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Best J, Duncan W, Sadre-Marandi F, Hashemi P, Nijhout HF, Reed M. Autoreceptor control of serotonin dynamics. BMC Neurosci 2020; 21:40. [PMID: 32967609 PMCID: PMC7509944 DOI: 10.1186/s12868-020-00587-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Accepted: 08/29/2020] [Indexed: 12/11/2022] Open
Abstract
BACKGROUND Serotonin is a neurotransmitter that has been linked to a wide variety of behaviors including feeding and body-weight regulation, social hierarchies, aggression and suicidality, obsessive compulsive disorder, alcoholism, anxiety, and affective disorders. Full understanding involves genomics, neurochemistry, electrophysiology, and behavior. The scientific issues are daunting but important for human health because of the use of selective serotonin reuptake inhibitors and other pharmacological agents to treat disorders. This paper presents a new deterministic model of serotonin metabolism and a new systems population model that takes into account the large variation in enzyme and transporter expression levels, tryptophan input, and autoreceptor function. RESULTS We discuss the steady state of the model and the steady state distribution of extracellular serotonin under different hypotheses on the autoreceptors and we show the effect of tryptophan input on the steady state and the effect of meals. We use the deterministic model to interpret experimental data on the responses in the hippocampus of male and female mice, and to illustrate the short-time dynamics of the autoreceptors. We show there are likely two reuptake mechanisms for serotonin and that the autoreceptors have long-lasting influence and compare our results to measurements of serotonin dynamics in the substantia nigra pars reticulata. We also show how histamine affects serotonin dynamics. We examine experimental data that show very variable response curves in populations of mice and ask how much variation in parameters in the model is necessary to produce the observed variation in the data. Finally, we show how the systems population model can potentially be used to investigate specific biological and clinical questions. CONCLUSIONS We have shown that our new models can be used to investigate the effects of tryptophan input and meals and the behavior of experimental response curves in different brain nuclei. The systems population model incorporates individual variation and can be used to investigate clinical questions and the variation in drug efficacy. The codes for both the deterministic model and the systems population model are available from the authors and can be used by other researchers to investigate the serotonergic system.
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Affiliation(s)
- Janet Best
- Department of Mathematics, The Ohio State University, 231 W 18th Ave., Columbus, OH 43210 USA
| | - William Duncan
- Department of Mathematics, Duke University, Durham, NC 27708 USA
| | | | - Parastoo Hashemi
- Department of Bioengineering, Imperial College, London, SW7 2AZ UK
| | | | - Michael Reed
- Department of Mathematics, Duke University, Durham, NC 27708 USA
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Goswami S, Das MK, Sain D, Goswami B. A concise treatment of pterins: some recent synthetic and methodology aspects and their applications in molecular sensors. Pteridines 2018. [DOI: 10.1515/pteridines-2018-0002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Abstract
A concise account of pterins in chemistry and biology and their applications in molecular sensors including their optical spectroscopic properties are described. Different natural, synthetic, biological and photophysical aspects are also discussed. Synthetic access to direct functionalised pterins and a recently reported new thiophene annulation technique are described for the synthesis of Form B of molybdenum cofactor. The receptor properties of fluorescent pterin molecules including selenopyrimidines which are rarely reported for their binding of anions and neutral molecules are also of major importance in this review. For such an old and still so young, unexplored pterin system on its power to be sensitive for physical studies especially the interaction with cations, anions and neutral molecules are fascinating and research in this area is relatively new and expected to increase fast. Pterin based receptors are for the first time put into a useful review for the advantage of those who want to explore pterin and modified pterin as chromogenic and fluorogenic sensors.
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Affiliation(s)
- Shyamaprosad Goswami
- Department of Chemistry, Indian Institute of Engineering Science and Technology, Shibpur, Howrah 711103, West Bengal , India
| | - Manas Kumar Das
- Department of Chemistry, Indian Institute of Engineering Science and Technology, Shibpur, Howrah 711103, West Bengal , India
| | - Dibyendu Sain
- Department of Chemistry, Indian Institute of Engineering Science and Technology, Shibpur, Howrah 711103, West Bengal , India
| | - Bhaswati Goswami
- Department of Chemistry, Indian Institute of Engineering Science and Technology, Shibpur, Howrah 711103, West Bengal , India
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Rodrigues MVN, Barbosa AF, da Silva JF, dos Santos DA, Vanzolini KL, de Moraes MC, Corrêa AG, Cass QB. 9-Benzoyl 9-deazaguanines as potent xanthine oxidase inhibitors. Bioorg Med Chem 2015; 24:226-31. [PMID: 26712096 DOI: 10.1016/j.bmc.2015.12.006] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2015] [Revised: 11/23/2015] [Accepted: 12/05/2015] [Indexed: 11/28/2022]
Abstract
A novel potent xanthine oxidase inhibitor, 3-nitrobenzoyl 9-deazaguanine (LSPN451), was selected from a series of 10 synthetic derivatives. The enzymatic assays were carried out using an on-flow bidimensional liquid chromatography (2D LC) system, which allowed the screening¸ the measurement of the kinetic inhibition constant and the characterization of the inhibition mode. This compound showed a non-competitive inhibition mechanism with more affinity for the enzyme-substrate complex than for the free enzyme, and inhibition constant of 55.1±9.80 nM, about thirty times more potent than allopurinol. Further details of synthesis and enzymatic studies are presented herein.
