Tetrahydrobiopterin (BH4) is an important cofactor for two hepatic enzymes, inducible nitric oxide synthase (iNOS) and phenylalanine hydroxylase (PAH), and competition for BH4 between the two enzymes might limit hepatic iNOS or PAH activity. To test this hypothesis, we determined whether conversion of phenylalanine to tyrosine was modified by changes in NO synthase activity, and conversely whet...

The metabolism of phenylalanine and leucine by Peptostreptococcus anaerobius and the effects of metronidazole on this metabolism were studied. The cells metabolized both phenylalanine and leucine under strict anaerobic conditions and produced hydroxylated products (i.e. phenyllactate from phenylalanine and hydroxyisocaproate from leucine). Other products were phenylpropionate, cinnamate and phe...

Fluorescence quenching of pyranine by tryptophan, phenylalanine, and nicotinic acid was investigated by using steady state and time resolved fluorescence spectroscopy. On a comparative basis, nicotinic acid is a very strong quencher of pyranine fluorescence, tryptophan is a moderate quencher and phenylalanine is a weak quencher. The strong quenching is the result of the hydrogen bonding complex...

A rapid procedure for measuring the specific radioactivity of phenylalanine in tissues was developed. This facilitates the accurate determination of rates of protein synthesis in a wide range of tissues by injection of 150 mumol of L-[4-(3)H]phenylalanine/100 g body wt. The large dose of amino acid results in a rapid rise in specific radioactivity of free phenylalanine in tissues to values clos...

Particulate and soluble fractions from leaves of Sorghum, Spinacia (spinach), and Coleus, capable of metabolizing l-phenylalanine to cinnamate or to caffeate, are also able to convert l-and d-phenylalanine to phenylacetate. Since cinnamate and phenylacetate are not effectively separated in commonly used chromatographic solvents, some of the isotropic assays used for phenylalanine ammonia-lyase ...

Volume 5 • Issue 6 • 1000e125 J Genet Syndr Gene Ther ISSN: 2157-7412 JGSGT, an open access journal Hyperphenylalaninemias (HPAs; OMIM 261600) are related to phenylalanine hydroxylase (PAH; OMIM *612349) deficiency; a hepatic enzyme, and are characterized by moderate and/or high levels of the amino acid phenylalanine and reduction of tyrosine. High levels of phenylalanine and low of tyrosine ch...

Friend mouse erythroleukemia cells do not synthesize detectable levels of phenylalanine hydroxylase [phenylalanine 4-monooxygenase; L-phenylalanine, tetrahydropteridine:oxygen oxidoreductase (4-hydroxylating), EC 1.14.16.1] and hence are unable to grow in medium totally lacking tyrosine. These cells were fused with the cytoplasts of rat hepatoma cells that synthesize phenylalanine hydroxylase c...

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...

L-Phenylalanine dehydrogenase catalyzes the NAD(+)-dependent, reversible, oxidative deamination of L-phenylalanine to form ammonia, phenyl pyruvate, and NADH. The enzyme has been purified to homogeneity from Rhodococcus sp. M4, and a partial amino acid sequence was obtained. A cosmid library of Rhodococcus sp. M4 genomic DNA was prepared and used to isolate a 2.5-kilobase PstI fragment that con...

GTP cyclohydrolase I feedback regulatory protein (GFRP) is a 9.7-kDa protein regulating GTP cyclohydrolase I activity in dependence of tetrahydrobiopterin and phenylalanine concentrations, thus enabling stimulation of tetrahydrobiopterin biosynthesis by phenylalanine to ensure its efficient metabolism by phenylalanine hydroxylase. Here, we were interested in regulation of GFRP expression by pro...