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.