Involved in the biosynthesis of the indolocarbazole antitumor agent rebeccamycin. Catalyzes the chlorination of tryptophan (Trp) at C7 position to yield 7-chlorotryptophan. The reaction between FADH2, Cl-, and O2 generates the powerful oxidant HOCl, which is presumed to carry out the chlorination reaction. The reaction of HOCl with the active site Lys-79 generates a lysine chloramine, which plays a key role in directing regiospecific chlorination of substrate in this important class of biosynthetic enzymes. It is also able to use bromide ions to generate monobrominated Trp. chloride + FADH2 + L-tryptophan + O2 = 7-chloro-L-tryptophan + FAD + 2 H2O kcat for tryptophan is 1.4 min(-1). Homodimer. Belongs to the flavin-dependent halogenase family. Bacterial tryptophan halogenase subfamily.