A tryptophan C-methyltransferase involved in streptonigrin biosynthesis in Streptomyces flocculus

A C-methyltransferase that catalyses the transfer of a methyl group from S-adenosylmethionine to C-3 of tryptophan, resulting in beta-methyltryptophan, has been identified in cell-free extracts of streptonigrin-producing Streptomyces flocculus. The absolute configuration of the product was shown to be (2S,3R)-beta-methyltryptophan by high-pressure liquid chromatography and reactivity with D- and L-amino acid oxidases. In shake culture, maximum specific activity occurs after S. flocculus enters stationary phase, but before significant streptonigrin accumulates.