Synthesis of 1,3-dihydroxy-N-methylacridone and its conversion to rutacridone by cell-free extracts of Ruta graveolens cell cultures
1993
Maier, W. | Baumert, A. | Schumann, B. | Furukawa, H. | Gröger, D.
Acridone synthase was isolated from cell suspension cultures of Ruta graveolens which catalysed the formation of 1,3-dihydroxy-N-methylacridone from N-methylanthraniloyl-CoA and malonyl-CoA. No cofactors were required for this enzyme reaction. Potassium phosphate buffer was superior compared to Tris-HCl. Sodium ascorbate instead of mercaptoethanol as oxidation protectant showed an advantageous effect on acridone synthase activity. The enzyme was strongly inhibited by 1,3-dihydroxy-N-methylacridone and by the antibiotic cerulenin. Microsomal preparations from Ruta graveolens cell suspension cultures catalysed an NADPH- and oxygen-dependent condensation of 1,3-dihydroxy-N-methylacridone and isopentenyl pyrophosphate. The reaction product was identified as rutacridone. Mg2+ or Mn2+ ions were necessary for optimal rutacridone synthase activity. The enzyme was inhibited by a number of inhibitors of cytochrome P-450 enzymes. A prenylated acridone, viz. glycocitrine-II was identified as an essential intermediate. Under in vivo conditions glycocitrine-II is incorporated into rutacridone, but a clear-cut conversion of glycocitrine-II by microsomal preparations (cyclase) was not observed. Microsomes converted rutacridone into furofoline-I. A number of detergents was used for solubilization of membrane-bound proteins of Ruta microsomes. Highest specific glycocitrine-II synthase (prenyltransferase) activity was obtained after solubilization with dodecylmaltoside.
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