Chasing the Key Enzymes of Secondary Metabolite— Biosynthesis from Thai Medicinal Plants

Novel enzymes involved in the biosynthesis of plant secondary metabolites have been discovered in our laboratory from both differentiated plants and in vitro cultures of Thai medicinal plants. The discovered enzymes included (1) geranylgeraniol-18-hydroxylase from Croton sublyratus containing plaunotol, an anti-peptic ulcer diterpenoid, (2) dopamine-secologanin condensing enzymes from Alangium lamarckii containing emetine, an amoebicidal tetrahydroisoquinoline monoterpene alkaloid, (3) lawsone-forming multienzyme complex from Impatiens balsamina root cultures containing lawsone, an antimicrobial naphthoquinone, and (4) 1,2-dehydroreticuline reductase from Papaver somniferum seedlings containing morphinan alkaloids. Each of these enzymes was isolated, partially purified, characterized and evaluated for its role involved in the biosynthetic pathway of each secondary metabolite accumulated in its producing plant.