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Glutamate Dehydrogenase - GDH -
The GDHs of E.coli and Salmonella typhimurium are of similar size and molecular weight, 300,000 and 280,000 respectively. E.coli GDH appears to consist of six identical, subunits. E. coli, S.typhimurium and Kleb siella aerogenes mutants lacking GDH do not require glutamate for growth. This indicates the existence of an alternate pathway for glutamate biosynthesis.

Strains lacking GDH activity do not have a distinct phenotype from wild type strains. Both wild type and mutant strains can grow on both high and low concentrations of ammonia and other nitrogen sources. It thus ap­pears that the function of GDH in ammonia assimilation can be completely replaced by the glutamate synthase glutamine synthetase pathway.