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. acetate + an acyl-CoA = a carboxylate + acetyl-CoA acetoacetate + acetyl-CoA = acetate + acetoacetyl-CoA Lipid metabolism; short-chain fatty acid metabolism. Heterotetramer composed of two alpha subunits (AtoD) and two beta subunits (AtoA). Belongs to the 3-oxoacid CoA-transferase subunit B family.