A subtype of phenylalanine hydroxylase (PAH) deficiency that responds to cofactor (tetrahydrobiopterin, BH4) supplementation has been associated with phenylketonuria (PKU) mutations. The underlying molecular mechanism of this responsiveness is as yet unknown and requires a detailed in vitro expression analysis of the associated mutations. With this aim, we optimized the analysis of the kinetic ...

Liver phenylalanine hydroxylase is allosterically activated by phenylalanine. The structural changes that accompany activation have not been identified, but recent studies of the effects of phenylalanine on the isolated regulatory domain of the enzyme support a model in which phenylalanine binding promotes regulatory domain dimerization. Such a model predicts that compounds that stabilize the r...

A method was developed to study the unsupplemented phenylalanine hydroxylase system in rat liver slices. All of the components of the system--tetrahydrobiopterin, dihydropteridine reductase, and the hydroxylase itself--are present under conditions which should be representative of the actual physiological state of the animal. The properties of the system in liver slices have been compared to th...

Four members spanning three generations of one family have phenylketonuria of varying degrees of severity. Two first cousins were screened in the neonatal period and have had dietary phenylalanine restriction since diagnosis, the older patient having been classified as having more severe PKU and the younger one as having mild PKU. Their mutual grandfather and his older brother also have a signi...

Reversible phosphorylation is the major mechanism underlying the short-term hormonal control of phenylalanine hydroxylase activity in the liver. We report here, for the first time, the impact of a range of hormonal effectors on both the phosphorylation state and enzymic activity of phenylalanine hydroxylase present in isolated rat proximal kidney tubules. The most potent stimulator of enzyme ph...

A monoclonal antibody directed against monkey liver phenylalanine hydroxylase was produced by using a rat-myeloma--rat-spleen-cell-fusion system. This antibody showed the interesting property of increasing mammalian phenylalanine hydroxylase activity more than 2-fold. Perhaps monoclonal antibodies with this effect on other enzyme or proteins could be developed.

Patients with phenylalanine hydroxylase deficiency show increased concentrations of biopterins and neopterins, and reduced concentrations of serotonin and catecholamines, when phenylalanine concentrations are raised. The pterin rise reflects increased synthesis of dihydroneopterin and tetrahydrobiopterin, and the amine fall a reduction in amine synthesis due to inhibition by phenylalanine of ty...

Phenylketonuria (PKU) is an autosomal recessive disorder caused by a deficiency of the enzyme phenylalanine hydroxylase (EC 1.14.16.1). Affected patients develop elevated plasma and tissue levels of phenylalanine and its related ketoacids. Untreated patients usually exhibit severe mental retardation and poor motor function, with characteristic T2 white matter signal abnormalities on conventiona...

We have investigated the p-chlorophenylalanine-dependent loss of phenylalanine hydroxylase activity in cultured hepatoma cells. The similarity of the effect of p-chlorophenylalanine on phenylalanine hydroxylase in the hepatoma cells and that reported from studies in uiuo indicates that the loss of phenylalanine hydroxylase activity is due to a direct interaction of the amino acid analog-ue with...