Myoglobin (symbol Mb or MB) is an iron- and oxygen-binding protein found in the cardiac and skeletalmuscle tissue of vertebrates in general and in almost all mammals.[5][6][7][8][9] 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.[8][10] 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 muscle injury.[11][12][13]
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.[13] 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, this has proved erroneous: there is also myoglobin in smooth muscle cells.[14]
Myoglobin was the first protein to have its three-dimensional structure revealed by X-ray crystallography.[15] This achievement was reported in 1958 by John Kendrew and associates.[16] For this discovery, Kendrew shared the 1962 Nobel Prize in chemistry with Max Perutz.[17][18] 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.[19]
In humans, myoglobin is encoded by the MBgene.[20]
Myoglobin can take the forms oxymyoglobin (MbO2), carboxymyoglobin (MbCO), and metmyoglobin (met-Mb), analogously to hemoglobin taking the forms oxyhemoglobin (HbO2), carboxyhemoglobin (HbCO), and methemoglobin (met-Hb).[21]
^Wick MR, Hornick JL (2011). "Immunohistology of Soft Tissue and Osseous Neoplasms". Diagnostic Immunohistochemistry. Elsevier. pp. 83–136. doi:10.1016/b978-1-4160-5766-6.00008-x. ISBN978-1-4160-5766-6. Myoglobin is a 17.8-kD protein that is found in cardiac and skeletal muscle and that forms complexes with iron molecules.
^Feher J (2017). "Oxygen and Carbon Dioxide Transport". Quantitative Human Physiology. Elsevier. pp. 656–664. doi:10.1016/b978-0-12-800883-6.00064-1. ISBN978-0-12-800883-6. 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.
^ abWilson MT, Reeder BJ (2006). "MYOGLOBIN". Encyclopedia of Respiratory Medicine. Elsevier. pp. 73–76. doi:10.1016/b0-12-370879-6/00250-7. ISBN978-0-12-370879-3. Myoglobin (Mb) is a heme-containing globular protein that is found in abundance in myocyte cells of heart and skeletal muscle.
^Boncyk JC (2007). "Perioperative Hypoxia". Complications in Anesthesia. Elsevier. pp. 193–199. doi:10.1016/b978-1-4160-2215-2.50052-1. ISBN978-1-4160-2215-2. 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.
^Chung MJ, Brown DL (July 2018). "Diagnosis of acute myocardial infarction.". In Brown DL (ed.). Cardiac Intensive Care-E-Book. pp. 91–98.e3. doi:10.1016/B978-0-323-52993-8.00009-6. ISBN9780323529938. S2CID260507329. Myoglobin is not specific for myocardial necrosis, however, especially in the presence of skeletal muscle injury and renal insufficiency.
^Sekhon N, Peacock WF (2019). "Biomarkers to Assist in the Evaluation of Chest Pain". Biomarkers in Cardiovascular Disease. Elsevier. pp. 115–128. doi:10.1016/b978-0-323-54835-9.00011-9. ISBN978-0-323-54835-9. S2CID59548142. 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.
^Harvey JW (2008). "Iron Metabolism and Its Disorders". Clinical Biochemistry of Domestic Animals. Elsevier. pp. 259–285. doi:10.1016/b978-0-12-370491-7.00009-x. ISBN978-0-12-370491-7. 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.
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