S-Adenosyl-l-methionine: Columbamine-O-methyl transferase, a compartmentalized enzyme in protoberberine biosynthesis

Suspension cultures of Berberis wilsoniae var. subcaulialata and B. aggregata are a useful source for the detection, partial purification and characterization of a new enzyme which specifically transfers the methyl group from (S)-adenosyl-L-methionine to the 2-OH-position of columbamine, thus producing palmatine. The enzyme was enriched approx. 30-fold; it is situated in a vesicle with the density ρ=1.14, has a pH-optimum of 8.9, a molecular weight of 52 kD and shows a high degree of substrate specificity.