TABLE 1.

Bioenergetics of nitrogen source assimilation

Enzyme(s)Gene(s)StepNo. of electronsNo. of ATP molecules
Nitrogenase nif clusterN2 → NH4+816
Nitrate reductase narB NO3 → NO220
Nitrite reductase nirA NO2 → NH3+60
Glutamine synthetase/ glutamate synthase glnA/gltB NH3+ → Glu21