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Affiliation(s)
- Marili V N Rodrigues
- Centro Pluridisciplinar de Pesquisas Químicas, Biológicas e Agrícolas, Universidade Estadual de Campinas, 13148-218 Paulínia, SP, Brazil; Separare-Nucleo de Pesquisa em Cromatografia, Departamento de Química, Universidade Federal de São Carlos, 13565-905 São Carlos, SP, Brazil
| | - Alexandre F Barbosa
- Laboratório de Síntese de Produtos Naturais-LSPN, Departamento de Química, Universidade Federal de São Carlos, 13565-905 São Carlos, SP, Brazil
| | - Júlia F da Silva
- Laboratório de Síntese de Produtos Naturais-LSPN, Departamento de Química, Universidade Federal de São Carlos, 13565-905 São Carlos, SP, Brazil
| | - Deborah A dos Santos
- Laboratório de Síntese de Produtos Naturais-LSPN, Departamento de Química, Universidade Federal de São Carlos, 13565-905 São Carlos, SP, Brazil
| | - Kenia L Vanzolini
- Separare-Nucleo de Pesquisa em Cromatografia, Departamento de Química, Universidade Federal de São Carlos, 13565-905 São Carlos, SP, Brazil
| | - Marcela C de Moraes
- Separare-Nucleo de Pesquisa em Cromatografia, Departamento de Química, Universidade Federal de São Carlos, 13565-905 São Carlos, SP, Brazil; Departamento de Química Orgânica, Instituto de Química, Universidade Federal Fluminense, 24020-141 Niterói, RJ, Brazil
| | - Arlene G Corrêa
- Laboratório de Síntese de Produtos Naturais-LSPN, Departamento de Química, Universidade Federal de São Carlos, 13565-905 São Carlos, SP, Brazil.
| | - Quezia B Cass
- Separare-Nucleo de Pesquisa em Cromatografia, Departamento de Química, Universidade Federal de São Carlos, 13565-905 São Carlos, SP, Brazil.
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Reed MC, Nijhout HF, Best JA. Mathematical insights into the effects of levodopa. Front Integr Neurosci 2012; 6:21. [PMID: 22783173 PMCID: PMC3389445 DOI: 10.3389/fnint.2012.00021] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2012] [Accepted: 04/28/2012] [Indexed: 12/17/2022] Open
Abstract
Parkinson’s disease has been traditionally thought of as a dopaminergic disease in which cells of the substantia nigra pars compacta (SNc) die. However, accumulating evidence implies an important role for the serotonergic system in Parkinson’s disease in general and in physiological responses to levodopa therapy, the first line of treatment. We use a mathematical model to investigate the consequences of levodopa therapy on the serotonergic system and on the pulsatile release of dopamine (DA) from dopaminergic and serotonergic terminals in the striatum. Levodopa competes with tyrosine and tryptophan at the blood-brain barrier and is taken up by serotonin neurons in which it competes for aromatic amino acid decarboxylase. The DA produced competes with serotonin (5HT) for packaging into vesicles. We predict the time courses of LD, cytosolic DA, and vesicular DA in 5HT neurons during an LD dose. We predict the time courses of DA and 5HT release from 5HT cell bodies and 5HT terminals as well as the changes in 5HT firing rate due to lower 5HT release. We compute the time course of DA release in the striatum from both 5HT and DA neurons and show how the time course changes as more and more SNc cells die. This enables us to explain the shortening of the therapeutic time window for the efficacy of levodopa as Parkinson’s disease progresses. Finally, we study the effects 5HT1a and 5HT1b autoreceptor agonists and explain why they have a synergistic effect and why they lengthen the therapeutic time window for LD therapy. Our results are consistent with and help explain results in the experimental literature and provide new predictions that can be tested experimentally.
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Affiliation(s)
- Michael C Reed
- Department of Mathematics, Duke University Durham, NC, USA
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Olsson E, Martinez A, Teigen K, Jensen VR. Substrate Hydroxylation by the Oxido-Iron Intermediate in Aromatic Amino Acid Hydroxylases: A DFT Mechanistic Study. Eur J Inorg Chem 2011. [DOI: 10.1002/ejic.201001218] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Abstract
The molybdenum cofactor is composed of a molybdenum coordinated by one or two rather complicated ligands known as either molybdopterin or pyranopterin. Pterin is one of a large family of bicyclic N-heterocycles called pteridines. Such molecules are widely found in Nature, having various forms to perform a variety of biological functions. This article describes the basic nomenclature of pterin, their biological roles, structure, chemical synthesis and redox reactivity. In addition, the biosynthesis of pterins and current models of the molybdenum cofactor are discussed.
