IUBMB Enzyme Nomenclature


Accepted name: tryptophan 7-halogenase

Reaction: L-tryptophan + FADH2 + chloride + O2 + H+ = 7-chloro-L-tryptophan + FAD + 2 H2O

For diagram of reaction click here.

Other name(s): prnA (gene name); rebH (gene name); ktzQ (gene name)

Systematic name: L-tryptophan:FADH2 oxidoreductase (7-halogenating)

Comments: A flavin-dependent halogenase. The enzyme from the bacterium Lechevalieria aerocolonigenes catalyses the initial step in the biosynthesis of rebeccamycin [2]. 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. Also acts on bromide ion. cf. EC, tryptophan 5-halogenase, and EC, tryptophan 6-halogenase.

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


1. Dong, C., Kotzsch, A., Dorward, M., van Pee, K.H. and Naismith, J.H. Crystallization and X-ray diffraction of a halogenating enzyme, tryptophan 7-halogenase, from Pseudomonas fluorescens. Acta Crystallogr. D Biol. Crystallogr. 60 (2004) 1438-1440. [PMID: 15272170]

2. Yeh, E., Garneau, S. and Walsh, C.T. Robust in vitro activity of RebF and RebH, a two-component reductase/halogenase, generating 7-chlorotryptophan during rebeccamycin biosynthesis. Proc. Natl. Acad. Sci. USA 102 (2005) 3960-3965. [PMID: 15743914]

3. Bitto, E., Huang, Y., Bingman, C.A., Singh, S., Thorson, J.S. and Phillips Jr., G.N. The structure of flavin-dependent tryptophan 7-halogenase RebH. Proteins Struct. Funct. Genet. 70 (2008) 289-293.

4. Heemstra, J.R., Jr. and Walsh, C.T. Tandem action of the O2- and FADH2-dependent halogenases KtzQ and KtzR produce 6,7-dichlorotryptophan for kutzneride assembly. J. Am. Chem. Soc. 130 (2008) 14024-14025. [PMID: 18828589]

[EC created 2009 as EC, transferred 2014 to EC, modified 2018]

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