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Maghsoud Y, Dong C, Cisneros GA. Investigation of the Inhibition Mechanism of Xanthine Oxidoreductase by Oxipurinol: A Computational Study. J Chem Inf Model 2023. [PMID: 37319436 PMCID: PMC10405278 DOI: 10.1021/acs.jcim.3c00624] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
Xanthine oxidoreductase (XOR) is an enzyme found in various organisms. It converts hypoxanthine to xanthine and urate, which are crucial steps in purine elimination in humans. Elevated uric acid levels can lead to conditions like gout and hyperuricemia. Therefore, there is significant interest in developing drugs that target XOR for treating these conditions and other diseases. Oxipurinol, an analogue of xanthine, is a well-known inhibitor of XOR. Crystallographic studies have revealed that oxipurinol directly binds to the molybdenum cofactor (MoCo) in XOR. However, the precise details of the inhibition mechanism are still unclear, which would be valuable for designing more effective drugs with similar inhibitory functions. In this study, molecular dynamics and quantum mechanics/molecular mechanics calculations are employed to investigate the inhibition mechanism of XOR by oxipurinol. The study examines the structural and dynamic effects of oxipurinol on the pre-catalytic structure of the metabolite-bound system. Our results provide insights on the reaction mechanism catalyzed by the MoCo center in the active site, which aligns well with experimental findings. Furthermore, the results provide insights into the residues surrounding the active site and propose an alternative mechanism for developing alternative covalent inhibitors.
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Affiliation(s)
- Yazdan Maghsoud
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, Richardson, Texas 75080, United States
| | - Chao Dong
- Department of Chemistry and Physics, The University of Texas Permian Basin, Odessa, Texas 79762, United States
| | - G Andrés Cisneros
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, Richardson, Texas 75080, United States
- Department of Physics, The University of Texas at Dallas, Richardson, Texas 75080, United States
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2
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Maghsoud Y, Dong C, Cisneros GA. Computational Characterization of the Inhibition Mechanism of Xanthine Oxidoreductase by Topiroxostat. ACS Catal 2023; 13:6023-6043. [PMID: 37547543 PMCID: PMC10399974 DOI: 10.1021/acscatal.3c01245] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/08/2023]
Abstract
Xanthine oxidase (XO) is a member of the molybdopterin-containing enzyme family. It interconverts xanthine to uric acid as the last step of purine catabolism in the human body. The high uric acid concentration in the blood directly leads to human diseases like gout and hyperuricemia. Therefore, drugs that inhibit the biosynthesis of uric acid by human XO have been clinically used for many years to decrease the concentration of uric acid in the blood. In this study, the inhibition mechanism of XO and a new promising drug, topiroxostat (code: FYX-051), is investigated by employing molecular dynamics (MD) and quantum mechanics/molecular mechanics (QM/MM) calculations. This drug has been reported to act as both a noncovalent and covalent inhibitor and undergoes a stepwise inhibition by all its hydroxylated metabolites, which include 2-hydroxy-FYX-051, dihydroxy-FYX-051, and trihydroxy-FYX-051. However, the detailed mechanism of inhibition of each metabolite remains elusive and can be useful for designing more effective drugs with similar inhibition functions. Hence, herein we present the computational investigation of the structural and dynamical effects of FYX-051 and the calculated reaction mechanism for all of the oxidation steps catalyzed by the molybdopterin center in the active site. Calculated results for the proposed reaction mechanisms for each metabolite's inhibition reaction in the enzyme's active site, binding affinities, and the noncovalent interactions with the surrounding amino acid residues are consistent with previously reported experimental findings. Analysis of the noncovalent interactions via energy decomposition analysis (EDA) and noncovalent interaction (NCI) techniques suggests that residues L648, K771, E802, R839, L873, R880, R912, F914, F1009, L1014, and A1079 can be used as key interacting residues for further hybrid-type inhibitor development.
