Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.14.16.2 (tyrosine hydroxylase)
 14,760 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Pseudomonas aeruginosa possesses a multigene operon that includes phenylalanine hydroxylase (PhhA; phenylalanine 4-monooxygenase, EC 1.14.16.1). phhA encodes PhhA (M(r) = 30,288), phhB (M(r) = 13,333) encodes a homologue of mammalian 4 alpha-carbinolamine dehydratase/homeodomain protein transregulator, and phhC encodes an aromatic aminotransferase (M(r) = 43,237). The reading frames specifying phhB and phhC overlap by 2 bases. The P. aeruginosa PhhA appears to contain iron and is pterin dependent. Unlike the multimeric mammalian hydroxylase, the native P. aeruginosa enzyme is a monomer. The P. aeruginosa PhhA is homologous with mammalian PhhA, tryptophan hydroxylase, and tyrosine hydroxylase. Expression of PhhA from its native promoter required phhB. This may suggest a positive regulatory role for phhB, consistent with the dual catalytic and regulatory roles of the corresponding mammalian homologue.
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PMID:Pseudomonas aeruginosa possesses homologues of mammalian phenylalanine hydroxylase and 4 alpha-carbinolamine dehydratase/DCoH as part of a three-component gene cluster. 810 17

hph-1 mice, which have defective tetrahydrobiopterin biosynthesis due to decreased GTP cyclohydrolase I activity, have been used to investigate the effects of tetrahydrobiopterin deficiency on aromatic L-amino acid monooxygenases and brain monoamine metabolism. Liver tetrahydrobiopterin levels were decreased, and tetrahydrobiopterin deficiency and reduced levels of dopamine, norepinephrine, serotonin, and their metabolites in the brain occurred both pre- and postnatally. Chronic subcutaneous tetrahydrobiopterin elevated brain levels to values higher than those seen in controls but had no effect on monoamine metabolism. In vivo activities of tyrosine hydroxylase and tryptophan hydroxylase were significantly decreased. There was a 30% decrease in the in vitro activity of striatal tyrosine hydroxylase and 50% decrease in liver phenylalanine hydroxylase. Western blotting demonstrated that the lower monooxygenase activities resulted from a reduced absolute amount of tyrosine hydroxylase and phenylalanine hydroxylase protein. The findings suggest involvement of tetrahydrobiopterin in the control of the steady-state concentration of the aromatic L-amino acid monooxygenases. In addition, demonstration of central monoamine changes in the hph-1 mouse make it a possible model system for the investigation of the neuropathological mechanisms in Dopa-responsive dystonia, which has recently been linked with mutations in the gene for GTP cyclohydrolase I.
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PMID:Tetrahydrobiopterin and biogenic amine metabolism in the hph-1 mouse. 876 4

Rat tyrosine hydroxylase was expressed in Escherichia coli. High-level expression was obtained after incubation at 27 degrees C for 18 h. The smallest fragment of tyrosine hydroxylase that gave a soluble active molecule was from Leu188 to Phe456. This fragment corresponds directly to the section of phenylalanine hydroxylase that had previously been shown to be this enzyme's catalytic core region. It has been shown that Glu288 plays a critical role in pterin function in phenylalanine hydroxylase. The corresponding residue in tyrosine hydroxylase (Glu332) has no significant role in pterin function. Substitution of a leucine for a proline at position 327 in tyrosine hydroxylase produces a molecule with a K(m) for tetrahydrobiopterin 20-fold higher than that of the wild-type molecule, whereas the same substitution at the corresponding residue in phenylalanine hydroxylase (pro281) has no effect on the kinetic constant for the cofactor. This suggests that corresponding residues in phenylalanine hydroxylase and tyrosine hydroxylase can have different roles in pterin function. Substitution of a leucine for a proline at position 281 in phenylalanine hydroxylase increases the K(m) for phenylalanine > 20-fold over that of the wild-type. Substitution of leucine or alanine for Pro327 or a glutamic acid for Gln313 in tyrosine hydroxylase eliminates the substrate inhibition shown by wild-type tyrosine hydroxylase.
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PMID:Identification of Gln313 and Pro327 as residues critical for substrate inhibition in tyrosine hydroxylase. 876 48

