Printed in Great Britain 81986 Perqamon Press Ltd. COLUMBAMINE, THE CENTRAL INTERMEDIATE IN THE LATE STAGES OF PROTOBERBERINE BIOSYNTHESIS

Abstract: A specific methyltransferase which in the presence of S-adenosylmethionine [SAM] converts columbamine to palmatine has been demonstrated to occur in Berberis cell cultures. The enzyme acts only on the quaternary alkaloid as substrate, not on its tetrahydro derivative, which fact is in sharp contrast to previous claims. The biosynthesis of the protoberberine alkaloids has been essentially clarified both at the precursor feeding stage' 2 and at the enzyme level. However, the modification of rings A and D of the protoberberine molecule during the late stages of the formation of these alkaloids are still not clear. Recently, utilizing crude extracts from Berberis aggregata, Beecher and Kelleher3 reported on the demonstration of a methyl transferase catalysing the methylation of tetrahydrocolumbamine to tetrahydropalmatin