And that prepares the ubiquitin It gives it enough energy to actually attach it ultimately onto that target protein. So the first step is catalyzed by Ubiquitin activating enzyme or E one. And this is catalyzed via the hydrolysis of ATP and the carboxyl. And the Ubiquitin is essentially linked to the enzyme via a thio ester bond. So on enzyme number one, on enzyme one, E one, we have a cysteine. And the side chain of that cysteine is used to attach that ubiquitous molecule.