View source for Nitric oxide

{{distinguish|nitrous oxide}}
{{Other uses|NO (disambiguation)}}

{{Chembox
| Verifiedfields = changed
| Watchedfields = changed
|  verifiedrevid = 269505247
|  ImageFileL1 = Nitric-oxide-2D.png
|   ImageNameL1 = Stick model of nitric oxide
|  ImageFileR1 = Nitric-oxide-3D-vdW.png
|   ImageNameR1 = Spacefill model of nitric oxide
|  PIN = Nitric oxide
|  SystematicName = Nitroso
| Section1 = {{Chembox Identifiers
|  CASNo_Ref = changed
| CASNo = 15917-77-8
|   CASNo_Comment = (<sup>15</sup>''N'')
|   CASNo1 = 10102-43-9
|   CASNo1_Ref = {{cascite}}
|  PubChem = 12858183
|   PubChem_Comment = (<sup>15</sup>''N'')
|   PubChem_Ref = {{Pubchemcite}}
|   PubChem1 = 145068
|   PubChem1_Ref = {{Pubchemcite}}
|  ChemSpiderID = 21170263
|   ChemSpiderID_Comment = (<sup>15</sup>''N'')
|   ChemSpiderID_Ref = {{Chemspidercite}}
|   ChemSpiderID1 = 127983
|   ChemSpiderID1_Ref = {{Chemspidercite}}
|  EINECS = 233-271-0
|  UNNumber = UN 1660
|  DrugBank = DB00435
|  KEGG = C00533
|  ChEBI = 16480
|  RTECS = QX0525000
|  ATCCode_prefix = R07
|   ATCCode_suffix = AX01
|  SMILES = [N]=O
|  InChI = 1S/NO/c1-2
|  InChIKey = MWUXSHHQAYIFBG-UHFFFAOYSA-N
|  Gmelin = 451
|  3DMet = B00122}}
| Section2 = {{Chembox Properties
| Formula = NO
| MolarMass = 30.006 g/mol
| Appearance = colourless gas <br> [[paramagnetic]]
| Density = 1.269 g/cm<sup>3</sup> (liquid)<br/>1.3402 g/l (gas)
| MeltingPtC = −163.6 
| BoilingPtC = −150.8
| Solubility = 7.4 ml/100 ml ([[STP]])
| SolubleOther = soluble in [[alcohol]], [[carbon disulfide|CS<sub>2</sub>]]
| RefractIndex = 1.0002697
 }}
| Section3 = {{Chembox Structure
| MolShape = linear, ''C''<sub>∞v</sub>
| Dipole = 
 }}
| Section4 = {{Chembox Thermochemistry
| DeltaHf = +90.29 kJ/mol
| Entropy = 210.76 J&thinsp;K<sup>−1</sup>&thinsp;mol<sup>−1</sup>
 }}
| Section5 = {{Chembox Pharmacology
| AdminRoutes = [[Inhalation]]
| Bioavail = good
| Metabolism = via pulmonary capillary bed
| HalfLife = 2–6 seconds
| ProteinBound =
| Excretion = 
| Legal_status = 
| Legal_US = 
| Legal_UK = 
| Legal_AU = 
| Legal_CA =
| PregCat =
| PregCat_AU =
| PregCat_US = 
 }}
| Section7 = {{Chembox Hazards
| ExternalMSDS = [http://avogadro.chem.iastate.edu/MSDS/nitric_oxide.pdf External MSDS]
| EUIndex = Not listed
| EUClass = 
| RPhrases = {{R26}}, {{R34}}
| SPhrases = {{S1}}, {{S9}}, {{S26}}, {{S36}}, {{S45}}
| MainHazards = Toxic
| NFPA-H = 3
| NFPA-F = 0
| NFPA-R = 0
| NFPA-O = OX
| FlashPt = Non-flammable
| LD50 = 
| PEL = 
 }}
| Section8 = {{Chembox Related
| OtherFunctn = [[Nitrous oxide]]<br/>[[Dinitrogen trioxide]]<br/>[[Nitrogen dioxide]]<br/>[[Dinitrogen tetroxide]]<br/>[[Dinitrogen pentoxide]]
| Function = [[nitrogen]] [[oxide]]s
| OtherCpds =
 }}
}}
'''Nitric oxide''' (common name) or '''nitrogen monoxide''' (systematic name) is a [[chemical compound]] with [[chemical formula]] [[Nitrogen|N]][[Oxygen|O]]. This [[gas]] is an important [[signaling molecule]] in the body of [[mammal]]s, including [[human]]s, and is an extremely important [[Reaction intermediate|intermediate]] in the [[chemical industry]]. It is also an [[air pollutant]] produced by cigarette smoke, [[automobile]] [[engine]]s and [[power plant]]s.

