Evidence for a ferryl intermediate in a heme-based dioxygenase

ARIEL LEWIS BALLESTER; DIPANWITA BATABYAL; TSUYOSHI EGAWA; CHANGYUAN LU; YU LIN; MARCELO A MARTI; LUCIANA CAPECE; DARIO A ESTRIN; SYUN-RU YEH

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA

Año: 2009

0027-8424

In contrast to the wide spectrum of cytochrome P450 monooxy-genases, 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 cleavagereaction of L-tryptophan to N-formyl kynurenine, the initial andrate-limiting step of the kynurenine pathway. Despite immenseinterest, the mechanism by which the 2 enzymes execute thedioxygenase reaction remains elusive. Here, we report experimen-tal evidence for a key ferryl intermediate of hIDO that supports amechanism in which the 2 atoms of dioxygen are inserted into thesubstrate via a consecutive 2-step reaction. This finding introducesa paradigm shift in our understanding of the heme-based dioxy-genase chemistry, which was previously believed to proceed viasimultaneous incorporation of both atoms of dioxygen into thesubstrate. The ferryl intermediate is not observable during thehTDO reaction, highlighting the structural differences between the2 dioxygenases, as well as the importance of stereoelectronicfactors in modulating the reactions.