Enzymic synthesis of isoflavones

The NADPH and oxygen‐dependent conversion of (2S)‐naringenin to genistein catalyzed by a microsomal preparation from elicitor‐treated soybean cell suspension cultures has been resolved into two steps. In the first step (2S)‐naringenin is converted to a product (P‐2) which yields genistein in a second step. The chemical behaviour of P‐2 and its ultraviolet and mass spectral data are consistent with a 2‐hydroxyisoflavanone structure. The conversion of (2S)‐naringenin to P‐2 requires NADPH, oxygen and cytochrome P‐450. The participation of cytochrome P‐450 was demonstrated by CO inhibition of the reaction and its partial reversal by light, and by inhibition with typical cytochrome P‐450 inhibitors. On a Percoll gradient the membrane fraction which catalyzes P‐2 formation coincides with marker enzymes for the endoplasmic reticulum and with the position of cytochrome P‐450. Enzymatic activity for conversion of P‐2 to genistein is mainly present in the supernatant of the 160000 x g fraction. This reaction, formally a dehydration, does not require NADPH or oxygen.