Nicotinamide adenine dinucleotide
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2008-06-29T19:08:37Z
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{{featured article}}
{{Chembox new
| ImageFile = NAD+ phys.svg
| ImageSize = 180px
| IUPACName =
| OtherNames = Diphosphopyridine nucleotide (DPN<sup>+</sup>), Coenzyme I
| Section1 = {{Chembox Identifiers
| CASNo = 53-84-9
| PubChem = 925
| SMILES = <small>C1=CC(=C[N+](=C1)C2 C(C(C(O2)COP(=O)([O-])OP(=O) (O)OCC3C(C(C(O3)N4C=NC5=C 4N=CN=C5N)O)O)O)O)C(=O)N</small>
| MeSHName =
| KEGG = C00003
| ChEBI = 13389
}}
| Section2 = {{Chembox Properties
| Formula = [[Carbon|C]]<sub>21</sub>[[Hydrogen|H]]<sub>27</sub>[[Nitrogen|N]]<sub>7</sub>[[Oxygen|O]]<sub>14</sub>[[Phosphorus|P]]<sub>2</sub>
| MolarMass = 663.425
| Appearance = White powder
| Density =
| MeltingPt = 160 °C
}}
| Section3 = {{Chembox Hazards
| Solubility =
| MainHazards = Not hazardous
| NFPA-H = 1
| NFPA-F = 1
| NFPA-R = 0
| RTECS = UU3450000
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'''Nicotinamide adenine dinucleotide''', abbreviated '''NAD<sup>+</sup>''', is a [[coenzyme]] found in all living [[cell (biology)|cell]]s. The compound is a dinucleotide, since it consists of two [[nucleotide]]s joined through their phosphate groups: with one nucleotide containing an [[adenosine]] ring, and the other containing [[nicotinamide]].
In [[metabolism]], NAD<sup>+</sup> is involved in [[redox]] reactions, carrying [[electron]]s from one reaction to another. The coenzyme is therefore found in two forms in cells: NAD<sup>+</sup> is an [[oxidizing agent]] – it accepts electrons from other molecules and becomes [[redox|reduced]], this reaction forms NADH, which can then be used as a [[reducing agent]] to donate electrons. These electron transfer reactions are the main function of NAD<sup>+</sup>. However, it is also used in other cellular processes, notably as a substrate of enzymes that add or remove [[functional group|chemical groups]] from proteins, in [[posttranslational modification]]s. Due to the importance of these functions, the [[enzyme]]s involved in NAD<sup>+</sup> metabolism are targets for [[drug discovery]].
In organisms, NAD<sup>+</sup><sup></sup> can be synthesized from scratch ([[De novo synthesis|''de novo'']]) from the amino acids [[tryptophan]] or [[aspartic acid]]. Alternatively, components of the coenzymes are taken up from food as the [[vitamin]] called [[niacin]]. Similar compounds are released by reactions that break down the structure of NAD<sup>+</sup>. These preformed components then pass through a salvage pathway that recycles them back into the active form. Some NAD<sup>+</sup> is also converted into [[nicotinamide adenine dinucleotide phosphate]] (NADP<sup>+</sup>); the chemistry of this related coenzyme is similar to that of NAD<sup>+</sup>, but it has different roles in metabolism.
==Physical and chemical properties==
{{further|[[Redox]]}}
Nicotinamide adenine dinucleotide is a ''dinucleotide'' since it consists of two [[nucleotide]]s joined by a pair of bridging phosphate groups. The nucleotides consist of [[ribose]] rings, one with [[adenine]] attached to the first carbon atom (the [[Nucleic acid nomenclature|1']] position) and the other with [[nicotinamide]] at this position. The nicotinamide group can be attached in two orientations to this [[anomer]]ic carbon atom, due to these two possible structures, the compound exists as two [[diastereomer]]s. It is the β-nicotinamide diastereomer of NAD<sup>+</sup> which is found in organisms. These nucleotides are joined together by a bridge of two [[phosphate]] groups through the 5' carbons.<ref name=Pollak>{{cite journal | last = Pollak | first = N | coauthors = Dölle C, Ziegler M | title = The power to reduce: pyridine nucleotides—small molecules with a multitude of functions | journal = Biochem. J. | volume = 402 | issue = 2 | pages = 205–18 | year = 2007 | pmid=17295611 | url = http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=17295611 | accessdate = 2007-12-23 | doi = 10.1042/BJ20061638}}</ref>
[[Image:NAD oxidation reduction.svg|thumb|left|250px|The [[redox]] reactions of nicotinamide adenine dinucleotide.]]
In metabolism the compound accepts or donates electrons in redox reactions.<ref name=Belenky>{{cite journal | author = Belenky P | coauthors = Bogan KL, Brenner C | title = NAD+ metabolism in health and disease | journal = Trends Biochem. Sci. | volume = 32 | issue = 1 | pages = 12–9 | year = 2007 | pmid = 17161604 | url = http://www.dartmouth.edu/~brenner/belenky07a.pdf | accessdate = 2007-12-23 | doi = 10.1016/j.tibs.2006.11.006}}</ref> Such reactions (summarized in formula below) involve the removal of two hydrogen atoms from the reactant (R), in the form of a [[hydride|hydride ion]], and a [[proton]] (H<sup>+</sup>). The proton is released into solution, while the reductant RH<sub>2</sub> is oxidized and NAD<sup>+</sup> reduced to NADH by transfer of the hydride to the nicotinamide ring.
:RH<sub>2</sub> + NAD<sup>+</sup> → NADH + H<sup>+</sup> + R
From the hydride electron pair, one electron is transferred to the positively-charged nitrogen of the nicotinamide ring of NAD<sup>+</sup>, and the second hydrogen atom transferred to the C4 carbon atom opposite this nitrogen. The [[Standard electrode potential#Non-standard condition|midpoint potential]] of the NAD<sup>+</sup>/NADH redox pair is −0.32 [[volt]]s, which makes NADH a strong reducing agent.<ref name=Unden>{{cite journal | author = Unden G | coauthors = Bongaerts J | title = Alternative respiratory pathways of Escherichia coli: energetics and transcriptional regulation in response to electron acceptors | journal = Biochim. Biophys. Acta | volume = 1320 | issue = 3 | pages = 217–34 | year = 1997 | pmid=9230919 | doi = 10.1016/S0005-2728(97)00034-0}}</ref> The reaction is easily reversible, when NADH reduces another molecule and is re-oxidized to NAD<sup>+</sup>. This means the coenzyme can continuously cycle between the NAD<sup>+</sup> and NADH forms without being consumed.<ref name=Pollak/>
In appearance, all forms of this coenzyme are white [[amorphous solid|amorphous]] powders that are [[hygroscopy|hygroscopic]] and highly water-soluble.<ref>''[[Merck Index|The Merck Index]]'' tenth edition, (Merck & Co. Ltd 1983) ISBN 9-11-91027-1 p 909</ref> The solids are stable if stored dry and in the dark. Solutions of NAD<sup>+</sup> are colorless and stable for about a week at 4 [[Celsius|°C]] and neutral [[pH]], but decompose rapidly in acids or alkalis. Upon decomposition, they form products that are [[enzyme inhibitor]]s.<ref>{{cite journal |author=Biellmann JF, Lapinte C, Haid E, Weimann G |title=Structure of lactate dehydrogenase inhibitor generated from coenzyme |journal=Biochemistry |volume=18 |issue=7 |pages=1212–7 |year=1979 |pmid=218616 |doi=10.1021/bi00574a015}}</ref>
[[Image:NADNADH.svg|thumb|right|250px|Absorbance spectra of NAD<sup>+</sup> and NADH.]]
