Evidence for a ferryl intermediate in a heme-based dioxygenase

doi:10.1073/pnas.0906655106

Evidence for a ferryl intermediate in a heme-based dioxygenase

^aDepartment of Physiology and Biophysics, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461; and
^bDepartamento de Química Inorgánica, Analítica y Química Física/Instituto de Química de los Materiales, Medio Ambiente y Energía-Consejo Nacional de Investigaciones Científicas y Técnicas, and
^cDepartamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón 2, Buenos Aires, C1428EHA, Argentina

Edited by Harry B. Gray, California Institute of Technology, Pasadena, CA, and approved August 18, 2009 (received for review June 15, 2009)

Abstract

In contrast to the wide spectrum of cytochrome P450 monooxygenases, there are only 2 heme-based dioxygenases in humans: tryptophan dioxygenase (hTDO) and indoleamine 2,3-dioxygenase (hIDO). hTDO and hIDO catalyze the same oxidative ring cleavage reaction of L-tryptophan to N-formyl kynurenine, the initial and rate-limiting step of the kynurenine pathway. Despite immense interest, the mechanism by which the 2 enzymes execute the dioxygenase reaction remains elusive. Here, we report experimental evidence for a key ferryl intermediate of hIDO that supports a mechanism in which the 2 atoms of dioxygen are inserted into the substrate via a consecutive 2-step reaction. This finding introduces a paradigm shift in our understanding of the heme-based dioxygenase chemistry, which was previously believed to proceed via simultaneous incorporation of both atoms of dioxygen into the substrate. The ferryl intermediate is not observable during the hTDO reaction, highlighting the structural differences between the 2 dioxygenases, as well as the importance of stereoelectronic factors in modulating the reactions.

Footnotes

¹To whom correspondence should be addressed. E-mail: syun-ru.yeh{at}einstein.yu.edu
Author contributions: A.L.-B., D.B., T.E., C.L., M.A.M., L.C., D.A.E., and S.-R.Y. designed research; A.L.-B., D.B., T.E., C.L., M.A.M., and L.C. performed research; Y.L. contributed new reagents/analytic tools; A.L.-B., D.B., T.E., C.L., M.A.M., L.C., D.A.E., and S.-R.Y. analyzed data; and A.L.-B., D.B., T.E., C.L., M.A.M., L.C., D.A.E., and S.-R.Y. wrote the paper;.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0906655106/DCSupplemental.