The Enzyme Database

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Accepted name: nitric-oxide synthase (NADPH)
Reaction: 2 L-arginine + 3 NADPH + 3 H+ + 4 O2 = 2 L-citrulline + 2 nitric oxide + 3 NADP+ + 4 H2O (overall reaction)
(1a) 2 L-arginine + 2 NADPH + 2 H+ + 2 O2 = 2 Nω-hydroxy-L-arginine + 2 NADP+ + 2 H2O
(1b) 2 Nω-hydroxy-L-arginine + NADPH + H+ + 2 O2 = 2 L-citrulline + 2 nitric oxide + NADP+ + 2 H2O
Glossary: nitric oxide = NO = nitrogen(II) oxide
Other name(s): NOS (gene name); nitric oxide synthetase (ambiguous); endothelium-derived relaxation factor-forming enzyme; endothelium-derived relaxing factor synthase; NO synthase (ambiguous); NADPH-diaphorase (ambiguous)
Systematic name: L-arginine,NADPH:oxygen oxidoreductase (nitric-oxide-forming)
Comments: The enzyme consists of linked oxygenase and reductase domains. The eukaryotic enzyme binds FAD, FMN, heme (iron protoporphyrin IX) and tetrahydrobiopterin, and its two domains are linked via a regulatory calmodulin-binding domain. Upon calcium-induced calmodulin binding, the reductase and oxygenase domains form a complex, allowing electrons to flow from NADPH via FAD and FMN to the active center. The reductase domain of the enzyme from the bacterium Sorangium cellulosum utilizes a [2Fe-2S] cluster to transfer the electrons from NADPH to the active center. cf. EC, nitric-oxide synthase (flavodoxin).
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 125978-95-2
1.  Bredt, D.S. and Snyder, S.H. Isolation of nitric oxide synthetase, a calmodulin-requiring enzyme. Proc. Natl. Acad. Sci. USA 87 (1990) 682–685. [DOI] [PMID: 1689048]
2.  Stuehr, D.J., Kwon, N.S., Nathan, C.F., Griffith, O.W., Feldman, P.L. and Wiseman, J. Nω-hydroxy-L-arginine is an intermediate in the biosynthesis of nitric oxide from L-arginine. J. Biol. Chem. 266 (1991) 6259–6263. [PMID: 1706713]
3.  Stuehr, D., Pou, S. and Rosen, G.M. Oxygen reduction by nitric-oxide synthases. J. Biol. Chem. 276 (2001) 14533–14536. [DOI] [PMID: 11279231]
4.  Agapie, T., Suseno, S., Woodward, J.J., Stoll, S., Britt, R.D. and Marletta, M.A. NO formation by a catalytically self-sufficient bacterial nitric oxide synthase from Sorangium cellulosum. Proc. Natl. Acad. Sci. USA 106 (2009) 16221–16226. [DOI] [PMID: 19805284]
5.  Foresi, N., Correa-Aragunde, N., Parisi, G., Calo, G., Salerno, G. and Lamattina, L. Characterization of a nitric oxide synthase from the plant kingdom: NO generation from the green alga Ostreococcus tauri is light irradiance and growth phase dependent. Plant Cell 22 (2010) 3816–3830. [DOI] [PMID: 21119059]
[EC created 1992, modified 2012, modified 2017]

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