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 degreesC. The apparent K-m 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 dehydro alangimakine with similar I-50 values of 10 muM. DIS presumably provides (R)-deacetylipecoside for the formation of tetrahydroisoquinoline monoterpene glucosides that also possess an (R)-configuration at the same chiral center. (C) 2000 Elsevier Science Ltd. All rights reserved.