And as they close in, they seal off this region so that the insulin cannot actually detach. On top of that, they also cause these two beta subunits to basically move closer together. Now, as these two beta subunits move closer together the activation region of one of the beta subunits actually moves into the active side of the other beta Subun. And this causes a cross phosphorylation process in which both of these beta units are actually phosphorylated in the presence of ATP. And what that does is it activates this insulin receptor. And because of the fact that this receptor itself contains a tyrosine protein kinase we also called the insulin receptor, the insulin receptor protein kinase.