But in this particular case, we have the T state, we have the r state, and we also have these three intermediate, intermediate one, intermediate two, and intermediate three. So in the sequential model, the binding of the oxygen stimulates a conformational change in that polypeptide, and that in turn, induces a conformational change in this nearby and this nearby polypeptide chain. And that tells us that because the conformation changes, that will increase the affinity of that heme group for the oxygen molecule. Now, what's the problem with this sequential model? Well, the problem with the sequential model is the following. Based on this model, the only time we have the r state is when all these four different hein groups are completely filled with oxygen.