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Affiliation(s)
- Yazdan Maghsoud
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, Richardson, Texas 75080, United States
| | - Chao Dong
- Department of Chemistry and Physics, The University of Texas Permian Basin, Odessa, Texas 79762, United States
| | - G Andrés Cisneros
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, Richardson, Texas 75080, United States; Department of Physics, The University of Texas at Dallas, Richardson, Texas 75080, United States
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3
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Yang N, Gonzalez-Vicente A, Garvin JL. Angiotensin II-induced superoxide and decreased glutathione in proximal tubules: effect of dietary fructose. Am J Physiol Renal Physiol 2019; 318:F183-F192. [PMID: 31760771 DOI: 10.1152/ajprenal.00462.2019] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Angiotensin II exacerbates oxidative stress in part by increasing superoxide (O2-) production by many renal tissues. However, whether it does so in proximal tubules and the source of O2- in this segment are unknown. Dietary fructose enhances the stimulatory effect of angiotensin II on proximal tubule Na+ reabsorption, but whether this is true for oxidative stress is unknown. We hypothesized that angiotensin II causes proximal nephron oxidative stress in part by stimulating NADPH oxidase (NOX)4-dependent O2- production and decreasing the amount of the antioxidant glutathione, and this is exacerbated by dietary fructose. We measured basal and angiotensin II-stimulated O2- production with and without inhibitors, NOX1 and NOX4 expression, and total and reduced glutathione (GSH) in proximal tubules from rats drinking either tap water (control) or 20% fructose. Angiotensin II (10 nM) increased O2- production by 113 ± 42 relative light units·mg protein-1·s-1 in controls and 401 ± 74 relative light units·mg protein-1·s-1 with 20% fructose (n = 11 for each group, P < 0.05 vs. control). Apocynin and the Nox1/4 inhibitor GKT136901 prevented angiotensin II-induced increases in both groups. NOX4 expression was not different between groups. NOX1 expression was undetectable. Angiotensin II decreased GSH by 1.8 ± 0.8 nmol/mg protein in controls and by 4.2 ± 0.9 nmol/mg protein with 20% fructose (n = 18 for each group, P < 0.047 vs. control). We conclude that 1) angiotensin II causes oxidative stress in proximal tubules by increasing O2- production by NOX4 and decreasing GSH and 2) dietary fructose enhances the ability of angiotensin II to stimulate O2- and diminish GSH, thereby exacerbating oxidative stress in this segment.
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Affiliation(s)
- Nianxin Yang
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, Ohio
| | - Agustin Gonzalez-Vicente
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, Ohio
| | - Jeffrey L Garvin
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, Ohio
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Yang J, Dong C, Kirk ML. Xanthine oxidase-product complexes probe the importance of substrate/product orientation along the reaction coordinate. Dalton Trans 2017; 46:13242-13250. [PMID: 28696463 PMCID: PMC5634921 DOI: 10.1039/c7dt01728f] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
A combination of reaction coordinate computations, resonance Raman spectroscopy, spectroscopic computations, and hydrogen bonding investigations have been used to understand the importance of substrate orientation along the xanthine oxidase reaction coordinate. Specifically, 4-thiolumazine and 2,4-dithiolumazine have been used as reducing substrates for xanthine oxidase to form stable enzyme-product charge transfer complexes suitable for spectroscopic study. Laser excitation into the near-infrared molybdenum-to-product charge transfer band produces rR enhancement patterns in the high frequency in-plane stretching region that directly probe the nature of this MLCT transition and provide insight into the effects of electron redistribution along the reaction coordinate between the transition state and the stable enzyme-product intermediate, including the role of the covalent Mo-O-C linkage in facilitating this process. The results clearly show that specific Mo-substrate orientations allow for enhanced electronic coupling and facilitate strong hydrogen bonding interactions with amino acid residues in the substrate binding pocket.
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Affiliation(s)
- Jing Yang
- Department of Chemistry and Chemical Biology, The University of New Mexico, MSC03 2060, 1 University of New Mexico, Albuquerque, NM87131-0001, USA.
