Enables tryptophan 2,3-dioxygenase activity. Acts upstream of or within several processes, including carboxylic acid metabolic process; regulation of apoptotic process; and regulation of cytokine production. Located in smooth muscle contractile fiber and stereocilium bundle. Is expressed in cerebral cortex; corpus striatum; embryo; extraembryonic component; and hippocampus. Used to study pre-eclampsia. Orthologous to human IDO1 (indoleamine 2,3-dioxygenase 1). [provided by Alliance of Genome Resources, Apr 2022]