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((More citations needed|date=September 2017))
[[File:Purine Nucleotide Cycle.jpg|thumb|446x446px|Phosphagen system (ATP-PCr) and purine nucleotide cycle (PNC)<ref>Lewis, Amy & Guicherit, Oivin & Datta, Surjit & Hanten, Gerri & Kellems, Rodney. (1996). Structure and Expression of the Murine Muscle Adenylosuccinate Synthetase Gene. The Journal of biological chemistry. 271. 22647-56. 10.1074/jbc.271.37.22647.</ref>]]
The '''Purine Nucleotide Cycle''' is a [[metabolic pathway]] in [[protein metabolism]] requiring the amino acids aspartate and glutamate. The cycle is used to regulate the levels of adenine nucleotides, in which [[ammonia]] and [[fumarate]] are generated.<ref name=":0">((cite journal |author1=Lowenstein J.M. |year=1972 |title=Ammonia Production in Muscle and Other Tissues: the Purine Nucleotide Cycle |journal=Physiological Reviews |volume=52 |issue=2 |pages=382–414 |doi=10.1152/physrev.1972.52.2.382 |pmid=4260884))</ref> [[Adenosine monophosphate|AMP]] converts into [[Inosine monophosphate|IMP]] and the byproduct ammonia.  IMP converts to S-AMP ([[adenylosuccinate]]), which then converts to AMP and the byproduct fumarate. The fumarate goes on to produce ATP (energy) via [[oxidative phosphorylation]] as it enters the [[Krebs cycle]] and then the [[electron transport chain]]. Lowenstein first described this pathway and outlined its importance in processes including [[Amino acid|amino acid catabolism]] and regulation of flux through [[glycolysis]] and the [[Krebs cycle]].<ref name=":0" /><ref>((Cite book|last=Salway, J. G.|url=https://www.worldcat.org/oclc/53178315|title=Metabolism at a glance|date=2004|publisher=Blackwell Pub|isbn=1-4051-0716-2|edition=3rd|location=Malden, Mass.|oclc=53178315))</ref><ref>((Cite book|last=Voet, Donald|url=https://www.worldcat.org/oclc/690489261|title=Biochemistry|date=2011|publisher=John Wiley & Sons|others=Voet, Judith G.|isbn=978-0-470-57095-1|edition=4th|location=Hoboken, NJ|oclc=690489261))</ref>

AMP is produced after strenuous muscle contraction when the ATP reservoir is low (ADP > ATP) by the [[adenylate kinase]] (myokinase) reaction.<ref name=":8" /><ref name=":3" /> AMP is also produced from adenine and adenosine directly; however, AMP can be produced through less direct metabolic pathways, such as [[de novo synthesis]] of IMP or through salvage pathways of [[guanine]] (a purine) and any of the [[Purine nucleotides|purine nucleotides and nucleosides]]. IMP is synthesized [[De novo synthesis|de novo]] from [[glucose]] through the [[pentose phosphate pathway]] which produces [[Ribose 5-phosphate|ribose 5-P]], which then converts to [[PRPP]] that with the amino acids glycine, glutamine, and aspartate (''see [[Purine metabolism]]'') can be further converted into IMP.<ref name=":2">((Cite web |date=2022-04-29 |title=Purine Synthesis : Synthesis of Purine RiboNucleotides |url=https://biochemden.com/purine-synthesis/ |access-date=2022-12-14 |language=en-US))</ref> 

==Reactions==
The cycle comprises three [[Enzyme|enzyme-catalysed]] reactions. The first stage is the deamination of the purine [[nucleotide]] [[adenosine monophosphate]] (AMP) to form [[inosine monophosphate]] (IMP), catalysed by the enzyme [[AMP deaminase]]:

:AMP + H<sub>2</sub>O + H<sup>+</sup> → IMP + NH<sub>3</sub>

The second stage is the formation of [[adenylosuccinate]] from IMP and the amino acid [[aspartate]], which is coupled to the energetically favourable hydrolysis of [[Guanosine triphosphate|GTP]], and catalysed by the enzyme [[adenylosuccinate synthetase]]:

