phenylalanine (Phe) /fen′ilal″ənēn/ , an essential amino acid necessary for the normal growth and development of infants and children and for normal protein metabolism throughout life. The normal value of this amino acid in serum is less than 3 mg/dL in adults and 1.2 to 3.5 mg/dL in newborns. It is abundant in milk, eggs, and other common foods. See also amino acid, phenylketonuria, protein.
