Myoglobin stores oxygen inside human skeletal muscle cells.
Myoglobin is an oxygen-binding protein found mainly in muscle tissue. It contains a heme group with an iron atom, giving it a structure related to hemoglobin. Its strong affinity for oxygen allows it to hold an intracellular reserve and help oxygen move through muscle cells toward mitochondria.
Myoglobin is especially abundant in muscles that rely heavily on aerobic metabolism, including cardiac muscle and many slow-twitch skeletal muscle fibers. Its concentration contributes to the darker colour of some muscle tissue.
Myoglobin and hemoglobin are often confused because both bind oxygen, but they have different locations and jobs. Hemoglobin is a multi-subunit protein inside red blood cells that transports oxygen through the bloodstream. Myoglobin is a single-chain protein within muscle cells. When muscle tissue is damaged, myoglobin can enter the blood and become a clinically useful marker.