:Aspartate + IMP + GTP → Adenylosuccinate + [[Guanosine diphosphate|GDP]] + [[Inorganic phosphate|P<sub>i</sub>]]

Finally, adenylosuccinate is cleaved by the enzyme [[adenylosuccinate lyase]] to release fumarate and regenerate the starting material of AMP:

:Adenylosuccinate → AMP + Fumarate

A recent study showed that activation of HIF-1α allows cardiomyocytes to sustain mitochondrial membrane potential during anoxic stress by utilizing fumarate produced by adenylosuccinate lyase as an alternate terminal electron acceptor in place of oxygen. This mechanism should help provide protection in the ischemic heart.<ref>Sridharan et al. (AJP Cell Physiology, 2008, 295:C29-C37)</ref>

==Occurrence==
The purine nucleotide cycle occurs in the [[cytosol]] (a gel-like substance) of the [[sarcoplasm]] of [[skeletal muscle]], and in the [[myocyte]]'s [[cytosol]]ic compartment of the [[cytoplasm]] of [[Cardiac muscle|cardiac]] and [[smooth muscle]]. The cycle occurs when ATP reservoirs run low (ADP > ATP), such as strenuous exercise, fasting or starvation.<ref name=":8">((Citation |last=Valberg |first=Stephanie J. |title=Chapter 15 - Skeletal Muscle Function |date=2008-01-01 |url=https://www.sciencedirect.com/science/article/pii/B9780123704917000155 |work=Clinical Biochemistry of Domestic Animals (Sixth Edition) |pages=459–484 |editor-last=Kaneko |editor-first=J. Jerry |access-date=2023-10-10 |place=San Diego |publisher=Academic Press |isbn=978-0-12-370491-7 |editor2-last=Harvey |editor2-first=John W. |editor3-last=Bruss |editor3-first=Michael L.))</ref><ref name=":7" />

Proteins catabolize into amino acids, and [[amino acid]]s are precursors for purines, nucleotides and nucleosides which are used in the purine nucleotide cycle.<ref name=":2" /> The amino acid [[Glutamic acid|glutamate]] is used to neutralize the ammonia produced when AMP is converted into IMP. Another amino acid, [[aspartate]], is used along with IMP to produce S-AMP in the cycle. Skeletal muscle contains amino acids for use in catabolism, known as the free amino acid pool; however, inadequate carbohydrate supply and/or strenuous exercise requires protein catabolism to sustain the free amino acids.<ref name=":7">Baker JS, McCormick MC, Robergs RA. Interaction among Skeletal Muscle Metabolic Energy Systems during Intense Exercise. J Nutr Metab. 2010;2010:905612. doi: 10.1155/2010/905612. Epub 2010 Dec 6. PMID 21188163; PMCID: PMC3005844.</ref>

When the [[Bioenergetic systems#ATP–CP: the phosphagen system|phosphagen system (ATP-PCr)]] has been depleted of [[phosphocreatine]] (creatine phosphate), the purine nucleotide cycle also helps to sustain the [[myokinase]] reaction by reducing accumulation of AMP produced after muscle contraction in the below reaction.<ref name=":3">N.V. Bhagavan, Chung-Eun Ha, in Essentials of Medical Biochemistry (Second Edition), 2015. Chapter 19 - Contractile Systems: Reaction and the Purine Nucleotide Cycle</ref>

