Nicotinamide adenine dinucleotide phosphate: Difference between revisions

{{Distinguish|text=[[Nicotinamide adenine dinucleotide]] (NAD{{+}}/NADH)}}

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| SMILES = O=C(N)c1ccc[n+](c1)[C@H]2[C@H](O)[C@H](O)[C@H](O2)COP([O-])(=O)OP(=O)(O)OC[C@H]3O[C@@H](n4cnc5c4ncnc5N)[C@@H]([C@@H]3O)OP(=O)(O)O

| MeSHName = NADP

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'''Nicotinamide adenine dinucleotide phosphate''', abbreviated '''NADP{{+}}''' or, in older notation, '''TPN''' (triphosphopyridine nucleotide), is a [[Cofactor (biochemistry)|cofactor]] used in [[anabolic reaction]]s, such as the [[Calvin cycle]] and [[lipid]] and [[nucleic acid]] syntheses, which require '''NADPH''' as a [[reducing agent]] ('hydrogen source'). NADPH is the [[redox|reduced]] form, whereas NADP{{+}} is the [[redox|oxidized]] form. NADP{{+}} is used by all forms of cellular life.<ref name="pmid26284036">{{cite journal | vauthors = Spaans SK, Weusthuis RA, van der Oost J, Kengen SW | title = NADPH-generating systems in bacteria and archaea | journal = Frontiers in Microbiology | volume = 6 | pages = 742 | date = 2015 | pmid = 26284036 | pmc = 4518329 | doi = 10.3389/fmicb.2015.00742 | doi-access = free }}</ref>

NADP{{+}} differs from [[NAD+|NAD{{+}}]] by the presence of an additional [[phosphate group]] on the 2' position of the [[ribose]] ring that carries the [[adenine]] [[Moiety (chemistry)|moiety]]. This extra phosphate is added by [[NAD+ kinase|NAD⁺ kinase]] and removed by NADP⁺ phosphatase.<ref>{{cite journal | vauthors = Kawai S, Murata K | title = Structure and function of NAD kinase and NADP phosphatase: key enzymes that regulate the intracellular balance of NAD(H) and NADP(H) | journal = Bioscience, Biotechnology, and Biochemistry | volume = 72 | issue = 4 | pages = 919–30 | date = April 2008 | pmid = 18391451 | doi = 10.1271/bbb.70738 | doi-access = free }}</ref>

== Biosynthesis ==

=== NADP{{+}} ===

In general, NADP⁺ is synthesized before NADPH is. Such a reaction usually starts with [[NAD+|NAD⁺]] from either the de-novo or the salvage pathway, with [[NAD+ kinase|NAD⁺ kinase]] adding the extra phosphate group. [[ADP-ribosyl cyclase]] allows for synthesis from [[nicotinamide]] in the salvage pathway, and NADP⁺ phosphatase can convert NADPH back to NADH to maintain a balance.<ref name="pmid26284036"/> Some forms of the NAD⁺ kinase, notably the one in mitochondria, can also accept NADH to turn it directly into NADPH.<ref>{{cite journal | vauthors = Iwahashi Y, Hitoshio A, Tajima N, Nakamura T | title = Characterization of NADH kinase from Saccharomyces cerevisiae | journal = Journal of Biochemistry | volume = 105 | issue = 4 | pages = 588–93 | date = April 1989 | pmid = 2547755 | doi = 10.1093/oxfordjournals.jbchem.a122709 }}</ref><ref>{{cite journal | vauthors = Iwahashi Y, Nakamura T | title = Localization of the NADH kinase in the inner membrane of yeast mitochondria | journal = Journal of Biochemistry | volume = 105 | issue = 6 | pages = 916–21 | date = June 1989 | pmid = 2549021 | doi = 10.1093/oxfordjournals.jbchem.a122779 }}</ref> The prokaryotic pathway is less well understood, but with all the similar proteins the process should work in a similar way.<ref name="pmid26284036"/>

