The pH optimum of rat liver phenylalanine hydroxylase is dependent on the structure of the cofactor employed and on the state of activation of the enzyme. The tetrahydrobiopterin-dependent activity of native phenylalanine hydroxylase has a pH optimum of about 8.5. In contrast, the 6,7-dimethyltetrahydropterin-dependent activity is highest at pH 7.0. Activation of phenylalanine hydroxylase eithe...

The enzymatic oxidation of phenylalanine to tyrosine has been studied as part of an investigation of the intermediates and enzyme systems involved in the biosynthesis of epinephrine. Womack and Rose (1) indicated that phenylalanine was converted to tyrosine in viva by showing that tyrosine is not essential when sufficient phenylalanine is available. Definite proof was provided by Moss and Schoe...

Kinetic analyses of the irreversible inhibition of L-tyrosine and L-phenylalanine transport in Bacillus subtilis by phenylalanine chloromethyl ketone revealed that the inhibition was due to an affinity labeling process. Phenylalanine chloromethyl ketone is a competetive inhibitor of L-tyrosine and L-phenylalanine transport. The K, values for irreversible inhibition of L-tyrosine and L-phenylala...

Dietary restriction of phenylalanine is the main treatment for phenylketonuria (PKU), and current estimates of requirements are based on plasma phenylalanine concentration and growth. The present study aimed to determine more precisely the phenylalanine requirements in patients with the disease by use of indicator amino acid oxidation, with L-[1-13C]lysine as the indicator. Breath 13CO2 product...

The derivation of a quantitative model of phenylalanine metabolism in humans is described. The model is based on the kinetic properties of pure recombinant human phenylalanine hydroxylase and on estimates of the in vivo rates of phenylalanine transamination and protein degradation. Calculated values for the steady-state concentration of blood phenylalanine, rate of clearance of phenylalanine fr...

To investigate intestinal and hepatic metabolism of phenylalanine, four conscious pigs (7.5 kg), bearing arterial, venous, and hepatic portal catheters, were fasted for 12 h and infused with [ phenyl-2H5]phenylalanine via a peripheral vein and [ carboxyl-13C]phenylalanine via the stomach. During the first 6 h of the infusion, the pigs remained fasted and received only the intravenous tracer. Du...

Phenylketonuria (PKU) is a disease characterized by an inability to metabolize the amino acid l-phenylalanine. The resulting buildup leads to brain damage and ultimately mental retardation in children if their phenylalanine intake is not carefully controlled. The National Institutes of Health recently suggested that people with PKU monitor their phenylalanine levels throughout their life and be...

Insufficient treatment adherence after early childhood is frequently observed in patients with phenylketonuria. Assessment of these individuals' long-term metabolic control could enable early detection of the risk of intellectual deterioration resulting from high blood phenylalanine concentration. However, the predictive value of specific parameters related to individual dynamics of hyperphenyl...

DeCicco, B. T. (Rutgers, The State University, New Brunswick, N.J.), and W. W. Umbreit. Utilization of aromatic amino acids by Hydrogenomonas facilis. J. Bacteriol. 88:1590-1594. 1964.-An auxotrophic mutant of Hydrogenomonas facilis was isolated which requires tryptophan, phenylalanine, and p-aminobenzoic acid (PABA) for growth. With glucose as the main carbon and energy source, the quantitativ...

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...