PHAR 332

Basic PKU Biochemistry

FAQ on Phenylketonuria

Genetics of PKU

Clinical Cases

References

Return to Amino Acid Metabolism Main Page

In humans, phenylalanine is normally oxidized by the enzyme phenylalanine hydroxylase (PAH) to form the amino acid tyrosine; this is in fact the normal biosynthetic route to tyrosine for humans.

From tyrosine, there are further connections to the biosynthesis of catecholamines, melanin, hormones, etc. Usually, dietary intake of Phe and Tyr, and the body's demand for Phe and Tyr, are fairly closely balanced.

However, when there is too much phenylalanine in the body's pool of amino acids, it must be eliminated, either by excretion or by biochemical reaction.

A defect in the transformation of phenylalanine will lead to an excess of Phe and a deficit of Tyr in the body. The excess Phe will undergo side reactions that normally are undetectable. These unusual metabolites of Phe can produce pathologies. One of the principal metabolites is a ketone derivative of phenylalanine, hence the disease is called phenylketonuria.