Partial Purification and Characterization of S-Adenosyl-ʟ-Methionine: Norreticuline N-Methyltransferases from Berberis Cell Suspension Cultures

Two new N-methyltransferases (NMT-I and NMT-II) were found to occur in Berberis vulgaris cell suspension cultures. One of these enzymes (NMT-I) was partially purified (100-fold) and characterized. This enzyme is specific for tetrahydrobenzylisoquinoline alkaloids and S-adenosyl-ʟ-methionine serves as the methyl donor. The apparent molecular weight of the enzyme is 68,000. The pH optimum of the enzyme is 7.6, the temperature optimum 35 °C. Apparent KM values for (R)-tetrahydropapaverin as substrate were 0.2 mᴍ and for SAM 0.04 mᴍ. The preparation of the same type of enzyme from B. wilsoniae var. subcaulialata was utilized as an efficient enzymatic system for the synthesis of stereochemically pure (R)-as well as (S)-reticuline labelled with tritium or 14C at the N-CH3 group. Enzymes catalyzing this type of reactions are named S-adenosyl-ʟ-methionine: norreticuline N-methyltransferases.