Both NAD<sup>+</sup> and NADH absorb strongly in the [[ultraviolet]] due to the adenine base. For example, peak absorption of NAD<sup>+</sup> is at a [[wavelength]] of 259 [[nanometer]]s (nm), with an [[Opacity (optics)#Extinction coefficient|extinction coefficient]] of 16,900 [[Concentration#Molarity|M]]<sup>-1</sup>[[Centimetre|cm]]<sup>-1</sup>. NADH also absorbs at higher wavelengths, with a second peak in UV absorption at 339 nm with an extinction coefficient of 6,220 M<sup>-1</sup>cm<sup>-1</sup>.<ref name=Dawson>Dawson MC (ed) ''Data for biochemical research'' third edition, (Oxford scientific publications, 1987) ISBN 0-19-855358-7 p 122</ref> This difference in the ultraviolet [[absorption spectra]] between the oxidized and reduced forms of the coenzymes at higher wavelengths makes it simple to measure the conversion of one to another in [[enzyme assay]]s – by measuring the amount of UV absorption at 340 nm using a [[spectrophotometry|spectrophotometer]].<ref name=Dawson/>
NAD<sup>+</sup> and NADH also differ in their [[fluorescence]]. NADH in solution has an emission peak at 460 nm and a [[Fluorescence#Lifetime|fluorescence lifetime]] of 0.4 [[nanosecond]]s, while the oxidized form of the coenzyme does not fluoresce.<ref name=Lakowicz>{{cite journal |author=Lakowicz JR, Szmacinski H, Nowaczyk K, Johnson ML |title=Fluorescence lifetime imaging of free and protein-bound NADH |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=89 |issue=4 |pages=1271–5 |year=1992 |pmid=1741380 |url=http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=48431&blobtype=pdf |doi=10.1073/pnas.89.4.1271}}</ref> The properties of the fluorescence signal changes when NADH binds to proteins, so these changes can be used to measure [[dissociation constant]]s, which are useful in the study of [[enzyme kinetics]].<ref name=Lakowicz/><ref>{{cite journal |author=Jameson DM, Thomas V, Zhou DM |title=Time-resolved fluorescence studies on NADH bound to mitochondrial malate dehydrogenase |journal=Biochim. Biophys. Acta |volume=994 |issue=2 |pages=187–90 |year=1989 |pmid=2910350}}</ref> These changes in fluorescence are also used to measure changes in the redox state of living cells, through [[fluorescence microscope|fluorescence microscopy]].<ref name=Kasimova>{{cite journal |author=Kasimova MR, Grigiene J, Krab K, ''et al.'' |title=The free NADH concentration is kept constant in plant mitochondria under different metabolic conditions |journal=Plant Cell |volume=18 |issue=3 |pages=688–98 |year=2006 |pmid=16461578 |url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=16461578 |doi=10.1105/tpc.105.039354}}</ref>
==Concentration and state in cells==
In rat liver, the total amount of NAD<sup>+</sup> and NADH is approximately 1 [[micromole|μmole]] per [[gram]] of wet weight, about 10 times the concentration of NADP<sup>+</sup> and NADPH in the same cells.<ref>{{cite journal |author=Reiss PD, Zuurendonk PF, Veech RL |title=Measurement of tissue purine, pyrimidine, and other nucleotides by radial compression high-performance liquid chromatography |journal=Anal. Biochem. |volume=140 |issue=1 |pages=162–71 |year=1984 |pmid=6486402 |doi=10.1016/0003-2697(84)90148-9}}</ref> The actual concentration of NAD<sup>+</sup> in cell [[cytosol]] is harder to measure, with recent estimates in animal cells, ranging around 0.3 [[Concentration#Molarity|mM]],<ref>{{cite journal |author=Yamada K, Hara N, Shibata T, Osago H, Tsuchiya M |title=The simultaneous measurement of nicotinamide adenine dinucleotide and related compounds by liquid chromatography/electrospray ionization tandem mass spectrometry |journal=Anal. Biochem. |volume=352 |issue=2 |pages=282–5 |year=2006 |pmid=16574057 |doi=10.1016/j.ab.2006.02.017}}</ref><ref name=Yang>{{cite journal |author=Yang H, Yang T, Baur JA, Perez E, Matsui T, Carmona JJ, Lamming DW, Souza-Pinto NC, Bohr VA, Rosenzweig A, de Cabo R, Sauve AA, Sinclair DA. |title=Nutrient-Sensitive Mitochondrial NAD+ Levels Dictate Cell Survival |journal=Cell |volume=130 |pages=1095–107 |year=2007 |doi=10.1016/j.cell.2007.07.035}}</ref> and approximately 1.0 to 2.0 mM in [[yeast]].<ref name=Belenky>{{cite journal |author=Belenky P, Racette FG, Bogan KL, McClure JM, Smith JS, Brenner C |title=Nicotinamide riboside promotes Sir2 silencing and extends lifespan via Nrk and Urh1/Pnp1/Meu1 pathways to NAD+ |journal=Cell |volume=129 |issue=3 |pages=473–84 |year=2007 |pmid=17482543 |doi=10.1016/j.cell.2007.03.024}}</ref> However, over 80% is bound to proteins, so the concentration in solution is much lower.<ref>{{cite journal |author=Blinova K, Carroll S, Bose S, ''et al'' |title=Distribution of mitochondrial NADH fluorescence lifetimes: steady-state kinetics of matrix NADH interactions |journal=Biochemistry |volume=44 |issue=7 |pages=2585–94 |year=2005 |pmid=15709771 |doi=10.1021/bi0485124}}</ref>
Data for other compartments in the cell are limited, although, in the [[mitochondrion]] the concentration of NAD<sup>+</sup> is similar to that in the cytosol.<ref name=Yang/> This NAD<sup>+</sup> is carried into the mitochondrion by a specific [[membrane transport protein]], since the coenzyme cannot [[diffusion|diffuse]] across membranes.<ref>{{cite journal |author=Todisco S, Agrimi G, Castegna A, Palmieri F |title=Identification of the mitochondrial NAD+ transporter in Saccharomyces cerevisiae |journal=J. Biol. Chem. |volume=281 |issue=3 |pages=1524–31 |year=2006 |pmid=16291748 |url=http://www.jbc.org/cgi/pmidlookup?view=long&pmid=16291748 |doi=10.1074/jbc.M510425200}}</ref>
The balance between the oxidized and reduced forms of nicotinamide adenine dinucleotide is called the NAD<sup>+</sup>/NADH ratio. This ratio is an important component of what is called the ''redox state'' of a cell, a measurement that reflects both the metabolic activities and the health of cells.<ref>{{cite journal |author=Schafer F, Buettner G |title=Redox environment of the cell as viewed through the redox state of the glutathione disulfide/glutathione couple |journal=Free Radic Biol Med |volume=30 |issue=11 |pages=1191–212 |year=2001 | pmid=11368918 |doi=10.1016/S0891-5849(01)00480-4}}</ref> The effects of the NAD<sup>+</sup>/NADH ratio are complex, controlling the activity of several key enzymes, including [[glyceraldehyde 3-phosphate dehydrogenase]] and [[pyruvate dehydrogenase]].<ref name=Lin/> In healthy mammalian tissues, estimates of the NAD<sup>+</sup>/NADH ratio range around 1, so the concentrations of NAD<sup>+</sup> and NADH are roughly comparable.<ref name=Lin>{{cite journal |author=Lin SJ, Guarente L |title=Nicotinamide adenine dinucleotide, a metabolic regulator of transcription, longevity and disease |journal=Curr. Opin. Cell Biol. |volume=15 |issue=2 |pages=241–6 |year=2003 |pmid=12648681 |doi=10.1016/S0955-0674(03)00006-1}}</ref> In contrast, the [[Nicotinamide adenine dinucleotide phosphate|NADP<sup>+</sup>/NADPH]] ratio is normally about 0.005, around 200 times lower than the NAD<sup>+</sup>/NADH ratio, so NADPH is the dominant form of this coenzyme.<ref>{{cite journal |author=Veech RL, Eggleston LV, Krebs HA |title=The redox state of free nicotinamide-adenine dinucleotide phosphate in the cytoplasm of rat liver |journal=Biochem. J. |volume=115 |issue=4 |pages=609–19 |year=1969 |pmid=4391039}}</ref> These different ratios are key to the different metabolic roles of NADH and NADPH.
