Indolamine dioxygenase

This group is illustrated by tryptophan 2,3-dioxygenase and indolamine 2,3-dioxygenase, which catalyze the insertion of molecular oxygen into the pyrrole ring of tryptophan derivatives. In these... 

Actually, it is noteworthy that there are examples of heme-containing dioxygenases that bind 02 with formation of a heme—Fe(II)—02 complex. This is the case of indolamine-2,3-dioxygenase (EC 1.13.11.11) and tryptophan-2,3-dioxygenase, which catalyze the insertion of 02 into L-tryptophan to yield A-for-mylkynurenine [21], The catalytic cycle involves the ternary complex L-trypto-phan-iron(II) enzyme-02 as an active intermediate. In this ternary complex, which yields A-formylkynurenine and the Fe(II) enzyme, 02 and/or the substrate is activated [21], a situation clearly different from that found for PGHS. 

Kwidzinski E, Bunse J, Aktas O, Richter D, Mutlu L, Zipp F, Nitsch R, Bechmann I (2005) Indolamine 2,3-dioxygenase is expressed in the CNS and down-regulates autoimmune inflammation. FASEB J 19 1347-1349. 

Dioxygenases Tryptophan 2,3 dioxygenase, Indolamine 2,3 dioxygenase haem Fe-oxo ... 

Figure 65 Catalytic cycles of indolamine dioxygenase (reproduced with permission from J. BioL Chem., 1979,254,3288)...

The more recent discovery that the enzyme indolamine dioxygenase (IDO) also is involved in the kynurenine-niacin pathway in nonhepatic tissues, such as lung, intestine, and epididymis, or in cells, such as monocytes, macrophages, and eosinophils, has been a major breakthrough. It has expanded the information about the utilization and involvement of tryptophan in cells considered to be active in immunologic reactivity and responses. 

Figure 26 Possible catalytic mechanisms for tryptophan/indolamine dioxygenase.

Indolamine dioxygenase (- Tryptamine oxygen 2,3-oxidoreductase (decyclizing). This enzyme which is either a ferroheme protein which uses oxygen as dioxygen substrate or a ferriheme protein using superoxide ion 129, 130) is non-specific in its choice of substrates (2,127). 

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