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Zhang W, Turney T, Surjancev I, Serianni AS. Enzymatic synthesis of ribo- and 2'-deoxyribonucleosides from glycofuranosyl phosphates: An approach to facilitate isotopic labeling. Carbohydr Res 2017; 449:125-133. [PMID: 28780317 DOI: 10.1016/j.carres.2017.07.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2017] [Revised: 07/13/2017] [Accepted: 07/14/2017] [Indexed: 01/25/2023]
Abstract
Milligram quantities of α-D-ribofuranosyl 1-phosphate (sodium salt) (αR1P) were prepared by the phosphorolysis of inosine, catalyzed by purine nucleoside phosphorylase (PNPase). The αR1P was isolated by chromatography in >95% purity and characterized by 1H and 13C NMR spectroscopy. Aqueous solutions of αR1P were stable at pH 6.4 and 4 °C for several months. The isolated αR1P was N-glycosylated with different nitrogen bases (adenine, guanine and uracil) using PNPase or uridine phosphorylase (UPase) to give the corresponding ribonucleosides in high yield based on the glycosyl phosphate. This methodology is attractive for the preparation of stable isotopically labeled ribo- and 2'-deoxyribonucleosides because of the ease of product purification and convenient use and recycling of nitrogen bases. The approach eliminates the need for separate reactions to prepare individual furanose-labeled ribonucleosides, since only one ribonucleoside (inosine) needs to be labeled, if desired, in the furanose ring, the latter achieved by a high-yield chemical N-glycosylation. 2'-Deoxyribonucleosides were prepared from 2'-deoxyinosine using the same methodology with minor modifications.
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Affiliation(s)
- Wenhui Zhang
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556-5670 USA.
| | - Toby Turney
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556-5670 USA
| | - Ivana Surjancev
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556-5670 USA
| | - Anthony S Serianni
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556-5670 USA.
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Newton AJH, Wall MJ, Richardson MJE. Modeling microelectrode biosensors: free-flow calibration can substantially underestimate tissue concentrations. J Neurophysiol 2016; 117:937-949. [PMID: 27927788 PMCID: PMC5338626 DOI: 10.1152/jn.00788.2016] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2016] [Accepted: 12/05/2016] [Indexed: 12/11/2022] Open
Abstract
Microelectrode biosensors are typically calibrated in a free-flow environment where the concentrations at the biosensor surface are constant. However, when in tissue, the analyte reaches the biosensor via diffusion and so analyte breakdown by the biosensor results in a concentration gradient and consequently a lower concentration around the biosensor. This effect means that naive free-flow calibration will underestimate tissue concentration. We develop mathematical models to better quantify the discrepancy between the calibration and tissue environment and experimentally verify our key predictions. Microelectrode amperometric biosensors are widely used to measure concentrations of analytes in solution and tissue including acetylcholine, adenosine, glucose, and glutamate. A great deal of experimental and modeling effort has been directed at quantifying the response of the biosensors themselves; however, the influence that the macroscopic tissue environment has on biosensor response has not been subjected to the same level of scrutiny. Here we identify an important issue in the way microelectrode biosensors are calibrated that is likely to have led to underestimations of analyte tissue concentrations. Concentration in tissue is typically determined by comparing the biosensor signal to that measured in free-flow calibration conditions. In a free-flow environment the concentration of the analyte at the outer surface of the biosensor can be considered constant. However, in tissue the analyte reaches the biosensor surface by diffusion through the extracellular space. Because the enzymes in the biosensor break down the analyte, a density gradient is set up resulting in a significantly lower concentration of analyte near the biosensor surface. This effect is compounded by the diminished volume fraction (porosity) and reduction in the diffusion coefficient due to obstructions (tortuosity) in tissue. We demonstrate this effect through modeling and experimentally verify our predictions in diffusive environments. NEW & NOTEWORTHY Microelectrode biosensors are typically calibrated in a free-flow environment where the concentrations at the biosensor surface are constant. However, when in tissue, the analyte reaches the biosensor via diffusion and so analyte breakdown by the biosensor results in a concentration gradient and consequently a lower concentration around the biosensor. This effect means that naive free-flow calibration will underestimate tissue concentration. We develop mathematical models to better quantify the discrepancy between the calibration and tissue environment and experimentally verify our key predictions.