==Biosynthesis==
NAD<sup>+</sup> is synthesized through two metabolic pathways. It is produced either in a ''[[De novo synthesis|de novo]]'' pathway from [[amino acid]]s, or in salvage pathways by recycling preformed components such as [[nicotinamide]] back to NAD<sup>+</sup>.
===''De novo'' production===
[[Image:NAD metabolism.svg|thumb|right|350px|Some [[metabolic pathway]]s that synthesize and consume NAD<sup>+</sup> in [[vertebrate]]s. The abbreviations are defined in the text.]]
Most organisms synthesize NAD<sup>+</sup> from simple components.<ref name=Belenky/> The specific set of reactions differs among organisms, but a common feature is the generation of quinolinic acid (QA) from an amino acid - either [[tryptophan]] (Trp) in animals and some bacteria, or [[aspartic acid]] in some bacteria and plants.<ref>{{cite journal |author=Katoh A, Uenohara K, Akita M, Hashimoto T |title=Early steps in the biosynthesis of NAD in Arabidopsis start with aspartate and occur in the plastid |journal=Plant Physiol. |volume=141 |issue=3 |pages=851–7 |year=2006 |pmid=16698895 |url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=16698895 |doi=10.1104/pp.106.081091}}</ref><ref>{{cite journal |author=Foster JW, Moat AG |title=Nicotinamide adenine dinucleotide biosynthesis and pyridine nucleotide cycle metabolism in microbial systems |journal=Microbiol. Rev. |volume=44 |issue=1 |pages=83–105 |year=1980 |pmid=6997723 |url=http://mmbr.asm.org/cgi/pmidlookup?view=long&pmid=6997723}}</ref> The quinolinic acid is converted to nicotinic acid mononucleotide (NaMN) by transfer of a phosphoribose group. An adenylate group is then transferred to form nicotinic acid adenine dinucleotide (NaAD). Finally, the nicotinic acid group in NaAD is [[amide|amidated]] to a nicotinamide (Nam) group, forming nicotinamide adenine dinucleotide.<ref name=Belenky/>
In a further step, some NAD<sup>+</sup> is converted into NADP<sup>+</sup> by [[NAD+ kinase]], which phosphorylates NAD<sup>+</sup>.<ref>{{cite journal |author=Magni G, Orsomando G, Raffaelli N |title=Structural and functional properties of NAD kinase, a key enzyme in NADP biosynthesis |journal=Mini reviews in medicinal chemistry |volume=6 |issue=7 |pages=739–46 |year=2006 |pmid=16842123 |doi=10.2174/138955706777698688}}</ref> In most organisms, this enzyme uses ATP as the source of the phosphate group, although in bacteria such as ''[[Mycobacterium tuberculosis]]'' and in [[archaea]] such as ''[[Pyrococcus|Pyrococcus horikoshii]]'', inorganic [[polyphosphate]] is an alternative phosphate donor.<ref>{{cite journal |author=Sakuraba H, Kawakami R, Ohshima T |title=First archaeal inorganic polyphosphate/ATP-dependent NAD kinase, from hyperthermophilic archaeon Pyrococcus horikoshii: cloning, expression, and characterization |journal=Appl. Environ. Microbiol. |volume=71 |issue=8 |pages=4352–8 |year=2005 |pmid=16085824 |url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=16085824 |doi=10.1128/AEM.71.8.4352-4358.2005}}</ref><ref>{{cite journal |author=Raffaelli N, Finaurini L, Mazzola F, ''et al'' |title=Characterization of Mycobacterium tuberculosis NAD kinase: functional analysis of the full-length enzyme by site-directed mutagenesis |journal=Biochemistry |volume=43 |issue=23 |pages=7610–7 |year=2004 |pmid=15182203 |doi=10.1021/bi049650w}}</ref>
[[Image:NA, N and NR.svg|thumb|left|300px|Salvage pathways use three precursors for NAD+.]]
===Salvage pathways===
Besides assembling NAD<sup>+</sup> ''de novo'' from simple amino acid precursors, cells also salvage preformed compounds containing nicotinamide. Although other precursors are known, the three natural compounds containing the nicotinamide ring and used in these salvage metabolic pathways are nicotinic acid (Na), nicotinamide (Nam) and nicotinamide riboside (NR).<ref>{{cite journal |author=Tempel W, Rabeh WM, Bogan KL, ''et al'' |title=Nicotinamide riboside kinase structures reveal new pathways to NAD+ |journal=PLoS Biol. |volume=5 |issue=10 |pages=e263 |year=2007 |pmid=17914902 |url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=17914902 |doi=10.1371/journal.pbio.0050263}}</ref> The precursors are fed into the NAD(P)<sup>+</sup> biosynthetic pathway, shown above, through adenylation and phosphoribosylation reactions.<ref name=Belenky/> These compounds can be taken up from the diet, where the mixture of nicotinic acid and nicotinamide are called vitamin B<sub>3</sub> or ''[[niacin]]''. However, these compounds are also produced within cells, when the nicotinamide group is released from NAD<sup>+</sup> in ADP-ribose transfer reactions. Indeed, the enzymes involved in these salvage pathways appear to be concentrated in the [[cell nucleus]], which may compensate for the high level of reactions that consume NAD<sup>+</sup> in this [[organelle]].<ref>{{cite journal |author=Anderson RM, Bitterman KJ, Wood JG, ''et al'' |title=Manipulation of a nuclear NAD+ salvage pathway delays aging without altering steady-state NAD+ levels |journal=J. Biol. Chem. |volume=277 |issue=21 |pages=18881–90 |year=2002 |pmid=11884393 |url=http://www.jbc.org/cgi/pmidlookup?view=long&pmid=11884393 |doi=10.1074/jbc.M111773200}}</ref> Cells can also take up extracellular NAD<sup>+</sup> from their surroundings.<ref>{{cite journal |author=Billington RA, Travelli C, Ercolano E, ''et al'' |title=Characterization of NAD Uptake in Mammalian Cells |journal=J. Biol. Chem. |volume=283 |issue=10 |pages=6367–74 |year=2008 |pmid=18180302 |doi=10.1074/jbc.M706204200 |url=http://www.jbc.org/cgi/pmidlookup?view=long&pmid=18180302}}</ref>
Despite the presence of the ''de novo'' pathway, the salvage reactions are essential in humans; a lack of niacin in the diet causes the [[vitamin deficiency]] disease [[pellagra]].<ref>{{cite journal |author=Henderson LM |title=Niacin |journal=Annu. Rev. Nutr. |volume=3 |issue= |pages=289–307 |year=1983 |pmid=6357238 |doi=10.1146/annurev.nu.03.070183.001445}}</ref> This high requirement for NAD<sup>+</sup> results from the constant consumption of the coenzyme in reactions such as posttranslational modifications, since the cycling of NAD<sup>+</sup> between oxidized and reduced forms in redox reactions does not change the overall levels of the coenzyme.<ref name=Belenky/>
The salvage pathways used in [[microorganism]]s differ from those of [[mammal]]s.<ref name=Rongvaux>{{cite journal |author=Rongvaux A, Andris F, Van Gool F, Leo O |title=Reconstructing eukaryotic NAD metabolism |journal=Bioessays |volume=25 |issue=7 |pages=683–90 |year=2003 |pmid=12815723 |doi=10.1002/bies.10297}}</ref> For example, some pathogens, such as the yeast ''[[Candida glabrata]]'' and the bacterium ''[[Haemophilus influenzae]]'' are NAD<sup>+</sup> [[auxotroph]]s - they cannot synthesize NAD<sup>+</sup> and are dependent on salvage pathways.<ref>{{cite journal |author=Ma B, Pan SJ, Zupancic ML, Cormack BP |title=Assimilation of NAD(+) precursors in Candida glabrata |journal=Mol. Microbiol. |volume=66 |issue=1 |pages=14–25 |year=2007 |doi=10.1111/j.1365-2958.2007.05886.x}}</ref><ref>{{cite journal |author=Reidl J, Schlör S, Kraiss A, Schmidt-Brauns J, Kemmer G, Soleva E |title=NADP and NAD utilization in Haemophilus influenzae |journal=Mol. Microbiol. |volume=35 |issue=6 |pages=1573–81 |year=2000 |pmid=10760156 |doi=10.1046/j.1365-2958.2000.01829.x}}</ref> Even more surprising is the intracellular [[pathogen]] ''[[Chlamydia trachomatis]]'', which lacks recognizable candidates for any genes involved in the salvage or biosynthesis of both NAD<sup>+</sup> and NADP<sup>+</sup>, and may instead salvage these coenzymes from its [[host (biology)|host]].<ref>{{cite journal |author=Gerdes SY, Scholle MD, D'Souza M, ''et al'' |title=From genetic footprinting to antimicrobial drug targets: examples in cofactor biosynthetic pathways |journal=J. Bacteriol. |volume=184 |issue=16 |pages=4555–72 |year=2002 |pmid=12142426 |url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=12142426 |doi=10.1128/JB.184.16.4555-4572.2002}}</ref>
