And this is called the r state or the relaxed state. Now, earlier I said that instead of looking at this hemoglobin molecule as consisting of four polypeptide chains, typically we examine the hemoglobin molecule as if it consists of two dimers the alpha one, beta one, and the alpha two beta two. Why is that? Well, that's because when our molecule goes from the 10th state, the deoxyhemoglobin state to the relaxed state, that oxymoglobin state, the two alpha beta dimers rotate 15 degrees with respect to one another. And this rotation is what causes this cooperative behavior of that hemoglobin molecule. This rotation is what causes that shift to take place from the 10th state to that relaxed state.