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Affiliation(s)
- Partha Basu
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, PA 15282, United States
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Best J, Nijhout HF, Reed M. Serotonin synthesis, release and reuptake in terminals: a mathematical model. Theor Biol Med Model 2010; 7:34. [PMID: 20723248 PMCID: PMC2942809 DOI: 10.1186/1742-4682-7-34] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2010] [Accepted: 08/19/2010] [Indexed: 12/14/2022] Open
Abstract
BACKGROUND Serotonin is a neurotransmitter that has been linked to a wide variety of behaviors including feeding and body-weight regulation, social hierarchies, aggression and suicidality, obsessive compulsive disorder, alcoholism, anxiety, and affective disorders. Full understanding of serotonergic systems in the central nervous system involves genomics, neurochemistry, electrophysiology, and behavior. Though associations have been found between functions at these different levels, in most cases the causal mechanisms are unknown. The scientific issues are daunting but important for human health because of the use of selective serotonin reuptake inhibitors and other pharmacological agents to treat disorders in the serotonergic signaling system. METHODS We construct a mathematical model of serotonin synthesis, release, and reuptake in a single serotonergic neuron terminal. The model includes the effects of autoreceptors, the transport of tryptophan into the terminal, and the metabolism of serotonin, as well as the dependence of release on the firing rate. The model is based on real physiology determined experimentally and is compared to experimental data. RESULTS We compare the variations in serotonin and dopamine synthesis due to meals and find that dopamine synthesis is insensitive to the availability of tyrosine but serotonin synthesis is sensitive to the availability of tryptophan. We conduct in silico experiments on the clearance of extracellular serotonin, normally and in the presence of fluoxetine, and compare to experimental data. We study the effects of various polymorphisms in the genes for the serotonin transporter and for tryptophan hydroxylase on synthesis, release, and reuptake. We find that, because of the homeostatic feedback mechanisms of the autoreceptors, the polymorphisms have smaller effects than one expects. We compute the expected steady concentrations of serotonin transporter knockout mice and compare to experimental data. Finally, we study how the properties of the the serotonin transporter and the autoreceptors give rise to the time courses of extracellular serotonin in various projection regions after a dose of fluoxetine. CONCLUSIONS Serotonergic systems must respond robustly to important biological signals, while at the same time maintaining homeostasis in the face of normal biological fluctuations in inputs, expression levels, and firing rates. This is accomplished through the cooperative effect of many different homeostatic mechanisms including special properties of the serotonin transporters and the serotonin autoreceptors. Many difficult questions remain in order to fully understand how serotonin biochemistry affects serotonin electrophysiology and vice versa, and how both are changed in the presence of selective serotonin reuptake inhibitors. Mathematical models are useful tools for investigating some of these questions.
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Affiliation(s)
- Janet Best
- Department of Mathematics, The Ohio State University, Columbus, OH 43210 USA
| | | | - Michael Reed
- Department of Mathematics, Duke University, Durham, NC 27708 USA
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8
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Melanogenesis inhibition by tetrahydropterines. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2009; 1794:1766-74. [DOI: 10.1016/j.bbapap.2009.08.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/07/2009] [Revised: 07/21/2009] [Accepted: 08/07/2009] [Indexed: 11/20/2022]
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Best JA, Nijhout HF, Reed MC. Homeostatic mechanisms in dopamine synthesis and release: a mathematical model. Theor Biol Med Model 2009; 6:21. [PMID: 19740446 PMCID: PMC2755466 DOI: 10.1186/1742-4682-6-21] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2009] [Accepted: 09/10/2009] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Dopamine is a catecholamine that is used as a neurotransmitter both in the periphery and in the central nervous system. Dysfunction in various dopaminergic systems is known to be associated with various disorders, including schizophrenia, Parkinson's disease, and Tourette's syndrome. Furthermore, microdialysis studies have shown that addictive drugs increase extracellular dopamine and brain imaging has shown a correlation between euphoria and psycho-stimulant-induced increases in extracellular dopamine 1. These consequences of dopamine dysfunction indicate the importance of maintaining dopamine functionality through homeostatic mechanisms that have been attributed to the delicate balance between synthesis, storage, release, metabolism, and reuptake. METHODS We construct a mathematical model of dopamine synthesis, release, and reuptake and use it to study homeostasis in single dopaminergic neuron terminals. We investigate the substrate inhibition of tyrosine hydroxylase by tyrosine, the consequences of the rapid uptake of extracellular dopamine by the dopamine transporters, and the effects of the autoreceoptors on dopaminergic function. The main focus is to understand the regulation and control of synthesis and release and to explicate and interpret experimental findings. RESULTS We show that the substrate inhibition of tyrosine hydroxylase by tyrosine stabilizes cytosolic and vesicular dopamine against changes in tyrosine availability due to meals. We find that the autoreceptors dampen the fluctuations in extracellular dopamine caused by changes in tyrosine hydroxylase expression and changes in the rate of firing. We show that short bursts of action potentials create significant dopamine signals against the background of tonic firing. We explain the observed time courses of extracellular dopamine responses to stimulation in wild type mice and mice that have genetically altered dopamine transporter densities and the observed half-lives of extracellular dopamine under various treatment protocols. CONCLUSION Dopaminergic systems must respond robustly to important biological signals such as bursts, while at the same time maintaining homeostasis in the face of normal biological fluctuations in inputs, expression levels, and firing rates. This is accomplished through the cooperative effect of many different homeostatic mechanisms including special properties of tyrosine hydroxylase, the dopamine transporters, and the dopamine autoreceptors.