==Functions==
[[Image:Rossman fold.png|thumb|right|250px|Rossmann fold in part of the [[lactate dehydrogenase]] of ''[[Cryptosporidium parvum]]'', showing NAD<sup>+</sup> in red, beta sheets in yellow, and alpha helices in purple.<ref>{{cite journal |author=Senkovich O, Speed H, Grigorian A, ''et al'' |title=Crystallization of three key glycolytic enzymes of the opportunistic pathogen Cryptosporidium parvum |journal=Biochim. Biophys. Acta |volume=1750 |issue=2 |pages=166–72 |year=2005 |pmid=15953771}}</ref>]]
Nicotinamide adenine dinucleotide has several essential roles in [[metabolism]]. It acts as a [[coenzyme]] in [[redox]] reactions, as a donor of ADP-ribose groups in [[ADP-ribosylation]] reactions, as a precursor of the [[second messenger system|second messenger]] molecule [[cyclic ADP-ribose]], as well as acting as a substrate for bacterial [[DNA ligase]]s and a group of enzymes called [[sirtuin]]s that use NAD<sup>+</sup> to remove [[acetyl|acetyl groups]] from proteins.
===Oxidoreductases===
{{further|[[Protein structure]] and [[Oxidoreductase]]s}}
The main role of NAD<sup>+</sup> in metabolism is the transfer of electrons from one redox reaction to another. This type of reaction are catalyzed by a large group of enzymes called [[oxidoreductase]]s. The correct names for these enzymes contain the names of both their substrates: for example [[NADH dehydrogenase|NADH-ubiquinone oxidoreductase]] catalyzes the oxidation of NADH by [[coenzyme Q]].<ref>{{cite web | url = http://www.chem.qmul.ac.uk/iubmb/enzyme | title = Enzyme Nomenclature, Recommendations for enzyme names from the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology | accessdate = 2007-12-06}}</ref> However, these enzymes are also referred to as ''dehydrogenases'' or ''reductases'', with NADH-ubiquinone oxidoreductase commonly being called ''NADH dehydrogenase'' or sometimes ''coenzyme Q reductase''.<ref>{{cite web |url=http://www.expasy.org/enzyme/1.6.5.3 |title=NiceZyme View of ENZYME: EC 1.6.5.3 |accessdate=2007-12-16 |publisher=Expasy}}</ref>
When bound to a protein, NAD<sup>+</sup> and NADH are usually held within a [[structural motif]] known as the [[Rossmann fold]].<ref>{{cite journal |author=Lesk AM |title=NAD-binding domains of dehydrogenases |journal=Curr. Opin. Struct. Biol. |volume=5 |issue=6 |pages=775–83 |year=1995 |pmid=8749365 |doi=10.1016/0959-440X(95)80010-7}}</ref> The motif is named after [[Michael Rossmann]] who was the first scientist to notice how common this structure is within nucleotide-binding proteins.<ref name=Rao>{{cite journal |author=Rao S, Rossmann M |title=Comparison of super-secondary structures in proteins |journal=J Mol Biol |volume=76 |issue=2 | pages=241–56 |year=1973 |pmid=4737475 |doi=10.1016/0022-2836(73)90388-4}}</ref> This fold contains three or more parallel [[beta sheet|beta strands]] linked by two [[alpha helix|alpha helices]] in the order beta-alpha-beta-alpha-beta. This forms a beta sheet flanked by a layer of alpha helices on each side. Because each Rossmann fold binds one nucleotide, binding domains for the dinucleotide NAD<sup>+</sup> consist of two paired Rossmann folds, with each fold binding one nucleotide within the cofactor.<ref name=Rao/> However, this fold is not universal among NAD-dependent enzymes, since a class of bacterial enzymes involved in [[amino acid]] metabolism have recently been discovered that bind the coenzyme, but lack this motif.<ref>{{cite journal |author=Goto M, Muramatsu H, Mihara H, ''et al'' |title=Crystal structures of Delta1-piperideine-2-carboxylate/Delta1-pyrroline-2-carboxylate reductase belonging to a new family of NAD(P)H-dependent oxidoreductases: conformational change, substrate recognition, and stereochemistry of the reaction |journal=J. Biol. Chem. |volume=280 |issue=49 |pages=40875–84 |year=2005 |pmid=16192274 |url=http://www.jbc.org/cgi/content/full/280/49/40875 |doi=10.1074/jbc.M507399200}}</ref>
[[Image:NAD-2FM3-3D-sticks.png|thumb|left|3-D conformation of NAD<sup>+</sup>.]]
When bound in the active site of an oxidoreductase, the nicotinamide ring of the coenzyme is positioned so that it can accept a hydride from the other substrate. Since the C4 carbon that accepts the hydrogen is [[prochiral]], this can be exploited in [[enzyme kinetics]] to give information about the enzyme's mechanism. This is done by mixing an enzyme with a substrate that has [[deuterium]] atoms substituted for the hydrogens, so the enzyme will reduce NAD<sup>+</sup> by transferring a deuterium, rather than a hydrogen atom. In this case an enzyme can produce one of two [[Stereoisomerism|sterioisomer]]s of NADH. In some enzymes the hydrogen is transferred from above the plane of the nicotinamide ring, these are called ''class A'' oxidoreductases, while class B enzymes transfer the atom from below.<ref>{{cite journal |author=Bellamacina CR |title=The nicotinamide dinucleotide binding motif: a comparison of nucleotide binding proteins |journal=FASEB J. |volume=10 |issue=11 |pages=1257–69 |year=1996 |pmid=8836039 |url=http://www.fasebj.org/cgi/pmidlookup?view=long&pmid=8836039}}</ref>
Despite this similarity in how proteins bind coenzymes, enzymes almost always show a high level of specificity for either NAD<sup>+</sup> or NADP<sup>+</sup>.<ref>{{cite journal |author=Carugo O, Argos P |title=NADP-dependent enzymes. I: Conserved stereochemistry of cofactor binding |journal=Proteins |volume=28 |issue=1 |pages=10–28 |year=1997 |pmid=9144787 |doi=10.1002/(SICI)1097-0134(199705)28:1<10::AID-PROT2>3.0.CO;2-N}}</ref> This specificity reflects the distinct metabolic roles of the two coenzymes, and is the result of distinct sets of [[amino acid]] residues in the two types of coenzyme-binding pocket. For instance, in the active site of NADP-dependent enzymes, an [[ionic bond]] is formed between a basic amino acid side chain and the acidic phosphate group of NADP<sup>+</sup>. Conversely, in NAD-dependent enzymes the charge in this pocket is reversed, preventing NADP<sup>+</sup> from binding. However, there are a few exceptions to this general rule, and enzymes such [[aldose reductase]], [[glucose-6-phosphate dehydrogenase]], and [[methylenetetrahydrofolate reductase]] can use both coenzymes in some species.<ref>{{cite journal |author=Vickers TJ, Orsomando G, de la Garza RD, ''et al'' |title=Biochemical and genetic analysis of methylenetetrahydrofolate reductase in Leishmania metabolism and virulence |journal=J. Biol. Chem. |volume=281 |issue=50 |pages=38150–8 |year=2006 |pmid=17032644 |url=http://www.jbc.org/cgi/content/full/281/50/38150#SEC3 |doi=10.1074/jbc.M608387200}}</ref>
===Role in redox metabolism===
[[Image:Catabolism schematic.svg|thumb|250px|A simplified outline of redox [[metabolism]], showing how NAD<sup>+</sup> and NADH link the [[citric acid cycle]] and [[oxidative phosphorylation]].]]
