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(searched for: pmid:14298464)
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Archives of Biochemistry and Biophysics, Volume 506, pp 42-47; doi:10.1016/j.abb.2010.11.010

Abstract:
The biosynthesis of morphine, a stereochemically complex alkaloid, has been shown to occur in plants and animals. A search in the human genome for methyltransferases capable of catalyzing the N-methylation of benzylisoquinoline alkaloids, as biosynthetic precursors of morphine, yielded two enzymes, PNMT (EC 2.1.1.28) and NMT (EC 2.1.1.49). Introduction of an N-terminal poly-histidine tag enabled purification of both proteins by immobilized metal affinity chromatography. Recombinant PNMT and NMT were characterized for their catalytic activity towards four benzylisoquinolines: tetrahydropapaveroline (THP), 6-O-methyl-THP, 4′-O-methyl-THP and norreticuline. Human PNMT accepted none of the offered alkaloids and was only active with its established substrate, phenylethanolamine. The second enzyme, human NMT, converted all four benzylisoquinolines, however, with a strict preference for (R)-configured morphine precursors. Determination of kinetic parameters of NMT for the four (R)-configured benzylisoquinoline alkaloids by LC–MS/MS revealed (R)-norreticuline to be the best substrate with an even higher catalytic activity as compared to the previously reported natural substrate tryptamine. In addition, isolation of the morphine precursor salutaridine from urine of mice injected (i.p.) with (R)-THP provides new evidence that the initial steps of morphine biosynthesis in mammals occur stereochemically and sequentially differently than in plants and suggests an involvement of the herein characterized (R)-specific NMT.
C. Poeaknapo, J. Schmidt, M. Brandsch, B. Drager,
Proceedings of the National Academy of Sciences, Volume 101, pp 14091-14096; doi:10.1073/pnas.0405430101

Abstract:
Morphine is a plant (opium poppy)-derived alkaloid and one of the strongest known analgesic compounds. Studies from several laboratories have suggested that animal and human tissue or fluids contain trace amounts of morphine. Its origin in mammals has been believed to be of dietary origin. Here, we address the question of whether morphine is of endogenous origin or derived from exogenous sources. Benzylisoquinoline alkaloids present in human neuroblastoma cells (SH-SY5Y) and human pancreas carcinoma cells (DAN-G) were identified by GC/tandem MS (MS/MS) as norlaudanosoline (DAN-G), reticuline (DAN-G and SH-SY5Y), and morphine (10 nM, SH-SY5Y). The stereochemistry of reticuline was determined to be 1-(S). Growth of the SH-SY5Y cell line in the presence of 18O2 led to the [18O]-labeled morphine that had the molecular weight 4 mass units higher than if grown in 16O2, indicating the presence of two atoms of 18O per molecule of morphine. Growth of DAN-G cells in an 18O2 atmosphere yielded norlaudanosoline and (S)-reticuline, both labeled at only two of the four oxygen atoms. This result clearly demonstrates that all three alkaloids are of biosynthetic origin and suggests that norlaudanosoline and (S)-reticuline are endogenous precursors of morphine. Feeding of [ring-13C6]-tyramine, [1-13C, N-13CH3]-(S)-reticuline and [N-CD3]-thebaine to the neuroblastoma cells led each to the position-specific labeling of morphine, as established by GC/MS/MS. Without doubt, human cells can produce the alkaloid morphine. The studies presented here serve as a platform for the exploration of the function of “endogenous morphine” in the neurosciences and immunosciences
H. Kodaira, C. A. Lisek, I. Jardine, A. Arimura, S. Spector
Proceedings of the National Academy of Sciences, Volume 86, pp 716-719; doi:10.1073/pnas.86.2.716

Abstract:
The convulsant opiate thebaine, an intermediate of morphine biosynthesis, was purified from bovine brain to homogeneity by gel filtration and high-performance liquid chromatography (HPLC) monitored by a radioimmunoassay. The immunoreactive material behaved identically to standard thebaine in two HPLC systems and was confirmed to be thebaine by combined gas chromatography/mass spectrometry. To our knowledge, the presence of thebaine in mammalian tissue has not been demonstrated previously. Codeine and morphine were also found to exist in ovine brain. The presence of thebaine in ovine brain provides strong evidence that morphine and codeine, in various mammalian tissues, are of endogenous origin and actually biosynthesized from a precursor.
J. Donnerer, K. Oka, A. Brossi, K. C. Rice, S. Spector
Proceedings of the National Academy of Sciences, Volume 83, pp 4566-4567; doi:10.1073/pnas.83.12.4566

Abstract:
Endogenous codeine and morphine were identified in rat brain by immunological determination following HPLC. To demonstrate occurrence of a biosynthetic pathway to morphine in mammals similar to that used by the poppy plant, (+)-salutaridine, (-)-thebaine, and (-)-codeine were administered to rats intravenously. These compounds, which are intermediates in the synthesis of morphine in Papaver somniferum, caused a marked increase in the codeine and morphine levels in rat tissues. This provides evidence for a biosynthetic pathway to morphine in mammalians.
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