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Muscle haemoglobin

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muscle haemoglobin --> myoglobin

(Science: physiology) protein (17.5 kD) found in red skeletal muscle. It was the first protein for which the tertiary structure was determined by x-ray diffraction, by J.C.Kendrew's group working on sperm whale myoglobin.

It is a single polypeptide chain of 153 amino acids, containing a haem group bonded via its ferric iron to two histidine residues. It binds oxygen noncooperatively and has a higher affinity for oxygen than haemoglobin at all partial pressures. In capillaries oxygen is effectively removed from haemoglobin and diffuses into muscle fibres where it binds to myoglobin which acts as an oxygen store.