NO is an important messenger molecule involved in many physiological and pathological processes within the mammalian body both beneficial and detrimental.<ref>{{cite journal|pmid=10390607|year=1999|last1=Hou|first1=YC|last2=Janczuk|first2=A|last3=Wang|first3=PG|title=Current trends in the development of nitric oxide donors.|volume=5|issue=6|pages=417–41|journal=Current pharmaceutical design}}</ref> Appropriate levels of NO production are important in protecting an organ such as the liver from [[ischemic damage]]. However sustained levels of NO production result in direct tissue toxicity and contribute to the vascular collapse associated with septic shock, whereas chronic expression of NO is associated with various carcinomas and inflammatory conditions including juvenile diabetes, multiple sclerosis, arthritis and ulcerative colitis.<ref>{{cite journal|pmid=9366709|year=1997|last1=Taylor|first1=BS|last2=Kim|first2=YM|last3=Wang|first3=Q|last4=Shapiro|first4=RA|last5=Billiar|first5=TR|last6=Geller|first6=DA|title=Nitric oxide down-regulates hepatocyte-inducible nitric oxide synthase gene expression.|volume=132|issue=11|pages=1177–83|journal=Archives of surgery (Chicago, Ill. : 1960)}}</ref> 

Nitric oxide should not be confused with [[nitrous oxide]] (N<sub>2</sub>O), an [[general anaesthetic|anesthetic]] and [[greenhouse gas]], or with [[nitrogen dioxide]] (NO<sub>2</sub>), a brown [[toxic gas]] and a major [[air pollutant]]. However, nitric oxide is rapidly oxidised in air to nitrogen dioxide, as [[Humphrey Davy]] found to his discomfort when he inhaled the gas early in his career. 

Despite being a simple molecule, NO is a fundamental player in the fields of [[neuroscience]], [[physiology]], and [[immunology]], and was proclaimed “[[Molecule of the Year]]” in 1992.<ref name="undefined">{{cite journal
| author = Elizabeth Culotta and Daniel E. Koshland Jr
| year = 1992
| title = NO news is good news. (nitric oxide; includes information about other significant advances & discoveries of 1992) (Molecule of the Year)
| journal = Science
| volume = 258
| issue = 5090
| pages = 1862–1864
| doi = 10.1126/science.1361684
| pmid = 1361684
}}</ref>

==Reactions==
*When exposed to [[oxygen]], NO is converted into [[nitrogen dioxide]].
:: 2 NO + O<sub>2</sub> → 2 NO<sub>2</sub>
:This conversion has been speculated as occurring via the ONOONO intermediate. In water, NO reacts with oxygen and water to form HNO<sub>2</sub> or [[nitrous acid]]. The reaction is thought to proceed via the following [[stoichiometry]]:
:: 4 NO + O<sub>2</sub> + 2 H<sub>2</sub>O → 4 HNO<sub>2</sub>

*NO will react with [[fluorine]], [[chlorine]], and [[bromine]] to form the XNO species, known as the nitrosyl halides, such as [[nitrosyl chloride]]. Nitrosyl iodide can form but is an extremely short-lived species and tends to reform I<sub>2</sub>.
:: 2 NO + Cl<sub>2</sub> → 2 NOCl
*[[Nitroxyl]] (HNO) is the reduced form of nitric oxide.

*Nitric oxide reacts with [[acetone]] and an [[alkoxide]] to a ''diazeniumdiolate'' or ''nitrosohydroxylamine'' and [[methyl acetate]]:<ref>{{cite journal|doi=10.1002/jlac.18983000108|title=Ueber Synthesen stickstoffhaltiger Verbindungen mit Hülfe des Stickoxyds|year=1898|last1=Traube|first1=Wilhelm|journal=Justus Liebig's Annalen der Chemie|volume=300|pages=81}}</ref>

:[[File:TraubeReaction.svg|400px|Traube reaction]]