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Affiliation(s)
- Janet A Best
- Department of Mathematics, The Ohio State University, Columbus, OH 43210, USA
| | | | - Michael C Reed
- Department of Mathematics, Duke University, Durham, NC 27708, USA
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Rajagopalan KV. Novel aspects of the biochemistry of the molybdenum cofactor. ADVANCES IN ENZYMOLOGY AND RELATED AREAS OF MOLECULAR BIOLOGY 2006; 64:215-90. [PMID: 2053467 DOI: 10.1002/9780470123102.ch5] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- K V Rajagopalan
- Department of Biochemistry, Duke University Medical Center, Durham, North Carolina
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11
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Hagedoorn PL, Schmidt PP, Andersson KK, Hagen WR, Flatmark T, Martínez A. The effect of substrate, dihydrobiopterin, and dopamine on the EPR spectroscopic properties and the midpoint potential of the catalytic iron in recombinant human phenylalanine hydroxylase. J Biol Chem 2001; 276:22850-6. [PMID: 11301319 DOI: 10.1074/jbc.m009458200] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phenylalanine hydroxylase (PAH) is a tetrahydrobiopterin (BH(4)) and non-heme iron-dependent enzyme that hydroxylates L-Phe to L-Tyr. The paramagnetic ferric iron at the active site of recombinant human PAH (hPAH) and its midpoint potential at pH 7.25 (E(m)(Fe(III)/Fe(II))) were studied by EPR spectroscopy. Similar EPR spectra were obtained for the tetrameric wild-type (wt-hPAH) and the dimeric truncated hPAH(Gly(103)-Gln(428)) corresponding to the "catalytic domain." A rhombic high spin Fe(III) signal with a g value of 4.3 dominates the EPR spectra at 3.6 K of both enzyme forms. An E(m) = +207 +/- 10 mV was measured for the iron in wt-hPAH, which seems to be adequate for a thermodynamically feasible electron transfer from BH(4) (E(m) (quinonoid-BH(2)/BH(4)) = +174 mV). The broad EPR features from g = 9.7-4.3 in the spectra of the ligand-free enzyme decreased in intensity upon the addition of L-Phe, whereas more axial type signals were observed upon binding of 7,8-dihydrobiopterin (BH(2)), the stable oxidized form of BH(4), and of dopamine. All three ligands induced a decrease in the E(m) value of the iron to +123 +/- 4 mV (L-Phe), +110 +/- 20 mV (BH(2)), and -8 +/- 9 mV (dopamine). On the basis of these data we have calculated that the binding affinities of L-Phe, BH(2), and dopamine decrease by 28-, 47-, and 5040-fold, respectively, for the reduced ferrous form of the enzyme, with respect to the ferric form. Interestingly, an E(m) value comparable with that of the ligand-free, resting form of wt-hPAH, i.e. +191 +/- 11 mV, was measured upon the simultaneous binding of both L-Phe and BH(2), representing an inactive model for the iron environment under turnover conditions. Our findings provide new information on the redox properties of the active site iron relevant for the understanding of the reductive activation of the enzyme and the catalytic mechanism.
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Affiliation(s)
- P L Hagedoorn
- Kluyver Department of Biotechnology, Delft University of Technology, Julianalaan 67, 2628 BC Delft, The Netherlands
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12
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Diaminomethyleneaminocarbonyldinitromethane, formed during the preparation of 2-amino-6-chloro-5-nitro-4(3H)-pyrimidinone by nitration of 2-amino-6-chloro-4(3H)-pyrimidinone. Tetrahedron Lett 2001. [DOI: 10.1016/s0040-4039(00)02360-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Teigen K, Frøystein NA, Martínez A. The structural basis of the recognition of phenylalanine and pterin cofactors by phenylalanine hydroxylase: implications for the catalytic mechanism. J Mol Biol 1999; 294:807-23. [PMID: 10610798 DOI: 10.1006/jmbi.1999.3288] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Phenylalanine hydroxylase (PAH) is a tetrahydrobiopterin and non-heme iron-dependent enzyme that hydroxylates L-Phe to l-Tyr using molecular oxygen as additional substrate. A dysfunction of this enzyme leads to phenylketonuria (PKU). 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. The resulting bound conformers of both ligands have been fitted into the crystal structure of the catalytic domain by molecular docking. In the docked structure L-Phe binds to the enzyme through interactions with Arg270, Ser349 and Trp326. 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. The pterin ring of BH2 pi-stacks with Phe254, and the N3 and the amine group at C2 hydrogen bond with the carboxylic group of Glu286. The ring also establishes specific contacts with His264 and Leu249. The distance between the O4 atom of BH2 and the iron (2.6(+/-0.3) A) is compatible with coordination, a finding that is important for the understanding of the mechanism of the enzyme. The hydroxyl groups in the side-chain at C6 hydrogen bond with the carbonyl group of Ala322 and the hydroxyl group of Ser251, an interaction that seems to have implications for the regulation of the enzyme by substrate and cofactor. Some frequent mutations causing PKU are located at residues involved in substrate and cofactor binding. The sites for hydroxylation, C4 in L-Phe and C4a in the pterin are located at a distance of 4.2 and 4.3 A from the iron moiety, respectively, and at 6.3 A from each other. These distances are adequate for the intercalation of iron-coordinated molecular oxygen, in agreement with a mechanistic role of the iron moiety both in the binding and activation of dioxygen and in the hydroxylation reaction.
