phenylalanine hydroxylase

absence in phenylketonuria

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  In phenylketonuria

  …organic catalyst, or enzyme, called phenylalanine hydroxylase. This enzyme is not active in individuals who have phenylketonuria. As a result of this metabolic block, abnormally high levels of phenylalanine accumulate in the blood, cerebrospinal fluid, and urine. Abnormal products of phenylalanine breakdown, such as highly reactive ketone compounds, can also…

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  In human genetic disease: Autosomal recessive inheritance

  …the gene encoding the enzyme phenylalanine hydroxylase (PAH). PAH normally catalyzes the conversion of phenylalanine, an amino acid prevalent in dietary proteins and in the artificial sweetener aspartame, to another amino acid called tyrosine. In persons with PKU, dietary phenylalanine either accumulates in the body or some of it is…

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  In metabolic disease: Disorders of amino acid metabolism

  …caused by decreased activity of phenylalanine hydroxylase (PAH), an enzyme that converts the amino acid phenylalanine to tyrosine, a precursor of several important hormones and skin, hair, and eye pigments. Decreased PAH activity results in accumulation of phenylalanine and a decreased amount of tyrosine and other metabolites. Persistent high levels…

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