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Affiliation(s)
- Adam J H Newton
- Warwick Mathematics Institute, University of Warwick, Coventry, United Kingdom; and
| | - Mark J Wall
- School of Life Sciences, University of Warwick, Coventry, United Kingdom
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7
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Stein BW, Kirk ML. Electronic structure contributions to reactivity in xanthine oxidase family enzymes. J Biol Inorg Chem 2015; 20:183-94. [PMID: 25425163 PMCID: PMC4867223 DOI: 10.1007/s00775-014-1212-8] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2014] [Accepted: 10/30/2014] [Indexed: 11/25/2022]
Abstract
We review the xanthine oxidase (XO) family of pyranopterin molybdenum enzymes with a specific emphasis on electronic structure contributions to reactivity. In addition to xanthine and aldehyde oxidoreductases, which catalyze the two-electron oxidation of aromatic heterocycles and aldehyde substrates, this mini-review highlights recent work on the closely related carbon monoxide dehydrogenase (CODH) that catalyzes the oxidation of CO using a unique Mo-Cu heterobimetallic active site. A primary focus of this mini-review relates to how spectroscopy and computational methods have been used to develop an understanding of critical relationships between geometric structure, electronic structure, and catalytic function.
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Affiliation(s)
- Benjamin W. Stein
- Department of Chemistry and Chemical Biology, University of New Mexico, MSC03 2060, 300 Terrace St. NE, Albuquerque, NM 87131
| | - Martin L. Kirk
- Department of Chemistry and Chemical Biology, University of New Mexico, MSC03 2060, 300 Terrace St. NE, Albuquerque, NM 87131
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8
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Affiliation(s)
- Russ Hille
- Department of Biochemistry, University of California, Riverside, Riverside, California 92521, United States
| | - James Hall
- Department of Biochemistry, University of California, Riverside, Riverside, California 92521, United States
| | - Partha Basu
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, Pennsylvania 15282, United States
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9
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Rani A, Pandita E, Rahman S, Deep S, Sau AK. Insight into temperature dependence of GTPase activity in human guanylate binding protein-1. PLoS One 2012; 7:e40487. [PMID: 22859948 PMCID: PMC3394710 DOI: 10.1371/journal.pone.0040487] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2012] [Accepted: 06/08/2012] [Indexed: 01/02/2023] Open
Abstract
Interferon-γ induced human guanylate binding protein-1(hGBP1) belongs to a family of dynamin related large GTPases. Unlike all other GTPases, hGBP1 hydrolyzes GTP to a mixture of GDP and GMP with GMP being the major product at 37°C but GDP became significant when the hydrolysis reaction was carried out at 15°C. The hydrolysis reaction in hGBP1 is believed to involve with a number of catalytic steps. To investigate the effect of temperature in the product formation and on the different catalytic complexes of hGBP1, we carried out temperature dependent GTPase assays, mutational analysis, chemical and thermal denaturation studies. The Arrhenius plot for both GDP and GMP interestingly showed nonlinear behaviour, suggesting that the product formation from the GTP-bound enzyme complex is associated with at least more than one step. The negative activation energy for GDP formation and GTPase assay with external GDP together indicate that GDP formation occurs through the reversible dissociation of GDP-bound enzyme dimer to monomer, which further reversibly dissociates to give the product. Denaturation studies of different catalytic complexes show that unlike other complexes the free energy of GDP-bound hGBP1 decreases significantly at lower temperature. GDP formation is found to be dependent on the free energy of the GDP-bound enzyme complex. The decrease in the free energy of this complex at low temperature compared to at high is the reason for higher GDP formation at low temperature. Thermal denaturation studies also suggest that the difference in the free energy of the GTP-bound enzyme dimer compared to its monomer plays a crucial role in the product formation; higher stability favours GMP but lower favours GDP. Thus, this study provides the first thermodynamic insight into the effect of temperature in the product formation of hGBP1.
