TABLE 1.

Bioenergetics of nitrogen source assimilation

Enzyme(s)Gene(s)StepNo. of electronsNo. of ATP molecules
Nitrogenasenif clusterN2 → NH4+816
Nitrate reductasenarBNO3 → NO220
Nitrite reductasenirANO2 → NH3+60
Glutamine synthetase/ glutamate synthaseglnA/gltBNH3+ → Glu21