6-Formylindolo[3,2-b]carbazole

6-Formylindolo[3,2-b]carbazole (FICZ) is a degradation product of tryptophan upon exposure to visible light that activates the aryl hydrocarbon receptor (AhR; Kd = 70 pM).{31887} This endogenous AhR ligand is also a good substrate for cytochromes P450 (CYP) 1A1, 1A2, and 1B1 (Kis = 15.4, 3.9, and 13.3 µM, respectively).{31888} When activated by either environmental toxins or endogenous ligands, the AhR induces detoxifying enzymes and modulates immune cell differentiation. FICZ has been used to study the immunomodulatory and host defense mechanisms of AhR signaling pathways.{27028}