During muscle contraction: 
: H<sub>2</sub>O + ATP → H<sup>+</sup> + ADP + P<sub>i</sub> ([[Magnesium in biology#Biological chemistry|Mg<sup>2+</sup>]] assisted, utilization of ATP for [[muscle contraction]] by [[ATPase]])
: H<sup>+</sup> + ADP + CP → ATP + Creatine (Mg<sup>2+</sup> assisted, catalyzed by [[creatine kinase]], ATP is used again in the above reaction for continued muscle contraction)
: 2 ADP → ATP + AMP (catalyzed by [[adenylate kinase]]/myokinase when CP is depleted, ATP is again used for muscle contraction)  
Muscle at rest:
: ATP + Creatine → H<sup>+</sup> + ADP + CP (Mg<sup>2+</sup> assisted, catalyzed by [[creatine kinase]])
: ADP + P<sub>i</sub> → ATP (during [[anaerobic glycolysis]] and [[oxidative phosphorylation]])
AMP can dephosphorylate to adenosine and [[Diffusion|diffuse]] out of the cell; the purine nucleotide cycle may therefore also reduce the loss of adenosine from the cell since nucleosides permeate cell membranes, whereas nucleotides do not.<ref name=":3" />

==Consequences==

=== Aspartate and glutamate synthesis ===
[[File:Interaction between Branched-Chain Amino Acids and the Purine Nucleotide Cycle in muscles.png|thumb|Interaction between branched-chain amino acids and the purine nucleotide cycle in muscles]]
[[Fumarate]], produced from the purine nucleotide cycle, is an intermediate of [[Citric acid cycle|TCA cycle]] and enters the [[mitochondria]] by converting into malate and utilizing the [[malate shuttle]] where it is converted into oxaloacetic acid (OAA). During exercise, OAA either enters into [[TCA cycle]] or converts into aspartate in the mitochondria.<ref name=":4">((Cite journal |last=Arinze |first=Ifeanyi J. |date=May 2005 |title=Facilitating understanding of the purine nucleotide cycle and the one-carbon pool: Part I: The purine nucleotide cycle |url=https://onlinelibrary.wiley.com/doi/10.1002/bmb.2005.494033032469 |journal=Biochemistry and Molecular Biology Education |language=en |volume=33 |issue=3 |pages=165–168 |doi=10.1002/bmb.2005.494033032469|pmid=21638570 |s2cid=35570434 |doi-access=free ))</ref>

As the purine nucleotide cycle produces ammonia ''(see below in ammonia synthesis)'', skeletal muscle needs to synthesize glutamate in a way that does not further increase ammonia, and as such the use of [[glutaminase]] to produce glutamate from glutamine would not be ideal. Also, plasma glutamine (released from the kidneys) requires [[active transport]] into the muscle cell (consuming ATP).<ref name=":5">((Cite journal |last1=Cruzat |first1=Vinicius |last2=Macedo Rogero |first2=Marcelo |last3=Noel Keane |first3=Kevin |last4=Curi |first4=Rui |last5=Newsholme |first5=Philip |date=2018-10-23 |title=Glutamine: Metabolism and Immune Function, Supplementation and Clinical Translation |journal=Nutrients |language=en |volume=10 |issue=11 |pages=1564 |doi=10.3390/nu10111564 |pmid=30360490 |pmc=6266414 |issn=2072-6643 |doi-access=free ))</ref> Consequently, during exercise when the ATP reservoir is low (ADP>ATP), glutamate is produced from branch-chained amino acids (BCAAs) and α-ketoglutarate, as well as from alanine and α-ketoglutarate.<ref>((Cite journal |last=Wagenmakers |first=A. J. |date=1998 |title=Muscle amino acid metabolism at rest and during exercise: role in human physiology and metabolism |url=https://pubmed.ncbi.nlm.nih.gov/9696993/ |journal=Exercise and Sport Sciences Reviews |volume=26 |pages=287–314 |doi=10.1249/00003677-199800260-00013 |issn=0091-6331 |pmid=9696993|s2cid=21127358 ))</ref> Glutamate is then used to produce aspartate. The aspartate enters the purine nucleotide cycle, where it is used to convert IMP into S-AMP.<ref name=":4" /><ref>((Cite journal |last1=Mann |first1=Gagandeep |last2=Mora |first2=Stephen |last3=Madu |first3=Glory |last4=Adegoke |first4=Olasunkanmi A. J. |date=2021 |title=Branched-chain Amino Acids: Catabolism in Skeletal Muscle and Implications for Muscle and Whole-body Metabolism |journal=Frontiers in Physiology |volume=12 |page=702826 |doi=10.3389/fphys.2021.702826 |pmid=34354601 |pmc=8329528 |issn=1664-042X |doi-access=free ))</ref>

