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Magill’s Medical Guide, 9th Edition

Myoglobin

by Janine Ungvarsky

Category: Biology

Anatomy or system affected: circulatory, muscular, excretory

Specialties and related fields: biochemistry, cardiovascular

Definition: an iron containing protein with a single heme at its center that transports oxygen within muscle

Key terms:

anoxia: a lack of oxygen

heme: an iron containing compound used by myoglobin, hemoglobin and other biological molecules to carry oxygen

hemoglobin: an iron and heme containing protein that carries oxygen in the blood

hypoxia: low blood oxygen

myoglobinuria: myoglobin in the urine

rhabdomyolysis: muscle damage and destruction

x-ray crystallography: a technique that passes x-rays through a molecule to determine its crystalline structure

STRUCTURE AND FUNCTION

Myoglobin, which is often abbreviated Mb or MB, is an iron containing protein with a single heme at its center that transports oxygen within muscle. Structurally and evolutionarily, myoglobin is closely related to hemoglobin, the oxygen transporting protein in the blood. Myoglobin is responsible for the red color of meat.

Myoglobin has a high affinity for oxygen and absorbs it from hemoglobin in the blood into cardiac and skeletal muscles as the blood circulates through muscle tissue. The oxygen-absorbing properties of myoglobin are important to life in most vertebrates, but they are especially important to deep-diving mammals such as whales, seals, and dolphins, as well as some marine birds, which rely on oxygen-rich myoglobin to sustain them while they are underwater. In these animals, the ability of myoglobin to store oxygen in the muscles is generally ten to thirty times above the levels found in animals that do not experience long periods without breathing due to submersion in water.

Although myoglobin is one of the most extensively studied proteins, it is not certain as to its precise role in physiology since mice with experimentally mutated and non-functional myoglobin are viable and fertile. These mutant mice, termed knock-out mice, seem to physiologically compensate for the lack of myoglobin. Since the myoglobin knock-out mice are viable and fertile, it has been hypothesized that myoglobin may serve as an accessory protein that facilitates transport of oxygen in muscle, a reserve oxygen store and/or a scavenger of highly damaging oxygen free radicals.

Although scientists may not fully understand how myoglobin functions, the basics are clear. Hemoglobin picks up oxygen as the blood passes through the lungs and transports it to the muscles and other tissue and organs. While hemoglobin attracts oxygen, myoglobin has a higher affinity for oxygen. Therefore, myoglobin can serve as in an oxygen storage capacity to provide reserves of oxygen at times of hypoxia (deficiency in the amount of oxygen reaching the tissues) or anoxia (the absence of oxygen). This function of myoglobin is what helps diving mammals such as whales remain submerged for long periods and allows humans to hold their breath even after the oxygen in the lungs is depleted. Research continues to determine the physiological function of myoglobin.

DISORDERS AND DISEASES

Myoglobin does not normally appear in the blood or urine. Because of this, its presence can be used as an indicator of certain pathological conditions such as damage to muscles, including the heart. When a muscle is damaged or undergoes a period of prolonged hypoxia, myoglobin is released into the blood and excreted in the urine. Thus physicians can use urine and/or blood myoglobin tests to determine if a patient has suffered muscle damage. This is especially important in determining damage from a myocardial infarction (heart attack). Within an hour of suffering a heart attack, a patient’s blood will contain myoglobin. It will reach its highest levels within about four to twelve hours after an attack and returns to normal levels within twenty-four to thirty-six hours. During the time in between, however, the physician can use a test for myoglobin to determine if a heart attack may have occurred. Additional tests can confirm a myocardial infarction.

Although the kidney normally excretes myoglobin, elevated blood myoglobin can prove toxic to the tubules of the kidneys. This happens most often when a person receives severe crushing injuries in an accident that damage a lot of muscles, a condition known as rhabdomyolysis. The damaged muscle tissue releases large quantities of myoglobin into the blood. As the blood passes through the kidneys, myoglobin will pass into the urine, a condition known as myoglobinuria. Myoglobin may precipitate from the blood and damage kidney tubules. In addition, the iron containing heme can be very toxic to the kidneys. Myoglobinuria can also be caused by muscle damage from drug overdoses, seizures, metabolic disorders, and some diseases.

PERSPECTIVE AND PROSPECTS

Myoglobin and its close relative, hemoglobin, are two of the most studied proteins. The structure of myoglobin was elucidated by John Cowdery Kendrew at the Cavendish Laboratory in Cambridge, England. Kendrew was one of the first to determine the structure of a protein by x-ray crystallography. He shared the 1962 Nobel Prize in chemistry with Max Ferdinand Perutz who determined the structure of hemoglobin in the same Cavendish laboratory as Kendrew.

See also: Cardiovascular system; Heart

For Further Information:

1 

Devarajan, Prasad. “Myoglobinuria.” Medscape, emedicine.med scape.com/article/982711-overview. Accessed 10 Nov. 2016.

2 

Feldberg, Ross. “Myoglobin and Hemoglobin Structure.” Tufts University, ase.tufts.edu/biology/MolecVisual/bio13/rightB13hemo. html. Accessed 10 Nov. 2016.

3 

“Myoglobin (Blood).” University of Rochester Medical Center, www.urmc.rochester.edu/encyclopedia/content.aspx?conte nt typeid=167&contentid=myoglobin_blood. Accessed 10 Nov. 2016.

4 

“Myoglobin Blood Test.” MedlinePlus, medlineplus.gov/ency/article/003663.htm. Accessed 10 Nov. 2016.

5 

“The Nobel Prize in Chemistry 1962.” NobelPrize.org, www.nobelprize.org/nobel_prizes/chemistry/laureates/1962. Accessed 10 Nov. 2016.

6 

O’Connell, Krista. “Myoglobin Urine Test: Purpose, Procedure, and Results.” Healthline, 21 June 2016, www.healthline.com/health/myoglobin-urine. Accessed 10 Nov. 2016.

7 

Ordway, George A., and Daniel J. Garry. “Myoglobin: An Essential Hemoprotein in Striated Muscle.” Journal of Experimental Biology, vol. 207, 2004, pp. 3441-3446. jeb.biologists.org/content/207/20/3441. Accessed 10 Nov. 2016.

8 

“A Tour of Myoglobin.” Department of Chemistry, University of Toronto, www.chem.utoronto.ca/coursenotes/GTM/JM/Mbstart.htm. Accessed 10 Nov. 2016.

Citation Types

Type
Format
MLA 9th
Ungvarsky, Janine. "Myoglobin." Magill’s Medical Guide, 9th Edition, edited by Anubhav Agarwal,, Salem Press, 2022. Salem Online, online.salempress.com/articleDetails.do?articleName=MMG2022_0920.
APA 7th
Ungvarsky, J. (2022). Myoglobin. In A. Agarwal, (Ed.), Magill’s Medical Guide, 9th Edition. Salem Press. online.salempress.com.
CMOS 17th
Ungvarsky, Janine. "Myoglobin." Edited by Anubhav Agarwal,. Magill’s Medical Guide, 9th Edition. Hackensack: Salem Press, 2022. Accessed October 22, 2025. online.salempress.com.