And that in turn pulls and shifts that entire polypeptide chain as shown in this diagram. So this shift causes a conformational change in the surface to surface interaction between the adjacent subunits. And this is precisely what leads to the cooperative behavior of the hemoglobin molecule. Now, if we examine the structure, the quarterly structure of the deoxy hemoglobin, deoxy hemoglobin is simply the hemoglobin molecule in which the four heme groups are unoccupied. The quarterinary structure of deoxy hemoglobin is very constrained because the interactions are not very good. And so because of this constrained nature of deoxyhemoglobin, we call that state the 10th state or simply the t state.