:BCAAs + α-Ketoglutarate ⇌ Glutamate + Branch-chain keto acids (BCKAs) (catalyzed by [[Branched-chain amino acid aminotransferase|Branched-chain aminotransferases (BCAT)]])
:Alanine + α-Ketoglutarate ⇌ Pyruvate + Glutamate (catalyzed by [[alanine transaminase]])
:
:Oxaloacetic acid + Glutamate ⇌ α-Ketoglutarate + Aspartate (catalyzed by [[aspartate aminotransferase]])

When skeletal muscle is at rest (ADP<ATP), the aspartate is no longer needed for the purine nucleotide cycle and can therefore be used with α-ketoglutarate to produce glutamate and oxaloacetic acid (the above reaction reversed).<blockquote>α-Ketoglutarate + Aspartate ⇌ Oxaloacetic acid + Glutamate (catalyzed by [[aspartate aminotransferase]])</blockquote>

=== Ammonia and glutamine synthesis ===
During exercise when the ATP reservoir is low (ADP>ATP), the purine nucleotide cycle produces ammonia (NH<sub>3</sub>) when it converts AMP into IMP. (With the exception of [[Adenosine monophosphate deaminase deficiency type 1|AMP deaminase deficiency]], where ammonia is produced during exercise when adenosine, from AMP, is converted into inosine). During rest (ADP<ATP), ammonia is produced from the conversion of adenosine into inosine by adenosine deaminase. 
:AMP + H<sub>2</sub>O + H<sup>+</sup> → IMP + NH<sub>3</sub> (catalyzed by [[AMP deaminase]] in skeletal muscle)

:Adenosine + H<sub>2</sub>O → Inosine + NH<sub>3</sub> (catalyzed by [[adenosine deaminase]] in skeletal muscle, blood, liver)
Ammonia is toxic, disrupts cell function, and permeates cell membranes. Ammonia becomes ammonium (NH<sub>4</sub><sup>+</sup>) depending on the pH of the cell or plasma. Ammonium is relatively non-toxic and does not readily permeate cell membranes.<ref>((Citation |title=Ammonia |date=2012-01-01 |url=https://www.sciencedirect.com/science/article/pii/B978141609979600355X |work=Clinical Veterinary Advisor |pages=905 |editor-last=Wilson |editor-first=David A. |access-date=2023-03-22 |place=Saint Louis |publisher=W.B. Saunders |language=en |doi=10.1016/b978-1-4160-9979-6.00355-x |isbn=978-1-4160-9979-6))</ref> <blockquote>NH<sub>3</sub> + H<sup>+</sup> ⇌ NH<sub>4</sub><sup>+</sup></blockquote>Ammonia (NH<sub>3</sub>) diffuses into the blood, circulating to the liver to be neutralized by the [[urea cycle]]. (N.b. [[urea]] is not the same as [[uric acid]], though both are end products of the purine nucleotide cycle, from ammonia and nucleotides respectively.) When the skeletal muscles are at rest (ADP<ATP), ammonia (NH<sub>3</sub>) combines with glutamate to produce [[glutamine]], which is an energy-consuming step, and the glutamine enters the blood.<ref name=":6">((Cite journal |last1=Taneja |first1=Vikas |last2=Jasuja |first2=Haneesh |date=November 2019 |title=Severe hyperammonemia from intense skeletal muscle activity: A rare case report and literature review |journal=Medicine |language=en |volume=98 |issue=47 |pages=e17981 |doi=10.1097/MD.0000000000017981 |pmid=31764807 |pmc=6882587 |s2cid=208276909 |issn=0025-7974))</ref><ref name=":5" /><blockquote>Glutamate + NH<sub>3</sub> + ATP → Glutamine + ADP + P<sub>i</sub> (catalyzed by [[glutamine synthetase]] in resting skeletal muscle)</blockquote>Excess glutamine is used by [[proximal tubule]] in the kidneys for ammoniagenesis, which may counteract any metabolic acidosis from anaerobic skeletal muscle activity.<ref name=":6" /> In kidneys, glutamine is deaminated twice to form glutamate and then [[α-ketoglutarate]]. These NH<sub>3</sub> molecules neutralise the organic acids ([[lactic acid]] and [[ketone bodies]]) produced in the muscles.<blockquote>Glutamine + H<sub>2</sub>O → Glutamate + NH<sub>4</sub><sup>+</sup> (catalyzed by [[glutaminase]] in the kidneys)</blockquote>