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Affiliation(s)
- K Teigen
- Department of Biochemistry and Molecular Biology, University of Bergen, Arstadveien 19, Bergen, N-5009, Norway
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14
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Affiliation(s)
- S W Bailey
- Department of Pharmacology, University of South Alabama, College of Medicine, Mobile 36688, USA
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15
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Affiliation(s)
- T. Joseph Kappock
- Department of Chemistry, Yale University, P.O. Box 208107 New Haven, Connecticut 06520-8107
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Døskeland AP, Martinez A, Knappskog PM, Flatmark T. Phosphorylation of recombinant human phenylalanine hydroxylase: effect on catalytic activity, substrate activation and protection against non-specific cleavage of the fusion protein by restriction protease. Biochem J 1996; 313 ( Pt 2):409-14. [PMID: 8573072 PMCID: PMC1216923 DOI: 10.1042/bj3130409] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The phosphorylation of human phenylalanine hydroxylase by cyclic AMP-dependent protein kinase was studied using recombinant enzyme expressed as a fusion protein in the pMAL system of Escherichia coli. Using the target sequence of the restriction protease enterokinase (Asp4-Lys) as the linker peptide, 100% full-length human phenylalanine hydroxylase was obtained on protease cleavage. The fusion protein and human phenylalanine hydroxylase were both phosphorylated at Ser-16 with a stoichiometry of 1 mol of Pi/mol of subunit. The rate of phosphorylation of human phenylalanine hydroxylase was inhibited about 40% by the cofactor tetrahydrobiopterin, and this inhibition was completely prevented by the simultaneous presence of L-phenylalanine (i.e. at turnover conditions). Phosphorylated enzyme revealed a 1.6-fold higher specific activity than the non-phosphorylated enzyme form, and it also required a lower concentration of L-Phe for substrate activation. Pre-incubation with L-Phe increased the specific activity of phenylalanine hydroxylase 2- to 4-fold, L-Phe acting with positive cooperativity. Thus, the basic catalytic and regulatory properties of recombinant human phenylalanine hydroxylase, as well as those observed for the enzyme as a fusion protein, are similar to those previously reported for the rat liver enzyme. When the target sequence of the restriction protease factor Xa (Ile-Glu-Gly-Arg) was used as the linker between maltose-binding protein and human phenylalanine hydroxylase, cleavage of the fusion protein gave a mixture of full-length hydroxylase and a truncated form of the enzyme lacking the 13 N-terminal residues. Interestingly, phosphorylation of the fusion protein, before exposure to factor Xa, almost completely protected against secondary cleavage by this restriction protease at Arg-13 of phenylalanine hydroxylase.
