Ammonia assimilation in Corynebacterium glutamicum and a glutamate dehydrogenase-deficient mutant

In the wild-type of Corynebacterium glutamicum, the specific activity of gl utamate dehydrogenase (GDH) remained constant at 1.3 U (mg protein)(-1) whe n raising the ammonia (NH4+) concentration in the growth medium from 1 to 9 0 mM. In contrast, the glutamine synthetase (GS) and glutamate synthase (GO GAT) activities decreased from 1.1 U (mg protein)(-1) and 42 mU (mg protein )(-1), respectively, to less than 10 % of these values at NH4+ concentratio ns > 10 mM suggesting that under these conditions the GDH reaction is the p rimary NH4+ assimilation pathway. Consistent with this suggestion, a GDH-de ficient C. glutamicum mutant showed slower growth at NH4+ concentrations gr eater than or equal to 10 mM and, in contrast to the wild-type, did not gro w in the presence of the GS inhibitor methionine sulfoximine.