Analysis of Reaction Intermediates in Tryptophan 2,3-Dioxygenase: A Comparison with Indoleamine 2,3-Dioxygenase
Analysis of Reaction Intermediates in Tryptophan 2,3-Dioxygenase: A Comparison with Indoleamine 2,3-Dioxygenase
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DOI：
10.1021/acs.biochem.6b01005
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发表时间：
2016-12-13
期刊：
影响因子：
2.9
通讯作者：
Raven, Emma L.
中科院分区：
文献类型：
--
作者：
Basran, Jaswir;Booth, Elizabeth S.;Raven, Emma L.
吲哚胺 2,3-双加氧酶 (IDO) 和色氨酸 2,3-双加氧酶 (TDO) 是含血红素的酶，可催化生物系统中 L-色氨酸 (L-Trp) 的 O-2 依赖性氧化。尽管自发现以来已经过去了几十年，但色氨酸氧化的机制尚未建立。人们普遍认为 IDO 和 TDO 使用相同的机制进行反应，尽管没有证据表明它们确实如此。对于 IDO，化合物 II（铁基）物质会在稳态下累积并参与该机制；在 TDO 中，尚未观察到此类物种。在本文中，我们研究了 TDO 中色氨酸氧化的动力学。我们没有发现化合物 II 在 TDO 催化过程中积累的证据。相反，在稳态条件下检测到三元 [Fe(II)-O-2, L-Trp] 复合物。 TDO 中不存在处于稳态的化合物 II 物质并不是由于 TDO 酶固有地无法形成亚铁血红素，因为化合物 II 可以通过亚铁血红素与过氧化物反应的不同途径直接形成。我们对数据的解释是，IDO 和 TDO 机制中的限速步骤并不相同。
Indoleamine 2,3-dioxygenase (IDO) and ttyptophan 2,3-dioxygenase (TDO) are heme-containing enzymes that catalyze the O-2-dependent oxidation of L-tryptophan (L-Trp) in biological systems. Although many decades have passed since their discovery, the mechanism of tryptophan oxidation has not been established. It has been widely assumed that IDO and TDO react using the same mechanism, although there is no evidence that they do. For IDO, a Compound II (ferryl) species accumulates in the steady state and is implicated in the mechanism; in TDO, no such species has ever been observed. In this paper, we examine the kinetics of tryptophan oxidation in TDO. We find no evidence for the accumulation of Compound II during TDO catalysis. Instead, a ternary [Fe(II)-O-2, L-Trp] complex is detected under steady state conditions. The absence of a Compound II species in the steady state in TDO is not due to an intrinsic inability of the TDO enzyme to form ferryl heme, because Compound II can be formed directly through a different route in which ferrous heme is reacted with peroxide. We interpret the data to mean that the rate-limiting step in the IDO and TDO mechanisms is not the same.