2-hydroxyisoflavanone 4'-O-methyltransferase involved in the biosynthesis of the phytoalexin medicarpin. Has also an in vitro (+)-6a-hydroxymaackiain-3-0-methyltransferase activity, converting the pterocarpan 6a-hydroxymaackiain into pisatin. No activity with di- or trihydroxylated isoflavones, including daidzein and genistein, or with (-)-medicarpin and maackiain. The dual activity for either 3- or 4'-O-methylation depends upon substrate availability. a 4'-hydroxyisoflavone + S-adenosyl-L-methionine = a 4'-methoxyisoflavone + H(+) + S-adenosyl-L-homocysteine (2R,3S)-2,4',7-trihydroxyisoflavanone + S-adenosyl-L-methionine = (2R,3S)-2,7-dihydroxy-4'-methoxyisoflavanone + H(+) + S-adenosyl-L-homocysteine Homodimer. Belongs to the class I-like SAM-binding methyltransferase superfamily. Cation-independent O-methyltransferase family. COMT subfamily.