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Affiliation(s)
- A P Døskeland
- Department of Biochemistry and Molecular Biology, University of Bergen, Norway
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Holland JC, Linn CE, DiGiammarino E, Nichols R, Howell EE. Does R67 dihydrofolate reductase possess a proton donor? ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1993; 338:493-8. [PMID: 8304165 DOI: 10.1007/978-1-4615-2960-6_99] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- J C Holland
- Department of Biochemistry, University of Tennessee, Knoxville 37996-0840
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19
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Bailey SW, Boerth SR, Dillard SB, Ayling JE. The mechanism of cofactor regeneration during phenylalanine hydroxylation. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1993; 338:47-54. [PMID: 8304161 DOI: 10.1007/978-1-4615-2960-6_9] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- S W Bailey
- Department of Pharmacology, College of Medicine, University of South Alabama, Mobile 36688
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20
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Characterization and nucleotide binding properties of a mutant dihydropteridine reductase containing an aspartate 37-isoleucine replacement. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(19)49538-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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21
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Bailey SW, Dillard SB, Ayling JE. Role of C6 chirality of tetrahydropterin cofactor in catalysis and regulation of tyrosine and phenylalanine hydroxylases. Biochemistry 1991; 30:10226-35. [PMID: 1681899 DOI: 10.1021/bi00106a022] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The chiral specificities of bovine striatal tyrosine hydroxylase (TH) (unphosphorylated and phosphorylated by cAMP-dependent protein kinase) and rat liver phenylalanine hydroxylase (PH) were examined at physiological pH using the pure C6 stereoisomers of 6-methyl- and 6-propyl-5,6,7,8-tetrahydropterin (6-methyl-PH4 and 6-propyl-PH4) and (6R)- and (6S)-tetrahydrobiopterin (BH4). Both PH and phosphorylated TH have substantially higher Vmax values with the unnatural (6R)-propyl-PH4 than the natural (6S)-propyl-PH4 (approximately 6- and 11-fold, respectively). However, the Km's are also higher such that Vmax/Km is almost unaffected by C6 chirality. Unphosphorylated TH has equal Km values for both isomers of 6-propyl-PH4, but has about a 6 times greater Vmax with the unnatural isomer, making it the fastest cofactor yet for this form of the enzyme. With the shorter 6-methyl group, chiral differences are still recognized by phosphorylated TH but hardly at all by PH. Inhibition of both PH and TH by amino acid substrate which occurs with (6R)-BH4 as cofactor is also observed with (6S)-propyl-PH4 but not with (6S)-BH4, (6R)-propyl-PH4, or (6R)- or (6R,S)-methyl-PH4. The Km for (6S)-BH4 with phosphorylated TH is nearly 3 times higher than with (6R)-BH4, but Vmax is unchanged. With unphosphorylated TH, (6S)-BH4 produces very low decelerating rates, which was shown not to be due to irreversible inactivation of the enzyme. The Km for (6R)-BH4 with either hydroxylase is 10 times higher than for the equivalently configured (6S)-propyl-PH4. Comparison of these two cofactors reveals that the 1' and 2' side-chain hydroxyl groups of the natural cofactor promote different regulatory functions in PH than in TH.
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Affiliation(s)
- S W Bailey
- Department of Pharmacology, College of Medicine, University of South Alabama, Mobile 36688
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22
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Gardlik S, Rajagopalan KV. The state of reduction of molybdopterin in xanthine oxidase and sulfite oxidase. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(19)38265-1] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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23
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Evidence for the Formation of the 4a-Carbinolamine during the Tyrosine-dependent Oxidation of Tetrahydrobiopterin by Rat Liver Phenylalanine Hydroxylase. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(18)81832-4] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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24
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Kwee S. Reactions of tetrahydropterins with oxygen and with other one-electron acceptors. ACTA ACUST UNITED AC 1987. [DOI: 10.1016/0302-4598(87)85010-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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25
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Shahbaz M, Hoch JA, Trach KA, Hural JA, Webber S, Whiteley JM. Structural studies and isolation of cDNA clones providing the complete sequence of rat liver dihydropteridine reductase. J Biol Chem 1987. [DOI: 10.1016/s0021-9258(18)49271-x] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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26
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Døskeland AP, Haavik J, Flatmark T, Døskeland SO. Modulation by pterins of the phosphorylation and phenylalanine activation of phenylalanine 4-mono-oxygenase. Biochem J 1987; 242:867-74. [PMID: 3036104 PMCID: PMC1147789 DOI: 10.1042/bj2420867] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The interaction between phenylalanine 4-mono-oxygenase and analogues of the natural cofactor (6R)-tetrahydrobiopterin [(6R)-BH4] was studied. The rate of cyclic AMP-dependent phosphorylation of phenylalanine 4-mono-oxygenase was inhibited only by those pterins [(6R)-BH4, (6S)-BH4 and 7,8-dihydrobiopterin (BH2)] that were able to decrease the potency and efficiency of phenylalanine as an allosteric activator of the hydroxylase. Since BH2 lacks cofactor activity, this was not required to modulate either the phosphorylation or the phenylalanine-activation of the hydroxylase. Half-maximal inhibition of the phosphorylation was observed at 1.9 microM-(6R)-BH4, 9 microM-(6S)-BH4 and 17 microM-BH2. Competition experiments indicated that all three pterins acted through binding to the cofactor site of the hydroxylase. Since the phosphorylation site and the cofactor binding site are known to reside, respectively, in the N- and C-terminal domains of the hydroxylase, the pterins were able to induce an interdomain conformational change. BH2, whose dihydroxypropyl group is not subject to epimerization, and (6S)-BH4 both inhibited the phosphorylation less efficiently than did the (6R)-epimer of BH4. Pterins with different spatial arrangements of the dihydroxypropyl side chain thus appeared to elicit different conformations of the phosphorylation site. The hydroxylase reaction showed a higher apparent Km for (6S)-BH4 than for (6R)-BH4 both when the native and the phenylalanine-activated enzyme were tested. For the activated enzyme Vmax was 40% lower with the (6S)-epimer than the (6R)-epimer, also when the more rapid enzyme inactivation occurring with the former cofactor was taken into account.
