In enzymology, a butyrate-acetoacetate CoA-transferase (EC 2.8.3.9) is an enzyme that catalyzes the chemical reaction

butanoyl-CoA + acetoacetate ${\displaystyle \rightleftharpoons }$ butanoate + acetoacetyl-CoA

Thus, the two substrates of this enzyme are butanoyl-CoA and acetoacetate, whereas its two products are butanoate and acetoacetyl-CoA.

This enzyme belongs to the family of transferases, specifically the CoA-transferases. The systematic name of this enzyme class is butanoyl-CoA:acetoacetate CoA-transferase. Other names in common use include butyryl coenzyme A-acetoacetate coenzyme A-transferase, and butyryl-CoA-acetoacetate CoA-transferase.

• Barker HA, Jeng IM, Neff N, Robertson JM, Tam FK, Hosaka S (1978). "Butyryl-CoA:acetoacetate CoA-transferase from a lysine-fermenting Clostridium". J. Biol. Chem. 253 (4): 1219–25. PMID 624727.