IUBMB Enzyme Nomenclature


Accepted name: tryptophan 6-halogenase

Reaction: (1) L-tryptophan + FADH2 + chloride + O2 + H+ = 6-chloro-L-tryptophan + FAD + 2 H2O
(2) D-tryptophan + FADH2 + chloride + O2 + H+ = 6-chloro-D-tryptophan + FAD + 2 H2O

Other name(s): sttH (gene name); thdH (gene name)

Systematic name: L-tryptophan:FADH2 oxidoreductase (6-halogenating)

Comments: The enzyme is a flavin-dependent halogenase that has been described from several bacterial species. It utilizes molecular oxygen to oxidize the FADH2 cofactor, giving C4a-hydroperoxyflavin, which then reacts with chloride to produce a hypochlorite ion. The latter reacts with an active site lysine to generate a chloramine, which chlorinates the substrate. cf. EC, tryptophan 5-halogenase, and EC, tryptophan 7-halogenase.

Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number:


1. Zeng, J. and Zhan, J. Characterization of a tryptophan 6-halogenase from Streptomyces toxytricini. Biotechnol. Lett. 33 (2011) 1607-1613. [PMID: 21424165]

2. Milbredt, D., Patallo, E.P. and van Pee, K.H. A tryptophan 6-halogenase and an amidotransferase are involved in thienodolin biosynthesis. Chembiochem 15 (2014) 1011-1020. [PMID: 24692213]

3. Shepherd, S.A., Menon, B.R., Fisk, H., Struck, A.W., Levy, C., Leys, D. and Micklefield, J. A structure-guided switch in the regioselectivity of a tryptophan halogenase. Chembiochem 17 (2016) 821-824. [PMID: 26840773]

[EC created 2018]

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