L-tryptophan is an essential amino acid. Besides its role in protein biosynthesis, L-tryptophan is converted in the cytosol to L-kynurenine, which is then used to synthesize eye pigment ommochromes. In addition, L-tryptophan is a precursor for the biosynthesis of neurotransmitter serotonin and melatonin. Unlike in mammals, L-tryptophan cannot be used to produce NAD(+) or catabolised to acetyl-CoA because Dmel has no homolog of kynureninase that converts L-kynurenine to 3-hydroxyanthranilate. (Adapted from
FBrf0161620,
FBrf0256069 and
PMID:29989284.)