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.

Coenzyme A thioesters of anthranilic acid and N‐methylanthranilic acid were synthesized. The corresponding N‐hydroxysuccinimidyl esters proved to be useful as activated intermediates to prepare anthraniloyl‐CoA and N‐methylanthraniloyl‐CoA. These compounds were characterized by positive and negative ion liquid secondary ion mass spectrometry. Acridone synthase from suspension cultures of Ruta graveolens catalyses the condensation of N‐methylanthraniloyl‐CoA and malonyl‐CoA. The reaction product 1,3‐dihydroxy‐N‐methylacridone was directly identified after the extraction of the assay mixture by electron impact mass spectrometry and capillary gas chromatography.