FIGURE 5.

Schematic presentation of the biosynthetic pathway leading from (R)-reticuline to morphine in the opium poppy. Along the biosynthetic pathway from (R)-reticuline to morphine, salutaridine synthase catalyzes the first step, the C-C phenol-coupling of (R)-reticuline to salutaridine. The genes encoding the two subsequent enzymes, salutaridine reductase and salutaridinol acetyltransferase as well as the penultimate gene in the pathway encoding codeinone reductase have been characterized (22, 26, 31).