Tryptophan

Definition

Tryptophan is one of the 20 protein amino acids (Fig. 1). Its three-letter symbol is Trp and one-letter symbol is W. The molecular formula of tryptophan is C₁₁H₁₂N₂O₂ (molecular weight: 204.23). It is the largest among protein amino acids. Its isoelectric point (pI) is 5.89. It was first reported in 1901 in the hydrolysate of casein. Its side chain has an aromatic bicyclic group (indolyl group); it is grouped as an aromatic amino acid together with phenylalanine and tyrosine. It has poorer solubility in water and organic solvents than most of other amino acids. Since it is decomposed during acid hydrolysis of proteins, alkali hydrolysis or enzymatic hydrolysis of samples is required to determine tryptophan. It has not been detected in extraterrestrial samples.

Fig. 1

Tryptophane