And the X axis is the partial pressure of oxygen given to us in millimeters of mercury. Now, when the hemoglobin actually takes the oxygen from the lungs and brings it to the muscle tissue of our body, it has to drop that oxygen off. Now, the question is, what exactly picks up that oxygen? So once oxygen is delivered to our muscle tissue the tissue must be able to store that oxygen for later use. And the protein that is responsible for storing the oxygen in our muscle tissue is known as myoglobin where Mayo means muscle and Globin means a polypeptide subunit. Now, in fact, if we compare the structure of hemoglobin to myoglobin we'll see that myoglobin, unlike hemoglobin, actually consists of only a single polypeptide Subun.