AcmB exhibited a high affinity for progesterone with KmA value of 4.4 ± 0.3 μM and a 20-fold lower affinity for DCPIP (KmB 79.3 ± 6.9 μM). These data are consistent with the apparent kinetic parameters reported previously . The established Vmax of the enzyme was 33.4 ± 1 μM min -1 , which corresponds to kcat of 21.3 s -1 .