Myoglobin

Myoglobin (Mb) is an iron- and oxygen-binding protein found in the muscle tissue of vertebrates in general and in almost all mammals. It is related to hemoglobin, which is the iron- and oxygen-binding protein in blood, specifically in the red blood cells. The only time myoglobin is found in the bloodstream is when it is released following muscle injury. It is an abnormal finding, and can be diagnostically relevant when found in blood.

Structure

Myoglobin contains hemes, pigments responsible for the color of red meat. The heme group is similar to those in hemoglobin. Each heme group contains one iron atom, that can bind one oxygen molecule through ion-induced dipole forces. The oxygen is stabilized within the heme group by a hydrogen bonded network. This network includes water molecules, NAD+, NADH and also the protein matrix. This network of hydrogen bonds stabilizes the oxygen molecule.

Function

Myoglobin is a monomeric protein that binds oxygen when present, and releases it in the absence of oxygen. When oxygen is bound, the coordination complex of Fe2+ is diamagnetic, meaning it has no net magnetic moment. When oxygen is not bound, the complex is paramagnetic, meaning it has a net magnetic moment.

Clinical significance

Myoglobin is released from damaged muscle tissue (rhabdomyolysis), which has very high concentrations of myoglobin. The released myoglobin is filtered by the kidneys but is toxic to the renal tubular epithelium and so may cause acute kidney injury. It is not the myoglobin itself that is toxic (it is a protein and is broken down by the body) but the ferrihemate portion that is dissociated from myoglobin in acidic environments (like the renal tubular lumen).

See also

• Hemoglobin
• Rhabdomyolysis
• Acute kidney injury

References

Myoglobin Resources
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