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Ellis HR, McCusker KP, Fitzpatrick PF. Use of a tyrosine hydroxylase mutant enzyme with reduced metal affinity allows detection of activity with cobalt in place of iron. Arch Biochem Biophys 2002; 408:305-7. [PMID: 12464285 DOI: 10.1016/s0003-9861(02)00568-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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102
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Sobrado P, Fitzpatrick PF. Analysis of the roles of amino acid residues in the flavoprotein tryptophan 2-monooxygenase modified by 2-oxo-3-pentynoate: characterization of His338, Cys339, and Cys511 mutant enzymes. Arch Biochem Biophys 2002; 402:24-30. [PMID: 12051679 DOI: 10.1016/s0003-9861(02)00063-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The flavoprotein tryptophan 2-monooxygenase catalyzes the oxidative decarboxylation of tryptophan to indoleacetamide. His338, Cys339, and Cys511 of the Pseudomonas savastanoi enzyme were previously identified as possible active-site residues by modification with 2-oxo-3-pentynoate ([G. Gadda, L.J. Dangott, W.H. Johnson Jr., C.P. Whitman, P.F. Fitzpatrick, Biochemistry 38 (1999) 5822-5828]). The H338N, C339A, and C511S enzymes have been characterized to determine the roles of these residues in catalysis. The steady-state kinetic parameters with both tryptophan and methionine decrease only slightly in the case of the H338N and C339A enzymes; the decrease in activity is greater for the C511S enzyme. Only in the case of the C511S enzyme do deuterium kinetic isotope effects on kinetic parameters indicate a significant change in catalytic rates. The structural bases for the effects of the mutations can be interpreted by identification of L-amino acid oxidase and tryptophan monooxygenase as homologous proteins.
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103
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Fitzpatrick PF. Kinetic Isotope Effects on Hydroxylation of Ring-Deuterated Phenylalanines by Tyrosine Hydroxylase Provide Evidence against Partitioning of an Arene Oxide Intermediate. J Am Chem Soc 2002. [DOI: 10.1021/ja00082a046] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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104
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Fitzpatrick PF, Villafranca JJ. Mechanism-based inhibitors of dopamine .beta.-hydroxylase containing acetylenic or cyclopropyl groups. J Am Chem Soc 2002. [DOI: 10.1021/ja00303a048] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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105
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Frantom PA, Pongdee R, Sulikowski GA, Fitzpatrick PF. Intrinsic deuterium isotope effects on benzylic hydroxylation by tyrosine hydroxylase. J Am Chem Soc 2002; 124:4202-3. [PMID: 11960436 DOI: 10.1021/ja025602s] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Tyrosine hydroxylase (TyrH) is a mononuclear, non-heme iron monooxygenase that catalyzes the pterin-dependent hydroxylation of tyrosine to dihydroxyphenylalanine. When 4-methylphenylalanine is used as a substrate for TyrH, 4-hydroxymethylphenylalanine is one of the amino acid products. To examine the mechanism of benzylic hydroxylation, the products and their isotopic compositions were determined with 4-methylphenylalanines containing a mono-, di-, or trideuterated methyl group as substrates. Intrinsic primary and secondary deuterium isotope effects for benzylic hydroxylation of 9.6 +/- 0.9 and 1.21 +/- 0.08, respectively, were derived from the data. The magnitudes of these isotope effects are consistent with quantum mechanical tunneling of the hydrogen. The similarity of the effects to those seen for benzylic hydroxylation by other enzymes supports a mechanism where a high valence iron-oxo species, Fe(IV)=O, is the hydroxylating intermediate.
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106
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Daubner SC, Moran GR, Fitzpatrick PF. Role of tryptophan hydroxylase phe313 in determining substrate specificity. Biochem Biophys Res Commun 2002; 292:639-41. [PMID: 11922614 DOI: 10.1006/bbrc.2002.6719] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The active site residue phenylalanine 313 is conserved in the sequences of all known tryptophan hydroxylases. The tryptophan hydroxylase F313W mutant protein no longer shows a preference for tryptophan over phenylalanine as a substrate, consistent with a role of this residue in substrate specificity. A tryptophan residue occupies the homologous position in tyrosine hydroxylase. The tyrosine hydroxylase W372F mutant enzyme does not show an increased preference for tryptophan over tyrosine or phenylalanine, so that this residue cannot be considered the dominant factor in substrate specificity in this family of enzymes.
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107
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Daubner SC, Gadda G, Valley MP, Fitzpatrick PF. Cloning of nitroalkane oxidase from Fusarium oxysporum identifies a new member of the acyl-CoA dehydrogenase superfamily. Proc Natl Acad Sci U S A 2002; 99:2702-7. [PMID: 11867731 PMCID: PMC122411 DOI: 10.1073/pnas.052527799] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The flavoprotein nitroalkane oxidase (NAO) from Fusarium oxysporum catalyzes the oxidation of nitroalkanes to the respective aldehydes with production of nitrite and hydrogen peroxide. The sequences of several peptides from the fungal enzyme were used to design oligonucleotides for the isolation of a portion of the NAO gene from an F. oxysporum genomic DNA preparation. This sequence was used to clone the cDNA for NAO from an F. oxysporum cDNA library. The sequence of the cloned cDNA showed that NOA is a member of the acyl-CoA dehydrogenase (ACAD) superfamily. The members of this family share with NAO a mechanism that is initiated by proton removal from carbon, suggesting a common chemical reaction for this superfamily. NAO was expressed in Escherichia coli and the recombinant enzyme was characterized. Recombinant NAO has identical kinetic parameters to enzyme isolated from F. oxysporum but is isolated with oxidized FAD rather than the nitrobutyl-FAD found in the fungal enzyme. NAO purified from E. coli or from F. oxysporum has no detectable ACAD activity on short- or medium-chain acyl CoAs, and medium-chain acyl-CoA dehydrogenase and short-chain acyl-CoA dehydrogenase are unable to catalyze oxidation of nitroalkanes.
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108
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Gadda G, Banerjee A, Fleming GS, Fitzpatrick PF. Evidence for an essential arginine in the flavoprotein nitroalkane oxidase. JOURNAL OF ENZYME INHIBITION 2001; 16:157-63. [PMID: 11342284 DOI: 10.1080/14756360109162365] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
The flavoprotein nitroalkane oxidase from the fungus Fusarium oxysporum catalyzes the oxidative denitrification of primary or secondary nitroalkanes to yield the respective aldehydes or ketones, hydrogen peroxide and nitrite. The enzyme is inactivated in a time-dependent fashion upon treatment with the arginine-directed reagents phenylglyoxal, 2,3-butanedione, and cyclohexanedione. The inactivation shows first order kinetics with all reagents. Valerate, a competitive inhibitor of the enzyme, fully protects the enzyme from inactivation, indicating that modification is active site directed. The most rapid inactivation is seen with phenylglyoxal, with a k(inact) of 14.3 +/- 1.1 M(-1) min(-1) in phosphate buffer at pH 7.3 and 30 degrees C. The lack of increase in the enzymatic activity of the phenylglyoxal-inactivated enzyme after removing the unreacted reagent by gel filtration is consistent with inactivation being due to covalent modification of the enzyme. A possible role for an active site arginine in substrate binding is discussed.
