Purification and characterization of a low-temperature ammonia monooxygenase from heterotrophic nitrifier Acinetobacter sp. Y16

Low-temperature ammonia monooxygenase (AMO) was purified from a heterotrophic nitrifier Acinetobacter sp. Y16 by anion-exchange and gel-filtration chromatography. The purified enzyme was a membrane-bound monomer with a molecular mass of approximately 31 kDa. It could catalyze the oxidation of ammonium without stabilizing agents in vitro at low temperature. Addition of CuCl₂ could stimulate AMO activity in vitro. The enzyme was stable in the temperature range of 4–15°C with less than 9% change in its activity. The optimal activity temperature was 15°C. Above 20°C, the enzyme completely lost its activity. The enzyme activity was stable when stored at 4°C for five days, at 10°C for two days, and at 15°C for one day. This study purified a highly pure AMO from a heterotrophic nitrifier Acinetobacter sp. for the first time.