Purification and characterization of deacetylipecoside synthase from Alangium lamarckii Thw.

Deacetylipecoside synthase (DIS), the enzyme catalyzing the condensation of dopamine and secologanin to form the (R)-epimer of deacetylipecoside, has been purified 570-fold from the leaves of Alangium lamarckii and partially characterized. The isolated enzyme is a single polypeptide with Mr 30,000, and has a pH optimum at 7.5 and a temperature optimum at 45 degrees C. The apparent Km values for dopamine and secologanin are 0.7 and 0.9 mM, respectively. DIS exhibits high substrate specificity toward dopamine, whereas neither tyramine nor tryptamine are utilized. The enzyme activity is not inhibited by its substrate dopamine, but is inhibited by alangimakine and dehydroalangimakine with similar I50 values of 10 microM. DIS presumably provides (R)-deacetylipecoside for the formation of tetrahydroisoquinoline monoterpene glucosides that also possess an (R)-configuration at the same chiral center.