How does phenylalanine hydroxylase normally process phenylalanine?

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metabolic disease Enzyme defects in urea cycle disorders.

In a healthy metabolic state, the enzyme phenylalanine hydroxylase functions as an organic catalyst that converts the amino acid phenylalanine into tyrosine.1

This process requires the presence of a chemical cofactor known as tetrahydrobiopterin (BH4) to maintain enzymatic activity. When this pathway functions normally, it prevents the toxic accumulation of phenylalanine in the body, which is essential for proper neurological development and the production of melanin. In conditions such as phenylketonuria, this metabolic conversion is blocked, leading to the buildup of phenylalanine and its abnormal metabolites, which can cause significant cognitive and physiological damage.1