Nitric Oxide—General Information
(interesting page: http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/N/NO.html)
Nitric oxide (NO) is a gas. It is highly reactive; that is, it participates in many chemical reactions. (It is one of the nitrogen oxides (“Nox”) in automobile exhaust and plays a major role in the formation of photochemical smog [ Link].)
But NO also has many physiological functions.
They share these features:
- NO is synthesized within cells by an enzyme NO synthase (NOS).
- The human (and mouse) genome contains 3 different genes encoding NO synthases.
- NNOS (or NOS-1): found in neurons (hence the “n”).
- iNOS (or NOS-2): found in macrophages. (the “i” stands for “inducible”. Whereas the levels of nNOS and eNOS are relatively steady, expression of iNOS genes awaits an appropriate stimulus (e.g., ingestion of a parasite).
- ENOS (or NOS-3): found in the endothelial (hence the “e”) cells that line the lumen of blood vessels.
- NO diffuses freely across cell membranes.
- There are so many other molecules with which it can interact, that it is quickly consumed close to where it is synthesized.
More NO General Information
From Affinity BioReagents (www.bioreagents.com/index.cfm/fuseaction/products.detail/CatNbr/PA3-031)
Nitric oxide (NO) is an inorganic, gaseous free radical that carries a variety of messages between cells. Vasorelaxation, neurotransmission and cytotoxicity can all be potentiated through cellular response to NO. NO production is mediated by members of the nitric oxide synthase (NOS) family. NOS catalyzes the oxidization of L-arginine to produce L-citrulline and NO. Two constitutive isoforms, brain or neuronal NOS (b or nNOS, type I) & endothelial cell NOS (eNOS, type III), and one inducible isoform (iNOS, type II), have been cloned. All NOS isoforms contain calmodulin, nicotinamide adenine dinucleotide phosphate (NADPH), flavin adenine dinucleotide (FAD), and flavin mononucleotide (FMN) binding domains.
eNOS synthesizes NO in vascular endothelial cells where it appears to play an important role in the control of vasotension and platelet aggregation. eNOS and bNOS share ~50% sequence homology, and their activity depends on binding to the calcium/calmodulin complex. Both constitutive isoforms respond immediately to increased levels of calcium to produce low levels of NO over a short period of time.
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