Rat Liver Phenylalanine Hydroxylase, an Iron Enzyme

Rat liver phenylalanine hydroxylase, an iron enzyme.

Phenylalanine hydroxylase that is essentially pure contains 1 to 2 moles of iron per mole of enzyme (assuming a molecular weight of 100,000). Electron spin resonance (ESR) studies have shown that the iron is present in the high spin ferric form. The addition of substrates (i.e. phenylalanine and dimethyltetrahydropterin) causes the signal for this form to disappear. The iron, 50 to 80%, can be ...

Regulation of Rat Liver Phenylalanine Hydroxylase

Effects of phenylalanine and diand tetrahydropterins on presteady-state and steady-state catalytic behavior of rat liver phenylalanine hydroxylase are analyzed. From this and previous work (Shiman, R, Xia, T., Hill, M., and Gray, D. (1994) J. BioZ. Chem. 269, 2464724656), which analyzed binding of the same compounds to the enzyme in the absence of catalysis, a model of phenylalanine hydroxylase...

Liver phenylalanine hydroxylase assay.

The first reaction is catalyzed by phenylalanine hydroxylase and the second reaction, which generates the reduced form of pteridine cofactor (biopterin), is catalyzed by dihydropteridine reductase (l-3). A direct assay of phenylalanine hydroxylase can be achieved by supplying optimal concentrations of reduced pteridine cofactor or an analog of the reduced cofactor (6,7-dimethyl-5,6,7,8-tetrahyd...

Tetrahydropterin oxidation without hydroxylation catalyzed by rat liver phenylalanine hydroxylase.

In vitro activation of rat liver phenylalanine hydroxylase by phosphorylation.

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...