Enzymatic function of nitric oxide synthases.
Nitric oxide (NO) is synthesised from L-arginine by the enzyme NO synthase (NOS). The complex reaction involves the transfer of electrons from NADPH, via the flavins FAD and FMN in the carboxy-terminal reductase domain, to the haem in the amino-terminal oxygenase domain, where the substrate L-arginine is oxidised to L-citrulline and NO. The haem is essential for dimerisation as well as NO production. The pteridine tetrahydrobiopterin (BH4) is a key feature of NOS, affecting dimerisation and electron transfer, although its full role in catalysis remains to be determined. NOS can also catalyse superoxide anion production, depending on substrate and cofactor availability. There are three main isoforms of the enzyme, named neuronal NOS (nNOS), inducible NOS (iNOS), and endothelial NOS (eNOS), which differ in their dependence on Ca2+, as well as in their expression and activities. These unique features give rise to the distinct subcellular localisations and mechanistic features which are responsible for the physiological and pathophysiological roles of each isoform.
Andrew
P J
PJ
Institut für Pharmakologie und Toxikologie, Karl-Franzens-Universität Graz, Austria.
Mayer
B
B
D000818:Animals; D000975:Antioxidants / Q000378:metabolism; D001120:Arginine / Q000378:metabolism; D001708:Biopterins / Q000031:analogs & derivatives / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism; D019281:Dimerization; D004730:Endothelium, Vascular / Q000378:metabolism*; D004789:Enzyme Activation; D006418:Heme / Q000378:metabolism; D006801:Humans; D009569:Nitric Oxide / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III
D000975:Antioxidants; D002147:Calmodulin; D001708:Biopterins; D009569:Nitric Oxide; D006418:Heme; D001120:Arginine; C496320:NOS1 protein, human; C496319:NOS2 protein, human; C496314:NOS3 protein, human; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; C003402:sapropterin; D002118:Calcium