PHE

Phe is the shorthand for phenylalanine, one of the 20 standard amino acids used to build proteins. It is an essential, L-stereoisomer in humans and is classified as an aromatic amino acid because of its benzyl side chain. In genetics, the codons for phenylalanine are UUU and UUC in mRNA (TTT and TTC in DNA).

Phenylalanine is not synthesized by the human body and must be obtained from the diet. It is incorporated into proteins during translation and also serves as a precursor to tyrosine, another important amino acid.

In metabolism, phenylalanine is normally converted to tyrosine by the enzyme phenylalanine hydroxylase, with tetrahydrobiopterin as a cofactor. Tyrosine then feeds into several pathways, including the synthesis of catecholamines (dopamine, norepinephrine, epinephrine) and the pigment melanin, among other metabolites.

Disorders related to phenylalanine metabolism are most notably phenylketonuria (PKU). PKU is typically caused by mutations in the PAH gene that reduce activity of phenylalanine hydroxylase, leading to elevated phenylalanine levels that can cause neurodevelopmental problems if not managed. PKU is usually detected through newborn screening, and management involves a lifelong diet restricting phenylalanine, with monitoring of blood levels. Some individuals may require specialized medical foods or, in rare cases, enzyme therapy.

Dietary sources of phenylalanine include high-protein foods such as meat, fish, eggs, dairy products, legumes, and nuts. Aspartame, a common artificial sweetener, also contains phenylalanine and is a consideration for people with PKU.