures of Anabaena and many other cyanobacteria. They have extended these studies to show that the labeling pattern observed after exposure of detached or attached soybean root nodules to [ N]N2 was similar to that observed in Anabaena. On this basis Meeks et al. (19) concluded that the primary pathway for assimilating NH4" derived from N2 in soybean nodules involves the sequential assimilatory activities of glutamine synthetase and glutamate synthase. 

Inhibitor studies (Leaet al., 1979) have shown that the synthesis of protein from glutamine by isolated pea cotyledons is unaffected by MSO but inhibited by azaserine, consistent with the action of glutamate synthase but not very conclusive because of the side effects of azaserine. Little if any labeling data on ammonia assimilation has so far been produced using developing seeds. 

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