{{further|[[Cellular respiration]] and [[Oxidative phosphorylation]]}}
The redox reactions catalyzed by oxidoreductases are vital in all parts of metabolism, but one particularly important area where these reactions occur is in the release of energy from nutrients. Here, reduced compounds such as [[glucose]] are oxidized, thereby releasing energy. This energy is transferred to NAD<sup>+</sup> by reduction to NADH, as part of [[glycolysis]] and the [[citric acid cycle]]. In [[eukaryote]]s the electrons carried by the NADH that is produced in the [[cytoplasm]] by glycolysis is transferred into the [[mitochondrion]] by [[mitochondrial shuttle]]s, such as the [[malate-aspartate shuttle]].<ref>{{cite journal |author=Bakker BM, Overkamp KM, van Maris AJ, ''et al'' |title=Stoichiometry and compartmentation of NADH metabolism in Saccharomyces cerevisiae |journal=FEMS Microbiol. Rev. |volume=25 |issue=1 |pages=15–37 |year=2001 |pmid=11152939 |doi=10.1111/j.1574-6976.2001.tb00570.x}}</ref> The NADH is then oxidized in turn by the [[electron transport chain]], which pumps protons across a membrane and generates ATP through [[oxidative phosphorylation]].<ref>{{cite journal |author=Rich PR |title=The molecular machinery of Keilin's respiratory chain |journal=Biochem. Soc. Trans. |volume=31 |issue=Pt 6 |pages=1095–105 |year=2003 |pmid=14641005 |url=http://www.biochemsoctrans.org/bst/031/1095/bst0311095.htm}}</ref> These shuttle systems also have the same transport function in [[chloroplast]]s.<ref>{{cite journal |author=Heineke D, Riens B, Grosse H, ''et al'' |title=Redox Transfer across the Inner Chloroplast Envelope Membrane |journal=Plant Physiol |volume=95 |issue=4 |pages=1131–1137 |year=1991 |pmid=16668101 |url=http://www.plantphysiol.org/cgi/pmidlookup?view=long&pmid=16668101}}</ref>
Since both the oxidized and reduced forms of nicotinamide adenine dinucleotide are used in these linked sets of reactions, the cell maintains approximately equal concentrations of NAD<sup>+</sup> and NADH; the high NAD<sup>+</sup>/NADH ratio allows this coenzyme to act as both an oxidizing and a reducing agent.<ref name=Nicholls>{{cite book|author=Nicholls DG|coauthors=Ferguson SJ|title=Bioenergetics 3 |edition=1st ed|publisher=Academic Press|year=2002|isbn=0-125-18121-3}}</ref> In contrast, the main function of NADP<sup>+</sup> is as a reducing agent in [[anabolism]], with this coenzyme being involved in pathways such as [[fatty acid synthesis]] and [[photosynthesis]]. Since NADPH is needed to drive redox reactions as a strong reducing agent, the NADP<sup>+</sup>/NADPH ratio is kept very low.<ref name=Nicholls/>
Although it is important in catabolism, NADH is also used in anabolic reactions, such as [[gluconeogenesis]].<ref>{{cite journal |author=Sistare FD, Haynes RC |title=The interaction between the cytosolic pyridine nucleotide redox potential and gluconeogenesis from lactate/pyruvate in isolated rat hepatocytes. Implications for investigations of hormone action |journal=J. Biol. Chem. |volume=260 |issue=23 |pages=12748–53 |year=1985 |pmid=4044607 |url=http://www.jbc.org/cgi/reprint/260/23/12748}}</ref> This need for NADH in anabolism poses a problem for prokaryotes growing on nutrients that release only a small amount of energy. For example, [[nitrification|nitrifying]] bacteria such as ''[[Nitrobacter]]'' oxidize nitrite to nitrate, which releases sufficient energy to pump protons and generate ATP, but not enough to produce NADH directly.<ref>{{cite journal |author=Freitag A, Bock E|year=1990 |title=Energy conservation in Nitrobacter |journal=FEMS Microbiology Letters |volume=66 |issue=1–3 |pages=157&ndash:62 |doi=10.1111/j.1574-6968.1990.tb03989.x}}</ref> As NADH is still needed for anabolic reactions, these bacteria use a [[nitrite oxidoreductase]] to produce enough [[chemiosmosis|proton-motive force]] to run part of the electron transport chain in reverse, generating NADH.<ref>{{cite journal |author=Starkenburg SR, Chain PS, Sayavedra-Soto LA, ''et al'' |title=Genome sequence of the chemolithoautotrophic nitrite-oxidizing bacterium Nitrobacter winogradskyi Nb-255 |journal=Appl. Environ. Microbiol. |volume=72 |issue=3 |pages=2050–63 |year=2006 |pmid=16517654 |url=http://aem.asm.org/cgi/content/full/72/3/2050?view=long&pmid=16517654 |doi=10.1128/AEM.72.3.2050-2063.2006}}</ref>
===Non-redox roles===
The coenzyme NAD<sup>+</sup> is also consumed in ADP-ribose transfer reactions. For example, enzymes called [[Glycosyltransferase|ADP-ribosyltransferases]] add the ADP-ribose moiety of this molecule to proteins, in a [[posttranslational modification]] called [[ADP-ribosylation]].<ref>{{cite journal |author=Ziegler M |title=New functions of a long-known molecule. Emerging roles of NAD in cellular signaling |journal=Eur. J. Biochem. |volume=267 |issue=6 |pages=1550–64 |year=2000 |pmid=10712584 |doi=10.1046/j.1432-1327.2000.01187.x}}</ref> This reaction involves either the addition of a single ADP-ribose group, in ''mono-ADP-ribosylation'', or the transferral of ADP-ribose to proteins in long branched chains, which is called ''poly(ADP-ribosyl)ation''.<ref name=Diefenbach>{{cite journal |author=Diefenbach J, Bürkle A |title=Introduction to poly(ADP-ribose) metabolism |journal=Cell. Mol. Life Sci. |volume=62 |issue=7-8 |pages=721–30 |year=2005 |pmid=15868397 |doi=10.1007/s00018-004-4503-3}}</ref> Mono-ADP-ribosylation was first identified as the mechanism of a group of bacterial [[toxin]]s, notably [[cholera toxin]], but it is also involved in normal [[cell signaling]].<ref>{{cite journal |author=Berger F, Ramírez-Hernández MH, Ziegler M |title=The new life of a centenarian: signaling functions of NAD(P) |journal=Trends Biochem. Sci. |volume=29 |issue=3 |pages=111–8 |year=2004 |pmid=15003268 |doi=10.1016/j.tibs.2004.01.007}}</ref><ref>{{cite journal |author=Corda D, Di Girolamo M |title=Functional aspects of protein mono-ADP-ribosylation |journal=EMBO J. |volume=22 |issue=9 |pages=1953–8 |year=2003 |pmid=12727863 |url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=12727863 |doi=10.1093/emboj/cdg209}}</ref> Poly(ADP-ribosyl)ation is carried out by the [[Poly ADP ribose polymerase|poly(ADP-ribose) polymerase]]s.<ref name=Burkle>{{cite journal |author=Burkle A |title=Poly(ADP-ribose). The most elaborate metabolite of NAD<sup>+</sup> |journal=FEBS J. |volume=272 |issue=18 |pages=4576–89 |year=2005 |pmid=16156780 |doi=10.1111/j.1742-4658.2005.04864.x}}</ref><ref name=Diefenbach>{{cite journal |author=Diefenbach J, Bürkle A |title=Introduction to poly(ADP-ribose) metabolism |journal=Cell. Mol. Life Sci. |volume=62 |issue=7-8 |pages=721–30 |year=2005 |pmid=15868397 |doi=10.1007/s00018-004-4503-3}}</ref> The poly(ADP-ribose) structure is involved in the regulation of several cellular events and is most important in the [[cell nucleus]], in processes such as [[DNA repair]] and [[telomere]] maintenance.<ref name=Burkle/> In addition to these functions within the cell, a group of [[extracellular]] ADP-ribosyltransferases has recently been discovered, but their functions remain obscure.<ref>{{cite journal |author=Seman M, Adriouch S, Haag F, Koch-Nolte F |title=Ecto-ADP-ribosyltransferases (ARTs): emerging actors in cell communication and signaling |journal=Curr. Med. Chem. |volume=11 |issue=7 |pages=857–72 |year=2004 |pmid=15078170 |doi=10.2174/0929867043455611}}</ref>
[[Image:Cyclic ADP Ribose.PNG|thumb|left|280px|The structure of [[cyclic ADP-ribose]].]]