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109
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McCulloch RI, Daubner SC, Fitzpatrick PF. Effects of substitution at serine 40 of tyrosine hydroxylase on catecholamine binding. Biochemistry 2001; 40:7273-8. [PMID: 11401575 DOI: 10.1021/bi010546d] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Phosphorylation of Ser40 in the regulatory domain of tyrosine hydroxylase activates the enzyme by increasing the rate of dissociation of inhibitory catecholamines [Ramsey, A. J., and Fitzpatrick, P. F. (1998) Biochemistry 37, 8980-8986]. To probe the structural basis for this effect and to ascertain the ability of other amino acids to functionally replace serine and serine phosphate, the effects of replacement of Ser40 with other amino acids were determined. Only minor changes in the Vmax value and the Km values for tyrosine and tetrahydropterin were seen upon replacement of Ser40 with alanine, valine, threonine, aspartate, or glutamate, in line with the minor effects of phosphorylation on steady-state kinetic parameters. More significant effects were seen on the binding of dopamine and dihydroxyphenylalanine. The affinity of the S40T enzyme for either catecholamine was very similar to that of the wild-type enzyme, while the S40E enzyme was similar to the phosphorylated enzyme. The S40D enzyme had an affinity for DOPA comparable to the phosphorylated enzyme but a higher affinity for dopamine than the latter. With both catecholamines, the S40V and S40A enzymes showed intermediate levels of activation. The results suggest that the serine hydroxyl contributes to the stabilization of the catecholamine-inhibited enzyme. In addition, the S40E enzyme will be useful in further studies of the effects of multiple phosphorylation on tyrosine hydroxylase, while the alanine enzyme does not provide an accurate mimic of the unphosphorylated enzyme.
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110
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Abstract
Enzymes with tightly bound FMN or FAD as cofactor catalyze the oxidation of a wide range of substrates. The chemical versatility of the isoalloxazine ring provides these enzymes with a range of potential mechanisms. Recent progress in elucidating the mechanisms of oxidation of organic substrates by flavoenzymes is described, focusing on the oxidation of alcohols, amino and hydroxy acids, amines, and nitroalkanes. With each family of enzymes, an attempt is made to integrate mechanistic, structural, and biomimetic data into a common catalytic mechanism.
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111
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Sobrado P, Daubner SC, Fitzpatrick PF. Probing the relative timing of hydrogen abstraction steps in the flavocytochrome b2 reaction with primary and solvent deuterium isotope effects and mutant enzymes. Biochemistry 2001; 40:994-1001. [PMID: 11170421 DOI: 10.1021/bi002283d] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Flavocytochrome b(2) catalyzes the oxidation of lactate to pyruvate. Primary deuterium and solvent kinetic isotope effects have been used to determine the relative timing of cleavage of the lactate O-H and C-H bonds by the wild-type enzyme, a mutant protein lacking the heme domain, and the D282N enzyme. The (D)V(max) and (D)(V/K(lactate)) values are both 3.0 with the wild-type enzyme at pH 7.5 and 25 degrees C, increasing to about 3.6 with the flavin domain and increasing further to about 4.5 with the D282N enzyme. Under these conditions, the (D20)V(max) values are 1.38, 1.18, and 0.98 for the wild-type enzyme, the flavin domain, and the D282N enzyme, respectively; the (D20)(V/K(lactate)) values are 0.9, 0.44, and 1.0, respectively. The (D)k(red) value is 5.4 for the wild-type enzyme and 3.5 for the flavin domain, whereas the solvent isotope effect on this kinetic parameter is 1.0 for both enzymes. The V(max) values for the wild-type enzyme and the flavin domain are 32 and 15% limited by viscosity, respectively. In contrast, the V/K(lactate) value for the flavin domain increases about 2-fold at moderate concentrations of glycerol. The data are consistent with a minimal chemical mechanism in which the lactate hydroxyl proton is not in flight in the transition state for C-H bond cleavage and there is an internal equilibrium involving the lactate-bound enzyme prior to C-H bond cleavage which is sensitive to solution conditions. Removal of the hydroxyl proton may occur in this pre-equilibrium.
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112
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Kurtz KA, Rishavy MA, Cleland WW, Fitzpatrick PF. Nitrogen Isotope Effects As Probes of the Mechanism ofd-Amino Acid Oxidase. J Am Chem Soc 2000. [DOI: 10.1021/ja002528+] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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113
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Gadda G, Banerjee A, Dangott LJ, Fitzpatrick PF. Identification of a cysteine residue in the active site of nitroalkane oxidase by modification with N-ethylmaleimide. J Biol Chem 2000; 275:31891-5. [PMID: 10913134 DOI: 10.1074/jbc.m003679200] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The flavoprotein nitroalkane oxidase catalyzes the oxidative denitrification of primary or secondary nitroalkanes to the corresponding aldehydes or ketones with production of hydrogen peroxide and nitrite. The enzyme is irreversibly inactivated by treatment with N-ethylmaleimide at pH 7. The inactivation is time-dependent and shows first-order kinetics for three half-lives. The second-order rate constant for inactivation is 3.4 +/- 0.06 m(-)(1) min(-)(1). The competitive inhibitor valerate protects the enzyme from inactivation, indicating an active site-directed modification. Comparison of tryptic maps of enzyme treated with N-[ethyl-1-(14)C]maleimide in the absence and presence of valerate shows a single radioactive peptide differentially labeled in the unprotected enzyme. The sequence of this peptide was determined to be LLNEVMCYPLFDGGNIGLR using Edman degradation and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The cysteine residue was identified as the site of alkylation by ion trap mass spectrometry.
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114
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Gadda G, Choe DY, Fitzpatrick PF. Use of pH and kinetic isotope effects to dissect the effects of substrate size on binding and catalysis by nitroalkane oxidase. Arch Biochem Biophys 2000; 382:138-44. [PMID: 11051107 DOI: 10.1006/abbi.2000.2009] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The flavoprotein nitroalkane oxidase catalyzes the oxidation of a broad range of primary and secondary nitroalkanes to the respective aldehydes or ketones, with production of hydrogen peroxide and nitrite. The V/K values for primary nitroalkanes increase with increasing chain length, reaching a maximum with 1-nitrobutane [Gadda, G., and Fitzpatrick, P. F. (1999) Arch. Biochem. Biophys. 363, 309-313]. In the present report, pH and deuterium kinetic isotope effects with a series of primary nitroalkanes and phenylnitromethane as substrates have been used to dissect the effects of chain length on binding and catalysis. The apparent pKa value for a group that must be unprotonated for catalysis decreases from about 7 to 5.3 with increasing size of the substrate. The D(V/K) values for these substrates decrease from 7.5 with nitroethane to 1 with phenylnitromethane. These results show that increasing the size of the substrate results in an increased partitioning forward to catalysis. The D(V/K) and DVmax values at pH 5.5 have been used to calculate the effect of substrate size on the Kd values for primary nitroalkanes. The Kd values decrease with increasing length of the substrate, with a deltadeltaG(binding) of 1.7 kcal mol(-1) for each additional methylene group. Such a value is less than the value of 2.6 kcal mol(-1) previously determined for the effect of a methylene group on the V/K value [Gadda, G., and Fitzpatrick, P. F. (1999) Arch. Biochem. Biophys. 363, 309-313], suggesting that the total energy available per methylene group is used not only to enhance binding but also to increase the rate of catalysis.
