Involved in the final steps of cholesterol and steroid degradation (PubMed:28377529, PubMed:29581275). Opens the last steroid ring of cholesterol by catalyzing the hydrolysis of (3E)-2-(2-carboxylatoethyl)-3-methyl-6-oxocyclohex-1-ene-1-carboxyl-CoA (COCHEA-CoA) to 6-methyl-3,7-dioxodecanedioyl-CoA (MeDODA-CoA) (Probable) (PubMed:29581275). (3E)-2-(2-carboxylatoethyl)-3-methyl-6-oxocyclohex-1-ene-1-carboxyl-CoA + H2O = 6-methyl-3,7-dioxodecanedioyl-CoA kcat is 5.8 sec(-1) with COCHEA-CoA as substrate. Steroid metabolism; cholesterol degradation. Heterotetramer composed of 2 IpdA subunits and 2 IpdB subunits. IpdAB double deletion mutant does not grow on cholesterol or HIP, but grows as the wild-type on pyruvate. In the presence of cholesterol, ipdAB double deletion mutant accumulates COCHEA-CoA. Belongs to the 3-oxoacid CoA-transferase subunit A family.