page_title: 6-formyl-indolo(3,2-b)carbazole
section_title: Biosynthesis and mechanisms of formation
hierarchical_section_title: 6-formyl-indolo(3,2-b)carbazole / Biosynthesis and mechanisms of formation
caption_attribution_description: English: Different known pathways leading from tryptophan to the endogenous high affinity AHR ligand 6-formylindolo[3,2-b]carbazole (FICZ)
context_page_description: 6-formyl-indolo[3,2-b]carbazole is a nitrogen heterocycle, having an extremely high affinity for binding to the Aryl hydrocarbon receptor.
  It was originally identified as a photooxidized derivative of the amino acid tryptophan and suggested to be the endogenous liagand of the AhR.
context_section_description: Microbiota both on human skin and in the gut can convert Trp to several metabolites, some of which with an affinity for the AHR. In the first report on the structure elucidation of the Trp photo-oxidation product FICZ indole-3-acetaldehyde (I3A) was suggested to be a precursor of FICZ   
  In addition to the light or H₂O₂-induced formation of FICZ, a number of other enzymatic pathways have been identified to convert Trp to FICZ via the precursor indole-3-acetaldehyde (I3A).  The oxidation product of I3A is indole-3 acetic acid, the most common natural plant hormone auxin Auxin. Decarboxylation of Trp catalyzed by the enzyme aromatic L-amino acid decarboxylase (AADC) yields tryptamine, while decarboxylation of 5-hydroxy-Trp, by the same enzyme also (called DOPA decarboxylase) gives serotonin.Serotonin Tryptamine is then oxidatively deaminated by monoamine oxidases MAO-A and B) Monoamine oxidase to produce the FICZ precursor I3A. Post incubation after deamination of the reaction mixture in the absence of an active enzyme generate  FICZ but also its oxidation product CICZ. These non-enzymatic reactions were favored by low pH or increased temperatur.
caption: This diagram shows three different  biosynthesis pathways generating the high affinity endogenous AHR ligand 6-formylindolo(3,2-b)carbazole FICZ
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