Editing Myoglobin (section)

{{short description|Iron and oxygen-binding protein}}
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'''Myoglobin''' (symbol '''Mb''' or '''MB''') is an [[iron]]- and [[oxygen]]-binding [[protein]] found in the cardiac and [[skeletal muscle|skeletal]] [[Muscle|muscle tissue]] of vertebrates in general and in almost all mammals.<ref name="hardison">{{cite journal | vauthors = Ordway GA, Garry DJ | title = Myoglobin: an essential hemoprotein in striated muscle | journal = The Journal of Experimental Biology | volume = 207 | issue = Pt 20 | pages = 3441–6 | date = Sep 2004 | pmid = 15339940 | doi = 10.1242/jeb.01172 | doi-access = free }}</ref><ref name="Wick Hornick 2011 pp. 83–136">{{cite book | vauthors = Wick MR, Hornick JL | title=Diagnostic Immunohistochemistry | chapter=Immunohistology of Soft Tissue and Osseous Neoplasms | publisher=Elsevier | year=2011 | isbn=978-1-4160-5766-6 | doi=10.1016/b978-1-4160-5766-6.00008-x | pages=83–136 | quote=Myoglobin is a 17.8-kD protein that is found in cardiac and skeletal muscle and that forms complexes with iron molecules. }}</ref><ref name="Feher 2017 pp. 656–664">{{cite book | vauthors = Feher J | title=Quantitative Human Physiology | chapter=Oxygen and Carbon Dioxide Transport | publisher=Elsevier | year=2017 | isbn=978-0-12-800883-6 | doi=10.1016/b978-0-12-800883-6.00064-1 | pages=656–664 | quote= Highly oxidative muscle fibers contain a lot of myoglobin. It has two functions in muscle: it stores oxygen for use during heavy exercise, and it enhances diffusion through the [[cytosol]] by carrying the oxygen. By binding O2, myoglobin (Mb) provides a second diffusive pathway for O2 through the cell cytosol. }}</ref><ref name="Wilson Reeder 2006 pp. 73–76">{{cite book | vauthors = Wilson MT, Reeder BJ | title=Encyclopedia of Respiratory Medicine | chapter=MYOGLOBIN | publisher=Elsevier | year=2006 | isbn=978-0-12-370879-3 | doi=10.1016/b0-12-370879-6/00250-7 | pages=73–76 | quote=Myoglobin (Mb) is a heme-containing globular protein that is found in abundance in myocyte cells of heart and skeletal muscle. }}</ref><ref name="Boncyk 2007 pp. 193–199">{{cite book | vauthors = Boncyk JC | title=Complications in Anesthesia | chapter=Perioperative Hypoxia | publisher=Elsevier | year=2007 | isbn=978-1-4160-2215-2 | doi=10.1016/b978-1-4160-2215-2.50052-1 | pages=193–199 | quote=Myoglobin serves both as an O2 buffer and to store O2 in muscle. All known vertebrate myoglobins and β-hemoglobin subunits are similar in structure, but myoglobin binds O2 more avidly at low Po2 (Fig. 47-5) because it is a monomer (i.e., it does not undergo a significant conformational change with oxygenation). Thus, myoglobin remains fully saturated at O2 tensions between 15 and 30 mm Hg and unloads its O2 to the muscle mitochondria only at very low O2 tensions. }}</ref> Myoglobin is distantly related to [[hemoglobin]]. Compared to [[hemoglobin]], myoglobin has a higher affinity for oxygen and does not have [[cooperative binding]] with oxygen like hemoglobin does.<ref name="Wilson Reeder 2006 pp. 73–76"/><ref name="review">{{cite journal | vauthors = Hardison RC | title = Evolution of Hemoglobin and Its Genes | journal = Cold Spring Harb Perspect Med | volume = 2 | issue = 12 | pages = a011627 | date = Dec 2012 | pmid = 23209182 | doi = 10.1101/cshperspect.a011627 | pmc = 3543078 }}</ref>  Myoglobin consists of non-polar amino acids at the core of the globulin, where the heme group is non-covalently bounded with the surrounding polypeptide of myoglobin. In humans, myoglobin is found in the bloodstream only after [[Strain (injury)|muscle injury]].<ref name="Chung_2018">{{cite book | vauthors = Chung MJ, Brown DL | chapter = Diagnosis of acute myocardial infarction. | veditors = Brown DL | title = Cardiac Intensive Care-E-Book | date = July 2018 | doi=10.1016/B978-0-323-52993-8.00009-6 | pages=91–98.e3 | isbn = 9780323529938 | s2cid = 260507329 | quote=Myoglobin is not specific for myocardial necrosis, however, especially in the presence of skeletal muscle injury and [[renal insufficiency]]. }}</ref><ref name="Sekhon Peacock 2019 pp. 115–128">{{cite book | vauthors = Sekhon N, Peacock WF | title=Biomarkers in Cardiovascular Disease | chapter=Biomarkers to Assist in the Evaluation of Chest Pain | publisher=Elsevier | year=2019 | isbn=978-0-323-54835-9 | doi=10.1016/b978-0-323-54835-9.00011-9 | pages=115–128 | s2cid=59548142 | quote=myoglobin is not specific for the death of cardiac myocytes, and levels can be elevated in [[renal disease]] as well as damage to skeletal muscle.}}</ref><ref name=Nelson00>{{cite book | vauthors = Nelson DL, Cox MM | title = Lehninger Principles of Biochemistry | publisher = Worth Publishers | location = New York | year = 2000 | page = 206 | edition = 3rd | isbn = 0-7167-6203-X | url=https://books.google.com/books?id=5Ek9J4p3NfkC&q=myoglobin}} (Google books link is the 2008 edition)</ref>

