The enzyme from the heterotrophic nitrifying bacterium Paracoccus denitrificans contains three to five non-heme, non-iron-sulfur iron atoms and interacts with cytochrome c556 and pseudoazurin [2,3]. Under anaerobic conditions in vitro only nitrous oxide is formed . Presumably nitroxyl is released and combines with a second nitroxyl to give nitrous oxide and water. When oxygen is present, nitrite is formed.
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SYSTEMATIC NAME
IUBMB Comments
hydroxylamine:oxygen oxidoreductase
The enzyme from the heterotrophic nitrifying bacterium Paracoccus denitrificans contains three to five non-heme, non-iron-sulfur iron atoms and interacts with cytochrome c556 and pseudoazurin [2,3]. Under anaerobic conditions in vitro only nitrous oxide is formed [3]. Presumably nitroxyl is released and combines with a second nitroxyl to give nitrous oxide and water. When oxygen is present, nitrite is formed.
under aerobic assay conditions nitrite is the major reaction product but N2O is also detected at low levels. Under anaerobic conditions no nitrite is produced but N2O is detected, though at non-stoichiometric levels. The production of nitrite by Paracoccus denitrificans hydroxylamine oxidase is an oxygen-dependent reaction
horse heart cytochrome. Under aerobic assay conditions nitrite is the major reaction product but N2O is also detected at low levels. Under anaerobic conditions no nitrite is produced but N2O is detected, though at non-stoichiometric levels. The production of nitrite by Paracoccus denitrificans hydroxylamine oxidase is an oxygen-dependent reaction
under aerobic assay conditions nitrite is the major reaction product but N2O is also detected at low levels. Under anaerobic conditions no nitrite is produced but N2O is detected, though at non-stoichiometric levels. The production of nitrite by Paracoccus denitrificans hydroxylamine oxidase is an oxygen-dependent reaction
the enzyme utilizes horse-heart cytochrome c as an electron acceptor but is unable to donate electrons to purified Pseudomonas denitrificans cytochrome c550 or pseudoazurin, or to Pseudomonas aeruginosa azurin
the enzyme utilizes horse-heart cytochrome c as an electron acceptor but is unable to donate electrons to purified Pseudomonas denitrificans cytochrome c550 or pseudoazurin, or to Pseudomonas aeruginosa azurin
one heme in each HAO monomer is a highly unusual heme P460 that is the site of catalysis. Heme P460 contains two covalent cross-links between the porphyrin and a Tyr residue, structure analysis, overview
non-heme iron enzyme, the enzyme could possess a non-heme ferric iron centre that is lost when the 20000 Da polypeptide is subjected to SDS-PAGE, but that can be reconstituted by addition of Fe3+ ions to the refolded enzyme
enzyme HAO catalyzes the conversion of hydroxylamine to nitrite in nitrifying bacteria, that is key reaction in the nitrogen cycle. The enzyme HAO, protein NE1300, may play a structural role in the ternary complex with cytochrome c554, the physiological electron acceptor of HAO. Two of HAO's product electrons are subsequently transferred back to ammonia monooxygenase as substrate electrons, and the other two electrons contribute to the electrochemical gradient through a terminal oxidase in the cytoplasmic membrane
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CRYSTALLIZATION (Commentary)
ORGANISM
UNIPROT
LITERATURE
purified native enzyme, mixing of 0.002 ml of protein in 20 mM Tris-HCl, pH 8.1, with 0.002 ml of crystallization solution containing 0.1 M potassium nitrate, 0.1 M MES-Na buffer, pH 7.5, and 46% v/v PEG 400, X-ray diffraction structure determination and analysis at 2.1 A resolution, modelling
Purification of hydroxylamine oxidase from Thiosphaera pantotropha. Identification of electron acceptors that couple heterotrophic nitrification to aerobic denitrification
Wehrfritz, J.; Carter, J.; Spiro, S.; Richardson, D.
Hydroxylamine oxidation in heterotrophic nitrate-reducing soil bacteria and purification of a hydroxylamine-cytochrome c oxidoreductase from a Pseudomonas species