A novel pterin intermediate, in addition to the expected 4a-hydroxytetrahydrobiopterin (4a-OH-BH4) and quinonoid dihydrobiopterin, was generated during catalytic turnover of tyrosine hydroxylase (TH) with tetrahydrobiopterin as the cofactor. Based on chromatographic, spectroscopic and stability properties its structure is proposed to be similar to the product formed by the non-enzymic conversion of synthetic 4a-OH-BH4 [Bailey, Rebrin, Boerth and Ayling (1995) J. Am. Chem. Soc. 117, 10203-10211]. This compound was tentatively described as a 4a-adduct of a side-chain hydroxy group, i.e. the O2', 4a-cyclic-tetrahydrobiopterin (4a-Cyc-BH4). The intermediate generated in the TH reaction has a UV spectrum which is similar to that of 4a-OH-BH4, but elutes with a longer retention time (tR = 1.69 min compared with 1.06 min) on reversed-phase chromatography. Its conversion into quinonoid dihydrobiopterin is catalysed by pterin-4a-carbinolamine dehydratase (EC 4.2.1.96), although 4a-OH-BH4 is the preferred substrate for that enzyme. A precursor-product relationship was demonstrated between 4a-OH-BH4 and the putative 4a-Cyc-BH4 intermediate. The apparent stability of this compound is dependent on pH as well as on the nature of the buffer ions. At pH 8.0 a large amount was generated in Hepes and Tris, but little in phosphate buffer. At pH 7.0 in Hepes (standard assay conditions) and Tris buffer the putative 4a-Cyc-BH4, but no 4a-OH-BH4, was observed. None of the intermediates was observed at pH 6.0. The accumulation of these intermediates in the absence of dehydratase has important implications for the assay of TH and phenylalanine hydroxylase activities, and is also compatible with a possible physiological role of the dehydratase in the synthesis of catecholamines in vivo.
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PMID:Characterization of a novel pterin intermediate formed in the catalytic cycle of tyrosine hydroxylase. 892 Oct 4

Tyrosine and phenylalanine hydroxylases contain homologous catalytic domains and dissimilar regulatory domains. To determine the effects of the regulatory domains upon the substrate specificities, truncated and chimeric mutants of tyrosine and phenylalanine hydroxylase were constructed: Delta117PAH, the C-terminal 336 amino acid residues of phenylalanine hydroxylase; Delta155TYH, the C-terminal 343 amino acid residues of tyrosine hydroxylase; and 2 chimeric proteins, 1 containing the C-terminal 331 residues of phenylalanine hydroxylase and the N-terminal 168 residues of tyrosine hydroxylase, and a second containing the C-terminal 330 residues of tyrosine hydroxylase and the 122 N-terminal residues of phenylalanine hydroxylase. Steady-state kinetic parameters with tyrosine and phenylalanine as substrate and the need for pretreatment with phenylalanine for full activity were determined. The truncated proteins showed low binding specificity for either amino acid. Attachment of either regulatory domain greatly increased the specificity, but the specificity was determined by the catalytic domain in the chimeric proteins. All three proteins containing the catalytic domain of phenylalanine hydroxylase were unable to hydroxylate tyrosine. Only wild-type phenylalanine hydroxylase required pretreatment with phenylalanine for full activity with tetrahydrobiopterin as substrate.
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PMID:Characterization of chimeric pterin-dependent hydroxylases: contributions of the regulatory domains of tyrosine and phenylalanine hydroxylase to substrate specificity. 930 47

The 2.0 A crystal structure of the catalytic domain of human phenylalanine hydroxylase reveals a fold similar to that of tyrosine hydroxylase. It provides the first structural view of where mutations occur and a rationale to explain molecular mechanisms of the enzymatic phenotypes in the autosomal recessive disorder phenylketoneuria.
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PMID:Crystal structure of the catalytic domain of human phenylalanine hydroxylase reveals the structural basis for phenylketonuria. 940 48

Phenylalanine hydroxylase (PheOH) catalyzes the conversion of L-phenylalanine to L-tyrosine, the rate-limiting step in the oxidative degradation of phenylalanine. Mutations in the human PheOH gene cause phenylketonuria, a common autosomal recessive metabolic disorder that in untreated patients often results in varying degrees of mental retardation. We have determined the crystal structure of human PheOH (residues 118-452). The enzyme crystallizes as a tetramer with each monomer consisting of a catalytic and a tetramerization domain. The tetramerization domain is characterized by the presence of a domain swapping arm that interacts with the other monomers forming an antiparallel coiled-coil. The structure is the first report of a tetrameric PheOH and displays an overall architecture similar to that of the functionally related tyrosine hydroxylase. In contrast to the tyrosine hydroxylase tetramer structure, a very pronounced asymmetry is observed in the phenylalanine hydroxylase, caused by the occurrence of two alternate conformations in the hinge region that leads to the coiled-coil helix. Examination of the mutations causing PKU shows that some of the most frequent mutations are located at the interface of the catalytic and tetramerization domains. Their effects on the structural and cellular stability of the enzyme are discussed.
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PMID:Structure of tetrameric human phenylalanine hydroxylase and its implications for phenylketonuria. 964 59