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Affiliation(s)
- Anjana Rani
- National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi, India
| | - Esha Pandita
- National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi, India
| | - Safikur Rahman
- National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi, India
| | - Shashank Deep
- Department of Chemistry, Indian Institute of Technology, New Delhi, India
| | - Apurba Kumar Sau
- National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi, India
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10
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Canepa C. On the curvature in logarithmic plots of rate coefficients for chemical reactions. Chem Cent J 2011; 5:22. [PMID: 21545752 PMCID: PMC3117758 DOI: 10.1186/1752-153x-5-22] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2010] [Accepted: 05/06/2011] [Indexed: 11/10/2022] Open
Abstract
In terms of the reduced potential energy barrier ζ = ΔuTS/kT, the rate coefficients for chemical reactions are usually expressed as proportional to e-ζ. The coupling between vibrational modes of the medium to the reaction coordinate leads to a proportionality of the regularized gamma function of Euler Q(a,ζ) = Γ(a,ζ)/Γ(a), with a being the number of modes coupled to the reaction coordinate. In this work, the experimental rate coefficients at various temperatures for several chemical reactions were fitted to the theoretical expression in terms of Q(a,ζ) to determine the extent of its validity and generality. The new expression affords lower deviations from the experimental points in 29 cases out of 38 and it accounts for the curvature in the logarithmic plots of rate coefficients versus inverse temperature. In the absence of tunneling, conventional theories predict the curvature of these plots to be identically zero.
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Affiliation(s)
- Carlo Canepa
- Dipartimento di Chimica Generale e Chimica Organica, Università di Torino Corso Massimo d'Azeglio 48, 10125 Torino, Italy.
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11
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Majumdar A, Sarkar S. Bioinorganic chemistry of molybdenum and tungsten enzymes: A structural–functional modeling approach. Coord Chem Rev 2011. [DOI: 10.1016/j.ccr.2010.11.027] [Citation(s) in RCA: 122] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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12
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Abstract
Recent progress in our understanding of the structural and catalytic properties of molybdenum-containing enzymes in eukaryotes is reviewed, along with aspects of the biosynthesis of the cofactor and its insertion into apoprotein.
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Affiliation(s)
- Russ Hille
- Department of Biochemistry, University of California, Riverside, CA 92521
| | - Takeshi Nishino
- Department of Biochemistry and Molecular Biology, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo, Japan and Department of Biochemistry, University of California, Riverside, CA 92521
| | - Florian Bittner
- Department of Plant Biology, Technical University of Braunschweig, 38023 Braunschweig, Germany
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13
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14
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Metz S, Thiel W. QM/MM Studies of Xanthine Oxidase: Variations of Cofactor, Substrate, and Active-Site Glu802. J Phys Chem B 2010; 114:1506-17. [DOI: 10.1021/jp909999s] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Sebastian Metz
- Max-Planck-Institut für Kohlenforschung, D-45470 Mülheim an der Ruhr, Germany
| | - Walter Thiel
- Max-Planck-Institut für Kohlenforschung, D-45470 Mülheim an der Ruhr, Germany
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15
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Metz S, Thiel W. A Combined QM/MM Study on the Reductive Half-Reaction of Xanthine Oxidase: Substrate Orientation and Mechanism. J Am Chem Soc 2009; 131:14885-902. [DOI: 10.1021/ja9045394] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Affiliation(s)
- Sebastian Metz
- Max-Planck-Institut für Kohlenforschung, D-45470 Mülheim an der Ruhr, Germany
| | - Walter Thiel
