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.
