RESUMEN
The gateway to morphine biosynthesis in opium poppy (Papaver somniferum) is the stereochemical inversion of (S)-reticuline since the enzyme yielding the first committed intermediate salutaridine is specific for (R)-reticuline. A fusion between a cytochrome P450 (CYP) and an aldo-keto reductase (AKR) catalyzes the S-to-R epimerization of reticuline via 1,2-dehydroreticuline. The reticuline epimerase (REPI) fusion was detected in opium poppy and in Papaver bracteatum, which accumulates thebaine. In contrast, orthologs encoding independent CYP and AKR enzymes catalyzing the respective synthesis and reduction of 1,2-dehydroreticuline were isolated from Papaver rhoeas, which does not accumulate morphinan alkaloids. An ancestral relationship between these enzymes is supported by a conservation of introns in the gene fusions and independent orthologs. Suppression of REPI transcripts using virus-induced gene silencing in opium poppy reduced levels of (R)-reticuline and morphinan alkaloids and increased the overall abundance of (S)-reticuline and its O-methylated derivatives. Discovery of REPI completes the isolation of genes responsible for known steps of morphine biosynthesis.
Asunto(s)
Aldehído Reductasa/metabolismo , Carbohidrato Epimerasas/metabolismo , Sistema Enzimático del Citocromo P-450/metabolismo , Regulación de la Expresión Génica de las Plantas , Morfina/biosíntesis , Papaver/metabolismo , Proteínas de Plantas/metabolismo , Aldehído Reductasa/genética , Aldo-Ceto Reductasas , Alcaloides/biosíntesis , Alcaloides/química , Secuencia de Bases , Bencilisoquinolinas/química , Bencilisoquinolinas/metabolismo , Bromoviridae/genética , Bromoviridae/metabolismo , Carbohidrato Epimerasas/antagonistas & inhibidores , Carbohidrato Epimerasas/genética , Sistema Enzimático del Citocromo P-450/genética , Escherichia coli/genética , Escherichia coli/metabolismo , Exones , Fusión Génica , Intrones , Ligasas/genética , Ligasas/metabolismo , Datos de Secuencia Molecular , Morfinanos/química , Morfinanos/metabolismo , Morfina/química , Sistemas de Lectura Abierta , Opio/química , Opio/metabolismo , Oxidación-Reducción , Papaver/genética , Proteínas de Plantas/genética , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , EstereoisomerismoRESUMEN
Dissolved organic matter (DOM) is a ubiquitous constituent of natural waters and is comprised of a variety of chemically heterogeneous molecular structures and functional groups. DOM is often considered to be a major ligand for metals in most natural waters and its reactivity is thought to be strongly dependent on its chemical composition and structure. In this study, a combination of UV/visible, emission excitation matrix fluorescence (EEM) and (1)H NMR spectroscopies were used to characterize DOM from the Athabasca River (Alberta, Canada). The chemical characterization of river DOM showed that the most upstream samples located in agricultural areas were blue-shifted and less aromatic and contained more hydrogens connected with oxygen functional groups than those in the wetland dominated area in the Athabasca oil sand deposit region. The presence of paramagnetic ions (Fe and Al) was not found to significantly affect the structural composition of DOM as revealed by (1)H NMR. Such change in the quality of DOM may have a profound impact on metal binding in the Athabasca River watershed.