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.
Lenz
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Lehrstuhl für Pharmazeutische Biologie, Universität München, Germany.
Zenk
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MH
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