'-Formylkynurenine is an intermediate in the catabolism of tryptophan. It is a formylated derivative of kynurenine. The formation of '-formylkynurenine is catalyzed by heme dioxygenases.
The enzyme indoleamine 2,3-dioxygenase is the first and rate-limiting enzyme of tryptophan catabolism through the kynurenine pathway.
Related enzymes performing a similar function are Indoleamine 2,3-dioxygenase 2 and tryptophan 2,3-dioxygenase.
In the main sequence of the kynurenine pathway, the formyl group is removed by the enzyme arylformamidase, giving the compound after which the pathway is named:
Alternatively, the enzyme kynureninase can produce N-formylanthranilic acid and L-alanine: