Myoglobin

myoglobin (mī'əglō`bĭn), protein molecule isolated from the cells of vertebrate skeletal muscle that is both a structural and functional relative of hemoglobin, the oxygen-transport protein of the blood of higher animals. Myoglobin, which is composed of a single polypeptide chain of 153 amino acid residues, has the ability to store oxygen by binding it to an iron atom; iron is part of myoglobin's essential chemical composition. The complete amino acid sequence of myoglobin has been determined; it is a relatively small protein with a molecular weight of approximately 17,000 grams per mole. The distribution of myoglobin among the higher animals is a reflection of its physiological function. It is found abundantly in the tissues of diving mammals, e.g., the whale, the seal, and the dolphin. High concentrations of myoglobin in these animals presumably allows them to store sufficient oxygen to remain underwater for long periods. Myoglobin is found abundantly in man only in cardiac muscle, which, by virtue of its essential function, must possess the capacity for continued activity when environmental oxygen concentrations are low. Myoglobin has been investigated intensely and is the first protein molecule to have been completely described in terms of its three-dimensional geometry. This achievement won the British scientist John Kendrew a share in the 1962 Nobel Prize for Chemistry.

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myoglobin [¦mī·ə¦glō·bən]

(biochemistry)

A hemoglobinlike iron-containing protein pigment occurring in muscle fibers. Also known as muscle hemoglobin; myohemoglobin.

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Myoglobin 

a globular protein that stores molecular oxygen in muscles and delivers it to the oxidative cell systems.

Myoglobin is the first protein whose structure was elucidated by X-ray diffraction analysis (J. Kendrew and his associates, 1957–60). It consists of a single polypeptide chain (about 70 percent of the 153 amino-acid residues are included in the spiral parts). As in hemoglobin, the active center of the myoglobin molecule that binds O₂ is heme. The molecular weight of myoglobin is 17,000. The spatial structure of myoglobin resembles the beta chain of hemoglobin. Myoglobin combines reversibly with oxygen even at low partial pressures of oxygen. This is of great physiological importance: the partial pressure of oxygen decreases sharply during muscle contraction as a result of compression of the capillaries, and it is at this very moment that the oxygen needed by the working muscle is released from myoglobin.

The muscles of vertebrates contain about two percent myoglobin per dry tissue mass; the muscles of marine animals capable of staying under water a long time (seal, whale, dolphin) contain about 20 percent. Myoglobin determines the color of muscles in vertebrates.

REFERENCES

Verbolovich, P. A. Mioglobin i ego rol’ v fiziologii i patologii zhivotnykh i cheloveka. Moscow, 1961.
Kendrew, J. C. “Mioglobin i struktura belkov.” Biofizika, 1963, vol. 8, no. 3.

V. O. SHPIKITER