Species specificity of estrogen biosynthesis in pregnancy. Immunochemical difference of placental NADPH-cytochrome c (P-450) reductase in human, baboon and horse.

Abstract NADPH-cytochrome c (P-450) reductases from human placental aromatase II and from horse placental microsomes were solubilized and purified to show a single band of 83,000 daltons in SDS-polyacrylamide gel electrophoresis. Rabbits were immunized with purified human placental aromatase II NADPHcytochrome c (P-450) reductase. The resulting antibodies (Reduc-Ab) were used to examine the species specificity of estrogen biosynthesis and the reductase activity in humans, baboons, horses and rats. Rcduc-Ab suppressed androstenedione aromatase activity in human, baboon and horse placental microsomes with sensitivities in the order of human ⪢ baboon ⪢ horse. Reduc-Ab was much less effective in inhibiting baboon and horse placental NADPH-cytochrome c reductase activity. On the other hand, rat liver microsomal NADPH-cytochrome c reductase activity and its purified preparation were effectively suppressed by Reduc-Ab and the sensitivity was much closer to that of human than to horse. The results suggest that there are common antigenic structure(s) in human, baboon and horse placental and rat liver NADPH-cytochrome c (P-450) reductases and also that there are distinct structural portions or multiple forms of NADPH-cytochrome c reductase among different species.