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In enzymology, a tryptophan 2,3-dioxygenase () is an enzyme that catalyzes the chemical reaction :L-tryptophan + O2 N-formyl-L-kynurenine Thus, the two substrates of this enzyme are L-tryptophan and O2, whereas its product is N-formyl-L-kynurenine. This enzyme participates in tryptophan metabolism. In humans, tryptophan 2,3-dioxygenase is encoded by the ''TDO2'' gene.〔(【引用サイトリンク】 url = http://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=6999 )〕 Tryptophan 2,3-dioxygenase plays a central role in the physiological regulation of tryptophan flux in the human body. It catalyses the first and rate limiting step of tryptophan degradation along the kynurenine pathway and thereby regulates systemic tryptophan levels.〔 == Function == This enzyme belongs to the family of oxidoreductases, specifically those acting on single donors with O2 as oxidant and incorporation of two atoms of oxygen into the substrate (oxygenases). The oxygen incorporated need not be derived from O2. This family of enzymes includes tryptophan 2,3-dioxygenase (TDO, also known as tryptophan oxygenase and L-tryptophan pyrrolase) and indoleamine 2,3-dioxygenase (IDO, also known as tryptophan pyrrolase). These two enzymes are oxidoreductase enzymes that contain one noncovalently bound iron–protoporphyrin IX per monomer. These enzymes catalyze the dioxygenation of L-tryptophan (L-Trp) to N-formyl-L-kynurenine in the first and rate-limiting step of the kynurenine pathway.〔 The same family of enzymes also includes sIDO from ''Shewanella oneidensis'' and PrnB, the second enzyme in the pyrrolnitrin biosynthesis pathway from ''Pseudomonas fluorescens'', although dioxygenase activity has not been demonstrated for either as yet. Recently, a new enzyme with the ability to catalyze L-tryptophan dioxygenation, INDOL1, was identified. Tryptophan 2,3-dioxygenase was initially discovered in the 1930s and is found in both eukaryotes (human, rat, and rabbit) and prokaryotes (''Xanthomonas campestris'',〔 and ''P. fluorescens''〔) Expression of tryptophan 2,3-dioxygenase in mammals is normally restricted to the liver, but it has been identified in the brain and epididymis of some species, and, in some tissues, its production can be induced in response to stimuli.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tryptophan 2,3-dioxygenase」の詳細全文を読む スポンサード リンク
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