Disease relevance of PAH

• We present the case of a girl affected by classical phenylketonuria who has been screened for mutations in the PAH gene [1].
• Benzo[a]pyrene-induced DNA damage and p53 modulation in human hepatoma HepG2 cells for the identification of potential biomarkers for PAH monitoring and risk assessment [2].
• To examine whether N-terminal PAH mutations affect the ability of PAH to bind phenylalanine at the regulatory domain, wild-type and five mutant (G46S, A47V, T63P/H64N, I65T, and R68S) forms of the N-terminal domain (residues 2-120) of human PAH were expressed as fusion proteins in Escherichia coli [3].
• Sex differences in risk of lung cancer: Expression of genes in the PAH bioactivation pathway in relation to smoking and bulky DNA adducts [4].
• The following variable number of tandem repeats (VNTR) were analyzed in the blood of 120 volunteers without cancer and in 27 patients with prostate cancer: D4S43, PAH, F13A1, APOB and vW-1 [5].

Psychiatry related information on PAH

• OBJECTIVES: In the search for chromosome 12 genes potentially involved in the pathogenesis of bipolar disorder we will screen Phenylalanine hydroxylase and human LIM-homeobox LHX5 genes for sequence variants, both of which have been suggested as candidate genes [6].
• Phenylketonuria (PKU) is a classic 'monogenic' autosomal recessive disease in which mutation at the human PAH locus was deemed sufficient to explain the impaired function of the enzyme phenylalanine hydroxylase (enzymic phenotype), the attendant hyperphenylalaninemia (metabolic phenotype) and the resultant mental retardation (cognitive phenotype) [7].
• The sources of the PAH burden in the lake are apportioned, and the implications of these results are discussed including likely response times to changes in loadings [8].
• PAH exposure of road builders was actually not higher than that of policemen; the slight difference resulted from diverging life-styles [9].
• Risk evaluation for human health was carried out using PCB and PAH concentrations measured in seven fish species from Lake Iseo (Italy) and comparing the experimental data with legal levels and the two new approaches proposed by the US FDA and the US EPA to protect local populations with different food habits [10].

High impact information on PAH

• Phenylalanine hydroxylase, tyrosine hydroxylase, and tryptophan hydroxylase constitute a small family of monooxygenases that utilize tetrahydropterins as substrates [11].
• In addition, phenylalanine hydroxylase is allosterically regulated by its substrates, phenylalanine and tetrahydrobiopterin [11].
• The transcription rate of genes like albumin and alpha1-antitrypsin is reduced, while the gene coding for phenylalanine hydroxylase is totally silent, giving rise to phenylketonuria [12].
• Phenylketonuria is a metabolic disorder that results from a deficiency of the hepatic enzyme phenylalanine hydroxylase [13].
• Its clinical phenotype varies widely, and to date more than 10 mutations in the phenylalanine hydroxylase gene have been identified in persons with the disorder [13].

Chemical compound and disease context of PAH

• The hyperphenylalaninemic disorders of classic phenylketonuria (PKU), mild phenylketonuria, and hyperphenylalaninemia (HPA), result from a deficiency of the hepatic enzyme phenylalanine hydroxylase (PAH) or its cofactor (tetrahydrobiopterin) [14].
• Human phenylalanine hydroxylase (hPAH) is a tetrameric enzyme that catalyzes the hydroxylation of L-phenylalanine (L-Phe) to L-tyrosine; a dysfunction of this enzyme causes phenylketonuria [15].
• Tetrameric full-length human PAH, dimeric double-truncated (DeltaN102-DeltaC428) human PAH, and monomeric Chromobacterium violaceum PAH were PEGylated with succinimidyl succinate polyethylene glycol of molecular weight 5000 or 20,000 Da [16].
• Glomerular filtration rate (GFR) and renal plasma flow (RPF) were measured by constant inulin and PAH infusion during euglycemia and intravenous dextrose-induced moderate hyperglycemia in seven insulin-dependent diabetics with persistently elevated GFR, seven diabetics with normal GFR, and in six normal control subjects [17].
• In this study we have investigated the effect of BH4 on PAH gene expression in human hepatoma [18].

Biological context of PAH

• During the last three years there has been a formidable increase in the amount of structural information about PAH and TH, which has provided new insights into the active site structure, the binding of substrates, inhibitors and pterins, as well as on the effect of disease-causing mutations in these hydroxylases [19].
• The mode of coordination of Glu330 to the iron moiety seems to determine the amino acid substrate specificity in PAH and in the homologous enzyme tyrosine hydroxylase [20].
• Using a common polymorphism within the gene, we found that this gene did not cause the discordant results and thus, did not modify the PAH phenotype [21].
• The possibility that a modifying gene was linked to the PAH gene on chromosome 12 was investigated using markers closely linked to the gene; however, no evidence for a modifying gene close to the PAH gene was found [21].
• Genetic evaluation of the family members of subjects with the PAH K274E mutation showed that all individuals with the K274E mutation also exhibited the PAH L321L polymorphism in the catalytic domain of the PAH enzyme [22].

