Now, a significant number of enzymes are regulated by adding or removing some type of group. And one very common type of group is our phosphoryl group. So basically a group or a class of proteins that are responsible for phosphorylating adding these phosphoryl groups onto enzymes are known as protein kinases. 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.