== Pathology ==
Some [[Metabolic myopathy|metabolic myopathies]] involve the under- or over-utilization of the purine nucleotide cycle. Metabolic myopathies cause a low ATP reservoir in muscle cells (ADP > ATP),  resulting in exercise-induced excessive AMP buildup in muscle, and subsequent exercise-induced hyperuricemia (myogenic hyperuricemia) through conversion of excessive AMP into uric acid by way of either AMP → adenosine or AMP → IMP.

During strenuous exercise, AMP is created through the use of the adenylate kinase (myokinase) reaction after the phosphagen system has been depleted of creatine phosphate and not enough ATP is being produced yet by other pathways ''(see above reaction in '[[Purine nucleotide cycle#Occurrence|Occurrence]]' section)''. In those affected by metabolic myopathies, exercise that normally wouldn't be considered strenuous for healthy people, is however strenuous for them due to their low ATP reservoir in muscle cells. This results in regular use of the myokinase reaction for normal, everyday activities.

Besides the myokinase reaction, a high ATP consumption and low ATP reservoir also increases protein catabolism and salvage of IMP, which results in increased AMP and IMP. These two nucleotides can then enter the purine nucleotide cycle to produce fumarate which will then produce ATP by oxidative phosphorylation. If the purine nucleotide cycle is blocked (such as AMP deaminase deficiency) or if exercise is stopped and increased fumarate production is no longer needed, then the excess nucleotides will be converted into uric acid.

=== AMP deaminase deficiency (MADD) ===
((main|Adenosine monophosphate deaminase deficiency type 1))

[[Adenosine monophosphate deaminase deficiency type 1|AMP deaminase deficiency]] (formally known as myoadenylate deaminase deficiency or MADD) is a [[metabolic myopathy]] which results in excessive AMP buildup brought on by exercise. AMP deaminase is needed to convert AMP into IMP in the purine nucleotide cycle. Without this enzyme, the excessive AMP buildup is initially due to the adenylate kinase (myokinase) reaction which occurs after a muscle contraction.<ref>((Cite journal |last1=Sabina |first1=Richard L. |last2=Swain |first2=Judith L. |last3=Patten |first3=Bernard M. |last4=Ashizawa |first4=Tetsuo |last5=O'Brien |first5=William E. |last6=Holmes |first6=Edward W. |date=1980-12-01 |title=Disruption of the Purine Nucleotide Cycle |url=http://www.jci.org/articles/view/109995 |journal=Journal of Clinical Investigation |language=en |volume=66 |issue=6 |pages=1419–1423 |doi=10.1172/JCI109995 |pmid=7440723 |pmc=371628 |issn=0021-9738))</ref> However, AMP is also used to allosterically regulate the enzyme [[myophosphorylase]] (''see [[Glycogen phosphorylase#Regulation|Glycogen phosphorylase § Regulation]]''), so the initial buildup of AMP triggers the enzyme myophosphorylase to release muscle glycogen into glucose-1-P (glycogen→glucose-1-P),<ref>((Cite journal |last1=Meyer |first1=Francois |last2=Heilmeyer |first2=Ludwig M.G. |last3=Haschke |first3=Richard H. |last4=Fischer |first4=Edmond H. |date=1970-12-25 |title=Control of Phosphorylase Activity in a Muscle Glycogen Particle |url=http://dx.doi.org/10.1016/s0021-9258(18)62582-7 |journal=Journal of Biological Chemistry |volume=245 |issue=24 |pages=6642–6648 |doi=10.1016/s0021-9258(18)62582-7 |s2cid=33852514 |issn=0021-9258|doi-access=free ))</ref> which eventually depletes the muscle glycogen, which in turn triggers protein metabolism, which then produces even more AMP. In AMP deaminase deficiency, excess [[adenosine]] is converted into uric acid in the following reaction:

