Phenylalanine

Lore & Background

Heinrich Matthaei and Marshall W. Nirenberg, who used mRNA with multiple uracil repeats in E. coli to produce a polypeptide of repeated phenylalanine, establishing the coding relationship between nucleic acids and proteins.

Reader's Guide

Phenylalanine is significant as an essential amino acid that must be obtained from diet, found in eggs, chicken, liver, beef, milk, soybeans, and aspartame-sweetened products. It serves as a precursor for tyrosine, dopamine, norepinephrine, epinephrine, and melanin. The genetic disorder phenylketonuria (PKU) results from an inability to metabolize phenylalanine due to lack of the enzyme phenylalanine hydroxylase, requiring dietary restriction. Phenylalanine is also used in supplements, with DL-phenylalanine marketed for purported analgesic and antidepressant activities, though clinical trials have not found an antidepressant effect from L-phenylalanine alone. Its role in neurotransmitter synthesis and its involvement in PKU highlight its importance in human health and metabolism.

Did You Know?

• Phenylalanine is one of the nine essential amino acids that humans cannot biosynthesize.
• Phenylalanine is a precursor for the neurotransmitters dopamine, norepinephrine, and epinephrine.
• Individuals with phenylketonuria must regulate phenylalanine intake and avoid aspartame, which metabolizes to phenylalanine.