Another function of this coenzyme in cell signaling is as a precursor of [[cyclic ADP-ribose]], which is produced from NAD<sup>+</sup> by ADP-ribosyl cyclases, as part of a [[second messenger system]].<ref>{{cite journal |author=Guse AH |title=Biochemistry, biology, and pharmacology of cyclic adenosine diphosphoribose (cADPR) |journal=Curr. Med. Chem. |volume=11 |issue=7 |pages=847–55 |year=2004 |pmid=15078169 |doi=10.2174/0929867043455602}}</ref> This molecule acts in [[calcium signaling]] by releasing calcium from intracellular stores.<ref>{{cite journal |author=Guse AH |title=Regulation of calcium signaling by the second messenger cyclic adenosine diphosphoribose (cADPR) |journal=Curr. Mol. Med. |volume=4 |issue=3 |pages=239–48 |year=2004 |pmid=15101682 |doi=10.2174/1566524043360771}}</ref> It does this by binding to and opening a class of calcium channels called [[ryanodine receptor]]s, which are located in the membranes of [[organelle]]s, such as the [[endoplasmic reticulum]].<ref>{{cite journal |author=Guse AH |title=Second messenger function and the structure-activity relationship of cyclic adenosine diphosphoribose (cADPR) |journal=FEBS J. |volume=272 |issue=18 |pages=4590–7 |year=2005 |pmid=16156781 |doi= 10.1111/j.1742-4658.2005.04863.x}}</ref>
NAD<sup>+</sup> is also consumed by [[sirtuin]]s, which are NAD-dependent deacetylases, such as [[Sir2]].<ref>{{cite journal |author=North B, Verdin E |title=Sirtuins: Sir2-related NAD-dependent protein deacetylases |journal=Genome Biol |volume=5 |issue=5 |pages=224 |year=2004 |pmid=15128440 |url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=416462 |doi=10.1186/gb-2004-5-5-224}}</ref> These enzymes act by transferring an [[acetyl]] group from their substrate protein to the ADP-ribose moiety of NAD<sup>+</sup>; this cleaves the coenzyme and releases nicotinamide and O-acetyl-ADP-ribose. The sirtuins mainly seem to be involved in regulating [[transcription (genetics)|transcription]] through deacetylating histones and altering [[nucleosome]] structure.<ref>{{cite journal |author=Blander G, Guarente L |title=The Sir2 family of protein deacetylases |journal=Annu. Rev. Biochem. |volume=73 |issue= |pages=417–35 |year=2004 |pmid=15189148 |doi=10.1146/annurev.biochem.73.011303.073651}}</ref> Although non-histone proteins can be deacetylated by sirtuins as well. These activities of sirtuins are particularly interesting due to their importance in the regulation of [[aging]].<ref>{{cite journal |author=Trapp J, Jung M |title=The role of NAD+ dependent histone deacetylases (sirtuins) in ageing |journal=Curr Drug Targets |volume=7 |issue=11 |pages=1553–60 |year=2006 |pmid=17100594}}</ref>
Other NAD-dependent enzymes include bacterial [[DNA ligase]]s, which join two DNA ends by using NAD<sup>+</sup> as a substrate to donate an [[Adenosine monophosphate]] (AMP) group to the 5' phosphate of one DNA end. This intermediate is then attacked by the 3' hydroxyl group of the other DNA end, forming a new [[phosphodiester bond]].<ref>{{cite journal |author=Wilkinson A, Day J, Bowater R |title=Bacterial DNA ligases |journal=Mol. Microbiol. |volume=40 |issue=6 |pages=1241–8 |year=2001 |pmid=11442824 |doi=10.1046/j.1365-2958.2001.02479.x}}</ref> This contrasts with [[eukaryotic]] DNA ligases, which use [[adenosine triphosphate|ATP]] to form the DNA-AMP intermediate.<ref>{{cite journal |author=Schär P, Herrmann G, Daly G, Lindahl T |title=A newly identified DNA ligase of ''Saccharomyces cerevisiae'' involved in ''RAD52''-independent repair of DNA double-strand breaks |journal=Genes and Development |volume=11 |issue=15 |pages=1912–24 |year=1997 |pmid=9271115 |doi=10.1101/gad.11.15.1912}}</ref>
==Pharmacology==
The enzymes that make and use NAD<sup>+</sup> and NADH are important in both current [[pharmacology]] and the research into future treatments for disease. [[Drug design]] and drug development exploits NAD<sup>+</sup> in three ways: as a direct target of drugs, by designing [[enzyme inhibitor]]s or activators based on its structure that change the activity of NAD-dependent enzymes, and by trying to inhibit NAD<sup>+</sup> biosynthesis.<ref>{{cite journal | author = Khan JA, Forouhar F, Tao X, Tong L | title = Nicotinamide adenine dinucleotide metabolism as an attractive target for drug discovery | journal = Expert Opin. Ther. Targets | volume = 11 | issue = 5 | pages = 695–705 | year = 2007 | pmid = 17465726 | doi = 10.1517/14728222.11.5.695}}</ref>
The coenzyme NAD<sup>+</sup> is not itself currently used as a treatment for any disease. However, it is potentially useful in the therapy of [[neurodegenerative disease]]s such as [[Alzheimer's disease|Alzheimer's]] and [[Parkinson disease]].<ref name=Belenky/> Evidence for these applications is mixed; studies in [[mouse|mice]] are promising,<ref>{{cite journal |author=Kaneko S, Wang J, Kaneko M, ''et al'' |title=Protecting axonal degeneration by increasing nicotinamide adenine dinucleotide levels in experimental autoimmune encephalomyelitis models |journal=J. Neurosci. |volume=26 |issue=38 |pages=9794–804 |year=2006 |pmid=16988050 |url=http://www.jneurosci.org/cgi/pmidlookup?view=long&pmid=16988050 |doi=10.1523/JNEUROSCI.2116-06.2006}}</ref> whereas a placebo-controlled clinical trial failed to show any effect.<ref>{{cite journal |author=Swerdlow RH |title=Is NADH effective in the treatment of Parkinson's disease? |journal=Drugs Aging |volume=13 |issue=4 |pages=263–8 |year=1998 |pmid=9805207 |doi=10.2165/00002512-199813040-00002}}</ref> NAD<sup>+</sup> is also a direct target of the drug [[isoniazid]], which is used in the treatment of [[tuberculosis]], an infection caused by ''[[Mycobacterium tuberculosis]]''. Isoniazid is a [[prodrug]] and once it has entered the bacteria, it is activated by a [[peroxidase]], which oxidizes the compound into a [[free radical]] form.<ref>{{cite journal |author=Timmins GS, Deretic V |title=Mechanisms of action of isoniazid |journal=Mol. Microbiol. |volume=62 |issue=5 |pages=1220–7 |year=2006 |pmid=17074073 |url=http://www.blackwell-synergy.com/doi/full/10.1111/j.1365-2958.2006.05467.x |doi=10.1111/j.1365-2958.2006.05467.x}}</ref> This radical then reacts with NADH, to produce adducts that are very potent inhibitors of the enzymes [[enoyl-acyl carrier protein reductase]],<ref>{{cite journal |author=Rawat R, Whitty A, Tonge PJ |title=The isoniazid-NAD adduct is a slow, tight-binding inhibitor of InhA, the Mycobacterium tuberculosis enoyl reductase: adduct affinity and drug resistance |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=100 |issue=24 |pages=13881–6 |year=2003 |pmid=14623976 |url=http://www.pnas.org/cgi/pmidlookup?view=long&pmid=14623976 |doi=10.1073/pnas.2235848100}}</ref> and [[dihydrofolate reductase]].<ref>{{cite journal |author=Argyrou A, Vetting MW, Aladegbami B, Blanchard JS |title=Mycobacterium tuberculosis dihydrofolate reductase is a target for isoniazid |journal=Nat. Struct. Mol. Biol. |volume=13 |issue=5 |pages=408–13 |year=2006 |pmid=16648861 |doi=10.1038/nsmb1089}}</ref>