:This is a very old reaction (1898) but of interest today in NO [[prodrug]] research. Nitric oxide can also react directly with sodium methoxide, forming [[sodium formate]] and [[nitrous oxide]].<ref>{{cite journal|doi=10.1021/jo7020423|title=Nitric Oxide Reacts with Methoxide|year=2008|last1=Derosa|first1=Frank|last2=Keefer|first2=Larry K.|last3=Hrabie|first3=Joseph A.|journal=The Journal of Organic Chemistry|volume=73|pages=1139|pmid=18184006|issue=3}}</ref>

===Preparation===
[[File:Nitric oxide production.png|thumb|right|200px|Nitric oxide production]]
Commercially, NO is produced by the [[oxidation]] of [[ammonia]] at 750 °C to 900 °C (normally at 850 °C) in the presence of [[platinum]] as [[catalyst]]:

:4 NH<sub>3</sub> + 5 O<sub>2</sub> → 4 NO + 6 H<sub>2</sub>O

The uncatalyzed [[endothermic]] reaction of [[Oxygen|O<sub>2</sub>]] and [[Nitrogen|N<sub>2</sub>]], which is performed at high temperature (>2000 °C) by lightning has not been developed into a practical commercial synthesis (see [[Birkeland–Eyde process]]):

:N<sub>2</sub> + O<sub>2</sub> → 2 NO

In the laboratory, nitric oxide is conveniently generated by reduction of [[nitric acid]] with [[copper]]:

:8 HNO<sub>3</sub> + 3 Cu → 3 Cu(NO<sub>3</sub>)<sub>2</sub> + 4 H<sub>2</sub>O + 2 NO

or by the reduction of nitrous acid in the form of [[sodium nitrite]] or [[potassium nitrite]]:

: 2 NaNO<sub>2</sub> + 2 NaI + 2 H<sub>2</sub>SO<sub>4</sub> → I<sub>2</sub> + 4 NaHSO<sub>4</sub> + 2 NO
: 2 NaNO<sub>2</sub> + 2 FeSO<sub>4</sub> + 3 H<sub>2</sub>SO<sub>4</sub> → Fe<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub> + 2 NaHSO<sub>4</sub> + 2 H<sub>2</sub>O + 2 NO
: 3 KNO<sub>2</sub> (l) + KNO<sub>3</sub> (l) + Cr<sub>2</sub>O<sub>3</sub>(s) → 2 K<sub>2</sub>CrO<sub>4</sub>(s) + 4 NO (g)
The iron(II) sulfate route is simple and has been used in undergraduate laboratory experiments.

So-called [[NONOate]] compounds are also used for NO generation.

===Coordination chemistry===
{{Main|Metal nitrosyl}}
NO forms complexes with all [[transition metal]]s to give complexes called [[metal nitrosyl]]s. The most common bonding mode of NO is the terminal linear type (M-NO). The angle of the M-N-O group can vary from 160° to 180° but are still termed as "linear". In this case, the NO group is considered a 3-electron donor under the covalent (neutral) method of electron counting, or a 2-electron donor under the ionic method.<ref>Robert H. Crabtree: [http://books.google.com/books?id=0bXMwefSs-kC&pg=PA32 "The Organometallic Chemistry of the Transition Metals"], John Wiley and Sons, 2005, ISBN 0471662569, p. 32.</ref> In the case of a bent M-N-O conformation, the NO group can be considered a one-electron donor using neutral counting, or a 2-electron donor using ionic counting.<ref>Robert H. Crabtree: [http://books.google.com/books?id=0bXMwefSs-kC&pg=PA96 "The Organometallic Chemistry of the Transition Metals"], John Wiley and Sons, 2005, ISBN 0471662569, pp. 96–98.</ref> One can view such complexes as derived from NO<sup>+</sup>, which is isoelectronic with CO.

Nitric oxide can serve as a one-electron pseudohalide. In such complexes, the M-N-O group is characterized by an angle between 120° and&nbsp;140°.

The NO group can also bridge between metal centers through the nitrogen atom in a variety of geometries.

===Measurement of nitric oxide concentration===
[[File:The production and diffusion of nitric oxide (NO) (white) in the cytoplasm (green) of clusters of conifer cells one hour after mechanical agitation.jpg|thumb|Nitric oxide (white) in [[pinophyta|conifer]] cells, visualized using DAF-2 DA (diaminofluorescein diacetate)]]
The concentration of nitric oxide can be determined using a simple [[chemiluminescence|chemiluminescent reaction]] involving [[ozone]]:<ref>{{cite journal|doi=10.1021/ac60288a034|title=Homogeneous chemiluminescent measurement of nitric oxide with ozone. Implications for continuous selective monitoring of gaseous air pollutants|year=1970|last1=Fontijn|first1=Arthur.|last2=Sabadell|first2=Alberto J.|last3=Ronco|first3=Richard J.|journal=Analytical Chemistry|volume=42|pages=575}}</ref> A sample containing nitric oxide is mixed with a large quantity of ozone. The nitric oxide reacts with the ozone to produce [[oxygen]] and [[nitrogen dioxide]]. This reaction also produces [[light]] ([[chemiluminescence]]), which can be measured with a [[photodetector]]. The amount of light produced is proportional to the amount of nitric oxide in the sample.

