So let's see exactly how this takes place in step four. Now, acetoacetate has one of two fates. It can be converted in one of two molecules. So because acetoacetate is a beta ketoacid, it will undergo a slow and spontaneous reaction in which it will decarboxylate itself. And so we release a carbon dioxide, this molecule here, to form an acetone. And this takes place spontaneously without using any enzyme.