Chapter 4 - Chapter 4 4.12 Structures of Myoglobin and...

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Chapter 4 4.12 Structures of Myoglobin and Hemoglobin Myoglobin is a relatively small monomeric protein that facilitates the diffusion of oxygen in vertebrates. It supplies oxygen to muscle tissue. Hemoglobin is a larger tetrameric protein that carries oxygen in blood. A prosthetic group is a protein-bound organic molecule essential to the activity of the protein. The polypeptide component of myoglobin is a member of a family of proteins called globins. Several groups of alpha helices that form a layered structure. Adjacent helices in each layer are tilted at an angle that allows the side chains of the amino acid residues to interdigitate. The interior of myoglobin is made up almost exclusively of hydrophobic amino acid residues. The surface of the protein contains both hydrophilic and hydrophobic residues. As is the case with most proteins, the tertiary structure of myoglobin is stabilized by hydrophobic interactions within the core. Folding of the polypeptide chain is driven by the energy minimization that results from formation of this hydrophobic core. Hemoglobin is more complex than myoglobin because it is a multisubunit protein. In adult mammals, hemoglobin contains two different globin subunits called alpha-globin and beta-globin. Each of the four globin chains contains a heme prosthetic group identical to that found in myoglobin. Each alpha chain interacts extensively with beta chain, so hemoglobin is actually a dimer of alpha beta subunits. Presence of multiple subunits is responsible for oxygen-binding properties that are not possible with single-chain myoglobin. 4.13 Oxygen Binding to Myoglobin and Hemoglobin The oxygen-binding activities of myoglobin and hemoglobin provide an excellent example of how protein structure relates to physiological function. A. Oxygen Binds Reversibly to Heme
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This note was uploaded on 09/08/2008 for the course BCMB 3100 taught by Professor Mendicino during the Spring '07 term at University of Georgia Athens.

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Chapter 4 - Chapter 4 4.12 Structures of Myoglobin and...

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