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Miller MC, Dregni AJ, Platt D, Mayo KH. PLG-007 and Its Active Component Galactomannan-α Competitively Inhibit Enzymes That Hydrolyze Glucose Polymers. Int J Mol Sci 2022; 23:ijms23147739. [PMID: 35887087 PMCID: PMC9316267 DOI: 10.3390/ijms23147739] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2022] [Revised: 07/07/2022] [Accepted: 07/11/2022] [Indexed: 02/05/2023] Open
Abstract
PLG-007 is a developmental therapeutic compound that has been clinically shown to reduce the magnitude of postprandial glucose excursions and has the potential to be an adjunct treatment for diabetes and inflammatory-related diseases. The present investigation is aimed at understanding the molecular mechanism of action of PLG-007 and its galactomannan (GM) components GMα and GMβ (in a 1:4 mass ratio, respectively) on enzyme (i.e., α-amylase, maltase, and lactase) hydrolysis of glucose polymers using colorimetric assays and 13C HSQC NMR spectroscopy. The starch–iodine colorimetric assay indicated that GMα strongly inhibits α-amylase activity (~16-fold more potent than GMβ) and thus is the primary active component in PLG-007. 13C HSQC experiments, used to follow the α-amylase-mediated hydrolysis of starch and amylopectin, further demonstrate the α-amylase inhibitory effect of GMα via α-amylase-mediated hydrolysis of starch and amylopectin. Maltohexaose (MT6) was used to circumvent the relative kinetic complexity of starch/amylopectin degradation in Michaelis–Menten analyses. The Vmax, KM, and Ki parameters were determined using peak volume integrals from 13C HSQC NMR spectra. In the presence of PLG-007 with α-amylase and MT6, the increase in KM from 7.5 ± 0.6 × 10−3 M (control) to 21 ± 1.4 × 10−3 M, with no significant change in Vmax, indicates that PLG-007 is a competitive inhibitor of α-amylase. Using KM values, Ki was estimated to be 2.1 ± 0.9 × 10−6 M; however, the microscopic Ki value of GMα is expected to be larger as the binding stoichiometry is likely to be greater than 1:1. Colorimetric assays also demonstrated that GMα is a competitive inhibitor of the enzymes maltase and lactase. Overall, this study provides insight as to how PLG-007 (GMα) is likely to function in vivo.
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Affiliation(s)
- Michelle C. Miller
- Department of Biochemistry, Molecular Biology & Biophysics, University of Minnesota Health Sciences Center, 6-155 Jackson Hall, 321 Church Street, Minneapolis, MN 55455, USA; (M.C.M.); (A.J.D.)
| | - Aurelio J. Dregni
- Department of Biochemistry, Molecular Biology & Biophysics, University of Minnesota Health Sciences Center, 6-155 Jackson Hall, 321 Church Street, Minneapolis, MN 55455, USA; (M.C.M.); (A.J.D.)
| | - David Platt
- Bioxytran Inc., 75 2nd Ave., Suite 605, Needham, MA 02494, USA;
| | - Kevin H. Mayo
- Department of Biochemistry, Molecular Biology & Biophysics, University of Minnesota Health Sciences Center, 6-155 Jackson Hall, 321 Church Street, Minneapolis, MN 55455, USA; (M.C.M.); (A.J.D.)
- Correspondence:
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Isoform-Specific NO Synthesis by Arabidopsis thaliana Nitrate Reductase. PLANTS 2019; 8:plants8030067. [PMID: 30884848 PMCID: PMC6473903 DOI: 10.3390/plants8030067] [Citation(s) in RCA: 40] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/06/2019] [Revised: 03/06/2019] [Accepted: 03/11/2019] [Indexed: 12/20/2022]
Abstract
Nitrate reductase (NR) is important for higher land plants, as it catalyzes the rate-limiting step in the nitrate assimilation pathway, the two-electron reduction of nitrate to nitrite. Furthermore, it is considered to be a major enzymatic source of the important signaling molecule nitric oxide (NO), that is produced in a one-electron reduction of nitrite. Like many other plants, the model plant Arabidopsis thaliana expresses two isoforms of NR (NIA1 and NIA2). Up to now, only NIA2 has been the focus of detailed biochemical studies, while NIA1 awaits biochemical characterization. In this study, we have expressed and purified functional fragments of NIA1 and subjected them to various biochemical assays for comparison with the corresponding NIA2-fragments. We analyzed the kinetic parameters in multiple steady-state assays using nitrate or nitrite as substrate and measured either substrate consumption (nitrate or nitrite) or product formation (NO). Our results show that NIA1 is the more efficient nitrite reductase while NIA2 exhibits higher nitrate reductase activity, which supports the hypothesis that the isoforms have special functions in the plant. Furthermore, we successfully restored the physiological electron transfer pathway of NR using reduced nicotinamide adenine dinucleotide (NADH) and nitrate or nitrite as substrates by mixing the N-and C-terminal fragments of NR, thus, opening up new possibilities to study NR activity, regulation and structure.
