Low-cost, effective, standards-compliant web design, development, online business and marketing consultation

• Home
• Portfolio
• Contact
• Site Map

Myoglobin

Myoglobin, 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.
The Columbia Encyclopedia, Sixth Edition | 2008

Myoglobin and haemoglobin are haemeproteins whose physiological importance is principally related to their ability to bind molecular oxygen. Myoglobin is a monomeric haeme protein found mainly in muscle tissue where it serves as an intracellular storage site for oxygen. During periods of oxygen deprivation oxymyoglobin releases its bound oxygen which is then used for metabolic purposes.

The tertiary structure of myoglobin is that of a typical water soluble globular protein. Its secondary structure is unusual in that it contains a very high proportion (75%) of α-helical secondary structure. A myoglobin polypeptide is comprised of 8 separate right handed α-helices, designated A through H, that are connected by short non helical regions. Amino acid R-groups packed into the interior of the molecule are predominantly hydrophobic in character while those exposed on the surface of the molecule are generally hydrophilic, thus making the molecule relatively water soluble.

Structure of Myoglobin with haeme

Each myoglobin molecule contains one haeme prosthetic group inserted into a hydrophobic cleft in the protein. Each haeme residue contains one central coordinately bound iron atom that is normally in the Fe2+, or ferrous, oxidation state. The oxygen carried by haemeproteins is bound directly to the ferrous iron atom of the haeme prosthetic group. Oxidation of the iron to the Fe3+, ferric, oxidation state renders the molecule incapable of normal oxygen binding.

Hydrophobic interactions between the tetrapyrrole ring and hydrophobic amino acid R groups on the interior of the cleft in the protein strongly stabilize the haeme protein conjugate. In addition a nitrogen atom from a histidine R group located above the plane of the haeme ring is coordinated with the iron atom further stabilizing the interaction between the haeme and the protein. In oxymyoglobin the remaining bonding site on the iron atom (the 6th coordinate position) is occupied by the oxygen, whose binding is stabilized by a second histidine residue.

Carbon monoxide also binds coordinately to haeme iron atoms in a manner similar to that of oxygen, but the binding of carbon monoxide to haeme is much stronger than that of oxygen. The preferential binding of carbon monoxide to haeme iron is largely responsible for the asphyxiation that results from carbon monoxide poisoning.

Last Updated: Mon May 2010 15:03