And the serene amino acid basically plays the catalytic role of actually forming a Covalent, a temporary Covalent bond between the oxygen and this carbon. So in this reaction, in the first step, this molecule actually forms a bond between the oxygen and this carbon, kicking off this terminal amino acid to form the following temporary transient acid intermediate molecule. Now, at the end of the reaction, of course, this bond is actually broken, but we formed the bond to basically keep this group attached into the active side so that another substrate can move in and grab this group. So the bacterial enzyme glycopeptide transpeptidase, utilizes Covalent catalysis. And as we'll see in just a moment, another enzyme that we can basically label as using Covalent catalysis is Kymatrypsin. And this is an important digestive enzyme that exists inside our digestive system.