Actinomycin synthesis in Streptomyces antibioticus: enzymatic conversion of 3-hydroxyanthranilic acid to 4-methyl-3-hydroxyanthranilic acid.

A methyltransferase which utilizes 3-hydroxyanthranilic acid (HAA) as a substrate was identified in detergent-treated extracts of the bacterium Streptomyces antibioticus. The enzyme catalyzes the transfer of methyl groups from [14C]S-adenosylmethionine to HAA, but does not catalyze the methylation of 3-hydroxy-DL-kynurenine. Enzyme, substrate, time, and pH dependencies for the methyl transfer reaction were examined. Reaction products obtained from scaled-up reaction mixtures were fractionated by chromatography on Dowex 1, and the Dowex 1 fractions were examined by paper and thin-layer chromatography. One Dowex fraction was shown to contain a radioactive product with the chromatographic properties of 4-methyl-3-hydroxyanthranilic acid (MHA), a known intermediate in the biosynthesis of actinomycin. Available evidence indicates that the conversion of HAA to MHA is an early step in the biosynthesis of actinomycin by S. antibioticus and other actinomycin-producing streptomycetes.