Fact number two is they all use secondary messenger molecules. Fact number three is or property number three is they all depend on specific interactions between proteins and other molecules to basically stimulate that process. And number four is they all have to be terminated once they are actually complete, once they carry out their specific type of physiological effect. So to demonstrate why this is actually true, let's take a look and summarize the four different pathways that we discussed so far. And let's begin by discussing what types of protein kinases are used by the four different types of pathways that we discussed up to this point. So let's begin with the epinephrine signaling pathway.