CHARACTERIZATION OF ENZYMES FROM ANCISTROCLADUS (ANCISTROCLADACEAE) AND TRIPHYOPHYLLUM (DIONCOPHYLLACEAE) CATALYZING OXIDATIVE COUPLING OF NAPHTHYLISOQUINOLINE ALKALOIDS TO MICHELLAMINES

Peroxidase active preparations from three Ancistrocladus species and f rom Triphyophyllum peltatum have been partially purified. They catalyz e the oxidative dimerization of korupensamines A and B to michellamine s A and C, respectively, as well as the mixed coupling to michellamine s A, B, and C. All of these enzymes consist of single polypeptides of approximately 65 kDa with peroxidase activity as monomers. They were c haracterized as soluble proteins predominantly localized in the leaf p hloem of all species examined, Comparative studies with various naphth ol precursors revealed an unexpected substrate specificity. Only korup ensamines were dimerized by the enzymes, while other monomers, even if closely related, were not accepted as substrates. The coupling reacti ons described here represent the first direct synthesis of michellamin es from korupensamines without previous protection of these precursors . (C) 1998 Academic Press.