The enzyme catalyses the formation of the additional ring in pterocarpan, the basic structure of phytoalexins produced by leguminous plants, including (?)-medicarpin, (+)-medicarpin, (?)-maackiain and (+)-maackiain. The enzyme requires that the hydroxyl group at C-4 of the substrate is in the (4R) configuration. The configuration of the hydrogen atom at C-3 determines whether the pterocarpan is the (+)- or (?)-enantiomer. The enzyme contains amino acid motifs characteristic of dirigent proteins. Formerly EC?1.1.1.246.