- Max-Planck-Institut für Kohlenforschung, D-45470 Mülheim an der Ruhr, Germany
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16
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Metz S, Wang D, Thiel W. Reductive Half-Reaction of Aldehyde Oxidoreductase toward Acetaldehyde: A Combined QM/MM Study. J Am Chem Soc 2009; 131:4628-40. [DOI: 10.1021/ja805938w] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Sebastian Metz
- Max-Planck-Institut für Kohlenforschung, D-45470 Mülheim an der Ruhr, Germany
| | - Dongqi Wang
- Max-Planck-Institut für Kohlenforschung, D-45470 Mülheim an der Ruhr, Germany
| | - Walter Thiel
- Max-Planck-Institut für Kohlenforschung, D-45470 Mülheim an der Ruhr, Germany
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17
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Buettner GR, Ng CF, Wang M, Rodgers VGJ, Schafer FQ. A new paradigm: manganese superoxide dismutase influences the production of H2O2 in cells and thereby their biological state. Free Radic Biol Med 2006; 41:1338-50. [PMID: 17015180 PMCID: PMC2443724 DOI: 10.1016/j.freeradbiomed.2006.07.015] [Citation(s) in RCA: 120] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/08/2006] [Revised: 06/09/2006] [Accepted: 07/14/2006] [Indexed: 10/24/2022]
Abstract
The principal source of hydrogen peroxide in mitochondria is thought to be from the dismutation of superoxide via the enzyme manganese superoxide dismutase (MnSOD). However, the nature of the effect of SOD on the cellular production of H(2)O(2) is not widely appreciated. The current paradigm is that the presence of SOD results in a lower level of H(2)O(2) because it would prevent the non-enzymatic reactions of superoxide that form H(2)O(2). The goal of this work was to: a) demonstrate that SOD can increase the flux of H(2)O(2), and b) use kinetic modelling to determine what kinetic and thermodynamic conditions result in SOD increasing the flux of H(2)O(2). We examined two biological sources of superoxide production (xanthine oxidase and coenzyme Q semiquinone, CoQ(*-) that have different thermodynamic and kinetic properties. We found that SOD could change the rate of formation of H(2)O(2) in cases where equilibrium-specific reactions form superoxide with an equilibrium constant (K) less than 1. An example is the formation of superoxide in the electron transport chain (ETC) of the mitochondria by the reaction of ubisemiquinone radical with dioxygen. We measured the rate of release of H(2)O(2) into culture medium from cells with differing levels of MnSOD. We found that the higher the level of SOD, the greater the rate of accumulation of H(2)O(2). Results with kinetic modelling were consistent with this observation; the steady-state level of H(2)O(2) increases if K<1, for example CoQ(*-)+O(2)-->CoQ+O(2)(*-). However, when K>1, e.g. xanthine oxidase forming O(2)(*-), SOD does not affect the steady state-level of H(2)O(2). Thus, the current paradigm that SOD will lower the flux of H(2)O(2) does not hold for the ETC. These observations indicate that MnSOD contributes to the flux of H(2)O(2) in cells and thereby is involved in establishing the cellular redox environment and thus the biological state of the cell.
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Affiliation(s)
- Garry R Buettner
- Free Radical and Radiation Biology Program, EMRB 68, The University of Iowa, Iowa City, IA 52242-1101, USA.
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Abstract
Molybdenum is the only second-row transition metal that is required by most living organisms, and the few species that do not require molybdenum use tungsten, which lies immediately below molybdenum in the periodic table. Because of their unique chemical versatility and unusually high bioavailability these two transition metals have been incorporated into the active sites of enzymes over the course of evolution. Enzymes that contain molybdenum or tungsten continue to be discovered and several crystal structures have become available recently. This new structural information has been complemented by spectroscopic and kinetic methods, as well as computational approaches. Together, these studies provide an increasingly detailed view of the reaction mechanisms and the correlation between the electronic structure of the active site and catalytic function, one of the fundamental goals in metallobiochemistry.