=== NADPH ===

NADPH is produced from NADP⁺. The major source of NADPH in animals and other non-photosynthetic organisms is the [[pentose phosphate pathway]], by [[glucose-6-phosphate dehydrogenase]] (G6PDH) in the first step. The pentose phosphate pathway also produces pentose, another important part of NAD(P)H, from glucose. Some bacteria also use G6PDH for the [[Entner–Doudoroff pathway]], but NADPH production remains the same.<ref name="pmid26284036"/>

[[Ferredoxin—NADP(+) reductase|Ferredoxin–NADP{{+}} reductase]], present in all domains of life, is a major source of NADPH in photosynthetic organisms including plants and cyanobacteria. It appears in the last step of the electron chain of the [[Light-dependent reactions|light reactions]] of [[photosynthesis]]. It is used as reducing power for the biosynthetic reactions in the [[Calvin cycle]] to assimilate carbon dioxide and help turn the carbon dioxide into glucose. It has functions in accepting electrons in other non-photosynthetic pathways as well: it is needed in the reduction of nitrate into ammonia for plant assimilation in [[nitrogen cycle]] and in the production of oils.<ref name="pmid26284036"/>

There are several other lesser-known mechanisms of generating NADPH, all of which depend on the presence of [[mitochondria]] in eukaryotes. The key enzymes in these carbon-metabolism-related processes are NADP-linked isoforms of [[malic enzyme]], [[isocitrate dehydrogenase]] (IDH), and [[glutamate dehydrogenase]]. In these reactions, NADP⁺ acts like NAD⁺ in other enzymes as an oxidizing agent.<ref>{{cite journal | vauthors = Hanukoglu I, Rapoport R | title = Routes and regulation of NADPH production in steroidogenic mitochondria | journal = Endocrine Research | volume = 21 | issue = 1–2 | pages = 231–41 | date = Feb–May 1995 | pmid = 7588385 | doi = 10.3109/07435809509030439 }}</ref> The isocitrate dehydrogenase mechanism appears to be the major source of NADPH in fat and possibly also liver cells.<ref name=Palmer>{{cite web|last=Palmer|first=Michael|title=10.4.3 Supply of NADPH for fatty acid synthesis|url=http://watcut.uwaterloo.ca/webnotes/Metabolism/page-10.4.3.html|work=Metabolism Course Notes|access-date=6 April 2012|url-status=dead|archive-url=https://web.archive.org/web/20130606001732/http://watcut.uwaterloo.ca/webnotes/Metabolism/page-10.4.3.html|archive-date=6 June 2013}}</ref> These processes are also found in bacteria. Bacteria can also use a NADP-dependent [[glyceraldehyde 3-phosphate dehydrogenase]] for the same purpose. Like the pentose phosphate pathway, these pathways are related to parts of [[glycolysis]].<ref name="pmid26284036"/> Another carbon metabolism-related pathway involved in the generation of NADPH is the mitochondrial folate cycle, which uses principally serine as a source of one-carbon units to sustain nucleotide synthesis and redox homeostasis in mitochondria. Mitochondrial folate cycle has been recently suggested as the principal contributor to NADPH generation in mitochondria of cancer cells.<ref>{{cite journal |last1=Ciccarese |first1=F. |last2=Ciminale |first2=V. |title=Escaping Death: Mitochondrial Redox Homeostasis in Cancer Cells |journal=Front Oncol |date= June 2017|volume=7 |page=117 |doi=10.3389/fonc.2017.00117|pmid=28649560 |pmc=5465272 |doi-access=free }}</ref>

NADPH can also be generated through pathways unrelated to carbon metabolism. The ferredoxin reductase is such an example. [[Nicotinamide nucleotide transhydrogenase]] transfers the hydrogen between NAD(P)H and NAD(P)⁺, and is found in eukaryotic mitochondria and many bacteria. There are versions that depend on a [[proton gradient]] to work and ones that do not. Some anaerobic organisms use [[Hydrogen dehydrogenase (NADP+)|NADP⁺-linked hydrogenase]], ripping a hydride from hydrogen gas to produce a proton and NADPH.<ref name="pmid26284036"/>

