Mammalian cytochrome P450 enzymes catalyze the phenol-coupling step in endogenous morphine biosynthesis.
A cytochrome P450 (P450) enzyme in porcine liver that catalyzed the phenol-coupling reaction of the substrate (R)-reticuline to salutaridine was previously purified to homogeneity (Amann, T., Roos, P. H., Huh, H., and Zenk, M. H. (1995) Heterocycles 40, 425-440). This reaction was found to be catalyzed by human P450s 2D6 and 3A4 in the presence of (R)-reticuline and NADPH to yield not a single product, but rather (-)-isoboldine, (-)-corytuberine, (+)-pallidine, and salutaridine, the para-ortho coupled established precursor of morphine in the poppy plant and most likely also in mammals. (S)-Reticuline, a substrate of both P450 enzymes, yielded the phenol-coupled alkaloids (+)-isoboldine, (+)-corytuberine, (-)-pallidine, and sinoacutine; none of these serve as a morphine precursor. Catalytic efficiencies were similar for P450 2D6 and P450 3A4 in the presence of cytochrome b(5) with (R)-reticuline as substrate. The mechanism of phenol coupling is not yet established; however, we favor a single cycle of iron oxidation to yield salutaridine and the three other alkaloids from (R)-reticuline. The total yield of salutaridine formed can supply the 10 nm concentration of morphine found in human neuroblastoma cell cultures and in brain tissues of mice.
Grobe
Nadja
N
Donald Danforth Plant Science Center, St. Louis, Missouri 63132, USA.
Zhang
Baichen
B
Fisinger
Ursula
U
Kutchan
Toni M
TM
Zenk
Meinhart H
MH
Guengerich
F Peter
FP
D000818:Animals; D044182:Benzylisoquinolines / Q000737:chemistry* / Q000378:metabolism; D002384:Catalysis; D045744:Cell Line, Tumor; D019389:Cytochrome P-450 CYP2D6 / Q000737:chemistry* / Q000378:metabolism; D051544:Cytochrome P-450 CYP3A / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D007501:Iron / Q000737:chemistry / Q000378:metabolism; D051379:Mice; D009019:Morphinans / Q000737:chemistry / Q000378:metabolism; D009020:Morphine / Q000096:biosynthesis*; D010084:Oxidation-Reduction; D010636:Phenols / Q000737:chemistry / Q000378:metabolism; D051381:Rats
D044182:Benzylisoquinolines; D009019:Morphinans; D010636:Phenols; D009020:Morphine; C009270:salutaridine; D007501:Iron; D019389:Cytochrome P-450 CYP2D6; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; C003298:reticuline