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115
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Daubner SC, Melendez J, Fitzpatrick PF. Reversing the substrate specificities of phenylalanine and tyrosine hydroxylase: aspartate 425 of tyrosine hydroxylase is essential for L-DOPA formation. Biochemistry 2000; 39:9652-61. [PMID: 10933781 DOI: 10.1021/bi000493k] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The catalytic domains of the pterin-dependent enzymes phenylalanine hydroxylase and tyrosine hydroxylase are homologous, yet differ in their substrate specificities. To probe the structural basis for the differences in specificity, seven residues in the active site of phenylalanine hydroxylase whose side chains are dissimilar in the two enzymes were mutated to the corresponding residues in tyrosine hydroxylase. Analysis of the effects of the mutations on the isolated catalytic domain of phenylalanine hydroxylase identified three residues that contribute to the ability to hydroxylate tyrosine, His264, Tyr277, and Val379. These mutations were incorporated into full-length phenylalanine hydroxylase and the complementary mutations into tyrosine hydroxylase. The steady-state kinetic parameters of the mutated enzymes showed that the identity of the residue in tyrosine hydroxylase at the position corresponding to position 379 of phenylalanine hydroxylase is critical for dihydroxyphenylalanine formation. The relative specificity of tyrosine hydroxylase for phenylalanine versus tyrosine, as measured by the (V/K(phe))/(V/K(tyr)) value, increased by 80000-fold in the D425V enzyme. However, mutation of the corresponding valine 379 of phenylalanine hydroxylase to aspartate was not sufficient to allow phenylalanine hydroxylase to form dihydroxyphenylalanine at rates comparable to that of tyrosine hydroxylase. The double mutant V379D/H264Q PheH was the most active at tyrosine hydroxylation, showing a 3000-fold decrease in the (V/K(phe))/(V/K(tyr)) value.
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116
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Abstract
Phenylalanine hydroxylase, tyrosine hydroxylase, and tryptophan hydroxylase constitute a small family of monooxygenases that utilize tetrahydropterins as substrates. When from eukaryotic sources, these enzymes are composed of a homologous catalytic domain to which are attached discrete N-terminal regulatory domains and short C-terminal tetramerization domains, whereas the bacterial enzymes lack the N-terminal and C-terminal domains. Each enzyme contains a single ferrous iron atom bound to two histidines and a glutamate. Recent mechanistic studies have begun to provide insights into the mechanisms of oxygen activation and hydroxylation. Although the hydroxylating intermediate in these enzymes has not been identified, the iron is likely to be involved. Reversible phosphorylation of serine residues in the regulatory domains affects the activities of all three enzymes. In addition, phenylalanine hydroxylase is allosterically regulated by its substrates, phenylalanine and tetrahydrobiopterin.
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117
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Fitzpatrick PF. The aromatic amino acid hydroxylases. ADVANCES IN ENZYMOLOGY AND RELATED AREAS OF MOLECULAR BIOLOGY 2000; 74:235-94. [PMID: 10800597 DOI: 10.1002/9780470123201.ch6] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
Abstract
The enzymes phenylalanine hydroxylase, tyrosine hydroxylase, and tryptophan hydroxylase constitute the family of pterin-dependent aromatic amino acid hydroxylases. Each enzyme catalyzes the hydroxylation of the aromatic side chain of its respective amino acid substrate using molecular oxygen and a tetrahydropterin as substrates. Recent advances have provided insights into the structures, mechanisms, and regulation of these enzymes. The eukaryotic enzymes are homotetramers comprised of homologous catalytic domains and discrete regulatory domains. The ligands to the active site iron atom as well as residues involved in substrate binding have been identified from a combination of structural studies and site-directed mutagenesis. Mechanistic studies with nonphysiological and isotopically substituted substrates have provided details of the mechanism of hydroxylation. While the complex regulatory properties of phenylalanine and tyrosine hydroxylase are still not fully understood, effects of regulation on key kinetic parameters have been identified. Phenylalanine hydroxylase is regulated by an interaction between phosphorylation and allosteric regulation by substrates. Tyrosine hydroxylase is regulated by phosphorylation and feedback inhibition by catecholamines.
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118
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Hanna JN, Carney IK, Smith GA, Tannenberg AE, Deverill JE, Botha JA, Serafin IL, Harrower BJ, Fitzpatrick PF, Searle JW. Australian bat lyssavirus infection: a second human case, with a long incubation period. Med J Aust 2000; 172:597-9. [PMID: 10914106 DOI: 10.5694/j.1326-5377.2000.tb124126.x] [Citation(s) in RCA: 147] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
In December 1998, a 37-year-old Queensland woman died from a rabies-like illness, 27 months after being bitten by a flying fox (fruit bat). Molecular techniques enabled diagnosis of infection with Australian bat lyssavirus (ABL), the second human case to be recognised and the first to be acquired from a flying fox. It must be assumed that any bat in Australia could transmit ABL; anyone bitten or scratched by a bat should immediately wash the wounds thoroughly with soap and water and promptly seek medical advice.
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119
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Simonian AL, Rainina EI, Fitzpatrick PF, Wild J. Enhancement of the specificity of an enzyme-based biosensor for L-tryptophan. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2000; 467:833-40. [PMID: 10721137 DOI: 10.1007/978-1-4615-4709-9_106] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/15/2023]
Abstract
A new selective amperometric biosensor for reagentless L-tryptophan determination has been developed using immobilized tryptophan-2-monooxygenase (TMO, EC 1.13.12.3). This enzyme-based biosensor provides a rapid-response detection system for concentrations of L-tryptophan between 25 and 1,000 microM in a batch mode system and between 100 and 50,000 microM in a flow-injection mode. The response time was 30 seconds, and the total analysis time was less than 3 minutes. The biosensor retained catalytic activity and fidelity of phenylalanine and tryptophan response for greater than 4 months with repeated usage. The biosensor selectivity to L-tryptophan was dramatically increased relative to phenylalanine when a competitive inhibitor of TMO, indole acetamide (IA), was included. The biosensor was successfully used for L-tryptophan determination in nutrition broth, giving values identical to those determined by HPLC analysis.
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120
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Moran GR, Derecskei-Kovacs A, Hillas PJ, Fitzpatrick PF. On the Catalytic Mechanism of Tryptophan Hydroxylase. J Am Chem Soc 2000. [DOI: 10.1021/ja994479a] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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121
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Ellis HR, Daubner SC, Fitzpatrick PF. Mutation of serine 395 of tyrosine hydroxylase decouples oxygen-oxygen bond cleavage and tyrosine hydroxylation. Biochemistry 2000; 39:4174-81. [PMID: 10747809 DOI: 10.1021/bi9928546] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Ser395 and Ser396 in the active site of rat tyrosine hydroxylase are conserved in all three members of the family of pterin-dependent hydroxylases, phenylalanine hydroxylase, tyrosine hydroxylase, and tryptophan hydroxylase. Ser395 is appropriately positioned to form a hydrogen bond to the imidazole nitrogen of His331, an axial ligand to the active site iron, while Ser396 is located on the wall of the active site cleft. Site-directed mutagenesis has been used to analyze the roles of these two residues in catalysis. The specific activities for formation of dihydroxyphenylalanine by the S395A, S395T, and S396A enzymes are 1.3, 26, and 69% of the wild-type values, respectively. Both the S395A and S396A enzymes bind a stoichiometric amount of iron and exhibit wild-type spectra when complexed with dopamine. The K(M) values for tyrosine, 6-methyltetrahydropterin, and tetrahydrobiopterin are unaffected by replacement of either residue with alanine. Although the V(max) value for tyrosine hydroxylation by the S395A enzyme is decreased by 2 orders of magnitude, the V(max) value for tetrahydropterin oxidation by either the S395A or the S396A enzyme is unchanged from the wild-type value. With both mutant enzymes, there is quantitative formation of 4a-hydroxypterin from 6-methyltetrahydropterin. These results establish that Ser395 is required for amino acid hydroxylation but not for cleavage of the oxygen-oxygen bond, while Ser396 is not essential. These results also establish that cleavage of the oxygen-oxygen bond occurs in a separate step from amino acid hydroxylation.
