IUBMB Enzyme Nomenclature


Accepted name: nitrosourea synthase

Reaction: Nω-methyl-L-arginine + 2 NADH + H+ + 3 O2 = Nδ-hydroxy-Nω-methyl-Nω-nitroso-L-citrulline + 2 NAD+ + 3 H2O (overall reaction)
(1a) Nω-methyl-L-arginine + NADH + H+ + O2 = Nδ-hydroxy-Nω-methyl-L-arginine + NAD+ + H2O
(1b) Nδ-hydroxy-Nω-methyl-L-arginine + NADH + H+ + O2 = Nδ,Nω'-dihydroxy-Nω-methyl-L-arginine + NAD+ + H2O
(1c) Nδ,Nω'-dihydroxy-Nω-methyl-L-arginine + O2 = Nδ-hydroxy-Nω-methyl-Nω-nitroso-L-citrulline + H2O

Other name(s): sznF (gene name); StzF

Systematic name: Nω-methyl-L-arginine,NADH:oxygen oxidoreductase (Nδ-hydroxy-Nω-methyl-Nω-nitroso-L-citrulline-forming)

Comments: The enzyme, characterized from the bacterium Streptomyces achromogenes subsp. streptozoticus, catalyses a complex multi-step reaction during the biosynthesis of the glucosamine-nitrosourea antibiotic streptozotocin. The overall reaction is an oxidative rearrangement of the guanidine group of Nω-methyl-L-arginine, generating an N-nitrosourea product. The enzyme hydroxylates its substrate at the Nδ position, followed by a second hydroxylation at the Nω' position. It then catalyses an oxidative rearrangement to form Nδ-hydroxy-Nω-methyl-Nω-nitroso-L-citrulline. This product is unstable, and degrades non-enzymically into nitric oxide and the denitrosated product Nδ-hydroxy-Nω-methyl-L-citrulline. The enzyme contains two active sites, each of which utilizes a different iron-containing cofactor.

Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number:


1. Ng, T.L., Rohac, R., Mitchell, A.J., Boal, A.K. and Balskus, E.P. An N-nitrosating metalloenzyme constructs the pharmacophore of streptozotocin. Nature 566 (2019) 94-99. [PMID: 30728519]

2. He, H.Y., Henderson, A.C., Du, Y.L. and Ryan, K.S. Two-enzyme pathway links l-arginine to nitric oxide in N-nitroso biosynthesis. J. Am. Chem. Soc. 141 (2019) 4026-4033. [PMID: 30763082]

3. McBride, M.J., Sil, D., Ng, T.L., Crooke, A.M., Kenney, G.E., Tysoe, C.R., Zhang, B., Balskus, E.P., Boal, A.K., Krebs, C. and Bollinger, J.M., Jr. A peroxodiiron(III/III) intermediate mediating both N-hydroxylation steps in biosynthesis of the N-nitrosourea pharmacophore of streptozotocin by the multi-domain metalloenzyme SznF. J. Am. Chem. Soc. 142 (2020) 11818-11828. [PMID: 32511919]

4. McBride, M.J., Pope, S.R., Hu, K., Okafor, C.D., Balskus, E.P., Bollinger, J.M., Jr. and Boal, A.K. Structure and assembly of the diiron cofactor in the heme-oxygenase-like domain of the N-nitrosourea-producing enzyme SznF. Proc. Natl. Acad. Sci. USA 118 (2021) . [PMID: 33468680]

5. Wang, J., Wang, X., Ouyang, Q., Liu, W., Shan, J., Tan, H., Li, X. and Chen, G. N-nitrosation mechanism catalyzed by non-heme iron-containing enzyme SznF involving intramolecular oxidative rearrangement. Inorg. Chem. 60 (2021) 7719-7731. [PMID: 34004115]

[EC created 2021]

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