An early step in the biosynthesis is the reaction of 7-chloro-L-tryptophan with oxygen catalysed by
7-chloro-L-tryptophan oxidase (RebO):
Dichlorochromopyrrolate synthase (RebD) couples two molecules of the intermediate 2-iminio-3-(7-chloroindol-3-yl)propionate to give dichlorochromopyrrolic acid: The enzyme
dichloroarcyriaflavin A synthase is responsible for forming the new
aromatic bond between the
indole components of dichlorochromopyrrolic acid, making a six-membered ring. The reaction proceeds in two stages. A protein component, called RebP, is an
oxidase which contains
heme and uses oxygen and
nicotinamide adenine dinucleotide (NADH) to link the rings. Then it acts with a
flavin-dependent partner called RebC to remove the two
carboxylic acid groups by
oxidative decarboxylation. The penultimate step in rebeccamycin's biosynthesis is the addition of a sugar group to one of the indole nitrogens by
4'-demethylrebeccamycin synthase (RebG). The final
methylation is carried out by
demethylrebeccamycin-D-glucose O-methyltransferase (RebM) using
S-adenosyl methionine as
cofactor. == References ==