BIOLOGY Volume 2 - A Guide to General Biology - 2004

14. TRANSPORT IN ANIMALS

14.8. Functions of blood in mammals

14.8.2. Myoglobin

Myoglobin is a red, heme-containing protein whose Structure is very similar to a single polypeptide chain of Hemoglobin, i.e., a monomer of this tetramer. It is believed that both Proteins evolved from a common ancestral molecule. Myoglobin is found in skeletal Muscles, which is the main reason for the characteristic red color of meat. It has a high affinity for oxygen, forming oxymyoglobin upon oxygenation; the dissociation curve of oxymyoglobin is shifted significantly to the left compared to that of oxyhemoglobin (Fig. 14.32). It begins to release oxygen only at a partial pressure of the latter below 20 mmHg. Thus, myoglobin acts essentially as an oxygen store in resting Muscle. Myoglobin begins to release oxygen only when oxyhemoglobin reserves are exhausted.

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Fig. 14.32. Comparison of the oxyhemoglobin and oxymyoglobin dissociation curves. Myoglobin remains 80% saturated with oxygen until the partial pressure of the latter drops below 20 mmHg. This means that myoglobin holds onto oxygen in resting muscle, but releases it when all the oxygen delivered by hemoglobin is depleted As a result of intense muscular activity.