Biosynthesis of coenzyme A (CoA) from pantothenic acid (vitamin B5) is an essential universal pathway in prokaryotes and eukaryotes. COASY is a bifunctional enzyme that catalyzes the 2 last steps in CoA synthesis. These activities are performed by 2 separate enzymes, phosphopantetheine adenylyltransferase and dephospho-CoA kinase, in prokaryotes.