Like [[NADH]], NADPH is [[fluorescent]]. NADPH in aqueous solution excited at the nicotinamide absorbance of ~335&nbsp;nm (near UV) has a fluorescence emission which peaks at 445-460&nbsp;nm (violet to blue). NADP{{+}} has no appreciable fluorescence.<ref name="Blacker Mann Gale Ziegler p. ">{{cite journal | last1=Blacker | first1=Thomas S. | last2=Mann | first2=Zoe F. | last3=Gale | first3=Jonathan E. | last4=Ziegler | first4=Mathias | last5=Bain | first5=Angus J. | last6=Szabadkai | first6=Gyorgy | last7=Duchen | first7=Michael R. | title=Separating NADH and NADPH fluorescence in live cells and tissues using FLIM | journal=Nature Communications | publisher=Springer Science and Business Media LLC | volume=5 | issue=1 | date=2014-05-29 | issn=2041-1723 | doi=10.1038/ncomms4936| pmc=4046109 | page=3936| pmid=24874098 | bibcode=2014NatCo...5.3936B | doi-access=free }}</ref>

== Function ==

NADPH provides the reducing agents, usually hydrogen atoms, for biosynthetic reactions and the [[oxidation-reduction]] involved in protecting against the toxicity of [[reactive oxygen species]] (ROS), allowing the regeneration of [[glutathione]] (GSH).<ref>{{cite journal | vauthors = Rush GF, Gorski JR, Ripple MG, Sowinski J, Bugelski P, Hewitt WR | title = Organic hydroperoxide-induced lipid peroxidation and cell death in isolated hepatocytes | journal = Toxicology and Applied Pharmacology | volume = 78 | issue = 3 | pages = 473–83 | date = May 1985 | pmid = 4049396 | doi = 10.1016/0041-008X(85)90255-8 }}</ref> NADPH is also used for [[anabolic]] pathways, such as [[cholesterol synthesis]], steroid synthesis,<ref name=":0">{{Cite book|last=Rodwell|first=Victor|title=Harper's illustrated Biochemistry, 30th edition|publisher=McGraw Hill|year=2015|isbn=978-0-07-182537-5|location=USA|pages=123–124, 166, 200–201}}</ref> ascorbic acid synthesis,<ref name=":0" /> xylitol synthesis,<ref name=":0" /> cytosolic fatty acid synthesis<ref name=":0" /> and microsomal [[fatty acid synthesis|fatty acid chain elongation]].

The NADPH system is also responsible for generating free radicals in immune cells by [[NADPH oxidase]]. These radicals are used to destroy pathogens in a process termed the [[respiratory burst]].<ref>{{cite journal | vauthors = Ogawa K, Suzuki K, Okutsu M, Yamazaki K, Shinkai S | title = The association of elevated reactive oxygen species levels from neutrophils with low-grade inflammation in the elderly | journal = Immunity & Ageing | volume = 5 | pages = 13 | date = October 2008 | pmid = 18950479 | pmc = 2582223 | doi = 10.1186/1742-4933-5-13 | doi-access = free }}</ref>

It is the source of reducing equivalents for [[cytochrome P450]] [[hydroxylation]] of [[aromatic compounds]], [[steroid]]s, [[Alcohol (chemistry)|alcohol]]s, and [[drug]]s.

== Stability ==

NADH and NADPH are very stable in basic solutions, but NAD⁺ and NADP⁺ are degraded in basic solutions into a fluorescent product that can be used conveniently for quantitation. Conversely, NADPH and NADH are degraded by acidic solutions while NAD⁺/NADP⁺ are fairly stable to acid.<ref name="Passonneau1993">{{cite book | last=Passonneau | first=Janet | title=Enzymatic analysis : a practical guide | publisher=Humana Press | publication-place=Totowa, NJ | year=1993 | isbn=978-0-89603-238-5 | oclc=26397387 | page=3,10}}</ref><ref>{{Cite journal |last1=Lu |first1=Wenyun |last2=Wang |first2=Lin |last3=Chen |first3=Li |last4=Hui |first4=Sheng |last5=Rabinowitz |first5=Joshua D. |date=2018-01-20 |title=Extraction and Quantitation of Nicotinamide Adenine Dinucleotide Redox Cofactors |journal=Antioxidants & Redox Signaling |language=en |volume=28 |issue=3 |pages=167–179 |doi=10.1089/ars.2017.7014 |issn=1523-0864 |pmc=5737638 |pmid=28497978}}</ref>

