Acetyl coenzyme A:salutaridinol-7-O-acetyltransferase from papaver somniferum plant cell cultures. The enzyme catalyzing the formation of thebaine in morphine biosynthesis.
Acetyl coenzyme A:salutaridinol-7-O-acetyltransferase, a highly substrate-specific enzyme, has been purified nearly 3,000-fold to homogeneity from Papaver somniferum plant cell suspension cultures. Purification was achieved by fractionated ammonium sulfate precipitation, dye-ligand affinity chromatography on matrex red A, gel filtration, ion exchange chromatography on Mono Q and a second dye-ligand affinity chromatography on fractogel TSK AF Blue. The purified enzyme was a single polypeptide with an M(r) = 50,000 displaying an isoelectric point of 4.8, a pH optimum between pH 6 and 9 and a temperature optimum at 47 degrees C. The Km values for the substrate salutaridinol and the co-substrate acetyl co-enzyme A were 7 and 46 microM, respectively. Salutaridinol-7-O-acetyltransferase catalyzes the stoichiometric transfer of the acetyl group from acetyl coenzyme A to the 7-OH group of salutaridinol yielding salutaridinol-7-O-acetate, which is a new intermediate in morphine biosynthesis. Salutaridinol-7-O-acetate undergoes a subsequent spontaneous allylic elimination at pH 8-9, leading to the formation of thebaine (1), the first morphinan alkaloid with the complete pentacyclic ring system, or at pH 7 leading to dibenz[d,f]azonine alkaloids that contain a nine-membered ring. Acetylation and subsequent allylic elimination is a new enzymic mechanism in alkaloid biosynthesis, which in the poppy plant can transform one precursor into alkaloids possessing markedly different ring systems, depending on the reaction pH.
Lehrstuhl für Pharmazeutische Biologie, Universität München, Germany.
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D000123:Acetyltransferases / Q000302:isolation & purification / Q000378:metabolism*; D002478:Cells, Cultured; D002850:Chromatography, Gel; D006863:Hydrogen-Ion Concentration; D009020:Morphine / Q000378:metabolism*; D059828:Plant Cells; D010944:Plants / Q000201:enzymology* / Q000378:metabolism; D013379:Substrate Specificity; D013797:Thebaine / Q000378:metabolism*
D013797:Thebaine; D009020:Morphine; D000123:Acetyltransferases; C097501:acetyl coenzyme A-salutaridinol-7-O-acetyltransferase