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27
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Duch DS, Bowers SW, Woolf JH, Davisson MT, Maltais LJ, Nichol CA. Differences in the metabolism of the aromatic amino acid hydroxylase cofactor, tetrahydrobiopterin, in mutant mice with neurological and immunological defects. Biochem Genet 1986; 24:657-68. [PMID: 3778424 DOI: 10.1007/bf00499000] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Tetrahydrobiopterin (BH4) levels and GTP cyclohydrolase activity (GTP-CH) were measured in tissues from mutants and controls of 24 different mouse strains to identify mutants that might be suitable models for diseases which are characterized by a deficiency of the biopterin cofactor, such as parkinsonism and atypical phenylketonuria. BH4 levels and GTP-CH activity were determined in brain, liver, and spleen obtained from 24 mutants with neurological or immunological defects. BH4 levels in brain were slightly but significantly decreased in only two mutants, spastic (spa) and jittery (ji), while GTP-CH activity in brain was not significantly lower than controls in any of the strains examined. GTP-CH levels in liver were significantly decreased in four mutant strains (jittery, ji; leaner, tgla; reeler, rl; and anorexia, anx); however, BH4 levels were significantly lower only in the mutant anorexia (anx). The most significant and widespread changes in both BH4 levels and GTP-CH activity were observed in spleen. In those mutants which were most affected, BH4 levels and GTP-CH activity were decreased 85-90%.
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Pike DC, Hora MT, Bailey SW, Ayling JE. Pyrimidodiazepine, a ring-strained cofactor for phenylalanine hydroxylase. Biochemistry 1986; 25:4762-71. [PMID: 3768311 DOI: 10.1021/bi00365a007] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Homologues of 6-methyl-7,8-dihydropterin (6-Me-7,8-PH2) and 6-methyl-5,6,7,8-tetrahydropterin (6-Me-PH4), expanded in the pyrazine ring, were synthesized to determine the effect of increased strain on the chemical and enzymatic properties of the pyrimidodiazepine series. 2-Amino-4-keto-6-methyl-7,8-dihydro-3H,9H-pyrimido[4,5-b] [1,4]diazepine (6-Me-7,8-PDH2) was found to be more unstable in neutral solution than 6-Me-7,8-PH2. Its decomposition appears to proceed by hydrolytic ring opening of the 5,6-imine bond, followed by autooxidation. 6-Me-7,8-PDH2 can be reduced, either chemically or by dihydrofolate reductase (Km = 0.16 mM), to the 5,6,7,8-tetrahydro form (6-Me-PDH4). This can be oxidized with halogen to quinoid dihydropyrimidodiazepine (quinoid 6-Me-PDH2), which is a substrate for dihydropteridine reductase (Km = 33 microM). Whereas quinoid 6-methyldihydropterin was found to tautomerize to 6-Me-7,8-PH2 in 95% yield in 0.1 M tris(hydroxymethyl)aminomethane hydrochloride (Tris-HCl), pH 7.4, quinoid 6-Me-PDH2 gives only 53% 6-Me-7,8-PDH2, the remainder decomposing via an initial opening of the diazepine ring. Additional evidence for the extra strain in the pyrimidodiazepine system is the cyclization of quinoid 6-N-(2'-aminopropyl)divicine to quinoid 6-Me-PH2 in 57% yield in 0.1 M Tris-HCl, pH 7.4. By comparison, no quinoid 6-Me-PDH2 is formed from the homologue quinoid 6-N-(3'-aminobutyl)divicine. A small (2%) yield of 6-Me-PDH4 is found if the unstable C4a-carbinolamine intermediate is trapped by enzymatic dehydration and reduction. Although phenylalanine hydroxylase utilizes 6-Me-PDH4 (Km = 0.15 mM), the maximum velocity of tyrosine production is 20 times slower than that with 6-Me-PH4, indicating that a ring opening reaction is not a rate-limiting step in the hydroxylase pathway. Further, the maximum velocities of 2,5,6-triamino-4(3H)-pyrimidinone, 2,6-diamino-5-(methylamino)-4(3H)-pyrimidinone, and 2,6-diamino-5-(benzylamino)-4(3H)-pyrimidinone span a 35-fold range. These cofactors would theoretically form the same oxide of quinoid divicine if oxygen activation involves a carbonyl oxide intermediate. Thus, the limiting step is also not transfer of oxygen from this hypothetical intermediate to the phenylalanine substrate.
