Definition for View source for Tryptophan

One of the 20 naturally-occurring amino acids, and one of three with aromatic side chains. It has the largest side chain, and occurs the least frequently in proteins.

Tryptophan possesses a large, mostly hydrophobic indole group attached to its beta (β) carbon, and is usually found mostly buried in the hydrophobic core of proteins. It is unique among residues considered to belong to the hydrophobic class in that its indole nitrogen is capable of acting as a hydrogen bond donor.

The indole group of the tryptophan side chain absorbs significantly at 280 nm, and also characteristically shows intrinsic fluorescence. Tryptophan has a single codon, UGG. (Methionine is the only other amino acid having only one codon.)

Tryptophan is the precursor to the neurotransmitter serotonin and the hormone melatonin. The first step in conversion of tryptophan to these molecules is the hydroxylation of the 5 position of the indole ring, forming 5-hydroxytryptophan. This reaction is catalyzed by tryptophan hydroxylase, a member of the monooxygenase class of enzymes.<br>

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