Tryptophan is an amino acid found in proteins. In mammals, tryptophan is an essential amino acid, meaning it must be present in the diet.

Tryptophan's side chain classifies it as an aromatic amino acid. The aromatic amino acids, like most compounds carrying conjugated rings, exhibit strong absorption of light in the near-ultraviolet region of the spectrum (Figure 5.6). This absorption is frequently used for the analytical detection of proteins. Tyrosine and tryptophan have some hydrophobic character, but it is tempered by the polar groups in their side chains. In addition, tyrosine can ionize at high pH.

Tryptophan is an allosteric inhibitor of glutamine synthetase, an enzyme with a central role in nitrogen metabolism in the cell.

One Letter Code	Three Letter Code	Molecular Wt. (Daltons)	Genetic Code Codons
W	TRP	186.21	UGG

1. Phenylalanine, Tyrosine, and Tryptophan Biosynthesis

2. Tryptophan Metabolism