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L-isomer of Tryptophan

Tryptophan (Trp or W) is encoded by the codon UGG. It is an α-amino acid used in the biosynthesis of proteins.

Tryptophan has an α-amino group (which is in the –NH3+ form under biological conditions), and an α-carboxylic acid group (which is in the deprotonated –COO form under biological conditions). It also has a side chain indole, which makes it a non-polar aromatic amino acid. Tryptophan is essential to humans: the body cannot synthesize it, so it must be got from the diet.

Tryptophan is also a precursor to the neurotransmitters serotonin and melatonin.[1]


  1. Slominski A. et al 2002. "Conversion of L-tryptophan to serotonin and melatonin in human melanoma cells". FEBS Letters 511 (1-3): 102–6. doi:10.1016/s0014-5793(01)03319-1. PMID 11821057.