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122
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Gadda G, Fitzpatrick PF. Iso-mechanism of nitroalkane oxidase: 1. Inhibition studies and activation by imidazole. Biochemistry 2000; 39:1400-5. [PMID: 10684620 DOI: 10.1021/bi9922547] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The flavoprotein nitroalkane oxidase catalyzes the oxidation of primary and secondary nitroalkanes to aldehydes and ketones, respectively, transferring electrons to oxygen to form hydrogen peroxide. The steady-state kinetic mechanism of the active flavin adenine dinucleotide-(FAD-) containing form of the enzyme has been determined with nitroethane at pH 7 to be bi-ter ping-pong, with oxygen reacting with the free reduced enzyme after release of the aldehyde product. The V(max) value is 5.5 +/- 0.3 s(-)(1) and the K(m) values for nitroethane and oxygen are 3.3 +/- 0.6 and 0.023 +/- 0.007 mM, respectively. The free reduced enzyme forms a dead-end complex with nitroethane, with a K(ai) value of 30 +/- 6 mM. Acetaldehyde and butyraldehyde are noncompetitive inhibitors versus nitroethane due to formation of a dead-end complex between the oxidized enzyme and the product. Acetaldehyde is an uncompetitive inhibitor versus oxygen, indicating that an irreversible isomerization of the free reduced enzyme occurs before the reaction with oxygen. Addition of unprotonated imidazole results in a 5-fold increase in the V(max) value, while the V/K values for nitroethane and oxygen are unaffected. A 5-fold increase in the K(ai) value for nitroethane and a 6.5-fold increase in the K(ii) value for butyraldehyde are observed in the presence of imidazole. These results are consistent with the isomerization of the free reduced enzyme being about 80% rate-limiting for catalysis and with a model in which unprotonated imidazole accelerates the rate of isomerization.
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123
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Gadda G, Fitzpatrick PF. Mechanism of nitroalkane oxidase: 2. pH and kinetic isotope effects. Biochemistry 2000; 39:1406-10. [PMID: 10684621 DOI: 10.1021/bi992255z] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Nitroalkane oxidase catalyzes the oxidation of nitroalkanes to aldehydes or ketones with production of nitrite and hydrogen peroxide. pH and kinetic isotope effects with [1, 1-(2)H(2)]nitroethane have been used to study the mechanism of this enzyme. The V/K(ne) pH profile is bell-shaped. A group with a pK(a) value of about 7 must be unprotonated and one with a pK(a) value of 9.5 must be protonated for catalysis. The lower pK(a) value is seen also in the pK(is) profile for the competitive inhibitor valerate, indicating that nitroethane has no significant external commitments to catalysis. The (D)(V/K)(ne) value is pH-independent with a value of 7.5, whereas the (D)V(max) value increases from 1.4 at pH 8.2 to a limiting value of 7.4 below pH 5. The V(max) pH profile decreases at low and high pH, with pK(a) values of 6.6 and 9.5, respectively. Imidazole, which activates the enzyme, affects the V(max) but not the V/K(ne) pH profile. In the presence of imidazole at pH 7 the (D)V(max) value increases to a value close to the intrinsic value, consistent with cleavage of the carbon-hydrogen bond of the substrate being fully rate-limiting for catalysis in the presence of imidazole.
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124
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Gadda G, Banerjee A, Fitzpatrick PF. Identification of an essential tyrosine residue in nitroalkane oxidase by modification with tetranitromethane. Biochemistry 2000; 39:1162-8. [PMID: 10653664 DOI: 10.1021/bi9921743] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The flavoprotein nitroalkane oxidase from Fusarium oxysporum catalyzes the oxidation of nitroalkanes to the respective aldehydes or ketones with production of nitrite and hydrogen peroxide. The enzyme is irreversibly inactivated by incubation with tetranitromethane, a tyrosine-directed reagent, at pH 7.3. The inactivation is time-dependent and shows first-order kinetics for two half-lives of inactivation. Further inactivation can be achieved upon a second addition of tetranitromethane. A saturation kinetic pattern is observed when the rate of inactivation is determined versus the concentration of tetranitromethane, indicating that a reversible enzyme-inhibitor complex is formed before irreversible inactivation occurs. Values of 0.096 +/- 0.013 min(-1) and 12.9 +/- 3.8 mM were determined for the first-order rate constant for inactivation and the dissociation constant for the reversibly formed complex, respectively. The competitive inhibitor valerate protects the enzyme from inactivation by tetranitromethane, suggesting an active-site-directed inactivation. The UV-visible absorbance spectrum of the inactivated enzyme is perturbed with respect to that of the native enzyme, suggesting that treatment with tetranitromethane resulted in nitration of the enzyme. Comparison of tryptic maps of nitroalkane oxidase treated with tetranitromethane in the presence and absence of valerate shows a single peptide differentially labeled in the inactivated enzyme. The spectral properties of the modified peptide are consistent with nitration of a tyrosine residue. The amino acid sequence of the nitrated peptide is L-L-N-E-V-M-C-(NO(2)-Y)-P-L-F-D-G-G-N-I-G-L-R. The possible role of this tyrosine in substrate binding is discussed.
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Ramsey AJ, Fitzpatrick PF. Effects of phosphorylation on binding of catecholamines to tyrosine hydroxylase: specificity and thermodynamics. Biochemistry 2000; 39:773-8. [PMID: 10651643 DOI: 10.1021/bi991901r] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
As the catalyst for the rate-limiting step in the biosynthesis of the catecholamine neurotransmitters, the activity of tyrosine hydroxylase is tightly regulated. A principle means of posttranslational regulation is reversible phosphorylation of serine residues in an N-terminal regulatory domain. Phosphorylation of serine 40 has been shown to have a large effect on the rate constant for dissociation of dopamine and a much smaller effect on that for DOPA [Ramsey, A. J., and Fitzpatrick, P. F. (1998) Biochemistry 37, 8980-8986]. To determine the structural basis for the differences in affinity and to further test the validity of the previously proposed model for regulation, the effects of phosphorylation of serine 40 on the affinities for a series of catechols have been determined. The affinities of the unphosphorylated enzyme vary by 3 orders of magnitude due to differences in the rates of dissociation. The highest affinities are found with catecholamines which lack a carboxylate. The affinities of the phosphorylated enzyme show a much smaller range. In the case of binding of dihydroxyphenylalanine, the decrease in affinity upon phosphorylation is due primarily to a decrease in the enthalpy of the interaction. Based upon these results, a structural model for the effect of phosphorylation is proposed.
