We use protein kinase to transfer a single phosphoryl from this ATP onto the enzyme to produce this complex here. And this can either activate or usually inactivate the activity of that enzyme. And we also produce that ADP molecule. And if we want to go in reverse, if we want to remove that P and add that P onto that ADP to reform the ATP and that active enzyme or in some cases inactive enzyme, we use protein phosphatase and we'll discuss these proteins in detail in future electrodes. Now, the third mechanism of control is proteolytic activation or proteolytic cleavage. Now, many enzymes produced by the cells of our body are produced in their inactive form.