Oxygenases tryptophan 2,3-dioxygenase

In the metabolism of the aromatic amino acid tryptophan in mammals, two pathways for the formation of pyridine nucleotide coenzyme and in-doleamines are initiated by two well-known oxygenases, tryptophan 2,3-dioxygenase and tryptophan-5-hydroxylase (monooxygenase) (Fig. 2). Kotake and Ito (5) found in 1937 that rabbits fed D-tryptophan excreted D-kynurenine in the urine. Although the tryptophan-cleaving activity in... 

The first enzyme of the pathway, tryptophan dioxygenase (also known as tryptophan oxygenase or tryptophanpyrrolase), is rate-limiting under normal conditions. In isolated hepatocytes, the control coefficient for flux through the pathway of tryptophan dioxygenase is 0.75 and that for tryptophan uptake into the cells is 0.25 (Salter et al., 1986). 

Oxygenases catalyze reactions in which an oxygen atom or molecule is incorporated into organic substrates. They may therefore be monooxygenases or dioxygenases. An example of a dioxygenase is tryptophan-2,3-dioxygenase (a heme enzyme), which participates in the catabolism of tryptophan (Chapter 17) ... 

Oxygenases - Oxygenases are enzymes that incorporate oxygen atoms from 02 into the oxidized products. Dioxygenases are uncommon enzymes that incorporate both atoms of 02 into one substrate. An example is tryptophan 2,3-dioxygenase, which catalyzes the reaction below ... 

The dioxygenases, which incorporate two atoms of oxygen into one molecule of the substrate, are enzymes which are frequently involved in the cleavage of bonds in an aromatic ring. Typical of these are homogentisate oxidase and L-tryptophan oxidase (L-tryptophan pyrrolase) and two bacterial oxygenases pyrocatechase and metapyrocatechase. ... 

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