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Moran GR, Phillips RS, Fitzpatrick PF. Influence of steric bulk and electrostatics on the hydroxylation regiospecificity of tryptophan hydroxylase: characterization of methyltryptophans and azatryptophans as substrates. Biochemistry 1999; 38:16283-9. [PMID: 10587452 DOI: 10.1021/bi991983j] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Tryptophan hydroxylase is a pterin-dependent amino acid hydroxylase that catalyzes the incorporation of one atom of molecular oxygen into tryptophan to form 5-hydroxytryptophan. The substrate specificity and hydroxylation regiospecificity of tryptophan hydroxylase have been investigated using tryptophan analogues that have methyl substituents or nitrogens incorporated into the indole ring. The products of the reactions show that the regiospecificity of tryptophan hydroxylase is stringent. Hydroxylation does not occur at the 4 or 6 carbon in response to changes in substrate topology or atomic charge. 5-Hydroxymethyltryptophan and 5-hydroxy-4-methyltryptophan are the products from 5-methyltryptophan. These products establish that the hydroxylating intermediate is sufficiently potent to hydroxylate benzylic carbons and that the direction of the NIH shift in tryptophan hydroxylase is from carbon 5 to carbon 4. The effects on the V/K values for the amino acids indicate that the enzyme is most sensitive to changes at position 5 of the indole ring. The V(max) values for amino acid hydroxylation differ at most by a factor of 3 from that observed for tryptophan, while the efficiencies of hydroxylation with respect to tetrahydropterin consumption vary 6-fold, consistent with oxygen transfer to the amino acid being partially or fully rate limiting in productive catalysis.
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Ellis HR, Daubner SC, McCulloch RI, Fitzpatrick PF. Phenylalanine residues in the active site of tyrosine hydroxylase: mutagenesis of Phe300 and Phe309 to alanine and metal ion-catalyzed hydroxylation of Phe300. Biochemistry 1999; 38:10909-14. [PMID: 10460145 DOI: 10.1021/bi991160u] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Residues Phe300 and Phe309 of tyrosine hydroxylase are located in the active site in the recently described three-dimensional structure of the enzyme, where they have been proposed to play roles in substrate binding. Also based on the structure, Phe300 has been reported to be hydroxylated due to a naturally occurring posttranslational modification [Goodwill, K. E., Sabatier, C., and Stevens, R. C. (1998) Biochemistry 37, 13437-13445]. Mutants of tyrosine hydroxylase with alanine substituted for Phe300 or Phe309 have now been purified and characterized. The F309A protein possesses 40% less activity than wild-type tyrosine hydroxylase in the production of DOPA, but full activity in the production of dihydropterin. The F300A protein shows a 2.5-fold decrease in activity in the production of both DOPA and dihydropterin. The K(6-MPH4) value for F300A tyrosine hydroxylase is twice the wild-type value. These results are consistent with Phe309 having a role in maintaining the integrity of the active site, while Phe300 contributes less than 1 kcal/mol to binding tetrahydropterin. Characterization of Phe300 by MALDI-TOF mass spectrometry and amino acid sequencing showed that hydroxylation only occurs in the isolated catalytic domain after incubation with a large excess of 7, 8-dihydropterin, DTT, and Fe(2+). The modification is not observed in the untreated catalytic domain or in the full-length protein, even in the presence of excess iron. These results establish that hydroxylation of Phe300 is an artifact of the crystallography conditions and is not relevant to catalysis.
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McCulloch RI, Fitzpatrick PF. Limited proteolysis of tyrosine hydroxylase identifies residues 33-50 as conformationally sensitive to phosphorylation state and dopamine binding. Arch Biochem Biophys 1999; 367:143-5. [PMID: 10375411 DOI: 10.1006/abbi.1999.1259] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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129
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Gadda G, Dangott LJ, Johnson WH, Whitman CP, Fitzpatrick PF. Characterization of 2-oxo-3-pentynoate as an active-site-directed inactivator of flavoprotein oxidases: identification of active-site peptides in tryptophan 2-monooxygenase. Biochemistry 1999; 38:5822-8. [PMID: 10231533 DOI: 10.1021/bi982777z] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
2-oxo-3-pentynoate has been characterized as an active-site-directed inhibitor of selected flavoprotein oxidases. Tryptophan 2-monooxygenase is irreversibly inactivated in an active-site-directed fashion. The addition of FAD affords no protection from inactivation, whereas the competitive inhibitor indole-3-acetamide fully protects the enzyme from inactivation. The inactivation follows first-order kinetics for at least five half-lives. The rate of inactivation shows saturation kinetics, consistent with the formation of a reversible complex between the alkylating agent and the enzyme before inactivation occurs. Values of 0.017 +/- 0.0005 min-1 and 44 +/- 7 microM were determined for the limiting rate of inactivation and the apparent dissociation constant for 2-oxo-3-pentynoate, respectively. Tryptic maps of tryptophan 2-monooxygenase treated with 2-oxo-3-pentynoate show that two peptides are alkylated in the absence of indole-3-acetamide but not in its presence. The two peptides were identified by mass spectrometry as residues 333-349 and 503-536. Based upon sequence analysis, cysteine 511 and either cysteine 339 or histidine 338 are the likely sites of modification. In contrast, incubation of D-amino acid oxidase or nitroalkane oxidase with 2-oxo-3-pentynoate results in a loss of 55% or 100%, respectively, of the initial activity. In neither case does a competitive inhibitor affect the rate of inactivation, suggesting that the effect is not due to modification of active-site residues.
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Daubner SC, Fitzpatrick PF. Site-directed mutants of charged residues in the active site of tyrosine hydroxylase. Biochemistry 1999; 38:4448-54. [PMID: 10194366 DOI: 10.1021/bi983012u] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The active site of tyrosine hydroxylase consists of a hydrophobic cleft with an iron atom near the bottom. Within the cleft are several charged residues which are conserved across the family of pterin-dependent hydroxylases. We have studied four of these residues, glutamates 326 and 332, aspartate 328, and arginine 316 in tyrosine hydroxylase, by site-directed substitution with alternate amino acid residues. Replacement of arginine 316 with lysine results in a protein with a Ktyr value that is at least 400-fold greater and a V/Ktyr value that is 4000-fold lower than those found in the wild-type enzyme; substitution with alanine, serine, or glutamine yields insoluble enzyme. Arginine 316 is therefore critical for the binding of tyrosine. Replacement of glutamate 326 with alanine has no effect on the KM value for tyrosine and results in a 2-fold increase in the KM value for tetrahydropterin. The Vmax for DOPA production is reduced 9-fold, and the Vmax for dihydropterin formation is reduced 4-fold. These data suggest that glutamate 326 is not directly involved in catalysis. Replacement of aspartate 328 with serine results in a 26-fold higher KM value for tyrosine, a 8-fold lower Vmax for dihydropterin formation, and a 13-fold lower Vmax for DOPA formation. These data suggest that aspartate 328 has a role in tyrosine binding. Replacement of glutamate 332 with alanine results in a 10-fold higher KM value for 6-methyltetrahydropterin with no change in the KM value for tyrosine, a 125-fold lower Vmax for DOPA formation, and an only 3.3-fold lower Vmax for tetrahydropterin oxidation. These data suggest that glutamate 332 is required for productive tetrahydropterin binding.