Since a large number of oxidoreductases use NAD<sup>+</sup> and NADH as substrates, and bind them using a highly-conserved structural motif, the idea that inhibitors based on NAD<sup>+</sup> could be specific to one enzyme is surprising.<ref name=Pankiewicz>{{cite journal |author=Pankiewicz KW, Patterson SE, Black PL, ''et al'' |title=Cofactor mimics as selective inhibitors of NAD-dependent inosine monophosphate dehydrogenase (IMPDH)--the major therapeutic target |journal=Curr. Med. Chem. |volume=11 |issue=7 |pages=887–900 |year=2004 |pmid=15083807 |doi=10.2174/0929867043455648}}</ref> However, this can be possible: for example, inhibitors based on the compounds [[mycophenolic acid]] and [[tiazofurin]] inhibit [[IMP dehydrogenase]] at the NAD<sup>+</sup> binding site. Due to importance of this enzyme in [[purine metabolism]], these compounds may be useful as anti-cancer, anti-viral, or [[immunosuppressive drug]]s.<ref name=Pankiewicz/><ref>{{cite journal |author=Franchetti P, Grifantini M |title=Nucleoside and non-nucleoside IMP dehydrogenase inhibitors as antitumor and antiviral agents |journal=Curr. Med. Chem. |volume=6 |issue=7 |pages=599–614 |year=1999 |pmid=10390603}}</ref> Other drugs are not enzyme inhibitors, but instead activate enzymes involved in NAD<sup>+</sup> metabolism. [[Sirtuin]]s are a particularly interesting target for such drugs, since activation of these NAD-dependent deacetylases extends lifespan.<ref name=Lin/> Compounds such as [[resveratrol]] increase the activity of these enzymes, which may be important in their ability to delay aging in both vertebrate,<ref>{{cite journal |author=Valenzano DR, Terzibasi E, Genade T, Cattaneo A, Domenici L, Cellerino A |title=Resveratrol prolongs lifespan and retards the onset of age-related markers in a short-lived vertebrate |journal=Curr. Biol. |volume=16 |issue=3 |pages=296–300 |year=2006 |pmid=16461283 |doi=10.1016/j.cub.2005.12.038}}</ref> and invertebrate [[model organism]]s.<ref>{{cite journal |author=Howitz KT, Bitterman KJ, Cohen HY, ''et al'' |title=Small molecule activators of sirtuins extend Saccharomyces cerevisiae lifespan |journal=Nature |volume=425 |issue=6954 |pages=191–6 |year=2003 |pmid=12939617 |doi=10.1038/nature01960}}</ref><ref>{{cite journal |author=Wood JG, Rogina B, Lavu S, ''et al'' |title=Sirtuin activators mimic caloric restriction and delay ageing in metazoans |journal=Nature |volume=430 |issue=7000 |pages=686–9 |year=2004 |pmid=15254550 |doi=10.1038/nature02789}}</ref>
Due to the differences in the [[metabolic pathway]]s of NAD<sup>+</sup> biosynthesis between organisms, such as between bacteria and humans, this area of metabolism is a promising area for the development of new [[antibiotic]]s.<ref>{{cite journal |author=Rizzi M, Schindelin H |title=Structural biology of enzymes involved in NAD and molybdenum cofactor biosynthesis |journal=Curr. Opin. Struct. Biol. |volume=12 |issue=6 |pages=709–20 |year=2002 |pmid=12504674 |doi=10.1016/S0959-440X(02)00385-8}}</ref><ref>{{cite journal |author=Begley TP, Kinsland C, Mehl RA, Osterman A, Dorrestein P |title=The biosynthesis of nicotinamide adenine dinucleotides in bacteria |journal=Vitam. Horm. |volume=61 |pages=103–19 |year=2001 |pmid=11153263 |doi=10.1016/S0083-6729(01)61003-3}}</ref> For example, the enzyme [[nicotinamidase]], which converts nicotinamide to nicotinic acid, is a target for drug design, as this enzyme is absent in humans but present in yeast and bacteria.<ref name=Rongvaux/>
==History==
{{Further|[[History of biochemistry]]}}
The coenzyme NAD<sup>+</sup> was first discovered by the [[United Kingdom|British]] biochemists [[Arthur Harden]] and William Youndin in 1906.<ref>{{cite journal | first = A | last = Harden | coauthors = Young, WJ | title = The Alcoholic Ferment of Yeast-Juice | work = Proceedings of the Royal Society of London | edition = Series B, Containing Papers of a Biological Character | volume = 78 | number = 526 | date = October 1906 | pages = pp. 369–375}}</ref> They noticed that adding boiled and filtered [[yeast]] extract greatly accelerated [[alcoholic fermentation]] in unboiled yeast extracts. They called the unidentified factor responsible for this effect a ''coferment''. Through a long and difficult purification from yeast extracts, this heat-stable factor was identified as a [[nucleotide]] sugar phosphate by [[Hans von Euler-Chelpin]].<ref>{{cite web | url=http://nobelprize.org/nobel_prizes/chemistry/laureates/1929/euler-chelpin-lecture.pdf | title = Fermentation of sugars and fermentative enzymes | work = Nobel Lecture, [[23 May]] [[1930]] | accessdate=2007-09-30 | publisher = Nobel Foundation}}</ref> In 1936, the [[Germany|German]] scientist [[Otto Heinrich Warburg]] showed the function of the nucleotide coenzyme in hydride transfer and identified the nicotinamide portion as the site of redox reactions.<ref>{{cite journal |author=Warburg O, Christian W.|title=Pyridin, the hydrogen-transferring component of the fermentation enzymes (pyridine nucleotide) |journal=Biochemische Zeitschrift |volume=287 |year=1936 |pages=291}}</ref>
