Tryptophan is an essential amino acid. Tryptophan (C₁₃H₁₀O₂N₂) is also the largest amino acid. Its main function is as a building block in protein synthesis. It was first isolated in 1902.

 

Tryptophan is a precursor for serotonin (a neurotransmitter), melatonin (a neurohormone), and niacin. It is responsible for most of the absorbance of ultraviolet light (c. 280 nanometers) by proteins.

 

As a component of dietary protein, tryptophan is especially plentiful in chocolate, oats, bananas, dried dates, milk, cottage cheese, meat, fish, turkey, chicken, sesame, and peanuts.