Phenylalanine has reputed analgesic and antidepressant effects. It is a direct precursor to the neuromodulator phenethylamine.
L-Phenylalanine is biologically converted into L-tyrosine, another one of the DNA-encoded amino acids. L-tyrosine in turn is converted into L-DOPA, which is further converted into dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline). The latter three are known as the catecholamines.
The genetic disorder phenylketonuria (PKU) is the inability to metabolize phenylalanine because of a lack of the enzyme phenylalanine hydroxylase. Individuals with this disorder are known as “phenylketonurics” and must regulate their intake of phenylalanine.
In the brain, L-phenylalanine is a competitive antagonist at the glycine binding site of NMDA receptor and at the glutamate binding site of AMPA receptor.
L-Phenylalanine also inhibits neurotransmitter release at glutamatergic synapses in hippocampus and cortex.