IDO1 is an indoleamine 2,3-dioxygenase - a heme enzyme that catalyzes the first and rate-limiting step in tryptophan catabolism to N-formyl-kynurenine. This enzyme acts on multiple tryptophan substrates including D-tryptophan, and serotonin. It is thought to play a role in a variety of pathophysiological processes such as antimicrobial and antitumor defense, neuropathology, immunoregulation, and antioxidant activity. Through its expression in dendritic cells, monocytes, and macrophages this enzyme modulates T-cell behavior by its pericellular catabolization of the essential amino acid tryptophan. Recombinant human IDO1 protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniqu