Nitric Oxide Synthase

Nitric Oxide Synthase

Nitric oxide synthases (EC 1.14.13.39) (NOSs) are a family of enzymes that catalyze the production of nitric oxide (NO) from L-arginine. NO is an important cellular signaling molecule, having a vital role in many biological processes. It is the intercellular signal that controls vascular tone (hence blood pressure), insulin secretion, airway tone, and peristalsis, and is involved in angiogenesis (growth of new blood vessels) and in the development of nervous system. It is believed to function as a retrograde neurotransmitter and hence is likely to be important in learning. Nitric oxide signalling is mediated in mammals by the calcium/calmodulin controlled isoenzymes eNOS (endothelial NOS) and nNOS (neuronal NOS); the inducible isoform iNOS is involved in immune response, binds calmodulin at all physiologically relevant concentrations, and produces large amounts of NO as a defense mechanism. It is the proximate cause of septic shock and may play a role in many diseases with an autoimmune etiology.

The canonical reaction catalyzed by NOS is:

  • L-arginine + 3/2 NADPH + H+ + 2 O2 = citrulline + nitric oxide + 3/2 NADP+

NOS isoforms catalyze many other leak and side reactions such as superoxide production at the expense of NADPH, so this stoichiometry is not generally observed. The unusual stoichiometry reflects the three electrons supplied per NO by NADPH; NO is a free radical with an unpaired electron.

NOSs are unusual in that they require five cofactors. Eukaryotic NOS isozymes are catalytically self-sufficient. The electron flow in the NO synthase reaction is: NADPH --> FAD --> FMN --> heme --> O2. Tetrahydrobiopterin provides an additional electron during the catalytic cycle which is replaced during turnover. ). NOS is the only known enzyme that binds flavin adenine dinucleotide (FAD), flavin mononucleotide (FMN), heme, tetrahydrobiopterin (BH4) and calmodulin.

Read more about Nitric Oxide Synthase:  Species Distribution, Function, Classification, Chemical Reaction, Structure

Other articles related to "nitric oxide synthase, nitric oxide":

Nitric Oxide Synthase - Structure
... O2 by donating a single electron, which is then recaptured to enable nitric oxide release ... The first nitric oxide synthase to be identified was found in neuronal tissue (NOS1 or nNOS) the endothelial NOS (eNOS or NOS3) was the third to be identified ... Nitric oxide may itself regulate NOS expression and activity ...
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... Relaxation of bovine coronary artery and activation of coronary arterial guanylate cyclase by nitric oxide, nitroprusside and a carcinogenic nitrosoamine ... of vascular smooth muscle relaxation by organic nitrates, nitrites, nitroprusside and nitric oxide Evidence for the involvement of Snitrosothiols as ... pharmacological and chemical properties that are identical to those for nitric oxide radical ...
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... Impaired NO synthesis Nitric oxide is known as an important stimulator of cell proliferation, maturation and differentiation ... Thus, nitric oxide increases fibroblast proliferation and thereby collagen production in wound healing ... Also, L-arginine and nitric oxide are required for proper cross linking of collagen fibers, via proline, to minimize scarring and maximize the ...
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... complex but also physically interacts with and inhibits the activity of neuronal nitric oxide synthase ... of this protein destabilizes the neuronal nitric oxide synthase dimer, a conformation necessary for activity, and it may regulate numerous biologic processes through its effects on nitric oxide synthase ...
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... At the occipital scalp, androgens enhance inducible nitric oxide synthase (iNOS), which catalyzes production of nitric oxide from L-arginine ... The induction of nitric oxide synthase usually occurs in an oxidative environment, where high levels of nitric oxide produced interact with superoxide, leading to peroxynitrite formation and cell ... The gene coding for nitric oxide synthase is on human chromosome 17 ...