: NO + O<sub>3</sub> → NO<sub>2</sub> + O<sub>2</sub> + light

Other methods of testing include [[electrochemistry|electroanalysis]] (amperometric approach), where NO reacts with an electrode to induce a current or voltage change. The detection of NO radicals in biological tissues is particularly difficult due to the short lifetime and concentration of these radicals in tissues. One of the few practical methods is [[spin trapping]] of nitric oxide with iron-[[dithiocarbamate]] complexes and subsequent detection of the mono-nitrosyl-iron complex with [[electron paramagnetic resonance]] (EPR).<ref>{{cite journal|doi=10.1016/S0076-6879(02)59169-2|title=Iron dithiocarbamate as spin trap for nitric oxide detection: Pitfalls and successes|year=2002|last1=Vanin|first1=A|last2=Huisman|first2=A|last3=Vanfaassen|first3=E|volume=359|pages=27}}</ref><ref>{{cite journal|pmid=11942795|year=2002|last1=Nagano|first1=T|last2=Yoshimura|first2=T|title=Bioimaging of nitric oxide.|volume=102|issue=4|pages=1235–70|journal=Chemical reviews|doi=10.1021/cr010152s}}</ref>

A group of [[fluorescent dye]] indicators that are also available in [[acetyl]]ated form for intracellular measurements exist. The most common compound is [[4,5-diaminofluorescein]] (DAF-2).<ref name="undefined">{{cite journal
| author = Kojima H, Nakatsubo N, Kikuchi K, Kawahara S, Kirino Y, Nagoshi H, Hirata Y, Nagano T
| year = 1998
| title = Detection and imaging of nitric oxide with novel fluorescent indicators: diaminofluoresceins
| journal = Anal. Chem.
| volume = 70
| issue = 13
| pages = 2446–2453| pmid = 9666719
| doi = 10.1021/ac9801723
}}</ref>

==Production environmental effects==
From a thermodynamic perspective, NO is unstable with respect to O<sub>2</sub> and N<sub>2</sub>, although this conversion is very slow at ambient temperatures in the absence of a [[catalyst]]. Because the heat of formation of NO is [[endothermic]], its synthesis from molecular nitrogen and oxygen requires elevated temperatures above 1000 °C. A major natural source is [[lightning]]. The use of [[internal combustion engine]]s has drastically increased the presence of nitric oxide in the environment. One purpose of [[catalytic converter]]s in cars is to minimize NO emission by catalytic reversion to O<sub>2</sub> and N<sub>2</sub>.

Nitric oxide in the air may convert to [[nitric acid]], which has been implicated in [[acid rain]]. Furthermore, both NO and NO<sub>2</sub> participate in [[ozone layer depletion]]. Nitric oxide is a small highly diffusible gas and a ubiquitous bioactive molecule.

==Technical applications==
Although NO has relatively few direct uses, it is produced on a massive scale as an intermediate in the [[Ostwald process]] for the synthesis of [[nitric acid]] from [[ammonia]]. In 2005, the US alone produced 6 million metric tons of nitric acid.<ref>“Production: Growth is the Norm” Chemical and Engineering News, July 10, 2006, p. 59.</ref> It finds use in the [[semiconductor]] industry for various processes. In one of its applications it is used along with [[nitrous oxide]] to form oxynitride gates in [[CMOS]] devices.

===Miscellaneous applications===
Nitric oxide can be used for detecting surface radicals on polymers. Quenching of surface [[Radical (chemistry)|radicals]] with nitric oxide results in incorporation of nitrogen, which can be quantified by means of [[X-ray photoelectron spectroscopy]].

