All cells require a nitrogen source to grow. The preferred nitrogen source for E. coli is an ammonium salt (e.g. NH4Cl ). The NH 4 is assimilated into cellular metabolism by glutamine synthetase (GS), which catalyzes the synthesis of glutamine from glutamate, NH 4, and ATP. Glutamine then serves as a precursor to many compounds such as histidine, tryptophan, and nucleotides. These compounds control the activity of GS by feedback inhibition. Therefore, GS responds to changes in the nitrogen balance within cells. Identify the correct feedback inhibition mechanism that controls GS and its advantage for E. coli grown in a medium with a high histidine concentration. Assume that glucose and NH, are not limiting.
A. GS is controlled by concerted feedback inhibition. Histidine alone does not alleci GS. Therefore. E. coli growth will be unaffected.
B. GS is controlled by sequential feedback inhibition. Complete inhibition of GS by histidine will impair NH+ assimilation and impair E. coli growth.
C. GS is controlled by cumulative feedback inhibition. Therefore, histidine will inhibit GS partially. The remaining GS activity can support NH+, assimilation and E. coli growth.
D. GS is controlled by enzyme multiplicity. Only histidine-responsive GS will be shut down. The other GS isoforms will remain active to support E. coli growth.

The glutamine Synthetase of E. coli can collectively and totally be hindered and inhibited by various and numerous nitrogen-containing compounds like histidine, tryptophan, glycine, alanine, etc at optimum concentrations. But, individually at higher concentrations, these inhibitors can only inhibit the catalytic enzyme action partially. In this way, GS is constrained by total feedback restraint. Consequently, histidine will repress GS halfway. The excess GS movement can uphold NH+, absorption, and E. coli growth development.