1,2-dehydroreticulinium reductase

Now, it is known (Scheme 13.42) that 1,2-dehydroreticuline is reduced by 1,2-dehydroreticulinium reductase (EC 1.5.1.27) with the reduced form of NADPH being oxidized to NADP. However, the enzyme required for the oxidation of (5)-reticuline to 1,2-dehydroreticuline has not yet been characterized. 

Reticuline is a chemical compound that can be found in Lindera aggregata. It is also one of the alkaloids found in opium. Metabolism showed that 3 -hydroxy-A -methyl-(S)-coclaurine 4 -0-methyltransferase uses 5-adenosyl methionine and 3 -hydroxy-A -methyl-(S)-coclaurine to produce S-adenosylhomocysteine and (S)-reticuline. Reticuline oxidase uses (S)-reticuline and O2 to produce (S)-scoulerine and H2O2. Salutaridine synthase uses (R)-reticuline, NADPH, H", and O2 to produce salutaridine, NADP", and H2O. 1,2-dehydroreticulinium reductase (NADPH) uses (R)-reticuline and NADP + to produce 1,2-dehydroreticulinium, NADPH, and H". ... 

The later steps of morphine biosynthesis have been investigated in P. somniferum cells and tissue. Notably, in morphine biosynthesis, (S)-reticuline is converted to (R)-reticuline, thereby epimerizing the stereocenter generated by norcoclaurine synthase at the start of the pathway (Fig. Id). (S)-reticuline is converted to (R)-reticuline through a 1,2-dehydroreticuline intermediate. Dehydroreticuline synthase catalyzes the oxidation of (S)-reticuline to 1,2-dehydroreticulinium ion (44). This enzyme has not been cloned but has been purified partially and shown to be membrane-associated. This intermediate then is reduced by dehydroreticuline reductase, an NADPH-dependent enzyme that stereoselectively transfers a hydride to dehydroreti-culinium ion to yield (R)-reticuline. This enzyme has not been cloned yet but has been purified to homogeneity (45). 

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