We report the isolation of a full-length eel tyrosine hydroxylase (TH) cDNA that is characterized by a long 3' untranslated region and by a diversity restricted to the 3' end owing to the differential use of three polyadenylation signals. The longest eel TH mRNA was distinctive in the presence of four pentameric elements (AUUUA) in the AU-rich 3' noncoding region. Such a diversity could provide the basis of posttranscriptional or translational regulation of eel TH gene expression. Comparison of the eel TH sequence with those of other aromatic amino acid hydroxylases (TH, tryptophan hydroxylase, and phenylalanine hydroxylase) and phylogenetic analysis confirmed that the N-terminal regulatory domain is highly divergent, contrasting with the conservation of the catalytic core of the enzyme. Molecular phylogenies including the available sequences of the three hydroxylase genes suggested that the duplication of their common ancestor occurred before the emergence of arthropods. The regional expression of the eel TH mRNA was studied by semiquantitative PCR, northern blots, and in situ hybridization and compared with the immunocytochemical localization of TH protein. The data showed that TH mRNA is mostly expressed in the olfactory and hypothalamic areas, whereas sparse TH-expressing cell bodies are present in the telencephalic region and brainstem. No labeling was detected in the mesencephalic area, in striking contrast with that found in amphibians and amniotes.
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PMID:Tyrosine hydroxylase in the european eel (Anguilla anguilla): cDNA cloning, brain distribution, and phylogenetic analysis. 968 35

The aromatic amino acid hydroxylases tyrosine and phenylalanine hydroxylase both contain non-heme iron, utilize oxygen and tetrahydrobiopterin, and are tetramers of identical subunits. The catalytic domains of these enzymes are homologous, and recent X-ray crystallographic analyses show the active sites of the two enzymes are very similar. The hydroxyl oxygens of tyrosine 371 in tyrosine hydroxylase and of tyrosine 325 of phenylalanine hydroxylase are 5 and 4.5 A, respectively, away from the active site iron in the enzymes. To determine whether this residue has a role in the catalytic mechanism as previously suggested [Erlandsen, H., et al. (1997) Nat. Struct. Biol. 4, 995-1000], tyrosine 371 of tyrosine hydroxylase was altered to phenylalanine by site-directed mutagenesis. The Y371F protein was fully active in tyrosine hydroxylation, eliminating an essential mechanistic role for this residue. There was no change in the product distribution seen with phenylalanine or 4-methylphenylalanine as a substrate, suggesting that the reactivity of the hydroxylating intermediate was unaffected. However, the KM value for phenylalanine was decreased 10-fold in the mutant protein. These results are interpreted as an indication of greater conformational flexibility in the active site of the mutant protein.
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PMID:Mutation to phenylalanine of tyrosine 371 in tyrosine hydroxylase increases the affinity for phenylalanine. 981 37

The aromatic amino acid hydroxylases represent a superfamily of structurally and functionally closely related enzymes, one of those functions being reversible inhibition by catechol derivatives. Here we present the crystal structure of the dimeric catalytic domain (residues 117-424) of human phenylalanine hydroxylase (hPheOH), cocrystallized with various potent and well-known catechol inhibitors and refined at a resolution of 2.0 A. The catechols bind by bidentate coordination to each iron in both subunits of the dimer through the catechol hydroxyl groups, forming a blue-green colored ligand-to-metal charge-transfer complex. In addition, Glu330 and Tyr325 are identified as determinant residues in the recognition of the inhibitors. In particular, the interaction with Glu330 conforms to the structural explanation for the pH dependence of catecholamine binding to PheOH, with a pKa value of 5.1 (20 degreesC). The overall structure of the catechol-bound enzyme is very similar to that of the uncomplexed enzyme (rms difference of 0.2 A for the Calpha atoms). Most striking is the replacement of two iron-bound water molecules with catechol hydroxyl groups. This change is consistent with a change in the ligand field symmetry of the high-spin (S = 5/2) Fe(III) from a rhombic to a nearly axial ligand field symmetry as seen upon noradrenaline binding using EPR spectroscopy [Martinez, A., Andersson, K. K., Haavik, J., and Flatmark, T. (1991) Eur. J. Biochem. 198, 675-682]. Crystallographic comparison with the structurally related rat tyrosine hydroxylase binary complex with the oxidized cofactor 7,8-dihydrobiopterin revealed overlapping binding sites for the catechols and the cofactor, compatible with a competitive type of inhibition of the catechols versus BH4. The comparison demonstrates some structural differences at the active site as the potential basis for the different substrate specificity of the two enzymes.
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PMID:Crystallographic analysis of the human phenylalanine hydroxylase catalytic domain with bound catechol inhibitors at 2.0 A resolution. 984 68


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