The reaction to make Acyl-CoA is also thermodynamically favored because in this reaction ATP becomes AMP[3] which is a two step reaction, and this is spontaneous. There is also an enzyme called Acyl-CoA thioesterase, and this enzyme does the opposite of Acyl-CoA synthase. This enzyme takes of the Acyl-CoA to form a free fatty acid and coenzyme A, in other words deactivates the fatty acid by breaking down Acyl-CoA.[3]