Myoglobin

Source: Wikipedia, the free encyclopedia.
MB
Gene ontology
Molecular function
Cellular component
Biological process
Sources:Amigo / QuickGO
Ensembl

ENSG00000198125

ENSMUSG00000018893

UniProt

P02144

P04247

RefSeq (mRNA)

NM_005368
NM_203377
NM_203378
NM_001362846

NM_001164047
NM_001164048
NM_013593

RefSeq (protein)

NP_001157519
NP_001157520
NP_038621

Location (UCSC)Chr 22: 35.61 – 35.64 MbChr 15: 76.9 – 76.93 Mb
PubMed search[3][4]
Wikidata
View/Edit HumanView/Edit Mouse

Myoglobin (symbol Mb or MB) is an iron- and oxygen-binding protein found in the cardiac and skeletal muscle 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.

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

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 MB gene.[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]

Differences from hemoglobin

Like hemoglobin, myoglobin is a cytoplasmic protein that binds oxygen on a heme group. It harbors only one globulin group, whereas hemoglobin has four. Although its heme group is identical to those in Hb, Mb has a higher affinity for oxygen than does hemoglobin but fewer total oxygen-storage capacities.[22] The newest discovery reveals that myoglobin facilitates oxygen diffusion down a gradient, enhancing oxygen transport in mitochondria.

Role in cuisine

Myoglobin contains hemes,

nitrites, it will remain pink, because the iron atom is bound to NO, nitric oxide (true of, e.g., corned beef or cured hams). Grilled meats can also take on a reddish pink "smoke ring" that comes from the heme center binding to carbon monoxide.[23] Raw meat packed in a carbon monoxide atmosphere also shows this same pink "smoke ring" due to the same principles. Notably, the surface of this raw meat also displays the pink color, which is usually associated in consumers' minds with fresh meat. This artificially induced pink color can persist, reportedly up to one year.[24] Hormel and Cargill (meat processing companies in the US) are both reported to use this meat-packing process, and meat treated this way has been in the consumer market since 2003.[25]

Role in disease

Myoglobin is released from damaged muscle tissue, which contain very high concentrations of myoglobin.

protoxin), but the ferrihemate portion that is dissociated from myoglobin in acidic environments (e.g., acidic urine, lysosomes
).

Myoglobin is a sensitive marker for muscle injury, making it a potential marker for

ECG, and clinical signs should be taken into account to make the diagnosis.[29]

Structure and bonding

Myoglobin belongs to the

alpha helices connected by loops. Myoglobin contains 153 amino acids.[30]

Myoglobin contains a porphyrin ring with an iron at its center. A proximal histidine group (His-93) is attached directly to iron, and a distal histidine group (His-64) hovers near the opposite face.[30] The distal imidazole is not bonded to the iron, but is available to interact with the substrate O2. This interaction encourages the binding of O2, but not carbon monoxide (CO), which still binds about 240× more strongly than O2.

The binding of O2 causes substantial structural change at the Fe center, which shrinks in radius and moves into the center of N4 pocket. O2-binding induces "spin-pairing": the five-coordinate ferrous deoxy form is

diamagnetic.[citation needed
]

  • Molecular orbital description of Fe-O2 interaction in myoglobin.[31]
    Molecular orbital description of Fe-O2 interaction in myoglobin.[31]
  • This is an image of an oxygenated myoglobin molecule. The image shows the structural change when oxygen is bound to the iron atom of the heme prosthetic group. The oxygen atoms are colored in green, the iron atom is colored in red, and the heme group is colored in blue.
    This is an image of an oxygenated myoglobin molecule. The image shows the structural change when oxygen is bound to the iron atom of the heme prosthetic group. The oxygen atoms are colored in green, the iron atom is colored in red, and the heme group is colored in blue.
  • Myoglobin
    Myoglobin

