phenylalanine

phenylalanine An essential amino acid that is required in the human diet. Abbreviated phe. Most of the phe that is ingested is transformed (hydroxylated) to form tyrosine, which is used in protein synthesis. Too little phe does not permit normal physical and intellectual growth. Too much phe (as in PKU) is highly toxic to the brain. See also phenylalanine hydroxylase deficiency; PKU; PKU, maternal.