Synthesis of
glutamine synthetase (GS) in anaerobic batch cultures of Escherichia coli was repressed when excess NH4+ was available, but derepressed during growth with a poor
nitrogen source. In wild-type bacteria there was only a weak inverse correlation between the activities of GS and
glutamate dehydrogenase (GDH) during growth in various media. No positive correlations were found between the activities of GS and
nitrite reductase, or between GS and
cytochrome c552: both of these
proteins were synthesized normally by mutants that contained no active GS. Although activities of GS and GDH were low in two mutants that are unable to synthesize
cytochrome c552 or reduce
nitrite because of defects in the nirA gene, the nirA defect was separated from the GS and GDH defects by transduction with bacteriophage P1. Attempts to show that catabolite repression of
proline oxidase synthesis could be relieved during NH4+
starvation also failed. It is, therefore, unlikely that
nitrite reduction or
proline oxidation by E. coli are under positive control by GS
protein. The regulation of the synthesis of
enzymes for the utilization of secondary
nitrogen sources in E. coli, therefore, different from that in Klebsiella aerogenes, but is similar to that in Salmonella typhimurium.