available evidence indicates that indoleamine 2,3-dioxygenase , which is particularly abundant in the lung , colon , and intestine , catalyzes the oxidative ring cleavage of the pyrrole moiety of not only tryptophan and 5-hydroxytryptophan but also serotonin , melatonin , and other indoleamine derivatives .
C0041249
tryptophan
C0000578
5-hydroxytryptophan