==Biological functions==
{{Main|Biological functions of nitric oxide}}
NO is one of the few gaseous signaling molecules known and is additionally exceptional due to the fact that it is a radical gas. It is a key [[vertebrate]] [[signal transduction|biological messenger]], playing a role in a variety of biological processes. Nitric oxide, known as the '[[endothelium-derived relaxing factor]]', or 'EDRF', is biosynthesized endogenously from [[L-arginine]], [[oxygen]] and [[NADPH]] by various [[nitric oxide synthase]] (NOS) [[enzyme]]s.  Reduction of inorganic nitrate may also serve to make nitric oxide. The [[endothelium]] (inner lining) of [[blood vessel]]s uses nitric oxide to signal the surrounding [[smooth muscle]] to relax, thus resulting in [[vasodilation]] and increasing blood flow. Nitric oxide is highly reactive (having a lifetime of a few seconds), yet diffuses freely across membranes. These attributes make nitric oxide ideal for a transient [[paracrine]] (between adjacent cells) and [[autocrine]] (within a single cell) signaling molecule.<ref name="stryer">{{cite book|last = Stryer| first = Lubert| title = Biochemistry, 4th Edition| publisher = W.H. Freeman and Company|year = 1995| pages = 732| isbn = 0-7167-2009-4}}</ref> 
The production of nitric oxide is elevated in populations living at high altitudes, which helps these people avoid [[Hypoxia (medical)|hypoxia]] by aiding in pulmonary vasculature [[vasodilation]]. Effects include vasodilatation, [[neurotransmitter|neurotransmission]] (see [[gasotransmitters]]), modulation of the [[hair|hair cycle]], production of reactive nitrogen intermediates and [[erection|penile erections]] (through its ability to [[vascular resistance|vasodilate]]). [[Glyceryl trinitrate (pharmacology)|Nitroglycerin]] and [[amyl nitrite]] serve as vasodilators because they are converted to nitric oxide in the body. [[Sildenafil|Sildenafil citrate]], popularly known by the trade name ''Viagra'', stimulates erections primarily by enhancing signaling through the nitric oxide pathway in the penis.

Nitric oxide (NO) contributes to vessel homeostasis by inhibiting vascular smooth muscle contraction and growth, platelet aggregation, and leukocyte adhesion to
the endothelium. Humans with [[atherosclerosis]], [[diabetes]], or [[hypertension]] often show impaired NO pathways.<ref>{{cite journal
 |last = Dessy
 |first = C.
 |last2 = Ferron
 |first2 = O.
 |title = Pathophysiological Roles of Nitric Oxide: In the Heart and the Coronary
Vasculature|doi=10.2174/1568014043355348
 |journal = Current Medical Chemistry – Anti-Inflammatory & Anti-Allergy Agents in Medicinal Chemistry
 |volume = 3
 |issue = 3
 |pages = 207–216
 |year = 2004}}</ref> A high salt intake was demonstrated to attenuate NO production, although bioavailability remains unregulated.<ref>{{cite journal|url=http://content.karger.com/ProdukteDB/produkte.asp?Aktion=ShowPDF&ProduktNr=223997&Ausgabe=228460&ArtikelNr=63555|pmid=12207094|year=2002|last1=Osanai|first1=T|last2=Fujiwara|first2=N|last3=Saitoh|first3=M|last4=Sasaki|first4=S|last5=Tomita|first5=H|last6=Nakamura|first6=M|last7=Osawa|first7=H|last8=Yamabe|first8=H|last9=Okumura|first9=K|title=Relationship between salt intake, nitric oxide and asymmetric dimethylarginine and its relevance to patients with end-stage renal disease.|volume=20|issue=5|pages=466–8|journal=Blood purification|doi=10.1159/000063555}}</ref>

Nitric oxide is also generated by phagocytes ([[monocyte]]s, [[macrophage]]s, and [[neutrophil]]s) as part of the human [[immune response]]. Phagocytes are armed with inducible nitric oxide synthase (iNOS), which is activated by [[interferon-gamma]] (IFN-γ) as a single signal or by [[tumor necrosis factor]] (TNF) along with a second signal.<ref>Gorczyniski and Stanely, Clinical Immunology. Landes Bioscience; Austin, TX. ISBN 1570596255</ref> On the other hand, [[transforming growth factor-beta]] (TGF-β) provides a strong inhibitory signal to iNOS, whereas [[interleukin]]-4 (IL-4) and IL-10 provide weak inhibitory signals. In this way the immune system may regulate the armamentarium of phagocytes that play a role in inflammation and immune responses. Nitric oxide secreted as an immune response is as free radicals and is toxic to bacteria; the mechanism for this includes DNA damage<ref>
{{cite journal|last1=Wink|first=DA |coauthors=et.al.|
title=DNA deaminating ability and genotoxicity of nitric oxide and its progenitors|journal=Science|year=1991 |volume=254|issue=5034|pages=1001–3|pmid=1948068|doi=10.1126/science.1948068
}} About killing of salmonella bacteria.</ref><ref>
{{cite journal|last1=Nguyen|first=T |coauthors= Brunson D, Crespi CL, Penman BW, Wishnok JS, Tannenbaum SR|title= DNA damage and mutation in human cells exposed to nitric oxide in vitro|journal= Proc Natl Acad Sci USA|year= 1992|volume=89|issue=7|pages=3030–4|pmid=1557408|doi=10.1073/pnas.89.7.3030|pmc=48797}} Free text.</ref><ref>{{cite journal|last1=Li|first1=CQ |coauthors=Pang B, Kiziltepe T, Trudel LJ, Engelward BP, Dedon PC, Wogan GN| title=Threshold Effects of Nitric Oxide-Induced Toxicity and Cellular Responses in Wild-Type and p53-Null Human Lymphoblastoid Cells|journal=Chem Res Toxicol|year=2006 |volume= 19|issue=3|pages=399–406|pmid=16544944|doi=10.1021/tx050283e|pmc=2570754}} free  text.</ref> and degradation of iron sulfur centers into iron ions and [[metal nitrosyl|iron-nitrosyl]] compounds.<ref>{{cite journal| last1=Hibbs|first1=JB|coauthors= Taintor RR, Vavrin Z, Rachlin EM|year=1988|title = Nitric oxide: a cytotoxic activated macrophage effector molecule|journal=Biochem Biophys Res Commun |volume=157|issue=1|pages=87–94|pmid=3196352| doi=10.1016/S0006-291X(88)80015-9}}</ref> In response, however, many bacterial pathogens have evolved mechanisms for nitric oxide resistance.<ref>{{cite book |author=C. A. Janeway, et al. |title=Immunobiology: the immune system in health and disease |publisher=Garland Science |location=New York |year=2005 |edition=6th |isbn=0-8153-4101-6}}</ref> Because nitric oxide might serve as an ''inflammometer'' in conditions like [[asthma]], there has been increasing interest in the use of [[exhaled nitric oxide]] as a [[breath test]] in diseases with [[airway]] inflammation.

Nitric oxide can contribute to [[reperfusion injury]] when an excessive amount produced during reperfusion (following a period of [[ischemia]]) reacts with [[superoxide]] to produce the damaging oxidant [[peroxynitrite]]. In contrast, inhaled nitric oxide has been shown to help survival and recovery from [[paraquat]] poisoning, which produces lung tissue–damaging superoxide and hinders NOS metabolism.

In plants, nitric oxide can be produced by any of four routes: (i) L-arginine-dependent nitric oxide synthase,<ref>{{cite journal|title=Cellular and subcellular localization of endogenous nitric oxide in young and senescent pea plants|author=Corpas, F. J. ''et al.''|journal=Plant Physiology|volume=136 |issue=1 |pages=2722–33 |year=2004|doi=10.1104/pp.104.042812|pmid=15347796|pmc=523336}}</ref><ref>{{cite journal |author=Corpas, F. J. ''et al.''|title=Constitutive arginine-dependent nitric oxide synthase activity in different organs of pea seedlings during plant development|journal=Planta|volume=224|issue=2 |pages=246–54|year=2006|doi=10.1007/s00425-005-0205-9 |pmid=16397797}}</ref><ref>{{cite journal |author=Valderrama, R. ''et al.''|title=Nitrosative stress in plants|journal=FEBS Lett|volume=581|issue=3 |pages=453–61|year=2007|doi=10.1016/j.febslet.2007.01.006 |pmid=17240373}}</ref> (although the existence of animal NOS homologs in plants is debated),<ref>{{cite journal |author=Corpas et al.|title=Enzymatic sources of nitric oxide in plant cells – beyond one protein–one function|journal=New Phytologist|volume=162|issue= |pages=246–7|year=2004|doi=10.1111/j.1469-8137.2004.01058.x |last2=Barroso |first2=Juan B. |last3=Del Rio |first3=Luis A.}}</ref> (ii) by plasma membrane-bound [[nitrate reductase]], (iii) by mitochondrial electron transport chain, or (iv) by non-enzymatic reactions. It is a signaling molecule, acts mainly against oxidative stress and also plays a role in plant pathogen interactions. Treating cut flowers and other plants with nitric oxide has been shown to lengthen the time before wilting.<ref>Judy Siegel-Itzkovich. [http://www.studentbmj.com/issues/99/09/news/313.php Viagra makes flowers stand up straight]. ''[[Student BMJ]]'', September 1999.</ref>

An important biological reaction of nitric oxide is S-[[nitrosylation]], the conversion of [[thiol]] groups, including [[cysteine]] residues in proteins, to form S-nitrosothiols (RSNOs). S-[[Nitrosylation]] is a mechanism for dynamic, post-translational regulation of most or all major classes of protein.

