Coenzyme A transferase which is involved in short-chain fatty acid degradation and catalyzes the activation of short-chain fatty acids to their respective CoA thiolesters (PubMed:1103739, PubMed:3025185). During acetoacetate degradation, catalyzes the transfer of CoA from acetyl-CoA to acetoacetate by a mechanism involving a covalent enzyme-CoA compound as a reaction intermediate (PubMed:1103741). Utilizes a variety of short chain acyl-CoA and carboxylic acid substrates but exhibits maximal activity with normal and 3-keto substrates (PubMed:1103739). acetate + an acyl-CoA = a carboxylate + acetyl-CoA acetoacetate + acetyl-CoA = acetate + acetoacetyl-CoA acetyl-CoA + butanoate = acetate + butanoyl-CoA acetoacetate + butanoyl-CoA = acetoacetyl-CoA + butanoate Inhibited by p-chloromercuribenzoate. Lipid metabolism; short-chain fatty acid metabolism. Heterotetramer composed of two alpha subunits (AtoD) and two beta subunits (AtoA). Membrane associated. Transcriptionally regulated by the regulatory protein AtoC. Mutant lacks acetoacetyl-CoA transferase activity. Belongs to the 3-oxoacid CoA-transferase subunit B family.