Now, as we will see in just a moment, the formation of this isopeptide bond is carried out by the hydrolysis of an ATP molecule. So we have to hydrolyze an ATP molecule to actually gain enough energy to carry out this process by which we attach a Ubiquitin onto that target protein. So in this lecture, we're going to look at the process by which we attach Ubiquitin onto the target protein. Now this process of Ubiquitination actually involves three different enzymes and three different processes. So enzyme number one, or step number one, basically utilize the enzyme we called Ubiquitin activating enzyme. And what this enzyme ultimately does is it harvests the energy that is released when we hydrolyze ATP and utilize that energy to actually activate that Ubiquitin molecule.