Now, the enzyme that we're going to focus on in the next several lectures that basically is controlled Alisterically is aspartate transcurbamylase. And we'll see exactly how this is done in the next several lectures. Now let's move on to the second regulation mechanism, reversible covalent modification. So the activity of many enzymes is basically controlled and regulated by creating some type of covalent bond, some type of covalent modification on that particular enzyme. And the most common type of modification that we create is the addition of a phosphoryl group by using an ATP molecule. So one example of covalent modification is the attachment of a phosphoryl group onto the enzyme.