We have histidine 274, we have histidine 320, and we also have Aspartate 375. Now, this here is basically the Cecil coenzyme A. And this here is the oxalo acetate. So let's suppose the oxalo acetate binds into the active side that induces a conformational change that then allows that acetyl coenzymen to bind into the active side. And so now we have this diagram. So in step one, what takes place is we ultimately want to form an enol intermediate.