Indoleamine 2,3-dioxygenase--a new antioxidant enzyme

Indoleamine 2,3-dioxygenase (IDO) was first found in rabbit intestine by Hayaishi et al. in 1963. The enzyme has a broad substrate specificity for various indoleamine derivatives and utilizes the superoxide anion as an oxygen source. IDO catalyzes the oxidative cleavage of the indole ring of several important regulatory molecules including tryptophan, tryptamine, serotonin and melatonin, and produces a new type of biogenic amine that may be termed an anthraniloylalkylamine, as shown in Fig. 1.