:AMP → Adenosine → Inosine → Hypoxanthine → Xanthine → Uric Acid

=== Glycogenoses (GSDs) ===
((main|Glycogen storage disease))

Myogenic [[hyperuricemia]], as a result of the purine nucleotide cycle running when ATP reservoirs in muscle cells are low (ADP > ATP), is a common pathophysiologic feature of [[Glycogen storage disease|glycogenoses]] such as [[Glycogen storage disease type III|GSD-III]], [[Glycogen storage disease type V|GSD-V]] and [[Glycogen storage disease type VII|GSD-VII]], as they are [[Metabolic myopathy|metabolic myopathies]] which impair the ability of ATP (energy) production within muscle cells. In these metabolic myopathies, myogenic hyperuricemia is exercise-induced; inosine, hypoxanthine and uric acid increase in plasma after exercise and decrease over hours with rest.<ref name=":1">((Cite journal |last1=Mineo |first1=Ikuo |last2=Kono |first2=Norio |last3=Hara |first3=Naoko |last4=Shimizu |first4=Takao |last5=Yamada |first5=Yuya |last6=Kawachi |first6=Masanori |last7=Kiyokawa |first7=Hiroaki |last8=Wang |first8=Yan Lin |last9=Tarui |first9=Seiichiro |date=1987-07-09 |title=Myogenic Hyperuricemia |url=http://www.nejm.org/doi/abs/10.1056/NEJM198707093170203 |journal=New England Journal of Medicine |language=en |volume=317 |issue=2 |pages=75–80 |doi=10.1056/NEJM198707093170203 |pmid=3473284 |issn=0028-4793))</ref> Excess [[Adenosine monophosphate|AMP (adenosine monophosphate)]] is converted into [[uric acid]].<ref name=":1" /> 

