FADH2-dependent halogenase

From biosynthetic and hybridization studies it is known that FADH2-dependent halogenases are involved in the biosynthesis of many halometabolites produced by bacteria119, 21 221 and it can be expected that other FADFh-dependent halogenases will be purified and characterized in the near future. 

The recently detected FADH2-dependent halogenases are substrate specific. Tryptophan 7-halogenase catalyzes the chlorination and bromination of d- and L-trypto-phan to 7-chloro- or 7-bromotryptophan, respectively1201. This enzyme also accepts a number of other indole derivatives such as tryptamine, indole-3-acetonitrile, 3-me-thylindole and 5-methylindole as substrates (Fig. 16.9-3a) 43L In addition to indoles, aminophenylpyrrole derivatives are also chlorinated by tryptophan 7-halogenase (Fig. 16.9-3b) 43L... 

In contrast to FADH2-dependent halogenases, haloperoxidases have no substrate specificity. The enzymatic iodination, bromination, and chlorination of a number of different aromatic compounds by haloperoxidases have been reported in the last few years. All aromatic substrates halogenated successfully by haloperoxidases are aromatic compounds activated for electrophilic substitution (Table 16.9-1). 

Table 16.9-1. FADH2-dependent halogenases, haloperoxidases and perhydrolases used for biotransformation of aromatic compounds and their sources. 

Heemstra JR, Walsh CT. Tandem action of the O2- and FADH2-dependent halogenases KtzQ and KtzR produce 6,7-dichlorotryptophan for kutzneride assembly. J. Am. Chem. Soc. 2008 130 14024-14025. 

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