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. So the coronary structure of deoxy hemoglobin is quite constrained. And for this reason, deoxy hemoglobin is said to exist in the t state where t stands for tense. Now, when oxygen begins to bind onto the heme group, it creates this conformational change and it causes this change in the interaction between the surfaces of the different polypeptide chains.