===Mechanism of action===
There are several mechanisms by which NO has been demonstrated to affect the biology of living cells. These include oxidation of iron-containing proteins such as ribonucleotide reductase and aconitase, activation of the soluble [[guanylate cyclase]], ADP ribosylation of proteins, protein sulfhydryl group [[nitrosylation]], and iron regulatory factor activation.<ref>{{cite journal|pmid=7658698|year=1995|last1=Shami|first1=PJ|last2=Moore|first2=JO|last3=Gockerman|first3=JP|last4=Hathorn|first4=JW|last5=Misukonis|first5=MA|last6=Weinberg|first6=JB|title=Nitric oxide modulation of the growth and differentiation of freshly isolated acute non-lymphocytic leukemia cells.|volume=19|issue=8|pages=527–33|journal=Leukemia research|doi=10.1016/0145-2126(95)00013-E}}</ref> NO has been demonstrated to activate [[NF-κB]] in peripheral blood mononuclear cells, an important transcription factor in iNOS gene expression in response to inflammation.<ref>{{cite journal|url=http://www.jhep-elsevier.com/article/S0168-8278(99)80270-0/abstract|author=Kaibori M., Sakitani K., Oda M., Kamiyama Y., Masu Y. and Okumura T.|year=1999|title=Immunosuppressant FK506 inhibits inducible nitric oxide synthase gene expression at a step of NF-κB activation in rat hepatocytes|journal=J. Hepatol.|volume=30|pages=1138–1145|doi=10.1016/S0168-8278(99)80270-0|pmid=10406194|issue=6}}</ref> It was found that NO acts through the stimulation of the soluble guanylate cyclase, which is a heterodimeric enzyme with subsequent formation of cyclic GMP. Cyclic GMP activates [[protein kinase G]], which causes phosphorylation of myosin light chain phosphatase, and therefore inactivation of [[myosin light-chain kinase]], and leads ultimately to the dephosphorylation of the myosin light chain, causing smooth muscle relaxation.<ref>{{cite journal|pmid=18040024|year=2007|last1=Surks|first1=HK|title=cGMP-dependent protein kinase I and smooth muscle relaxation: a tale of two isoforms.|volume=101|issue=11|pages=1078–80|doi=10.1161/CIRCRESAHA.107.165779|journal=Circulation research}}</ref>

===Use in pediatric intensive care===
Nitric oxide/oxygen blends are used in critical care to promote capillary and pulmonary dilation to treat primary [[pulmonary hypertension]] in neonatal patients<ref>{{cite journal |author=Finer NN, Barrington KJ |title=Nitric oxide for respiratory failure in infants born at or near term |journal=Cochrane Database Syst Rev |volume= |issue=4 |pages=CD000399 |year=2006 |pmid=17054129 |doi=10.1002/14651858.CD000399.pub2}}</ref><ref>{{cite journal |author=Chotigeat U, Khorana M, Kanjanapattanakul W |title=Inhaled nitric oxide in newborns with severe hypoxic respiratory failure |journal=J Med Assoc Thai |volume=90 |issue=2 |pages=266–71 |year=2007 |pmid=17375630}}</ref> post-meconium aspiration and related to birth defects. These are often a last-resort gas mixture before the use of [[extracorporeal membrane oxygenation]] (ECMO). Nitric oxide therapy has the potential to significantly increase the quality of life and, in some cases, save the lives of infants at risk for pulmonary vascular disease.<ref>{{cite journal|pmid=10690334|year=1999|last1=Hayward|first1=CS|last2=Kelly|first2=RP|last3=MacDonald|first3=PS|title=Inhaled nitric oxide in cardiology practice.|volume=43|issue=3|pages=628–38|journal=Cardiovascular research|doi=10.1016/S0008-6363(99)00114-5}}</ref>