Synthetic analogues

Many models of myoglobin have been synthesized as part of a broad interest in transition metal dioxygen complexes. A well known example is the picket fence porphyrin, which consists of a ferrous complex of a sterically bulky derivative of tetraphenylporphyrin.[32] In the presence of an imidazole ligand, this ferrous complex reversibly binds O2. The O2 substrate adopts a bent geometry, occupying the sixth position of the iron center. A key property of this model is the slow formation of the μ-oxo dimer, which is an inactive diferric state. In nature, such deactivation pathways are suppressed by protein matrix that prevents close approach of the Fe-porphyrin assemblies.[33]

dioxygen
. The R groups flank the O2-binding site.

See also

References

  1. ^ a b c GRCh38: Ensembl release 89: ENSG00000198125 – Ensembl, May 2017
  2. ^ a b c GRCm38: Ensembl release 89: ENSMUSG00000018893 – Ensembl, May 2017
  3. ^ "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  4. ^ "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  5. PMID 15339940
    .
  6. ISBN 978-1-4160-5766-6
    . Myoglobin is a 17.8-kD protein that is found in cardiac and skeletal muscle and that forms complexes with iron molecules.
  7. ISBN 978-0-12-800883-6. 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.
  8. ^
    ISBN 978-0-12-370879-3
    . Myoglobin (Mb) is a heme-containing globular protein that is found in abundance in myocyte cells of heart and skeletal muscle.
  9. ISBN 978-1-4160-2215-2
    . 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.
  10. PMID 23209182
    .
  11. renal insufficiency
    .
  12. renal disease
    as well as damage to skeletal muscle.
  13. ^
    ISBN 0-7167-6203-X
    . (Google books link is the 2008 edition)
  14. PMID 9722578
    .
  15. ^ (U.S.) National Science Foundation: Protein Data Bank Chronology (Jan. 21, 2004). Retrieved 3.17.2010
  16. S2CID 4162786
    .
  17. doi:10.1146/knowable-022822-1
    . Retrieved 25 March 2022.
  18. ^ The Nobel Prize in Chemistry 1962
  19. PMID 18269197
    .
  20. PMID 2989088
    .
  21. ISBN 978-0-12-370491-7
    . 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.
  22. ISBN 978-0-12-370879-3
  23. ISBN 0-684-80001-2
    .
  24. PMID 21844276
    .
  25. ^ "Meat companies defend use of carbon monoxide". Business. Minneapolis Star Tribune. Associated Press. 2007-10-30. Archived from the original on 2013-12-25. Retrieved 2013-02-11.
  26. ISBN 978-0-12-415759-0
    . Myoglobin is a low molecular weight oxygen binding heme protein that is found exclusively in heart and skeletal muscle cells. In blood, myoglobin is bound primarily to plasma globulins, a complex which is filtered by the kidneys. If the plasma concentration exceeds the plasma binding capacity (1.5 mg/dl in humans), myoglobin begins to appear in the urine. High concentrations of myoglobin can change the color of the urine to a dark red-brown color.
  27. PMID 15774055
    .
  28. PMID 16125162
    .
  29. ISBN 978-0-12-407821-5. Myoglobin is a heme protein found in both skeletal and cardiac muscle. Myoglobin is typically released in the circulation as early as 1 h after myocardial infarction,... Myoglobin has poor clinical specificity due to the presence of large quantities of myoglobin in skeletal muscle. Some studies suggest adding the myoglobin test to the troponin I test in order to improve diagnostic value [4]. Myoglobin, being a small protein, is excreted in urine, and a high level of serum myoglobin is encountered in patients with acute renal failure (uremic syndrome
    ). Acute renal failure is also a complication of rhabdomyolysis, ...
  30. ^ a b Universal protein resource accession number P02144 at UniProt.
  31. doi:10.1016/S0010-8545(00)80372-0
    .
  32. PMID 1068445
    .
  33. ISBN 0-935702-73-3
    .

Further reading

External links
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