Purification and properties of (S)-tetrahydroprotoberberine oxidase from suspension-cultured cells of Berberis wilsoniae

A novel oxidase, catalyzing in the presence of oxygen the removal of four hydrogen atoms from a number of tetrahydroprotoberberines with simultaneous production of 1 mol H2O2 and H2O each, has been discovered and purified to homogeneity from Berberis wilsoniae cell cultures. This enzyme, (S)‐tetrahydroprotoberberine oxidase, exhibited strict specificity for the (S)‐enantiomer of tetrahydroprotoberberines and 1‐benzylisoquinoline alkaloids, a pH optimum at 8.9, a molecular mass of 105 kDa and consisted of two subunits each of 53 kDa and covalently bound flavin. The Km values for (S‐scoulerine and (S)‐norreticuline were 25 μM and 150 μM respectively. Concentration of the end‐products, either protoberberines or H2O2, greater than 0.5 mM caused severe enzyme inhibition. This catalyst was responsible for the conversion of (S)‐tetrahydrocolumbamine to the key intermediate, columbamine, in the metabolic pathway leading to berberine, jatrorrhizine and palmatine.