:AMP → IMP → Inosine → Hypoxanthine → Xanthine → Uric acid

[[Hyperammonemia]] is also seen post-exercise in McArdle disease (GSD-V) and [[phosphoglucomutase deficiency]] (PGM1-CDG, formerly GSD-XIV), due to the purine nucleotide cycle running when the ATP reservoir is low due to the glycolytic block.<ref>((Cite journal |last1=Altassan |first1=Ruqaiah |last2=Radenkovic |first2=Silvia |last3=Edmondson |first3=Andrew C. |last4=Barone |first4=Rita |last5=Brasil |first5=Sandra |last6=Cechova |first6=Anna |last7=Coman |first7=David |last8=Donoghue |first8=Sarah |last9=Falkenstein |first9=Kristina |last10=Ferreira |first10=Vanessa |last11=Ferreira |first11=Carlos |last12=Fiumara |first12=Agata |last13=Francisco |first13=Rita |last14=Freeze |first14=Hudson |last15=Grunewald |first15=Stephanie |date=January 2021 |title=International consensus guidelines for phosphoglucomutase 1 deficiency (PGM1-CDG): Diagnosis, follow-up, and management |journal=Journal of Inherited Metabolic Disease |volume=44 |issue=1 |pages=148–163 |doi=10.1002/jimd.12286 |issn=0141-8955 |pmc=7855268 |pmid=32681750))</ref><ref>((Cite journal |last1=Stojkovic |first1=Tanya |last2=Vissing |first2=John |last3=Petit |first3=François |last4=Piraud |first4=Monique |last5=Orngreen |first5=Mette C. |last6=Andersen |first6=Grete |last7=Claeys |first7=Kristl G. |last8=Wary |first8=Claire |last9=Hogrel |first9=Jean-Yves |last10=Laforêt |first10=Pascal |date=2009-07-23 |title=Muscle Glycogenosis Due to Phosphoglucomutase 1 Deficiency |url=http://www.nejm.org/doi/abs/10.1056/NEJMc0901158 |journal=New England Journal of Medicine |language=en |volume=361 |issue=4 |pages=425–427 |doi=10.1056/NEJMc0901158 |pmid=19625727 |issn=0028-4793|doi-access=free ))</ref><ref>Jean-Yves Hogrel, Jorien B E Janssen, Isabelle Ledoux, Gwenn Ollivier, Anthony Béhin, et al.. The diagnostic value of hyperammonaemia induced by the non-ischaemic forearm exercise test. Journal of Clinical Pathology, 2017, 70 (10), pp.896 - 898. 10.1136/jclinpath-2017-204324 . hal-01618833</ref><ref>((Cite journal |last1=Rumpf |first1=K. W. |last2=Wagner |first2=H. |last3=Kaiser |first3=H. |last4=Meinck |first4=H. M. |last5=Goebel |first5=H. H. |last6=Scheler |first6=F. |date=1981-12-01 |title=Increased ammonia production during forearm ischemic work test in McArdle's disease |url=https://pubmed.ncbi.nlm.nih.gov/6947119/ |journal=Klinische Wochenschrift |volume=59 |issue=23 |pages=1319–1320 |doi=10.1007/BF01711182 |issn=0023-2173 |pmid=6947119|s2cid=25192276 ))</ref><ref>((Cite journal |last1=Vissing |first1=J. |last2=MacLean |first2=D. A. |last3=Vissing |first3=S. F. |last4=Sander |first4=M. |last5=Saltin |first5=B. |last6=Haller |first6=R. G. |date=2001-12-01 |title=The exercise metaboreflex is maintained in the absence of muscle acidosis: insights from muscle microdialysis in humans with McArdle's disease |journal=The Journal of Physiology |volume=537 |issue=Pt 2 |pages=641–649 |doi=10.1111/j.1469-7793.2001.00641.x |issn=0022-3751 |pmc=2278977 |pmid=11731594))</ref><ref>((Cite journal |last1=Wagenmakers |first1=A. J. |last2=Coakley |first2=J. H. |last3=Edwards |first3=R. H. |date=May 1990 |title=Metabolism of branched-chain amino acids and ammonia during exercise: clues from McArdle's disease |url=https://pubmed.ncbi.nlm.nih.gov/2193889/ |journal=International Journal of Sports Medicine |volume=11 Suppl 2 |pages=S101–113 |doi=10.1055/s-2007-1024861 |issn=0172-4622 |pmid=2193889))</ref><blockquote>AMP + H<sub>2</sub>O + H<sup>+</sup> → IMP + NH<sub>3</sub> </blockquote>

== See also ==

* [[Adenosine monophosphate deaminase deficiency type 1|AMP deaminase deficiency]] (MADD)
* [[Bioenergetic systems]]
* [[Glycogenosis|Glycogenoses]] (GSDs)
* [[Metabolic myopathy|Metabolic myopathies]]
* [[Bioenergetic systems#ATP–CP: the phosphagen system|Phosphagen System]] (ATP-PCr)
* [[Protein catabolism]]
* [[Uric acid#High uric acid|Uric Acid § High uric acid]]

==References==
((Reflist))
((Nucleotide metabolism enzymes))
((Nucleotide metabolism intermediates))
((Nucleobases, nucleosides, and nucleotides))
((Inborn errors of purine–pyrimidine metabolism))((Metabolism))((Myopathy))
[[Category:Purines|*]]
[[Category:Metabolic pathways]]
[[Category:Biochemistry]]

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