nitric oxide synthase

Synonyms:
  • endothelium-derived relaxing factor synthase
  • NO synthase
  • NOS
German: Stickstoffmonoxid-Synthase
Japanese: 一酸化窒素合成酵素

Enzymology. An enzyme that catalyses the conversion of arginine, NADPH, and oxygen to citrulline, nitric oxide, and NADP+. Three distinct isoforms of nitric oxide synthase (NOS) are found in mammals:
neuronal NOS (nNOS or nitric oxide synthase type I) which is a calcium-dependent form found primarily in nerve tissue;

inducible (iNOS or nitric oxide synthase type II) which is a calcium-independent subtype, inducible enzyme whose expression is transcriptionally regulated by a variety of cytokines;

endothelial (eNOS or nitric oxide synthase type III) which is a calcium-dependent form found primarily in endothelial cells.

eNOS and nNOS are constitutive isoforms which are always present whereas the expression of iNOS can be induced by cytokines (e.g., interferon-gamma, tumor necrosis factor, interleukin). The stimuli and conditions that determine iNOS expression are cell and species specific.

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