Ammonia oxidation pathway

The ammonia oxidation pathway is a central component of the global nitrogen cycle, responsible for the aerobic conversion of ammonia (NH₃) to nitrite (NO₂⁻) and then to nitrate (NO₃⁻) via nitrifying microorganisms. The initial oxidation of ammonia to hydroxylamine is catalyzed by ammonia monooxygenase (AMO), a copper-containing membrane-bound enzyme found in ammonia-oxidizing bacteria (AOB) and archaea (AOA). Hydroxylamine is subsequently oxidized to nitrite by hydroxylamine oxidoreductase (HAO). Some bacteria (comammox, e.g., certain Nitrospira) are capable of complete ammonia oxidation to nitrate within a single organism. These reactions are essential for nitrogen turnover in soils, aquatic systems, and engineered environments such as wastewater treatment plants. The pathway itself is not a drug target, but the key enzymes (such as AMO) may be targeted to inhibit nitrification in agricultural and environmental contexts.

Other names

ammonia oxidationnitrification (first step)ammonia-oxidizing enzyme systemammonia monooxygenase (AMO)hydroxylamine oxidoreductase (HAO)

Enzyme inhibition (e.g., covalent or competitive inhibition of AMO prevents the oxidation of ammonia, thereby inhibiting nitrification)