Then we have the blue domain. The blue domain accepts that phosphoryl group when that ATP is hydrolyzed into ADP. And so that's why we call it the P domain. And the A domain actually links that conformational change in these two domains to the conformational change in the transmembrane domain. So the A domain is responsible for stimulating the conformational change, as we'll see in just a moment. So let's actually take a look at the details of how the calcium Atph actually works.