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An essential amino acid. Tryptophan is also the largest amino acid. Its main function is as a building block in protein synthesis.

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 nm) 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.

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