title: Evidence for a ferryl intermediate in a heme-based dioxygenase.
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.
authors.affiliation: Department of Physiology and Biophysics, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.
authors.forename: Ariel
authors.initials: A
authors.lastname: Lewis-Ballester
authors.forename: Dipanwita
authors.initials: D
authors.lastname: Batabyal
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Egawa
authors.forename: Changyuan
authors.initials: C
authors.lastname: Lu
authors.forename: Yu
authors.initials: Y
authors.lastname: Lin
authors.forename: Marcelo A
authors.initials: MA
authors.lastname: Marti
authors.forename: Luciana
authors.initials: L
authors.lastname: Capece
authors.forename: Dario A
authors.initials: DA
authors.lastname: Estrin
authors.forename: Syun-Ru
authors.initials: SR
authors.lastname: Yeh
mesh_terms: D003198:Computer Simulation; D018360:Crystallography, X-Ray; D049308:Dioxygenases / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D007737:Kynurenine / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism; D013059:Spectrum Analysis, Raman; D014364:Tryptophan / Q000737:chemistry / Q000378:metabolism
chemical_list: D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; C007772:N'-formylkynurenine; D007737:Kynurenine; D014364:Tryptophan; D049308:Dioxygenases