Together with cefD1, catalyzes the reversible isomerization between isopenicillin N and penicillin N. This two-component IPN epimerase system may function by two sequential steps, an activation of isopenicillin N by the acyl-CoA synthase component cefD1, followed by epimerization by the acyl-CoA racemase component cefD2. isopenicillin N = penicillin N Antibiotic biosynthesis; cephalosporin C biosynthesis. Belongs to the CoA-transferase III family.