Opening Image: Ribbon model of human myoglobin. Myoglobin contains eight α helices, designated by the letters A through H, counting from the N-terminus. These helices provide a rigid structural framework for the heme pocket.

The heme group is shown in CPK colors. Choose between the following models:

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In this tutorial you will learn how myoglobin binds oxygen. However, the mechanism of oxygen binding is identical in all myoglobins and hemoglobins. After a brief description of the tertiary structure of myoglobin, we will look at how the protein provides a pocket into which the O₂ can fit. Finally, we will discuss what happens when the heme group binds oxygen.

All myoglobin and hemoglobin polypeptide chains adopt remarkably similar backbone conformations known as the globin fold. The heme pocket is the same in all the globins.

The heme is wedged into a hydrophobic pocket between the E and F helices. Five invariant residues in the heme pocket are crucial for oxygen binding. We will explore the heme pocket in the next section.