PURIFICATION AND CHARACTERIZATION OF 3 ISOFORMS OF S-ADENOSYL-L-METHIONINE - (R,S)-TETRAHYDROBENZYLISOQUINOLINE-N-METHYLTRANSFERASE FROM BERBERIS-KOETINEANA CELL-CULTURES

Three distinctly different isoforms. of S-adenosyl-l-methionine-(R,S)-tetrahydrobenzylisoquinoline-N-methyltransferases could be isolated from cell suspension cultures of Berberis koetineana. These isoforms were designated NMT-I, -II and -III. The three enzymes have different molecular weights (60-78 × 103), pH optima (6.8/7.4), kinetic properties and substrate specificities. NMT-I showed maximal activity with (R)-tetrahydropapaverine as substrate, NMT-II and -III were most active against (R)-coclaurine. The mixture of all three NMT's was immobilized on CH-Sepharose or CPG-10 glass beads. The enzymes under these conditions retained their properties and represent a useful tool for the preparative synthesis of isotopically labelled N-methylated benzylisoquinoline alkaloids. © 1990.