Tyrosine is the only aromatic amino acid made in animals. This occurs in the reaction catalyzed by phenylalanine hydroxylase, as follows (Figure 21.18):

Phenylalanine + Dihydrobiopterin + O2 <=> Tyrosine + Tetrahydrobiopterin + H2O

Deficiency of phenylalanine hydroxylase is responsible for phenylketonuria (PKU), an autosomal recessive disease that results in production of too much phenylalanine, due to the block in synthesis of tyrosine.

1. Phenylalanine, Tyrosine, and Tryptophan Biosynthesis

2. Tyrosine Metabolism

3. Phenylalanine Metabolism

4. Tryptophan Metabolism