== Enzymes that use NADP(H) as a coenzyme ==

* [[Adrenodoxin reductase]]: This enzyme is present ubiquitously in most organisms.<ref name="2017-Hanukoglu-JME">{{cite journal | vauthors = Hanukoglu I | title = Conservation of the Enzyme-Coenzyme Interfaces in FAD and NADP Binding Adrenodoxin Reductase-A Ubiquitous Enzyme | journal = Journal of Molecular Evolution | volume = 85 | issue = 5–6 | pages = 205–218 | date = December 2017 | pmid = 29177972 | doi = 10.1007/s00239-017-9821-9 | bibcode = 2017JMolE..85..205H | s2cid = 7120148 }}</ref> It transfers two electrons from NADPH to FAD. In vertebrates, it serves as the first enzyme in the chain of mitochondrial P450 systems that synthesize steroid hormones.<ref name="1992-Hanukoglu">{{cite journal | vauthors = Hanukoglu I | title = Steroidogenic enzymes: structure, function, and role in regulation of steroid hormone biosynthesis | journal = The Journal of Steroid Biochemistry and Molecular Biology | volume = 43 | issue = 8 | pages = 779–804 | date = December 1992 | pmid = 22217824 | doi = 10.1016/0960-0760(92)90307-5 | s2cid = 112729 | url = https://zenodo.org/record/890723 }}</ref>

== Enzymes that use NADP(H) as a substrate ==

In 2018 and 2019, the first two reports of enzymes that catalyze the removal of the 2' phosphate of NADP(H) in eukaryotes emerged. First the [[cytoplasm]]ic protein MESH1 ({{uniprot|Q8N4P3}}),<ref name="Ding 2018">{{Cite journal |vauthors=((Ding CKC)), Rose J, Wu J, Sun T, Chen KY, Chen PH, Xu E, Tian S, Akinwuntan J, Guan Z, Zhou P, ((Chi JTA)) | doi = 10.1101/325266 | title = Mammalian stringent-like response mediated by the cytosolic NADPH phosphatase MESH1| journal = [[bioRxiv]] | year = 2018 | doi-access =free}}</ref> then the [[mitochondrial]] protein [[nocturnin]]<ref name="Estrella 2019">{{Cite journal | vauthors = Estrella MA, Du J, Chen L, Rath S, Prangley E, Chitrakar A, Aoki T, Schedl P, Rabinowitz J, Korennykh A | doi = 10.1101/534560 | title = The Metabolites NADP+ and NADPH are the Targets of the Circadian Protein Nocturnin (Curled)| journal = [[bioRxiv]] | year = 2019 | volume = 10 | issue = 1 | page = 2367 | pmid = 31147539 | pmc = 6542800 | doi-access = free}}</ref><ref name="Estrella 2019b">{{cite journal | vauthors = Estrella MA, Du J, Chen L, Rath S, Prangley E, Chitrakar A, Aoki T, Schedl P, Rabinowitz J, Korennykh A | display-authors = 6 | title = + and NADPH are the targets of the circadian protein Nocturnin (Curled) | journal = Nature Communications | volume = 10 | issue = 1 | pages = 2367 | date = May 2019 | pmid = 31147539 | pmc = 6542800 | doi = 10.1038/s41467-019-10125-z }}</ref> were reported. Of note, the structures and NADPH binding of MESH1 ([https://www.rcsb.org/structure/5vxA 5VXA]) and nocturnin ([https://www.rcsb.org/structure/6nf0 6NF0]) are not related.

{{Gallery

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| File:NADP-3D-balls.png|alt1=NADP+|NADP+

| File:NADPH-3D-balls.png|alt2=NADPH|NADPH}}

== References ==

{{Enzyme cofactors}}

[[Category:Pyridinium compounds]]