Propionyl-CoA is also a substrate for post-translational modification of proteins by reacting with lysine residues on proteins, a reaction called protein propionylation. Due to structural similarities of Acetyl-CoA and Propionyl-CoA, propionylation reaction are thought to use many of the same enzymes used for protein acetylation. Although functional consequences of protein propionylation are currently not completely understood, in vitro propionylation of the Propionyl-CoA Synthetase enzyme controls its activity.