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29
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Webber S, Hural JA, Whiteley JM. Multiple forms of rat-liver dihydropteridine reductase identified by their differing isoelectric points. Arch Biochem Biophys 1986; 248:358-67. [PMID: 3729422 DOI: 10.1016/0003-9861(86)90432-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Purified rat-liver dihydropteridine reductase is homogeneous by gel filtration (Mr approximately 51,000), sodium dodecyl sulfate-polyacrylamide gel electrophoresis (Mr approximately 25,500), and native polyacrylamide gel electrophoresis, suggesting that the enzyme is composed of two identical subunits. However, analysis by isoelectric focusing has revealed three enzyme forms with approximate isoelectric points of 6.5, 5.9, and 5.7 (designated forms, I, II, and III, respectively). The three forms, isolated in 65% yield by preparative chromatofocusing, are stable in 0.05 M phosphate buffer, pH 6.8, containing 1 mM beta-mercaptoethanol and exhibit similar kinetic constants when the catalytic activities of the isolated forms are compared with quinonoid dihydrobiopterin as substrate. All forms generate complexes with the enzymatic cofactor NADH which are also detectable by IEF. When examined further by IEF under denaturing conditions in 6 M urea the enzyme demonstrates a differing subunit composition for its three forms. Two distinct subunits, designated alpha and beta, can be identified, and additional evidence suggests that the native enzyme forms I, II, and III represent the three differing dimeric combinations alpha alpha (form I), alpha beta (form II), and beta beta (form III).
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Armarego WL, Ohnishi A, Taguchi H. New pteridine substrates for dihydropteridine reductase and horseradish peroxidase. Biochem J 1986; 234:335-42. [PMID: 3718470 PMCID: PMC1146570 DOI: 10.1042/bj2340335] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The oxidation of 4,5-diaminopyrimidin-6(1H)-one, 5,6,7,8-tetrahydropteridin-4(3H)-one, its 6-methyl and cis-6,7-dimethyl derivatives, and 6-methyl- and cis-6-7-dimethyl-5,6,7,8-tetrahydropterins, by horseradish peroxidase/H2O2 is enzymic and follows Michaelis-Menten kinetics, and its Km and kcat. values were determined. This oxidation of 5,6,7,8-tetrahydropterins produces quinonoid dihydropterins of established structure, and they are known to be specific substrates for dihydropteridine reductase. By analogy the peroxidase/H2O2 oxidation of the 5,6,7,8-tetrahydropteridin-4(3H)-ones should produce similar quinonoid dihydro species. The quinonoid species derived from 5,6,7,8-tetrahydropteridin-4(3H)-one and its 6-methyl and cis-6,7-dimethyl derivatives are shown to be viable substrates for human brain dihydropteridine reductase, and apparent Km and Vmax. values are reported.
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31
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Matthews DA, Webber S, Whiteley JM. Preliminary x-ray diffraction characterization of crystalline rat liver dihydropteridine reductase. J Biol Chem 1986. [DOI: 10.1016/s0021-9258(17)35730-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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32
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Noar J, Venkataram U, Bruice TC, Bollag G, Whittle R, Sammons D, Henry R, Benkovic SJ. The reaction of nucleophilic species with quinonoid 6,6,7,7-tetramethyldihydropterin. Bioorg Chem 1986. [DOI: 10.1016/0045-2068(86)90014-3] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Abstract
A model for tetrahydrobiopterin deficiency in mice is described. Elevated levels of phenylalanine produced in the model were shown to be dramatically reduced after injection of tetrahydrobiopterin. A comparison of several reduced pterins for their efficacy in the system is described. The unnatural S isomer of tetrahydrobiopterin was shown to be active in the system.
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Randles D, Armarego WL. Reduced 6,6,8-trimethylpterins. Preparation, properties and enzymic reactivities with dihydropteridine reductase, phenylalanine hydroxylase and tyrosine hydroxylase. EUROPEAN JOURNAL OF BIOCHEMISTRY 1985; 146:467-74. [PMID: 2857123 DOI: 10.1111/j.1432-1033.1985.tb08674.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The substrates of dihydropteridine reductase (EC 1.6.99.7), quinonoid 7,8-dihydro(6 H)pterins, are unstable and decompose in various ways. In attempting to prepare a more stable substrate, 6,6,8-trimethyl-5,6,7,8-tetrahydro(3 H)pterin was synthesised and the quinonoid 6,6,8-trimethyl-7,8-dihydro(6 H)pterin derived from it is extremely stable with a half-life in 0.1 M Tris/HCl (pH 7.6, 25 degrees C) of 33 h. Quinonoid 6,6,8-trimethyl-7,8-dihydro(6 H)pterin is not a substrate for dihydropteridine reductase but it is reduced non-enzymically by NADH at a significant rate and it is a weak inhibitor of the enzyme: I50 200 microM, pH 7.6, 25 degrees C when using quinonoid 6-methyl-7,8-dihydro(6 H)pterin as substrate. 6,6,8-Trimethyl-5,6,7,8-tetrahydropterin is a cofactor for phenylalanine hydroxylase (EC 1.14.16.1) with an apparent Km of 0.33 mM, but no cofactor activity could be detected with tyrosine hydroxylase (EC 1.14.16.2). Its phenylalanine hydroxylase activity, together with the enhanced stability of quinonoid 6,6,8-trimethyl-7,8-dihydro(6 H)pterin, suggest that it may have potential for the treatment of variant forms of phenylketonuria.
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Armarego WL, Randles D, Waring P. Dihydropteridine reductase (DHPR), its cofactors, and its mode of action. Med Res Rev 1984; 4:267-321. [PMID: 6379341 DOI: 10.1002/med.2610040302] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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