PLANT PHYSIOLOGY , Vol 109, Issue 1 131-139, Copyright © 1995 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
A Cytochrome P-450 Monooxygenase Catalyzes the First Step in the Conversion of Tabersonine to Vindoline in Catharanthus roseus
B. St-Pierre and V. De Luca
Institut de Recherche en Biologie Vegetale, Departement de Sciences Biologiques, Universite de Montreal, Montreal, Quebec, Canada H1X 2B2
Hydroxylation at the C-16 position of the indole alkaloid tabersonine has
been suggested as the first step toward vindoline biosynthesis in
Catharanthus roseus. Tabersonine 16-hydroxylase (16-OH) activity was
detected in total protein extracts from young leaves of C. roseus using a
novel coupled assay system. Enzyme activity was dependent on NADPH and
molecular oxygen and was inhibited by CO, clotrimazole, miconazole, and
cytochrome c. 16-OH was localized to the endoplasmic reticulum by linear
sucrose density gradient centrifugation. These data suggest that 16-OH is a
cytochrome P-450-dependent monooxygenase. The activity of 16-OH reached a
maximum in seedlings 9 d postimbibition and was induced by light. The
leaf-specific distribution of 16-OH in the mature plant is consistent with
the localization of other enzymes in the tabersonine to vindoline pathway.
However, in contrast to enzymes that catalyze the last four steps of
vindoline biosynthesis, enzymes responsible for the first two steps from
tabersonine (16-OH and 16-O-methyltransfersase) were detected in C. roseus
cell-suspension cultures. These data complement the complex model of
vindoline biosynthesis that has evolved with respect to enzyme
compartmentalization, metabolic transport, and control mechanisms.
