InterPro domain: IPR004136

Nitronate monooxygenase (NMO), formerly referred to as 2-nitropropane dioxygenase (NPD) ( 1.13.11.32 ), is an FMN-dependent enzyme that uses molecular oxygen to oxidise (anionic) alkyl nitronates and, in the case of the enzyme from Neurospora crassa, (neutral) nitroalkanes to the corresponding carbonyl compounds and nitrite. Previously classified as 2-nitropropane dioxygenase [ 1 , 2 , 3 ], but it is now recognised that this was the result of the slow ionisation of nitroalkanes to their nitronate (anionic) forms [ 4 ]. The enzymes from the fungus Neurospora crassa and the yeast Williopsis saturnus var. mrakii (formerly classified as Hansenula mrakii) contain non-covalently bound FMN as the cofactor. Active towards linear alkyl nitronates of lengths between 2 and 6 carbon atoms and, with lower activity, towards propyl-2-nitronate. The enzyme from N. crassa can also utilise neutral nitroalkanes, but with lower activity. One atom of oxygen is incorporated into the carbonyl group of the aldehyde product. The reaction appears to involve the formation of an enzyme-bound nitronate radical and an a-peroxynitroethane species, which then decomposes, either in the active site of the enzyme or after release, to acetaldehyde and nitrite.

1. Purification, characterization, and mechanism of a flavin mononucleotide-dependent 2-nitropropane dioxygenase from Neurospora crassa. Appl. Environ. Microbiol. 64, 1029-33
2. Involvement of a flavosemiquinone in the enzymatic oxidation of nitroalkanes catalyzed by 2-nitropropane dioxygenase. J. Biol. Chem. 280, 5195-204
3. Crystal structure of 2-nitropropane dioxygenase complexed with FMN and substrate. Identification of the catalytic base. J. Biol. Chem. 281, 18660-7
4. Nitronate monooxygenase, a model for anionic flavin semiquinone intermediates in oxidative catalysis. Arch. Biochem. Biophys. 493, 53-61