is a primary amino acid that is abundant in dietary
protein. It's main metabolic pathway yields the amino acid Tyrosine,
which is involved in the production of Melanin pigments.
Defects of enzymes responsbile for interconversion of
metabolites in the pathway are the cause of three
well-studied, single-gene Inborn Errors of Metabolism:
Phenylketonuria (PKU), Albinism (Melanin
deficiency), and Alkaptonuria (excess HA).