A source of nicotinamide was identified in 1938, when [[Conrad Elvehjem]] purified [[niacin]] from liver and showed this vitamin contained nicotinic acid and nicotinamide.<ref>{{cite journal |author=Elvehjem CA, Madden RJ, Strong FM, Woolley DW. |title=The isolation and identification of the anti-black tongue factor |journal=J. Biol. Chem. |volume=123 |issue=1 |pages=137–49 |year=1938 |url=http://www.jbc.org/cgi/reprint/123/1/137.pdf}}</ref> Then, in 1939, he provided the first strong evidence that niacin was used to synthesize NAD<sup>+</sup>.<ref>{{cite journal |author=Axelrod AE, Madden RJ, Elvehjem CA, |title=The effect of a nicotinic acid deficiency upon the coenzyme I content of animal tissues |journal=J. Biol. Chem. |volume=131 |issue=1 |pages=85–93 |year=1939 |url=http://www.jbc.org/cgi/reprint/131/1/85.pdf}}</ref> In the early 1940s, [[Arthur Kornberg]] made another important contribution towards understanding NAD<sup>+</sup> metabolism, by being the first to detect an enzyme in the biosynthetic pathway.<ref>{{cite journal |author=Kornberg, A. |title=The participation of inorganic pyrophosphate in the reversible enzymatic synthesis of diphosphopyridine nucleotide |journal=J. Biol. Chem. |volume=176 |issue=3 |pages=1475–76 |year=1948 |url=http://www.jbc.org/cgi/reprint/176/3/1475.pdf}}</ref> Subsequently, in 1949, the [[United States|American]] biochemists Morris Friedkin and [[Albert L. Lehninger]] proved that NADH linked metabolic pathways such as the citric acid cycle with the synthesis of ATP in oxidative phosphorylation.<ref>{{cite journal |author=Friedkin M, Lehninger AL. |title=Esterification of inorganic phosphate coupled to electron transport between dihydrodiphosphopyridine nucleotide and oxygen |journal=J. Biol. Chem. |volume=178 |issue=2 |pages=611–23 |year=1949 |url=http://www.jbc.org/cgi/reprint/178/2/611}}</ref> Finally, in 1959, Jack Preiss and Philip Handler discovered the intermediates and enzymes involved in the biosynthesis of NAD<sup>+</sup>;<ref>{{cite journal |author=Preiss J, Handler P. |title=Biosynthesis of diphosphopyridine nucleotide. I. Identification of intermediates |journal=J. Biol. Chem. |volume=233 |issue=2 |pages=488–92 |year=1958 |pmid=13563526 |url=http://www.jbc.org/cgi/reprint/233/2/488}}</ref><ref>{{cite journal |author=Preiss J, Handler P. |title=Biosynthesis of diphosphopyridine nucleotide. II. Enzymatic aspects |journal=J. Biol. Chem. |volume=233 |issue=2 |pages=493–500 |year=1958 |pmid=13563527 |url=http://www.jbc.org/cgi/pmidlookup?view=long&pmid=13563527}}</ref> consequently, ''de novo'' synthesis is often called the Preiss-Handler pathway in their honor.
The non-redox roles of NAD(P) are a recent discovery.<ref name=Pollak/> The first of these functions to be identified was the use of NAD<sup>+</sup> as the ADP-ribose donor in ADP-ribosylation reactions, observed in the early 1960s.<ref>{{cite journal |author=Chambon P, Weill JD, Mandel P |title=Nicotinamide mononucleotide activation of new DNA-dependent polyadenylic acid synthesizing nuclear enzyme |journal=Biochem. Biophys. Res. Commun. |volume=11 |pages=39–43 |year=1963 |pmid=14019961 |doi=10.1016/0006-291X(63)90024-X}}</ref> Later studies in the 1980s and 1990s revealed the activities of NAD<sup>+</sup> and NADP<sup>+</sup> metabolites in cell signaling - such as the action of [[cyclic ADP-ribose]], which was discovered in 1987.<ref>{{cite journal |author=Clapper DL, Walseth TF, Dargie PJ, Lee HC |title=Pyridine nucleotide metabolites stimulate calcium release from sea urchin egg microsomes desensitized to inositol trisphosphate |journal=J. Biol. Chem. |volume=262 |issue=20 |pages=9561–8 |year=1987 |pmid=3496336 |url=http://www.jbc.org/cgi/reprint/262/20/9561}}</ref> The metabolism of NAD<sup>+</sup> has remained an area of intense research into the 21st century, with interest being heightened after the discovery of the NAD<sup>+</sup>-dependent protein deacetylases called [[sirtuin]]s in 2000, by Shin-ichiro Imai and coworkers at the [[Massachusetts Institute of Technology]].<ref>{{cite journal |author=Imai S, Armstrong CM, Kaeberlein M, Guarente L |title=Transcriptional silencing and longevity protein Sir2 is an NAD-dependent histone deacetylase |journal=Nature |volume=403 |issue=6771 |pages=795–800 |year=2000 |pmid=10693811 |doi=10.1038/35001622}}</ref>
==See also==
*[[List of EC numbers (EC 1)|List of oxidoreductases]]
*[[Enzyme catalysis]]
==References==
{{reflist|2}}
==Further reading==
'''Function'''
*{{cite book|author=Nelson DL|coauthors=Cox MM|title=Lehninger Principles of Biochemistry|edition=4th ed|publisher=W. H. Freeman|year=2004|isbn=0-716-74339-6}}
*{{cite book|author=Bugg, T |title=Introduction to Enzyme and Coenzyme Chemistry |year=2004 |publisher=Blackwell Publishing Limited |edition=2nd ed |isbn=1-40511-452-5}}
*{{cite book|author=Lee HC |title=Cyclic ADP-Ribose and NAADP: Structure, Metabolism and Functions |year=2002 |publisher=Kluwer Academic Publishers |isbn=1-40207-281-3}}
'''History'''
*[http://bip.cnrs-mrs.fr/bip10/buchner.htm ''New Beer in an Old Bottle: Eduard Buchner and the Growth of Biochemical Knowledge'', edited by Athel Cornish-Bowden and published by Universitat de València (1997): ISBN 84-370-3328-4], A history of early enzymology.
*[http://etext.lib.virginia.edu/toc/modeng/public/Wil4Sci.html Williams, Henry Smith, 1863–1943. ''A History of Science: in Five Volumes. Volume IV: Modern Development of the Chemical and Biological Sciences''], A textbook from the 19th century.
== External links ==
*[http://www.sigmaaldrich.com/sigma-aldrich/product_information_sheet/n8285pis.pdf β-Nicotinamide adenine dinucleotide (NAD<sup>+</sup>, oxidized)] and [http://www.sigmaaldrich.com/sigma/product%20information%20sheet/n4505pis.pdf NADH (reduced)] Chemical data sheet from [[Sigma-Aldrich]]
*[http://biocyc.org/META/NEW-IMAGE?type=COMPOUND&object=NAD NAD<sup>+</sup>], [http://biocyc.org/META/NEW-IMAGE?type=COMPOUND&object=NADH NADH] and [http://biocyc.org/META/NEW-IMAGE?type=PATHWAY&object=PWY-3502 NAD synthesis pathway] at the [[MetaCyc]] database
*[http://www.expasy.org/enzyme/1.-.-.- List of oxidoreductases] at the [[Swiss-Prot|SWISS-PROT]] database
{{Enzyme cofactors}}
[[Category:Cellular respiration]]
[[Category:Nucleotides]]
[[Category:Photosynthesis]]
[[Category:Coenzymes]]
[[ar:ثنائي نيكليوتيدة الأدنين وأميد النيكوتنك]]
[[cs:Nikotinamid adenin dinukleotid]]
[[da:Nikotinamidadenindinukleotid]]
[[de:Nicotinamidadenindinukleotid]]
[[es:Nicotinamida adenina dinucleótido]]
[[eo:NADH]]
[[fr:Nicotinamide adénine dinucléotide]]
[[ko:니코틴아미드 아데닌 디뉴클레오티드]]
[[id:Nikotinamid adenin dinukleotida]]
[[it:Nicotinammideadenindinucleotide]]
[[he:NAD]]
[[nl:NADH]]
[[ja:ニコチンアミドアデニンジヌクレオチド]]
[[pl:Dinukleotyd nikotynamidoadeninowy]]
[[pt:Dinucleótido de nicotinamida e adenina]]
[[zh:NAD]]