Pure phenylalanine hydroxylase from rat liver can be activated by limited proteolysis with alpha-chymotrypsin. As with most other types of activation of this enzyme, including activation by exposure to lysolecithin, the increase in activity is expressed in the presence of the naturally occurring pterin cofactor, tetrahydrobiopterin, but not in the presence of synthetic pterin cofactors such as ...

Phenylketonuria (PKU) is the most common autosomal recessive disorder of amino acid metabolism. The disease is caused mainly by mutations in the phenylalanine hydroxylase (PAH) gene, encoding phenylalanine hydroxylase (PAH) enzyme. The PAH enzyme deficiency results in the elevation of phenylalanine in the blood, which may cause severe irreversible mental retardation in the affected individuals....

Phenylketonuria (PKU) results from a deficiency in phenylalanine hydroxylase, the enzyme catalyzing the conversion of phenylalanine (PHE) to tyrosine. Although this inborn error of metabolism was among the first in humans to be understood biochemically and genetically, little is known of the mechanism(s) involved in the pathology of PKU. We have combined mouse germline mutagenesis with screens ...

Phenylalanine hydroxylase undergoes an obligatory prereduction step in order to become catalytically active as shown by stopped-flow kinetics and by measuring tyrosine formation at limiting 6-methyltetrahydropterin levels. This initial step requires oxygen and involves conversion of 6-methyltetrahydropterin directly to the quinonoid form with or without phenylalanine. The EPR spectrum of the re...

A cell-free system for the synthesis of a phenylalanine hydroxylase cofactor from guanosine triphosphate was obtained from extracts of Pseudomonas species (ATCC 11299a). This preparation produced formic acid from the ureido carbon of labeled GTP. The preparation also made specific pteridines from GTP. Among the products, xanthopterin, neopterin, and a cyclic phosphate derivative of neopterin we...

The two major forms of rat liver phenylalanine hydroxylase have been resolved by calcium phosphate chromatography and have been highly purified. These different forms of the enzyme contain dissimilar amounts of endogenous protein-bound phosphate. The hydroxylase activity of these forms, as assayed in the presence of tetrahydrobiopterin, can be differentially stimulated by treatment with Mg2+, A...

Essentially pure phenylalanine hydroxylase from rat liver can be activated between 2.5- and 3.0-fold by treatment with Mg2+, ATP, protein kinase, and cyclic AMP. The activation is seen when the hydroxylase is assayed in the presence of tetrahydrobiopterin, but not in the presence of 2-amino-4-hydroxy-6,7-dimethyltetrahydropteridine. In the presence of [gamma-32P]ATP, activation is accompanied b...

In the presence of phenylalanine and molecular oxygen, activated phenylalanine hydroxylase catalyzes the oxidation of tetrahydrobiopterin. The oxidation of this tetrahydropterin cofactor also proceeds if the substrate, phenylalanine, is replaced by its product, tyrosine, in the initial reaction mixture. These two reactions have been defined as coupled and uncoupled, respectively, because in the...