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  • Title: Crystal structure and mechanism of tryptophan 2,3-dioxygenase, a heme enzyme involved in tryptophan catabolism and in quinolinate biosynthesis.
    Author: Zhang Y, Kang SA, Mukherjee T, Bale S, Crane BR, Begley TP, Ealick SE.
    Journal: Biochemistry; 2007 Jan 09; 46(1):145-55. PubMed ID: 17198384.
    Abstract:
    The structure of tryptophan 2,3-dioxygenase (TDO) from Ralstonia metallidurans was determined at 2.4 A. TDO catalyzes the irreversible oxidation of l-tryptophan to N-formyl kynurenine, which is the initial step in tryptophan catabolism. TDO is a heme-containing enzyme and is highly specific for its substrate l-tryptophan. The structure is a tetramer with a heme cofactor bound at each active site. The monomeric fold, as well as the heme binding site, is similar to that of the large domain of indoleamine 2,3-dioxygenase, an enzyme that catalyzes the same reaction except with a broader substrate tolerance. Modeling of the putative (S)-tryptophan hydroperoxide intermediate into the active site, as well as substrate analogue and mutagenesis studies, are consistent with a Criegee mechanism for the reaction.
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