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Abstract
The flavoprotein nitroalkane oxidase from Fusarium oxysporum catalyzes the oxidation of nitroalkanes to aldehydes with production of hydrogen peroxide and nitrite. The substrate specificity of the FAD-containing enzyme has been determined as a probe of the active site structure. Nitroalkane oxidase is active on primary and secondary nitroalkanes, with a marked preference for unbranched primary nitroalkanes. The V/K values for primary nitroalkanes increase with increasing length of the alkyl chain, reaching a maximum with 1-nitrobutane, suggesting a hydrophobic binding site sufficient to accommodate a four carbon chain. Each methylene group of the substrate contributes approximately 2.6 kcal mol-1 in binding energy. The V/K values for substrates containing a hydroxyl group are two orders of magnitude smaller than those of the corresponding nitroalkanes, also consistent with a hydrophobic binding site. 3-Nitro-1-propionate is a competitive inhibitor with a Kis value of 3.1 +/- 0.2 mM.
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Abstract
Hansen's disease (leprosy) is rare in Australia and usually imported from endemic areas. We report a 23-year-old white male with multibacillary leprosy who had lived all his life in North Queensland and initially appeared to have no risk factors. However, historical records revealed his grandfather to have been infected; because of stigma, this was unknown to the patient. As Hansen's disease has an incubation period of years, isolated cases may still occur as a result of previous endemicity in Queensland.
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Abstract
A continuous fluorometric assay for tryptophan hydroxylase activity based on the different spectral characteristics of tryptophan and 5-hydroxytryptophan is presented. Hydroxylation of tryptophan at the 5-position results in a large increase in the fluorescence of the molecule. The assay selectively monitors the fluorescence yield of 5-hydroxytryptophan by exciting the reaction mix at 300 nm. The rate of increase of the emission signal was found to be directly proportional to the enzyme concentration. Inner filter effects due to quinonoid dihydropterin accumulation were eliminated by the inclusion of a thiol reductant. Activity measured using this assay method was found to be the same as that determined by established discontinuous HPLC assay methods. The application of the assay to routine activity measurements and to steady-state determinations with the substrates tryptophan and tetrahydropterin is described.
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134
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Daubner SC, Fitzpatrick PF. Mutation to phenylalanine of tyrosine 371 in tyrosine hydroxylase increases the affinity for phenylalanine. Biochemistry 1998; 37:16440-4. [PMID: 9819237 DOI: 10.1021/bi981648f] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
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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Ramsey AJ, Fitzpatrick PF. Effects of phosphorylation of serine 40 of tyrosine hydroxylase on binding of catecholamines: evidence for a novel regulatory mechanism. Biochemistry 1998; 37:8980-6. [PMID: 9636040 DOI: 10.1021/bi980582l] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The effects of phosphorylation at Ser40 of rat tyrosine hydroxylase on the affinities of catechols have been determined with both the ferric and ferrous forms of the enzyme. Phosphorylation had no effect on the Ki value for the inhibition of the ferrous enzyme by either dopamine or DOPA when the initial rate of turnover was measured in assays. However, phosphorylation of the ferric enzyme resulted in a 17-fold decrease in affinity for DOPA and a 300-fold decrease in the affinity for dopamine, while the affinity for dihydroxynaphthalene was unchanged. The changes in binding affinity for the two catecholamines were almost exclusively due to large increases in the dissociation rate constants upon phosphorylation. These results support a novel mechanism for regulation in which phosphorylation affects binding of catecholamines to the catalytically inactive ferric form of the tyrosine hydroxylase.
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Moran GR, Daubner SC, Fitzpatrick PF. Expression and characterization of the catalytic core of tryptophan hydroxylase. J Biol Chem 1998; 273:12259-66. [PMID: 9575176 DOI: 10.1074/jbc.273.20.12259] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Wild type rabbit tryptophan hydroxylase (TRH) and two truncated mutant proteins have been expressed in Escherichia coli. The wild type protein was only expressed at low levels, whereas the mutant protein lacking the 101 amino-terminal regulatory domain was predominantly found in inclusion bodies. The protein that also lacked the carboxyl-terminal 28 amino acids, TRH102-416, was expressed as 30% of total cell protein. Analytical ultracentrifugation showed that TRH102-416 was predominantly a monomer in solution. The enzyme exhibited an absolute requirement for iron (ferrous or ferric) for activity and did not turn over in the presence of cobalt or copper. With either phenylalanine or tryptophan as substrate, stoichiometric formation of the 4a-hydroxypterin was found. Steady state kinetic parameters were determined with both of these amino acids using both tetrahydrobiopterin and 6-methyltetrahydropterin.
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Gadda G, Fitzpatrick PF. Biochemical and physical characterization of the active FAD-containing form of nitroalkane oxidase from Fusarium oxysporum. Biochemistry 1998; 37:6154-64. [PMID: 9558355 DOI: 10.1021/bi973085y] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Nitroalkane oxidase from Fusarium oxysporum catalyzes the oxidation of nitroalkanes to aldehydes with production of nitrite and hydrogen peroxide. The enzyme has a molecular weight of 47 955 +/- 39, as determined by MALDI-TOF mass spectrometry; under nondenaturing conditions, the aggregation state of the enzyme is best described by a tetramer-dimer self-associating model, with an association constant of (8.5 +/- 4.4) x 10(6) M-1 (pH 7.0 and 4 degreesC). The amino acid composition and the N-terminal amino acid sequence do not match any known protein or open reading frame. The inactive 5-nitrobutyl-1,5-dihydroflavin found in the enzyme as purified was converted to FAD, allowing characterization of the active FAD-containing enzyme. With nitroethane as substrate, the Vmax and Km values are 655 +/- 45 min-1 and 2.9 +/- 0.5 mM at pH 8.0 and 30 degreesC, respectively. One mole of FAD per mole of monomer enzyme is required for catalysis. No activity can be detected with amino acids or alpha-hydroxy acids as substrates. Reversible removal of the FAD cofactor yields inactive enzyme. The properties of the FAD cofactor in nitroalkane oxidase are within the range described for other oxidases. The UV-visible absorbance spectrum of the active enzyme shows maxima at 446, 384, and 274 nm; the extinction coefficient at 446 nm is 11.7 mM-1 cm-1. The neutral form of the flavin semiquinone, with maxima at 536 and 342 nm, is kinetically stabilized. The UV-visible absorbance spectrum of the reduced enzyme is typical of the anionic form of a flavin, with a peak centered at 335 nm. The affinity of the enzyme for sulfite is low (Kd value of 13.8 +/- 0.9 mM at pH 7.0 and 25 degreesC); this result, along with the stabilization of the neutral flavin semiquinone, suggests the presence of a weak positive charge near the N(1)-C(2)=O of FAD. The reduction potential of the enzyme is -367 mV. Benzoate and phenylacetic acid are competitive inhibitors, with Kis values of 5.1 +/- 0.6 and 13.1 +/- 2.3 mM, respectively. Binding of benzoate to nitroalkane oxidase results in spectral changes similar to those observed with d-amino acid oxidase. The absorbance spectrum of the flavin bound to nitroalkane oxidase is pH-dependent, with a pKa value of 8.4.