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Affiliation(s)
- Russ Hille
- Dept of Molecular and Cellular Biochemistry and The Protein Research Group, The Ohio State University, Columbus, OH 43210-1218, USA.
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19
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Affiliation(s)
- R Hille
- Department of Medical Biochemistry, Ohio State University, 333 Hamilton Hall, 1645 Neil Avenue, Columbus, OH 43210-1218, USA
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20
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Sau AK, Mondal MS, Mitra S. Interaction of Cu2+ ion with milk xanthine oxidase. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1544:89-95. [PMID: 11341919 DOI: 10.1016/s0167-4838(00)00207-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The interaction of Cu2+ ion with milk xanthine oxidase (XO) has been studied by optical spectroscopy, circular dichroism, ESR and transient kinetic techniques. It is observed that XO forms optically observable complexes with Cu2+ ion. The pH dependence studies of the formation of Cu2+-XO complex by optical spectroscopy and circular dichroism show that at least one ionizable group may be responsible for the formation of the complex. The EPR studies show that Cu2+ ion binds to XO with sulfur and nitrogenous ligands. The transient kinetic study of the interaction of Cu2+ with XO shows the existence of two Cu2+ bound XO complexes formed at two different time scales of the interaction, one at < or =5 ms and the other one at around 20 s. The complex formed at longer time scale may be responsible for the inhibition of the enzyme activity.
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Affiliation(s)
- A K Sau
- Department of Chemical Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, 40 0005, Mumbai, India.
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Mondal MS, Sau AK, Mitra S. Mechanism of the inhibition of milk xanthine oxidase activity by metal ions: a transient kinetic study. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1480:302-10. [PMID: 11004570 DOI: 10.1016/s0167-4838(00)00084-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The nature and mechanism of the inhibition of the oxidoreductase activity of milk xanthine oxidase (XO) by Cu(2+), Hg(2+) and Ag(+) ions has been studied by steady state and stopped flow transient kinetic measurements. The results show that the nature of the inhibition is noncompetitive. The inhibition constants for Cu(2+) and Hg(2+) are in the micromolar and that for Ag(+) is in the nanomolar range. This suggests that the metal ions have strong affinity towards XO. pH dependence studies of the inhibition indicate that at least two ionisable groups of XO are involved in the binding of these metal ions. The effect of the interaction of the metal ions on the reductive and oxidative half reactions of XO has been investigated, and it is observed that the kinetic parameters of the reductive half reaction are not affected by these metal ions. However, the interaction of these metal ions with XO significantly affects the kinetic parameters of the oxidative half reaction. It is suggested that this may be the main cause for the inhibition of XO activity by the metal ions.
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Affiliation(s)
- M S Mondal
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, 400 005, Mumbai, India
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Mondal MS, Mitra S. Altered redox affinity of xanthine oxidase active sites by copper(II) ions. J CHEM SCI 1999. [DOI: 10.1007/bf02870847] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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Affiliation(s)
- Russ Hille
- Department of Medical Biochemistry, The Ohio State University, Columbus, Ohio 43210-1218
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Das SK, Biswas D, Maiti R, Sarkar S. Modeling the Tungsten Sites of Inactive and Active Forms of Hyperthermophilic Pyrococcus furiosus Aldehyde Ferredoxin Oxidoreductase. J Am Chem Soc 1996. [DOI: 10.1021/ja9511580] [Citation(s) in RCA: 99] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Samar K. Das
- Contribution from the Department of Chemistry, Indian Institute of Technology, Kanpur, Kanpur-208016, India
| | - Dulali Biswas
- Contribution from the Department of Chemistry, Indian Institute of Technology, Kanpur, Kanpur-208016, India
| | - Rabindranath Maiti
- Contribution from the Department of Chemistry, Indian Institute of Technology, Kanpur, Kanpur-208016, India
| | - Sabyasachi Sarkar
- Contribution from the Department of Chemistry, Indian Institute of Technology, Kanpur, Kanpur-208016, India
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