Myoglobin is a water-soluble protein found in animal muscle cells that binds to oxygen. It is abundant in red muscles used for endurance activities and in diving mammals. Myoglobin levels are used to diagnose heart attacks, but high levels can be toxic to the kidneys.
Myoglobin is an iron-containing red pigment found in the muscle cells of animals. It is a water-soluble single-chain globular protein made up of 153 amino acids, with an iron-containing prosthetic group at the center. Although similar in structure to hemoglobin, it exhibits a higher level of affinity for oxygen than hemoglobin. The physiological importance of myoglobin is primarily attributed to its ability to bind oxygen.
Myoglobin is generally found in abundance in cardiac muscles and skeletal muscles adapted for endurance activities. These high-strength muscles are called “red muscles.” The myoglobin in these red muscles binds to oxygen molecules and forms oxyglobin, which serves as an emergency oxygen storage site for the body. Oxygen is generally released when the body is in a state of oxygen deprivation. This happens during strenuous exercise or physical exertion, when the oxygen supplied by the blood alone does not meet the body’s demands.
The distribution of red muscles is also high in diving mammals, such as whales and dolphins. The higher level of myoglobin stored in these muscles allows these animals to store more oxygen so they can stay underwater for long periods. Myoglobin levels are also high in the muscles of waterfowl and penguins.
In humans, myoglobin is used as an important biochemical marker for the diagnosis of myocardial infarction or stroke. It is found in abundance in the heart muscles, so any damage to the heart muscles releases large amounts of myoglobin into the bloodstream. Myoglobin tests are, therefore, conducted in people who show symptoms of a heart attack. Blood levels rise within 2 to 3 hours of a heart attack and peak within about 8 to 12 hours. However, it generally returns to normal about 24 hours after injury, so it cannot be used for evaluation in patients whose symptoms have persisted for more than a day.
Severe damage to muscle tissue can lead to a condition called rhabdomyolysis and can result in acute kidney failure. In large quantities, myoglobin can be toxic to the tubular epithelium of the kidney. It causes severe damage to the renal epithelium when blood is filtered through them. This condition usually occurs to victims of acute physical injury, such as in the case of earthquakes or bomb explosions.
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