High concentrations of myoglobin in muscle cells allow organisms to hold their breath for a longer period of time. Diving mammals such as whales and seals have muscles with particularly high abundance of myoglobin.<ref name=Nelson00/> Myoglobin is found in Type I muscle, Type II A, and Type II B; although many older texts describe myoglobin as not found in [[smooth muscle tissue|smooth muscle]], this has proved erroneous: there is also myoglobin in smooth muscle cells.<ref name="qiu">{{cite journal | vauthors = Qiu Y, Sutton L, Riggs AF | title = Identification of myoglobin in human smooth muscle | journal = Journal of Biological Chemistry | volume = 273 | issue = 36 | pages = 23426–32 | date = Sep 1998 | doi = 10.1074/jbc.273.36.23426 | pmid = 9722578 | doi-access = free }}</ref>

Myoglobin was the first protein to have its three-dimensional structure revealed by [[X-ray crystallography]].<ref>[https://www.nsf.gov/news/news_summ.jsp?cntn_id=100689 (U.S.) National Science Foundation: Protein Data Bank Chronology (Jan. 21, 2004)]. Retrieved 3.17.2010</ref> This achievement was reported in 1958 by [[John Kendrew]] and associates.<ref name="architecture">{{cite journal | vauthors = Kendrew JC, Bodo G, Dintzis HM, Parrish RG, Wyckoff H, Phillips DC | title = A three-dimensional model of the myoglobin molecule obtained by x-ray analysis | journal = Nature | volume = 181 | issue = 4610 | pages = 662–6 | date = Mar 1958 | pmid = 13517261 | doi = 10.1038/181662a0 | bibcode = 1958Natur.181..662K | s2cid = 4162786 }}</ref> For this discovery, Kendrew shared the 1962 [[Nobel Prize in Chemistry]] with [[Max Perutz]].<ref name="Stoddart">{{cite journal | vauthors = Stoddart C |title=Structural biology: How proteins got their close-up |journal=Knowable Magazine |date=1 March 2022 |doi=10.1146/knowable-022822-1|doi-access=free |url=https://knowablemagazine.org/article/living-world/2022/structural-biology-how-proteins-got-their-closeup |access-date=25 March 2022}}</ref><ref name="nobel">[http://nobelprize.org/chemistry/laureates/1962/index.html The Nobel Prize in Chemistry 1962]</ref> Despite being one of the most studied proteins in biology, its physiological function is not yet conclusively established: mice genetically engineered to lack myoglobin can be viable and fertile, but show many cellular and physiological adaptations to overcome the loss. Through observing these changes in myoglobin-depleted mice, it is hypothesised that myoglobin function relates to increased oxygen transport to muscle, and to oxygen storage; as well, it serves as a scavenger of [[reactive oxygen species]].<ref name="mice-function">{{cite book | vauthors = Garry DJ, Kanatous SB, Mammen PP | title = Hypoxia and the Circulation | chapter = Molecular Insights into the Functional Role of Myoglobin | series = Advances in Experimental Medicine and Biology | volume = 618 | pages = [https://archive.org/details/hypoxiacirculati00inte/page/181 181–93] | date = 2007 | publisher = Springer | pmid = 18269197 | doi = 10.1007/978-0-387-75434-5_14 | isbn = 978-0-387-75433-8 | chapter-url = https://archive.org/details/hypoxiacirculati00inte/page/181 }}</ref>

In humans, myoglobin is encoded by the ''MB'' [[gene]].<ref name="pmid2989088">{{cite journal | vauthors = Akaboshi E | title = Cloning of the human myoglobin gene | journal = Gene | volume = 33 | issue = 3 | pages = 241–9 | year = 1985 | pmid = 2989088 | doi = 10.1016/0378-1119(85)90231-8 }}</ref>

Myoglobin can take the forms oxymyoglobin (MbO<sub>2</sub>), carboxymyoglobin (MbCO), and [[metmyoglobin]] (met-Mb), analogously to hemoglobin taking the forms oxyhemoglobin (HbO<sub>2</sub>), [[carboxyhemoglobin]] (HbCO), and [[methemoglobin]] (met-Hb).<ref name="Harvey 2008 pp. 259–285">{{cite book | vauthors = Harvey JW | title=Clinical Biochemistry of Domestic Animals | chapter=Iron Metabolism and Its Disorders | publisher=Elsevier | year=2008 | isbn=978-0-12-370491-7 | doi=10.1016/b978-0-12-370491-7.00009-x | pages=259–285 | quote=Myoglobin is an oxygen-binding protein located primarily in muscles. Myoglobin serves as a local oxygen reservoir that can temporarily provide oxygen when blood oxygen delivery is insufficient during periods of intense muscular activity. Iron within the heme group must be in the Fe+2 state to bind oxygen. If iron is oxidized to the Fe+3 state, metmyoglobin is formed. }}</ref>