An essential amino acid, C9H11NO2, that occurs as a constituent of many proteins and is normally converted to tyrosine in the human body. It is necessary for growth in infants and for nitrogen equilibrium in adults.
An essential amino acid contained in many foods, especially meat and dairy products. It is also one of the amino acids in the artificial sweetener, aspartame. Excess phenylalanine is not stored in the body and has to be broken down by a specific enzyme. People lacking this enzyme develop the condition known as phenylketonuria. For this reason, aspartame products carry a warning that they contain phenylalanine.
An essential amino acid; in addition to its role in protein synthesis, it is the metabolic precursor of tyrosine (and hence noradrenaline, adrenaline, and the thyroid hormones). Dietary tyrosine spares phenylalanine, so reducing the requirement.