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Francisco WA, Tian G, Fitzpatrick PF, Klinman JP. Oxygen-18 Kinetic Isotope Effect Studies of the Tyrosine Hydroxylase Reaction: Evidence of Rate Limiting Oxygen Activation. J Am Chem Soc 1998. [DOI: 10.1021/ja973543q] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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139
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Daubner SC, Hillas PJ, Fitzpatrick PF. Expression and characterization of the catalytic domain of human phenylalanine hydroxylase. Arch Biochem Biophys 1997; 348:295-302. [PMID: 9434741 DOI: 10.1006/abbi.1997.0435] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
A truncated version of human phenylalanine hydroxylase which contains the carboxy terminal 336 amino acids was produced in Escherichia coli. It was purified by ammonium sulfate precipitation, Q-Sepharose chromatography, and hydroxyapatite chromatography. The K(m) values of the truncated enzyme for tetrahydropterin substrates are not different from those of the full-length enzyme, nor are the Vmax values. The KM value for phenylalanine is 2-fold lower for the truncate than for the full-length enzyme. The metal content of the enzyme is 0.27 mol Fe per mole enzyme subunit, and it is activated 2.3-fold by addition of ferrous ion to assays; it is not activated by addition of copper. The truncated enzyme shows no lag in activity when an assay is started with phenylalanine, while the full-length enzyme shows a marked lag.
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140
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Daubner SC, Hillas PJ, Fitzpatrick PF. Characterization of chimeric pterin-dependent hydroxylases: contributions of the regulatory domains of tyrosine and phenylalanine hydroxylase to substrate specificity. Biochemistry 1997; 36:11574-82. [PMID: 9305947 DOI: 10.1021/bi9711137] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
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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141
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Edmondson RD, Gadda G, Fitzpatrick PF, Russell DH. Identification of Native Flavin Adducts from Fusarium oxysporum Using Accurate Mass Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry. Anal Chem 1997. [DOI: 10.1021/ac9700989] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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142
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Goodwill KE, Sabatier C, Marks C, Raag R, Fitzpatrick PF, Stevens RC. Crystal structure of tyrosine hydroxylase at 2.3 A and its implications for inherited neurodegenerative diseases. NATURE STRUCTURAL BIOLOGY 1997; 4:578-85. [PMID: 9228951 DOI: 10.1038/nsb0797-578] [Citation(s) in RCA: 214] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Tyrosine hydroxylase (TyrOH) catalyzes the conversion of tyrosine to L-DOPA, the rate-limiting step in the biosynthesis of the catecholamines dopamine, adrenaline, and noradrenaline. TyrOH is highly homologous in terms of both protein sequence and catalytic mechanism to phenylalanine hydroxylase (PheOH) and tryptophan hydroxylase (TrpOH). The crystal structure of the catalytic and tetramerization domains of TyrOH reveals a novel alpha-helical basket holding the catalytic iron and a 40 A long anti-parallel coiled coil which forms the core of the tetramer. The catalytic iron is located 10 A below the enzyme surface in a 17 A deep active site pocket and is coordinated by the conserved residues His 331, His 336 and Glu 376. The structure provides a rationale for the effect of point mutations in TyrOH that cause L-DOPA responsive parkinsonism and Segawa's syndrome. The location of 112 different point mutations in PheOH that lead to phenylketonuria (PKU) are predicted based on the TyrOH structure.
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143
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Gadda G, Edmondson RD, Russell DH, Fitzpatrick PF. Identification of the naturally occurring flavin of nitroalkane oxidase from fusarium oxysporum as a 5-nitrobutyl-FAD and conversion of the enzyme to the active FAD-containing form. J Biol Chem 1997; 272:5563-70. [PMID: 9038163 DOI: 10.1074/jbc.272.9.5563] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Nitroalkane oxidase from Fusarium oxysporum catalyzes the oxidation of nitroalkanes to aldehydes with production of nitrite and hydrogen peroxide. The UV-visible absorbance spectrum of the purified enzyme shows a single absorption peak at 336 nm with an extinction coefficient of 7.4 mM-1 cm-1. Upon denaturation of the enzyme at pH 7.0, a stoichiometric amount of FAD is released. The spectral properties of the enzyme as isolated are consistent with an N(5) adduct of the flavin. This is not due to a covalent linkage with the protein, since the free flavin adduct can be isolated from the enzyme at pH 2.1. The free flavin adduct shows an absorbance spectrum with a lambdamax at 346 nm (10.7 mM-1 cm-1) and is not fluorescent. Under alkaline conditions the free adduct decays, yielding FAD; the rate of this process is pH-dependent with a pKa of 7.4. Adduct decay is also observed with the native enzyme; in this case, however, the rate of decay is 160-fold slower (at pH 8.0) and not dependent on pH. During this process a large increase in enzymatic activity ( approximately 26-fold at pH 7.0) is observed, the rate of which is equal to the rate of flavin adduct conversion to FAD. Thus, the native flavin adduct is not active but can be converted to FAD, the active form of the flavin. Maximal activation is pH- and FAD-dependent; two groups with pKa values of 5.65 +/- 0. 25 and 8.75 +/- 0.05 must be unprotonated and protonated, respectively. The m/z- of the free flavin adduct is 103.0645 higher than that of FAD, as determined by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. This corresponds to a molecule of nitrobutane linked to FAD. A mechanism is proposed for the formation in vivo of the nitrobutyl-FAD of nitroalkane oxidase.
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144
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Kurtz KA, Fitzpatrick PF. pH and Secondary Kinetic Isotope Effects on the Reaction of d-Amino Acid Oxidase with Nitroalkane Anions: Evidence for Direct Attack on the Flavin by Carbanions. J Am Chem Soc 1997. [DOI: 10.1021/ja962783n] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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145
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Simonian AL, Rainina EI, Fitzpatrick PF, Wild JR. A tryptophan-2-monooxygenase based amperometric biosensor for L-tryptophan determination: use of a competitive inhibitor as a tool for selectivity increase. Biosens Bioelectron 1997; 12:363-71. [PMID: 9228729 DOI: 10.1016/s0956-5663(97)00002-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
A new flow-injection amperometric biosensor based on immobilized tryptophan-2-monooxygenase (TMO) has been developed for reagentless L-tryptophan determination. Concentrations of L-tryptophan between 0.1 and 50 mM could be measured with the linear part of the calibration curve between 0.1 and 2 mM. The response time was 30 s and the total analysis time was less than 3 min. The biosensor retained activity for greater than 4 months, when operated daily at 25 degrees C and stored at 8 degrees C. The biosensor was characterized by a relatively high sensitivity to phenylalanine (54% that of L-tryptophan), a modest response to L-methionine (less than 6%) and virtually no response to other amino acids. However, the biosensor selectivity to L-tryptophan could be dramatically increased when indoleacetamide (IA), a competitive inhibitor of TMO, was introduced. In the presence of 10 microM IA, the biosensor response to L-phenylalanine decreased to 7-4% of the unaffected rate for L-tryptophan. In the absence of L-tryptophan and IA the biosensor could be used for L-phenylalanine determination in the concentration range from 1 to 50 mM. The biosensor was successfully used for L-tryptophan determination in nutritional broth.
