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 160 000 X g fraction. This reaction, formally a dehydration, does not require NADPH or oxygen.