The Mechanism of Formation of N-Formylkynurenine by Heme Dioxygenases

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• 作者：Jaswir Basran ; Igor Efimov ; Nishma Chauhan ; Sarah J. Thackray ; James L. Krupa ; Graham Eaton ; Gerry A. Griffith ; Christopher G. Mowat ; Sandeep Handa ; Emma Lloyd Raven
• 刊名：Journal of the American Chemical Society
• 出版年：2011
• 出版时间：October 12, 2011
• 年：2011
• 卷：133
• 期：40
• 页码：16251-16257
• 全文大小：916K
• 年卷期：v.133,no.40(October 12, 2011)
• ISSN：1520-5126

文摘

Heme dioxygenases catalyze the oxidation of an class="smallcaps">lan>-tryptophan to N-formylkynurenine (NFK), the first and rate-limiting step in tryptophan catabolism. Although recent progress has been made on early stages in the mechanism, there is currently no experimental data on the mechanism of product (NFK) formation. In this work, we have used mass spectrometry to examine product formation in a number of dioxygenases. In addition to NFK formation (m/z = 237), the data identify a species (m/z = 221) that is consistent with insertion of a single atom of oxygen into the substrate during O₂-driven turnover. The fragmentation pattern for this m/z = 221 species is consistent with a cyclic amino acetal structure; independent chemical synthesis of the 3a-hydroxypyrroloindole-2-carboxylic acid compound is in agreement with this assignment. Labeling experiments with ¹⁸O₂ confirm the origin of the oxygen atom as arising from O₂-dependent turnover. These data suggest that the dioxygenases use a ring-opening mechanism during NFK formation, rather than Criegee or dioxetane mechanisms as previously proposed.