. Author manuscript; available in PMC: 2015 Jan 21.

Published in final edited form as: Chem Soc Rev. 2014 Jan 21;43(2):676–706. doi: 10.1039/c3cs60249d

Table 1.

Biogenic processes involved in the nitrogen cycle

Pathway(s)	Reactions catalyzed	Enzyme	Redox potential (mV)	Ref.
Assimilatory and dissimilatory nitrate reduction	NO₃⁻ + 2H⁺ + 2e⁻ → NO₂⁻ + H₂O	Nitrate reductase (NR: eukNR, Nar, Nap and Nas)	+433	313
	NO₂⁻ + 8H⁺ + 6e⁻ → NH₄⁺ + 2H₂O	Nitrite reductase (Nrf)	+340	314
Denitrifieation	NO₂⁻ + 2H⁺ + e⁻ → NO + H₂O	Nitrite reductase (NiR)	+350	313
	2NO + 2H⁺ + 2e⁻ → N₂O + H₂O	Nitric oxide reductase (NoR)	+1175	313
	N₂O + 2H⁺ + 2e⁻ → N₂ + H₂O	Nitrous oxide reductase	+1355	313
Anammox	NO + NH₃ + 3H⁺ + 3e⁻ → N₂H₄ + H₂O	Hydrazine hydrolase (HH)	+340	315, 316
	N₂H₄ → N₂ + 4H⁺ + 4e⁻	Hydrazine dehydrogenase (HDH)	−230	313
Nitrification	NO₂⁻ + H₂O → NO₃⁻ + 2H⁺ + 2e⁻	Nitrite oxidase (NO)	+420	317, 318
	NH₂OH + H₂O → NO₂⁻ + 5H⁺ + 4e−	Hydroxylamine oxidoreductase (HAO)	+60	317
	NH₃ + O₂ + 2H⁺ + 2e⁻ → NH₂OH + H₂O	Ammonia oxidase (AMO)	+730	317
Nitrogen fixation	N₂ + 6H⁺ + 6e⁻ → 2NH₃	Nitrogenase	−92	319