Anatomical context of PAH

• Amplification of phenylalanine hydroxylase and cystathionine beta-synthase transcripts in human peripheral lymphocytes by RT-PCR [23].
• The recombinant D143G mutant enzyme had the same physicochemical properties as the wild-type PAH and was stable when expressed in eukaryotic cells [24].
• We used three different in vitro PAH expression systems (in Escherichia coli, cell-free rabbit reticulocyte lysates, and human embryonal kidney cells), as well as a unique assay for phenylalanine oxidation in vivo [25].
• METHODS: BMPR2 mRNA from lymphoblastoid cell lines of 30 families with PAH and 14 patients with idiopathic PAH (IPAH) was subjected to reverse transcriptase-polymerase chain reaction (RT-PCR) and sequencing [26].
• Epidermal phenylalanine hydroxylase (PAH) produces L-tyrosine from the essential amino acid L-phenylalanine supporting melanogenesis in human melanocytes [27].

Associations of PAH with chemical compounds

• The conformation and distances to the catalytic iron of both L-Phe and the cofactor analogue L-erythro-7,8-dihydrobiopterin (BH2) simultaneously bound to recombinant human PAH have been estimated by (1)H NMR [20].
• Tyrosine-, tryptophan- and phenylalanine hydroxylase (TH, TPH and PAH, respectively) were transiently activated at low urea concentrations and rapidly inactivated in >3 M urea [28].
• A mutation in the functionally critical tetrahydrobiopterin cofactor binding domain of the PAH gene had been identified in African-American patients with the diagnosis of schizophrenia, and biochemical analyses suggested that this mutation has physiological consequences related to amine neurotransmitter function [22].
• Despite favorable energy scores, tyrosine in a position trans to PAH residue His290 or TH residue His336 interferes with the access of the essential cofactor dioxygen to the catalytic center, thereby blocking the enzymatic reaction [29].
• Nevertheless, significant problems such as the substrate specificity of PAH and the different susceptibility of TH to feedback inhibition by l-3,4-dihydroxyphenylalanine (l-DOPA) compared with dopamine (DA) remain unresolved [29].

Regulatory relationships of PAH

• Moreover, we show that the pulmonary vasculature of patients with familial and idiopathic PAH are deficient in the activated form of Smad1 [30].
• These results are also consistent with the hypothesis that BP (PAH) induce G:C to T:A transversion mutations in the hotspot codons of the p53 tumor suppressor gene and are thus involved in malignant transformation of the lung tissue of smokers [31].
• Mutagenicity of C24H14 PAH in human cells expressing CYP1A1 [32].
• The AhR is a ligand-activated transcription factor that mediates immunosuppression by environmental PAH [33].

Other interactions of PAH

• The deletion of the PAH, IGF1, and ASCL1 genes could explain the patient's phenotype corresponding to a contiguous gene syndrome [1].
• METHODS: We screened the coding and intronic flanking regions of the phenylalanine hydroxylase and LHX5 genes for sequence variation by denaturing high-performance liquid chromatography in individuals from the pedigrees [6].
• Point mutations in the protein coding region and splice junction mutations of PAH and CBS can be analyzed by this method [23].
• Mutational analysis of two positional candidate susceptibility genes for bipolar disorder on chromosome 12q23-q24: phenylalanine hydroxylase and human LIM-homeobox LHX5 [6].
• Linkage analysis demonstrated that IGF1 is tightly linked to the phenylalanine hydroxylase gene on chromosome 12q22-24.1 [34].

Analytical, diagnostic and therapeutic context of PAH

• A clone encoding PAH was used for in vitro transcription/translation, followed by immunoprecipitation with sera from 94 APS I patients and 70 healthy controls [35].
• Western-blot analysis of liver extracts showed that PH8 reacted with phenylalanine hydroxylase from a wide range of vertebrate species [36].
• These results support the use of the human PAH probe in prenatal diagnosis and detection of carriers, to provide new opportunities for the biochemical characterization of normal and mutant enzymes, and in the investigation of alternative genetic therapies for PKU [37].
• Sequence analysis of DNA from a single individual, homozygous for the new MspI associated haplotype, shows homozygosity for a C----T transition at nucleotide 896 in exon 7 of the PAH cDNA, resulting in the conversion of leucine 255 to serine (L255S) [38].
• On this basis, single-site mutagenesis of key residues in these regions of the human PAH tetramer was performed in the present study, and their functional impact was measured by steady-state kinetics and the global conformational transition as assessed by surface plasmon resonance and intrinsic tryptophan fluorescence spectroscopy [39].

References