Aromatic amino-acid

Aromatic amino acids (AAA) are amino acids that include an aromatic ring.

Examples include:

Phenylalanine → Tyrosine → L-DOPA → (Dopamine) → (Epinephrine) → (Norepinephrine)

Tryptophan → 5-hydroxytryptophan → (Serotonin)

Phenylalanine, tryptophan, and histidine are essential amino acids for animals. Since they are not synthesized in the human body, they must be derived from the diet. Tyrosine is semi-essential; it can be synthesized, but only from phenylalanine. A lack of the enzyme phenylalanine hydroxylase, used in tyrosine synthesis, causes phenylketonuria and concurrently renders tyrosine an essential amino acid.

Aromatic amino acids are able to absorb light due to their conjugated double bonds. This characteristic of aromatic amino acids is used to quantify the concentration of proteins in an unknown sample. These amino acids are able to absorb light which excites its electron to the excited state. When the electron falls back to its ground state, it will either emit light or release energy. If the molecule is able to emit light it is known as a fluorescent molecule. Tryptophan is widely used as a fluorescent molecule.

Animals obtain aromatic amino acids from their diet, but all plants and micro-organisms must synthesize their aromatic amino acids through the metabolically costly shikimate pathway in order to make them.

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