Rüffer, Martina and Zenk, Meinhart H.
Columbamine, the central intermediate in the late stages of protoberberine biosynthesis.
In: Tetrahedron Letters, Vol. 27, No. 8: pp. 923-924
A specific methyltransferase which in the presence of S-adenosylmethionine [SAM] converts columbamine to palmatine has been demonstrated to occur in 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.