===Pharmacology===

Nitric oxide is considered an [[Antianginal|anti]][[Angina pectoris|anginal]] drug: it causes [[vasodilation]], which can help with ischemic pain known as angina by decreasing the cardiac workload. By dilating the veins there is less blood returned to the heart per cycle<ref name="Jonathan Abrams 1996">{{cite journal|doi=10.1016/S0002-9149(96)00186-5|title=Beneficial actions of nitrates in cardiovascular disease|year=1996|last1=Abrams|first1=J|journal=The American Journal of Cardiology|volume=77|pages=C31}}</ref>. This decreases the amount of volume that the heart has to pump. Nitroglycerin pills, taken sublingually (under the tongue), are used to prevent or treat acute chest pain. The nitroglycerin reacts with a [[thiol|sulfhydryl]] group (–SH) to produce nitric oxide, which eases the pain by causing vasodilation. Recent evidence suggests that nitrates may be beneficial for treatment of angina due to reduced myocardial oxygen consumption both by decreasing preload and afterload and by some direct vasodilation of coronary vessels<ref name="Jonathan Abrams 1996"/>

==References==
{{Reflist|2}}

==Further reading==
*Butler A. and Nicholson R.; [http://books.google.com/books?id=0d1Z0m76YeYC&printsec=frontcover "Life, death and NO."] Cambridge 2003. ISBN 978-0-85404-686-7.
*van Faassen, E. E.; Vanin, A. F. (eds); [http://books.google.com/books?id=UJ4glFNEcn0C&printsec=frontcover "Radicals for life: The various forms of Nitric Oxide."] Elsevier, Amsterdam 2007. ISBN 978-0-444-52236-8.

==External links==
*[http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc13/icsc1311.htm International Chemical Safety Card 1311]
*[http://www.npi.gov.au/database/substance-info/profiles/67.html National Pollutant Inventory – Oxides of nitrogen Fact Sheet]
*[http://www.nobel.se/medicine/laureates/1998/index.html 1998 Nobel Prize in Physiology/Medicine for discovery of NO's role in cardiovascular regulation]
*[http://www.diabetesincontrol.com/annodyne/burkeseries.php Nitric Oxide and its Role in Diabetes, Wound Healing and Peripheral Neuropathy]
*[http://mattson.creighton.edu/NOx/index.html Microscale Gas Chemistry: Experiments with Nitrogen Oxides]
*[http://www.livescience.com/humanbiology/060817_brain_boot.html Your Brain Boots Up Like a Computer] – new insights about the biological role of nitric oxide.
*[http://www.podiatrytoday.com/article/5164 Assessing The Potential of Nitric Oxide in the Diabetic Foot]
*[http://www.sciencedaily.com/releases/2007/11/071121213845.htm New Discoveries About Nitric Oxide Can Provide Drugs For Schizophrenia]
*[http://ull.chemistry.uakron.edu/erd/Chemicals/8000/6828.html Nitric Oxide at the Chemical Database]

{{Neurotransmitters}}

{{DEFAULTSORT:Nitric Oxide}}
[[Category:Oxides]]
[[Category:Inorganic nitrogen compounds]]
[[Category:Neurotransmitters]]
[[Category:Nitrogen metabolism]]
[[Category:Free radicals]]

[[ar:أحادي أكسيد النيتروجين]]
[[bn:নাইট্রিক অক্সাইড]]
[[ca:Monòxid de nitrogen]]
[[cs:Oxid dusnatý]]
[[da:Nitrogenmonoxid]]
[[de:Stickstoffmonoxid]]
[[es:Óxido de nitrógeno (II)]]
[[fr:Monoxyde d'azote]]
[[ko:일산화 질소]]
[[hi:नाइट्रिक ऑक्साइड]]
[[it:Monossido di azoto]]
[[he:חנקן חמצני]]
[[hu:Nitrogén-monoxid]]
[[nl:Stikstofmonoxide]]
[[ja:一酸化窒素]]
[[no:Nitrogenmonoksid]]
[[pl:Tlenek azotu(II)]]
[[pt:Óxido nítrico]]
[[ro:Monoxid de azot]]
[[ru:Оксид азота(II)]]
[[simple:Nitric oxide]]
[[sk:Oxid dusnatý]]
[[sr:Азот-моноксид]]
[[fi:Typpioksidi]]
[[sv:Kväveoxid]]
[[tr:Azot oksit]]
[[uk:Монооксид азоту]]
[[vi:Mônôxít nitơ]]
[[zh-yue:一氧化氮]]
[[zh:一氧化氮]]
[[Category:2Fix]]