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Phosphagen
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<h2 id="reactions">Reactions</h2> <p class="note">Main article: <a href="/facts/Bioenergetic_systems/mdu3B590">Bioenergetic systems § ATP–CP: the phosphagen system</a></p> <p>The Phosphagen System (<a href="/facts/ATP-PC/mdu3B590">ATP-PCr</a>) occurs in the <a href="/facts/Cytosol/VyXgygWm">cytosol</a> (a gel-like substance) of the <a href="/facts/Sarcoplasm/hImz4xN7">sarcoplasm</a> of <a href="/facts/Skeletal_muscle/en1tVYFN">skeletal muscle</a>, and in the <a href="/facts/Myocyte/cP7Jea3q">myocyte</a>'s <a href="/facts/Cytosol/VyXgygWm">cytosolic</a> compartment of the <a href="/facts/Cytoplasm/Wa0sE6xf">cytoplasm</a> of <a href="/facts/Cardiac_muscle/oMqU4Sdu">cardiac</a> and <a href="/facts/Smooth_muscle/mpcpTsHp">smooth muscle</a>.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> </p> <p>During muscle contraction: </p> H2O + ATP → <a href="/facts/Hydron_(chemistry)/v5Qkumvm">H+</a> + ADP + Pi (<a href="/facts/Magnesium_in_biology/ENuowoyY">Mg2+</a> assisted, utilization of ATP for <a href="/facts/Muscle_contraction/EbloCYfV">Muscle contraction</a> by <a href="/facts/ATPase/8aEJlNgl">ATPase</a>) <a href="/facts/Hydron_(chemistry)/v5Qkumvm">H+</a> + ADP + CP → ATP + Creatine (Mg2+ assisted, catalyzed by <a href="/facts/Creatine_kinase/kYtNQKjy">creatine kinase</a>, ATP is used again in the above reaction for continued muscle contraction) 2 ADP → ATP + AMP (catalyzed by <a href="/facts/Adenylate_kinase/XVLmsCUa">adenylate kinase</a>/myokinase when CP is depleted, ATP is again used for muscle contraction) <p>Muscle at rest: </p> ATP + Creatine → ADP + CP + <a href="/facts/Hydron_(chemistry)/v5Qkumvm">H+</a> (Mg2+ assisted, catalyzed by <a href="/facts/Creatine_kinase/kYtNQKjy">creatine kinase</a>) ADP + Pi → ATP (during <a href="/facts/Anaerobic_glycolysis/GwU4yYvo">anaerobic glycolysis</a> and <a href="/facts/Oxidative_phosphorylation/en2l08P9">oxidative phosphorylation</a>) <p>When the Phosphagen System has been depleted of phosphocreatine (creatine phosphate), the resulting AMP produced from the <a href="/facts/Adenylate_kinase/XVLmsCUa">adenylate kinase</a> (myokinase) reaction is primarily regulated by the <a href="/facts/Purine_nucleotide_cycle/AWagGvCk">Purine Nucleotide Cycle</a>.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a><a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> </p> <h2 id="further-reading">Further reading</h2> <ul><li>Ellington, W Ross (2001). "Evolution and Physiological Roles of Phosphagen Systems". <i>Annual Review of Physiology</i>. 63 (1): 289–325. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.1146%2Fannurev.physiol.63.1.289">10.1146/annurev.physiol.63.1.289</a>. <a href="/facts/PMID_(identifier)/JlHAvMHt">PMID</a> <a href="https://pubmed.ncbi.nlm.nih.gov/11181958">11181958</a>.</li> <li>Eggleton, Philip; Eggleton, Grace Palmer (1927). <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1514923">"The physiological significance of "phosphagen""</a>. <i>Journal of Physiology</i>. 63 (2): 155–161. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.1113%2Fjphysiol.1927.sp002391">10.1113/jphysiol.1927.sp002391</a>. <a href="/facts/PMC_(identifier)/dX1zMt71">PMC</a> <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1514923">1514923</a>. <a href="/facts/PMID_(identifier)/JlHAvMHt">PMID</a> <a href="https://pubmed.ncbi.nlm.nih.gov/16993876">16993876</a>.</li> <li>Eggleton, Philip; Eggleton, Grace Palmer (1928). <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1515019">"Further observations on phosphagen"</a>. <i>Journal of Physiology</i>. 65 (1): 15–24. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.1113%2Fjphysiol.1928.sp002457">10.1113/jphysiol.1928.sp002457</a>. <a href="/facts/PMC_(identifier)/dX1zMt71">PMC</a> <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1515019">1515019</a>. <a href="/facts/PMID_(identifier)/JlHAvMHt">PMID</a> <a href="https://pubmed.ncbi.nlm.nih.gov/16993934">16993934</a>.</li> <li>Baldwin, Ernest (1933). "PHOSPHAGEN". <i>Biological Reviews</i>. 8 (1): 74–105. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.1111%2Fj.1469-185X.1933.tb01088.x">10.1111/j.1469-185X.1933.tb01088.x</a>. <a href="/facts/ISSN_(identifier)/DPAflDvU">ISSN</a> <a href="https://search.worldcat.org/issn/1464-7931">1464-7931</a>. <a href="/facts/S2CID_(identifier)/ldJsHa2Y">S2CID</a> <a href="https://api.semanticscholar.org/CorpusID:221532329">221532329</a>.</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Selected Topics in the History of Biochemistry, G Semenza <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Wallimann T, Wyss M, Brdiczka D, Nicolay K, Eppenberger HM (January 1992). "Intracellular compartmentation, structure and function of creatine kinase isoenzymes in tissues with high and fluctuating energy demands: the 'phosphocreatine circuit' for cellular energy homeostasis". Biochem J. 281 (Pt 1): 21–40. doi:10.1042/bj2810021. PMC 1130636. PMID 1731757. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1130636" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1130636</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Bhagavan, N.V.; Ha, Chung-Eun (2015). "19. Contractile Systems". Essentials of Medical Biochemistry. Elsevier. pp. 339–361. doi:10.1016/B978-0-12-416687-5.00019-1. ISBN 978-0-12-416687-5. <a href="978-0-12-416687-5" target="_blank">978-0-12-416687-5</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Valberg, Stephanie J. (2008), "15. Skeletal Muscle Function", in Kaneko, J. Jerry; Harvey, John W.; Bruss, Michael L. (eds.), Clinical Biochemistry of Domestic Animals (6th ed.), Academic Press, pp. 459–484, ISBN 978-0-12-370491-7, retrieved 2023-10-10 <a href="978-0-12-370491-7" target="_blank">978-0-12-370491-7</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> </ol>