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Ramsey AJ, Hillas PJ, Fitzpatrick PF. Characterization of the active site iron in tyrosine hydroxylase. Redox states of the iron. J Biol Chem 1996; 271:24395-400. [PMID: 8798695 DOI: 10.1074/jbc.271.40.24395] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Tyrosine hydroxylase is an iron-containing monooxygenase that uses a tetrahydropterin to catalyze the hydroxylation of tyrosine to dihydroxyphenylalanine in catecholamine biosynthesis. The role of the iron in this enzyme is not understood. Purification of recombinant rat tyrosine hydroxylase containing 0.5-0.7 iron atoms/subunit and lacking bound catecholamine has permitted studies of the redox states of the resting enzyme and the enzyme during catalysis. As isolated, the iron is in the ferric form. Dithionite or 6-methyltetrahydropterin can reduce the iron to the ferrous form. Reduction by 6-methyltetrahydropterin consumes 0.5 nmol/nmol of enzyme-bound iron, producing quinonoid 6-methyldihydropterin as the only detectable product. In the presence of oxygen, reoxidation to ferric iron occurs. During turnover the enzyme is in the ferrous form. However, a fraction is oxidized during turnover; this can be trapped by added catechol or by the dihydroxyphenylalanine formed during turnover.
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147
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Heasley CJ, Fitzpatrick PF. Kinetic mechanism and substrate specificity of nitroalkane oxidase. Biochem Biophys Res Commun 1996; 225:6-10. [PMID: 8769086 DOI: 10.1006/bbrc.1996.1122] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Nitroalkane oxidase from Fusarium oxysporum catalyzes the oxidation of nitroalkanes to aldehydes, transferring the electrons to oxygen to form hydrogen peroxide. The steady-state kinetic patterns have been determined with nitroethane, 1-nitropropane, and 1-nitropentane as substrates. In all three cases, the data fit best to a ping pong kinetic mechanism. The pH dependences of the V/K values for 1-nitropentane and phenylnitromethane show that an amino acid residue on the enzyme with a pKa-value of 6.7 must be unprotonated for activity with both substrates. A second group must be protonated for activity. The pKa value of this group matches the pKa values of the nitroalkanes, 9.3 with nitropropane and 6.7 with phenylnitromethane, establishing that the nitroalkane must be in the neutral rather than the anionic form for catalysis.
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148
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Hillas PJ, Fitzpatrick PF. A mechanism for hydroxylation by tyrosine hydroxylase based on partitioning of substituted phenylalanines. Biochemistry 1996; 35:6969-75. [PMID: 8679520 DOI: 10.1021/bi9606861] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The iron-containing enzyme tyrosine hydroxylase catalyzes the hydroxylation of tyrosine to dihydroxyphenylalanine. A series of 4-X-substituted (X = H, F, Br, Cl, CH3, or CH3O) phenylalanines have been characterized as substrates to gain insight into the mechanism of hydroxylation. Multiple hydroxylated products were formed in most cases. As the size of the substituent at the 4-position increased, the site of hydroxylation switched from the 4- to the 3-position of the aromatic ring. The total amount of product formed with each amino acid showed a very good correlation with the sigma parameter of the substituent, with rho values of -4.3 +/- 0.7 or -5.6 +/- 0.8 when tetrahydrobiopterin or 6-methyltetrahydropterin, respectively, was used as cosubstrate. These values are consistent with a highly electron deficient transition state for hydroxylation. Oxygen addition at the 4-position resulted in either elimination of the substituent to form tyrosine or an NIH shift to form the respective 3-X-tyrosine. The relative amount of the product due to an NIH shift decreased in the order Br > CH3 > Cl >> F approximately CH3O approximately 0. A chemical mechanism for hydroxylation by tyrosine hydroxylase is presented to account for product formation from the various 4-substituted phenylalanines.
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149
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Ramsey AJ, Daubner SC, Ehrlich JI, Fitzpatrick PF. Identification of iron ligands in tyrosine hydroxylase by mutagenesis of conserved histidinyl residues. Protein Sci 1995; 4:2082-6. [PMID: 8535244 PMCID: PMC2142982 DOI: 10.1002/pro.5560041013] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Tyrosine hydroxylase catalyzes the hydroxylation of tyrosine and other aromatic amino acids using a tetrahydropterin as the reducing substrate. The enzyme is a homotetramer; each monomer contains a single nonheme iron atom. Five histidine residues are conserved in all tyrosine hydroxylases that have been sequenced to date and in the related eukaryotic enzymes phenylalanine and tryptophan hydroxylase. Because histidine has been suggested as a ligand to the iron in these enzymes, mutant tyrosine hydroxylase proteins in which each of the conserved histidines had been mutated to glutamine or alanine were expressed in Escherichia coli. The H192Q, H247Q, and H317A mutant proteins contained iron in comparable amounts to the wild-type enzyme, about 0.6 atoms/sub-unit. In contrast, the H331 and H336 mutant proteins contained no iron. The first three mutant enzymes were active, with Vmax values 39, 68, and 7% that of the wild-type enzyme, and slightly altered V/Km values for both tyrosine and 6-methyltetrahydropterin. In contrast, the H331 and H336 mutant enzymes had no detectable activity. The EPR spectra of the H192Q and H247Q enzymes are indistinguishable from that of wild-type tyrosine hydroxylase, whereas that of the H317A enzyme indicated that the ligand field of the iron had been slightly perturbed. These results are consistent with H331 and H336 being ligands to the active site iron atom.
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150
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Emanuele JJ, Fitzpatrick PF. Mechanistic studies of the flavoprotein tryptophan 2-monooxygenase. 2. pH and kinetic isotope effects. Biochemistry 1995; 34:3716-23. [PMID: 7893668 DOI: 10.1021/bi00011a029] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
pH and kinetic isotope effects on steady-state kinetic parameters have been determined for the flavoprotein tryptophan 2-monooxygenase with tryptophan, phenylalanine, 2-hydrazino-3-propanoic acid, and methionine as substrates. The V/K values of the amino acid substrates show that a residue with an apparent pKa value of 5 must be unprotonated for activity, a residue with a pKa value equal to that of the amino group of the substrate must be protonated, and deprotonation of a residue with pKa value of 10 increases the V/K value. A group in the free enzyme with a pKa value of 6 must be deprotonated for tight binding of amide inhibitors and protonated for tight binding of acids, establishing this as the intrinsic pKa value. The temperature dependence of this pKa value is consistent with involvement of a histidinyl residue. Deprotonation of the residue with a pKa value of 10 decreases binding of amide inhibitors. The D(V/Ktrp) value is less than 1.7 between pH 5 and 10, consistent with a forward commitment to catalysis of 7-15 with this substrate. The D(V/K)met value is pH dependent, increasing from a minimal value of 1.8 at pH 8.3 to a limiting value of 5.3 at both high and low pH, with pKa values of 5.1 and 10. The increase in both the isotope effect and the V/Kmet value at high pH is consistent with a conformational change to a more open active site above pH 10. The D(V/K)ala value is 5.3 at pH 8.3; this is probably the intrinsic isotope effect with this substrate.(ABSTRACT TRUNCATED AT 250 WORDS)
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