N-methylation of anthranilic acid to N-methylanthranilic acid by cell-free extracts of Ruta graveolens tissue cultures

Abstract Cell-free extracts from acridone synthesizing cell suspension cultures of RUTA GRAVEOLENS L. catalyze the N-methylation of anthranilic acid using S-adenosyl-L-methionine as methyl donor. The stability of enzyme preparations was remarkably high during storage at -20° C. Optimum activity was exhibited at pH 8.2, Mg 2+ was not required for maximum activity and EDTA did not affect the reaction rate. The rate of N-methylanthranilic acid formation was shown to be linear for about 45 min and was proportional to the protein concentration up to at least 0.350 mg of the enzyme preparation. In a number of suspension cultures of plant species not belonging to the Rutaceae this particular N-methyltransferase was not found. Apparantly N-methylation of anthranilic acid is the first pathway-specific reaction in acridone alkaloid biosynthesis.