Indolyl-3-acryloylglycine, also known as trans-indolyl-3-acryloylglycine, or IAG for short, is a compound consisting of an indole group attached to an acrylic acid moiety, which is in turn attached to a glycine molecule. This compound has been shown to isomerize when exposed to light. It is likely a metabolic intermediate in the biosynthesis of tryptophan, and is synthesized from tryptophan via indolepropionic acid and indoleacrylicacid (IAcrA). It is also likely that IAcrA is converted into IAG in the gut wall. It may also be produced by certain elements of the mammalian gut microbiota by phenylalanine ammonia-lyase. Identifiable in the urine by high-performance liquid chromatography, it may be a biomarker for autism spectrum disorders, as demonstrated by the research of Paul Shattock and