Myoglobin
Myoglobin is a single-chain protein of 153 amino acids, containing an iron porphyrin group in the center. It is the primary oxygen-carrying pigment of muscle tissues. Unlike the blood-borne hemoglobin, to which it is structurally related, this protein does not exhibit cooperative binding of oxygen. Instead, the binding of oxygen by myoglobin is unaffected by the oxygen tension in the surrounding tissue. In 1957, John Kendrew and associates successfully determined the structure of myoglobin by high-resolution X-ray crystallography.For this discovery, John Kendrew shared the 1962 Nobel Prize in chemistry with Max Perutz.
See also hemoglobin, hemoprotein