So protein kinase is catalyzed the addition of the phosphoryl group onto other enzymes. Now another class of enzymes known as protein phosphatases are basically responsible for catalyzing the removal of that phosphoryl group from our enzyme. Now the molecule that acts to basically donate that phosphoryl group is commonly our ATP. So adenosine triphosphate, but other high energy molecules can also be used. It's just this ATP is the most common. Now, what is an example of our protein kinase?