And the shape of our oxygen myoglobin dissociation curve is given by the red curve. So once again, the y axis is percent saturation of myoglobin and the X axis is the partial pressure of diatomic oxygen given in millimeters of mercury. Now, the next question is what exactly determines the difference between these two curves? Well, it's basically the Cooperativity, the fact that hemoglobin is cooperative. It consists of four individual polypeptide subunits and these units interact with one another that creates this S shape. But because myoglobin does not have those four polypeptide subunits, it only contains one.