S-ADENOSYL-L-METHIONINE, NORCOCLAURINE 6-O-METHYLTRANSFERASE FROM THALICTRUM-MINUS CELL-CULTURES

S-Adenosyl-L-methionine (SAM): norcoclaurine 6-O-methyltransferase (NCMT), which controls berberine biosynthesis in Thalictrum minus cell cultures, was purified to homogeneity. The purified NCMT had a native M(r) of 72 000 consisting of two subunits of 37 000 each, a pH optimum of 9.0 and a pI of 4.3. The enzyme did not require Mg2+ for activation, but was strongly inhibited by divalent cations of heavy metals and by SH reagents. Kinetic studies indicated a sequential mechanism with K-m values of 56 mu M for norcoclaurine and 260 mu M for SAM. S-Adenosyl-L-homocysteine (SAH) was a potent inhibitor of NCMT and its K-i value for SAH vs SAM was 89 mu M.