Partial Characterization of an Enzyme from the Fungus Ascochyta rabiei for the Reductive Cleavage of Pterocarpan Phytoalexins to 2'-Hydroxyisoflavans

Crude protein extracts from the chickpea (Cicer arietinum L .) pathogenic fungus Ascochyta rabiei catalyze the N A D PH dependent conversion of the pterocarpan phytoalexins medicarpin and maackiain to 1) 2'-hydroxyisoflavans, 2) 1 a-hydroxypterocarp-l,4-diene-3-one, and 3) 10,2'dihydroxyisoflav-8-ene-7-one derivatives. A pterocarpan: N A D PH oxidoreductase which cleaves the benzylphenyl ether bond of the phytoalexins was purified some 100-fold and partially charac­ terized with regard to its kinetic properties. The oxidoreductase was shown to be specific for N A D PH and 3-hydroxypterocarpans. The enzyme appears to be constitutively expressed by A. rabiei.