[4] There are two types of NXR; one where the NxrA subunit is located in the periplasmic space of a cell, and the other where NxrA is located in the cytoplasm[5] The enzyme is bound to the inner cytoplasmic surface of the bacterial membrane and contains iron-sulfur centers and a molybdenum cofactor.
[6][7] The enzyme is relatively abundant, making up 10-30% of the total protein in these bacteria and forms densely packed structures on the membrane surface.
When it oxidizes nitrite to nitrate, two electrons are shuttled into the respiratory chain.
[4] The two electrons that are generated from the nitrite oxidation are then donated to molecular oxygen, which yields energy.
[5] The NXR pathway for nitrite oxidation generally has a low energy yield (ΔG’ = -74 kJ/mol NO2).