Molecular characterization of the salutaridinol 7-O-acetyltransferase involved in morphine biosynthesis in opium poppy Papaver somniferum

Salutaridinol 7-O-acetyltransferase (EC 2.3.1.150) catalyzes the conversion of the phenanthrene alkaloid salutaridinol to salutaridinol-7-O-acetate, t he immediate precursor of thebaine along the morphine biosynthetic pathway. We have isolated a cDNA clone that corresponds to the internal amino acid sequences of the native enzyme purified from a cell suspension culture of o pium poppy Papaver somniferum. The recombinant enzyme acetylated the 7-hydr oxyl moiety of salutaridinol in the presence of acetyl-CoA. The apparent K. value for salutaridinol was determined to be 9 mum and 54 mum for acetyl-C oA. The gene transcript was detected in extracts from Papaver orientale and Papaver bracteatum in addition to P. somniferum. Genomic DNA gel blot anal ysis indicated that there is likely a single copy of this gene in the P. so mniferum genome. The amino acid sequence of salutaridinol 7-O-acetyltransfe rase is most similar (37% identity) to that of deacetylvindoline acetyltran sferase of Catharanthus roseus. Salutaridinol 7-O-acetyltransferase is the second enzyme specific to morphine biosynthesis for which we have isolated a cDNA. Taken together with the other cDNAs cloned encoding norcoclaurine 6 -O-methyl-transferase, (S)-N-methylcoclaurine 3 ' -hydroxylase, the cytochr ome P-450 reductase, and codeinone reductase, significant progress has been made toward accumulating genes of this pathway to enable the end goal of a biotechnological production of morphinan alkaloids.