Purification and characterization of S-adenosyl-L-methionine :norcoclaurine 6-0-methyltransferase from cultured Coptis japonica cells

S-adenosyl-L-methionine:norcoclaurine 6-0-methyltransferase (norcoclaurine 6-0-methyltransferase), which catalyzes the transfer of the S-methyl group of S-adenosyl-L-methionine to the 6-hydroxyl group of 2,3,4-tetrahydro-l-[(4-hydroxyphenyl)methyl]-6,7-isoquinolinediol (norcoclaurine), was purified from cultured Coptisjuponica cells and its enzymic properties were characterized. Purified norcoclaurine 6-0-methyltransferase had apparent PI 4.7, a native molecular mass of 95 kDa (determined by gel filtration)and subunit molecular mass of 40 kDa (SDSFAGE). The enzyme did not require a divalent cation for activity, and the addition of Fez+, Cuz+, Co2+, Zn2+, Mn '+, or Ni2' at 5 mh4 severely inhibited enzyme activity. Neither p-chloromercuribenzoate, Nmethylmaleimide nor iodoacetamide inhibited enzyme activity at 1 mM. 5,6-Dihydro-9,10-dimethoxybenzo[ g]-l,3-benzodioxolo[5,6-u]quinolizinium(b erberine, the end-product of the biosynthetic pathway in which norcoclaurine 6-0-methyltransferase catalyzes an intermediate step)also inhibited the activity by 50