Molecular cloning and functional expression of codeinone reductase: the penultimate enzyme in morphine biosynthesis in the opium poppy Papaver somniferum.
Also acts on some other alkaloids, including codeine, normorphine and ethylmorphine, but only very slowly on 7,8-saturated derivatives such as dihydromorphine and dihydrocodeine. In the reverse direction, also reduces naloxone to the 6alpha-hydroxy analogue. Activated by 2-sulfanylethan-1-ol (2-mercaptoethanol).