IUBMB Enzyme Nomenclature


Accepted name: 3,5,6-trichloropyridin-2-ol monooxygenase

Reaction: (1) 3,5,6-trichloropyridin-2-ol + FADH2 + O2 = 3,6-dichloropyridine-2,5-dione + Cl- + FAD + H2O
(2) 3,6-dichloropyridine-2,5-diol + FADH2 + O2 = 6-chloro-3-hydroxypyridine-2,5-dione + Cl- + FAD + H2O
(3) 6-chloropyridine-2,3,5-triol + FADH2 + O2 = 3,6-dihydroxypyridine-2,5-dione + Cl- + FAD + H2O

Other name(s): tcpA (gene name)

Systematic name: 3,5,6-trichloropyridin-2-ol,FADH2:oxygen oxidoreductase (dechlorinating)

Comments: The enzyme, characterized from a number of bacterial species, participates in the degradation of 3,5,6-trichloropyridin-2-ol (TCP), a metabolite of the common organophosphorus insecticide chlorpyrifos. The enzyme is a multifunctional flavin-dependent monooxygenase that displaces three chlorine atoms by attacking three different positions in the substrate. Each reaction catalysed by the enzyme displaces a single chlorine and results in formation of a dione, which must be reduced by FADH2 before the monooxygenase could catalyse the next step. The large amount of FADH2 that is required is generated by a dedicated flavin reductase (TcpX). cf. EC, 2,4,6-trichlorophenol monooxygenase.

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


1. Li, J., Huang, Y., Hou, Y., Li, X., Cao, H. and Cui, Z. Novel gene clusters and metabolic pathway involved in 3,5,6-trichloro-2-pyridinol degradation by Ralstonia sp. strain T6. Appl. Environ. Microbiol. 79 (2013) 7445-7453. [PMID: 24056464]

2. Fang, L., Shi, T., Chen, Y., Wu, X., Zhang, C., Tang, X., Li, Q.X. and Hua, R. Kinetics and catabolic pathways of the insecticide chlorpyrifos, annotation of the degradation genes, and characterization of enzymes TcpA and Fre in Cupriavidus nantongensis X1(T). J. Agric. Food Chem. 67 (2019) 2245-2254. [PMID: 30721044]

[EC created 2020]

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