Crotonyl-CoA is a derivative of coenzyme A (CoA) found in liver, muscle, brain, and heart, with different abundance depending on tissue and metabolic status. ECHS1 and CDYL convert crotonyl-CoA to β-hydroxybutyryl-CoA which, in mitochondria, can be converted to acetyl-CoA by dehydrogenation and thiolysis, and then enter the tricarboxylic acid (TCA) cycle. Importantly, acetyltransferases transfer the crotonyl residue from crotonyl-CoA to functional proteins, such as histones, enzymes, and structure proteins.