phenylalanine

2-Amino-3-phenylpropionic acid; the l-isomer is one of the common amino acid s in proteins; a nutritionally essential amino acid.

- p. ammonia-lyase a nonmammalian enzyme that catalyzes the conversion of l-p. to trans-cinnamate and ammonia; it has been used in the treatment of phenylketonuria.

- p. 4-hydroxylase SYN: p. 4-monooxygenase.

- p. 4-monooxygenase an enzyme that catalyzes the oxidation of l-p. to l-tyrosine with O₂ and tetrahydrobiopterin (the latter forming the dihydro derivative) which is, in turn, reduced by NADPH and a reductase to the active form; a deficiency of either of these enzymes will result in phenylketonuria. SYN: p. 4-hydroxylase.

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phe·nyl·al·a·nine .fen-əl-'al-ə-.nēn, .fēn- n an essential amino acid C₉H₁₁NO₂ that is obtained in its levorotatory L-form by the hydrolysis of proteins (as lactalbumin), that is essential in human nutrition, and that is converted in the normal body to tyrosine abbr. Phe see PHENYLKETONURIA, PHENYLPYRUVIC ACID

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n.

an essential amino acid that is readily converted to tyrosine. Blockade of this metabolic pathway gives rise to phenylketonuria, which is associated with abnormally large amounts of phenylalanine and phenylpyruvic acid in the blood and retarded mental development.

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phen·yl·al·a·nine (Phe) (F) (fen″əl-alґə-nēn) an aromatic essential amino acid, α-amino-β-phenylpropionic acid; most of that ingested is hydroxylated to form tyrosine, which is used for protein synthesis, but small amounts are transaminated to phenylpyruvic acid or decarboxylated. See also table at amino acid. [USP] a preparation of phenylalanine used as a dietary supplement.