Regulation of the Synthesis of Enzymes Responsible for Glutamate Formation in Klebsiella aerogenes

Abstract

Abstract A mutant of Klebsiella aerogenes lacking glutamine (amide):α-ketoglutarate (NADP+) amidotransferase oxidoreductase (glutamate synthetase) cannot grow in minimal media containing ammonia as the only nitrogen source at a concentration lower than 1 mm. In addition, in a glucose containing medium, it fails to utilize amino acids, such as histidine, that are converted to glutamate, as sources of nitrogen. It can use glutamate as source of nitrogen. Revertants were isolated capable of growth on glucose-histidine, but unable to use ammonia. These revertants still lack glutamate synthetase, but produce glutamine synthetase constitutively (glnC-). They fail to produce glutamate dehydrogenase, and thus cannot use ammonia as a nitrogen source. An analysis of the levels of glutamine synthetase, glutamate synthetase, and glutamate dehydrogenase in the parent organism, in mutants lacking glutamine synthetase, and in mutants producing it constitutively, reveals that glutamine synthetase represses the formation of glutamate dehydrogenase. A lack of glutamate synthetase appears to interfere with the derepression of glutamine synthetase. On the other hand, the loss of glutamate dehydrogenase by mutation does not affect glutamine synthetase. These results, together with those reported in an earlier paper (Prival, M. J., Brenchley, J. E., and Magasanik, B. (1973) J. Biol. Chem. 248, 4334–4344), indicate that glutamine synthetase is the key element in the regulation of the synthesis of enzymes capable of supplying the cell with glutamate.