Myoglobin is an iron- and oxygen-binding protein found in the cardiac and skeletal muscle tissue of vertebrates in general and in almost all mammals. 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. High concentrations of myoglobin in muscle cells allow organisms to hold their breath for a longer period of time. Myoglobin is released from damaged muscle tissue. The released myoglobin enters the bloodstream, where high levels may indicate rhabdomyolysis. The myoglobin is filtered by the kidneys, but is toxic to the renal tubular epithelium and so may cause acute kidney injury.
