Isolation of NADPH:isoflavone oxidoreductase, a new enzyme of Pterocarpan phytoalexin biosynthesis in cell suspension cultures of Cicer arietinum

Chickpea Cicer arietinum L.) cell suspension cultures transferred into a medium containing yeast extract accumulate the phytoalexins medicarpin and maackiain. Concomitant with accumulation of the pterocarpans a new enzyme activity is induced which was characterized as NADPH:isoflavone oxidoreductase. Maximum enzyme activity was reached 16 h after transfer of cells and then activity rapidly declined. The soluble enzyme was partially purified and shown to catalyze the reduction of the isoflavone 2'‐hydroxyformononetin to the isoflavanone vestitone which is an intermediate in medicarpin biosynthesis. The enzyme data suggest that 2'‐hydroxylation is a prerequisite for the conversion of isoflavones to pterocarpans.