ISOFLAVONE O-METHYLTRANSFERASE ACTIVITIES IN ELICITOR-TREATED CELL SUSPENSION CULTURES OF MEDICAGO SATIVA

Article abstract of DOI:10.1016/0031-9422(91)85107-B

Treatment of alfalfa cell suspension cultures with elicitor preparations from baker's yeast or from cell walls of Colletotrichum lindemuthianum resulted in a ca 200-fold induction of isoflavone O-methyltransferase (IOMT) activity.The elicited cultures contained O-methyltransferase activity against isoflavone, isoflavan and pterocarpan substrates.These activities could be separated into two distinct fractions by ion-exchange chromatography.The major IOMT activity (IOMT II) was purified to homogeneity by a combination of anion exchange chromatography, hydrophobic interaction chromatography and chromatofocussing.It is a monomeric enzyme of subunit M_r 41000 which could be photoaffinity labelled with tritiated SAM.IOMT II converted the isoflavone daidzein to its 7-O-methyl ether isoformononetin, with K_m values of 20 μM for daidzein and 150 μM for SAM and a pH optimum of 8.5.Both IOMT II and the less abundant IOMT species (IOMT I) exhibited greatest activity with 6,7,4'-trihydroxyisoflavone as methyl acceptor.IOMT I, but not IOMT II, also catalysed the A-ring methylation of the pterocarpan phytoalexin medicarpin.Isoflavone 4'-OMT activity, which is believed necessary for the formation of the B-ring methoxy substituent of medicarpin, was present at very low activity in extracts from the cultures and was only weakly induced by elicitor.Key Word Index - Medicago sativa; Leguminosae; isoflavone 7-O-methyltransferase; phytoalexin biosynthesis