Phenylalanine to tyrosine

Route: Phenylalanine → Tyrosine

Phenylalanine hydroxylase hydroxylates phenylalanine and gives tyrosine. It has an iron atom in the active site and uses oxygen and the helper tetrahydrobiopterin (BH₄). One oxygen atom goes into tyrosine and the other into the cofactor, as 4a-hydroxy-BH₄. The next enzyme removes that oxygen as water. Two more enzymes, pterin-4a-carbinolamine dehydratase and dihydropteridine reductase (which uses NADH or NADPH), turn it back into BH₄. Tyrosine is therefore not essential as long as the diet has enough phenylalanine. When this enzyme is missing or weak, phenylalanine builds up in the blood, the disease called phenylketonuria.

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Steps

Enzyme names and EC numbers are those used on the interactive board. Checked against sources: see the claim table in the repository (tools/pathway_data/checks).