The kynurenine pathway is the major route of tryptophan metabolism. The first step of this pathway is catalysed by one of two heme-dependent dioxygenase enzymes – tryptophan 2,3-dioxygenase (TDO) and indoleamine 2,3-dioxygenase (IDO) – leading initially to the formation of N-formylkynurenine (NFK). In this paper, we present a crystal structure of a bacterial TDO from X. campestris in complex with l-kynurenine, the hydrolysed product of NFK. l-kynurenine is bound at the active site in a similar location to the substrate (l-Trp). Hydrogen bonding interactions with Arg117 and the heme 7-propionate anchor the l-kynurenine molecule into the pocket. A mechanism for the hydrolysis of NFK in the active site is presented.

犬尿氨酸途径是色氨酸代谢的主要途径。该途径的第一步是由两种血红素依赖性双加氧酶中的一种催化 - 色氨酸 2,3-双加氧酶 (TDO) 和吲哚胺 2,3-双加氧酶 (IDO) - 最初导致N-甲酰基犬尿氨酸 (NFK)的形成. 在本文中，我们展示了来自野菜的细菌 TDO 与NFK 的水解产物l-犬尿氨酸复合的晶体结构。l-犬尿氨酸结合在与底物 ( l - Trp) 相似位置的活性位点。与 Arg117 和血红素 7-丙酸盐的氢键相互作用锚定l-犬尿氨酸分子放入口袋。提出了 NFK 在活性位点水解的机制。