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Mesbahi-Nowrouzi M, Mollania N. Purification of selenate reductase from Alcaligenes sp. CKCr-6A with the ability to biosynthesis of selenium nanoparticle: Enzymatic behavior study in imidazolium based ionic liquids and organic solvent. J Mol Liq 2018. [DOI: 10.1016/j.molliq.2017.10.117] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Adouani N, Limousy L, Lendormi T, Voit EO, Sire O. Simulation of the Denitrification Process of Waste Water with a Biochemical Systems Model: A Non-Conventional Approach. INTERNATIONAL JOURNAL OF CHEMICAL REACTOR ENGINEERING 2014. [DOI: 10.1515/ijcre-2014-0050] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Abstract
Matching experimental and theoretical approaches have often been fruitful in the investigation of complex biological processes. Here we develop a novel non-conventional model for the denitrification of waste water. Earlier models of the denitrification process were compiled by the International Association on Water Quality group. The Activated Sludge Models 1–3, which are the most frequently used all over the world, are presently not adapted towards the integration of both nitrous and nitric oxide emissions during the denitrification process. In the present work, a Generalized Mass Action model, based on Biochemical Systems Theory, was designed to simulate the nitrate reduction observed in specific experimental conditions. The model was implemented and analysed with the software package PLAS. Data from a representative experiment were chosen (T=10°C, pH=7, C/N=3, with acetate as carbon source) to simulate greenhouse NO and N2O gas emissions, in order to test hypotheses about the corresponding bacterial metabolic pathways. The results show that the reduction of nitrate and nitrite is kinetically limiting and that nitrate reduction is limited by diffusion and support that distinct microbial subpopulations are involved in the denitrification pathway, which has consequences for NO emissions.
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Affiliation(s)
| | | | - Thomas Lendormi
- Univ. Bretagne-Sud, EA4250, Laboratoire d’Ingénierie des Matéraiux de Bretagne (LIMATB), F-56300 Pontivy, France
| | - Eberhard O. Voit
- Department of Biomedical Engineering, Georgia Tech and Emory University, 313 Ferst Drive, Suite 4103, Atlanta, GA 30332-0535, USA
| | - Olivier Sire
- Univ. Bretagne-Sud, EA4250, Laboratoire d’Ingénierie des Matéraiux de Bretagne (LIMATB), F-56300 Pontivy, France
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Alavi S, Amoozegar MA, Khajeh K. Enzyme(s) responsible for tellurite reducing activity in a moderately halophilic bacterium, Salinicoccus iranensis strain QW6. Extremophiles 2014; 18:953-61. [PMID: 24984690 DOI: 10.1007/s00792-014-0665-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2014] [Accepted: 06/05/2014] [Indexed: 10/25/2022]
Abstract
Oxyanions of tellurium, like tellurate (TeO4 (2-)) and tellurite (TeO3 (2-)), are highly toxic for most microorganisms. There are a few reports on the bacterial tellurite resistance mechanism(s). Salinicoccus iranensis, a Gram-positive halophilic bacterium, shows high tellurite resistance and NADH-dependent tellurite reduction activity in vitro. Since little is known regarding TeO3 (2-) resistance mechanisms in halophilic microorganisms, here one of the enzymatic reduction activities presented in this microorganism is investigated. To enhance the enzymatic activity during purification, the effect of different parameters including time, inoculation, different pHs, different tellurite concentrations and different salts were optimized. We also examined the tellurite removal rates by diethyldithiocarbamate (DDTC) during optimization. In the culture medium the optimum conditions obtained showed that at 30 h, 2 % inoculum, pH 7.5, without tellurite and with 5 % NaCl (w/v) the highest enzyme activity and tellurite removal were observed. Results of the purification procedure done by hydroxyapatite batch-mode, ammonium sulfate precipitation, followed by phenyl-Sepharose and Sephadex G-100 column chromatography, showed that the enzyme consisted of three subunits with molecular masses of 135, 63 and 57 kDa. In addition to tellurite reduction activity, the enzyme was able to reduce nitrate too. Our study extends the knowledge regarding this process in halophilic microorganisms. Besides, this approach may suggest an application for the organism or the enzyme itself to be used for bioremediation of polluted areas with different contaminants due to its nitrate reductase activity.
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Affiliation(s)
- Sana Alavi
- Extremophiles Laboratory, Department of Microbiology, Faculty of Biology and Center of Excellence in Phylogeny of Living Organisms, College of Science, University of Tehran, P.O. Box 14155-6455, Tehran, Iran
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Carlisle E, Yarnes C, Toney MD, Bloom AJ. Nitrate reductase (15)N discrimination in Arabidopsis thaliana, Zea mays, Aspergillus niger, Pichea angusta, and Escherichia coli. FRONTIERS IN PLANT SCIENCE 2014; 5:317. [PMID: 25071800 PMCID: PMC4078254 DOI: 10.3389/fpls.2014.00317] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2014] [Accepted: 06/15/2014] [Indexed: 05/06/2023]
Abstract
Stable (15)N isotopes have been used to examine movement of nitrogen (N) through various pools of the global N cycle. A central reaction in the cycle involves the reduction of nitrate (NO(-) 3) to nitrite (NO(-) 2) catalyzed by nitrate reductase (NR). Discrimination against (15)N by NR is a major determinant of isotopic differences among N pools. Here, we measured in vitro (15)N discrimination by several NRs purified from plants, fungi, and a bacterium to determine the intrinsic (15)N discrimination by the enzyme and to evaluate the validity of measurements made using (15)N-enriched NO(-) 3. Observed NR isotope discrimination ranged from 22 to 32‰ (kinetic isotope effects of 1.022-1.032) among the different isozymes at natural abundance (15)N (0.37%). As the fractional (15)N content of substrate NO(-) 3 increased from natural abundance, the product (15)N fraction deviated significantly from that expected based on substrate enrichment and (15)N discrimination measured at natural abundance. Additionally, isotopic discrimination by denitrifying bacteria used to reduce NO(-) 3 and NO(-) 2 in some protocols became a greater source of error as (15)N enrichment increased. We briefly discuss potential causes of the experimental artifacts with enriched (15)N and recommend against the use of highly enriched (15)N tracers to study N discrimination in plants or soils.
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Affiliation(s)
- Eli Carlisle
- Department of Plant Sciences, University of CaliforniaDavis, CA, USA
| | - Chris Yarnes
- Department of Plant Sciences, University of CaliforniaDavis, CA, USA
| | | | - Arnold J. Bloom
- Department of Plant Sciences, University of CaliforniaDavis, CA, USA
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Puchkov EO. Intracellular viscosity: Methods of measurement and role in metabolism. BIOCHEMISTRY MOSCOW SUPPLEMENT SERIES A-MEMBRANE AND CELL BIOLOGY 2013. [DOI: 10.1134/s1990747813050140] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
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Adjustment of Arrhenius activation energy of laccase-based time–temperature integrator (TTI) using sodium azide. Food Control 2013. [DOI: 10.1016/j.foodcont.2013.01.046] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Žižić M, Živić M, Spasojević I, Bogdanović Pristov J, Stanić M, Cvetić-Antić T, Zakrzewska J. The interactions of vanadium with Phycomyces blakesleeanus mycelium: enzymatic reduction, transport and metabolic effects. Res Microbiol 2012; 164:61-9. [PMID: 22992386 DOI: 10.1016/j.resmic.2012.08.007] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2012] [Accepted: 08/21/2012] [Indexed: 10/27/2022]
Abstract
The biological and chemical basis of vanadium action and transport in fungi is relatively poorly understood. In this study we investigated the interactions of vanadium in physiologically-relevant redox states: vanadate (+5) and vanadyl (+4), with mycelium of fungus Phycomyces blakesleeanus using EPR and (31)P NMR spectroscopy and biochemical assays. We determined that P. blakesleeanus reduces V(5+) to V(4+) in the extracellular compartment by the means of cell surface enzyme with ferricyanide reductase activity, which contains molybdenum-molybdopterin as a cofactor. Both, V(5+) and V(4+) bind to cell wall. They enter the cytoplasm via phosphate transporter and cation channels, respectively, and exhibit different metabolic effects. Vanadate provokes increased biomass production, the effects being inverted to toxic at higher V(5+) concentrations. In addition, V(5+) activates the synthesis of sugar phosphates and oligophosphates. On the other hand, V(4+) exhibits toxic effects even at low concentrations. The V(4+) detoxification route involves binding to vacuolar polyphosphates. Altogether our results imply that the mechanism of interaction of vanadium with P. blakesleeanus involves three major steps: extracellular enzymatic V(5+)/V(4+) reduction, V(4+) influx, and vacuolar storage, with an additional step - V(5+) import occurring at higher vanadate concentrations.
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Affiliation(s)
- Milan Žižić
- Department of Life Sciences, Institute for Multidisciplinary Research, University of Belgrade, Kneza Višeslava 1, 11030 Belgrade, Serbia.
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Karsh KL, Granger J, Kritee K, Sigman DM. Eukaryotic assimilatory nitrate reductase fractionates N and O isotopes with a ratio near unity. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2012; 46:5727-35. [PMID: 22534036 DOI: 10.1021/es204593q] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
In order to (i) establish the biological systematics necessary to interpret nitrogen (N) and oxygen (O) isotope ratios of nitrate ((15)N/(14)N and (18)O/(16)O) in the environment and (ii) investigate the potential for isotopes to elucidate the mechanism of a key N cycle enzyme, we measured the nitrate N and O isotope effects ((15)ε and (18)ε) for nitrate reduction by two assimilatory eukaryotic nitrate reductase (eukNR) enzymes. The (15)ε for purified extracts of NADPH eukNR from the fungus Aspergillus niger and the (15)ε for NADH eukNR from cell homogenates of the marine diatom Thalassiosira weissflogii were indistinguishable, yielding a mean (15)ε for the enzyme of 26.6 ± 0.2‰. Both forms of eukNR imparted near equivalent fractionation on N and O isotopes. The increase in (18)O/(16)O versus the increase in (15)N/(14)N (relative to their natural abundances) was 0.96 ± 0.01 for NADPH eukNR and 1.09 ± 0.03 for NADH eukNR. These results are the first reliable measurements of the coupled N and O isotope effects for any form of eukNR. They support the prevailing view that intracellular reduction by eukNR is the dominant step in isotope fractionation during nitrate assimilation and that it drives the (18)ε:(15)ε ≈ 1 observed in phytoplankton cultures, suggesting that this O-to-N isotope signature will apply broadly in the environment. Our measured (15)ε and (18)ε may represent the intrinsic isotope effects for eukNR-mediated N-O bond rupture, a potential constraint on the nature of the enzyme's transition state.
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Affiliation(s)
- Kristen L Karsh
- Department of Geosciences, Princeton University, Guyot Hall, Princeton, New Jersey 08544, United States.
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Lambeck IC, Fischer-Schrader K, Niks D, Roeper J, Chi JC, Hille R, Schwarz G. Molecular mechanism of 14-3-3 protein-mediated inhibition of plant nitrate reductase. J Biol Chem 2011; 287:4562-71. [PMID: 22170050 DOI: 10.1074/jbc.m111.323113] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
14-3-3 proteins regulate key processes in eukaryotic cells including nitrogen assimilation in plants by tuning the activity of nitrate reductase (NR), the first and rate-limiting enzyme in this pathway. The homodimeric NR harbors three cofactors, each of which is bound to separate domains, thus forming an electron transfer chain. 14-3-3 proteins inhibit NR by binding to a conserved phosphorylation site localized in the linker between the heme and molybdenum cofactor-containing domains. Here, we have investigated the molecular mechanism of 14-3-3-mediated NR inhibition using a fragment of the enzyme lacking the third domain, allowing us to analyze electron transfer from the heme cofactor via the molybdenum center to nitrate. The kinetic behavior of the inhibited Mo-heme fragment indicates that the principal point at which 14-3-3 acts is the electron transfer from the heme to the molybdenum cofactor. We demonstrate that this is not due to a perturbation of the reduction potentials of either the heme or the molybdenum center and conclude that 14-3-3 most likely inhibits nitrate reductase by inducing a conformational change that significantly increases the distance between the two redox-active sites.
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Affiliation(s)
- Iris C Lambeck
- Institute of Biochemistry, Department of Chemistry and Center for Molecular Medicine, University of Cologne, 50674 Cologne, Germany
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Lambeck I, Chi JC, Krizowski S, Mueller S, Mehlmer N, Teige M, Fischer K, Schwarz G. Kinetic analysis of 14-3-3-inhibited Arabidopsis thaliana nitrate reductase. Biochemistry 2010; 49:8177-86. [PMID: 20690630 DOI: 10.1021/bi1003487] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Eukaryotic assimilatory nitrate reductase (NR) is a dimeric multidomain molybdo-heme-flavo protein that catalyzes the first and rate-limiting step in the nitrate assimilation of plants, algae, and fungi. Nitrate reduction takes place at the N-terminal molybdenum cofactor-containing domain. Reducing equivalents are derived from NADH, which reduce the C-terminal FAD domain followed by single-electron transfer steps via the middle heme domain to the molybdenum center. In plants, nitrate reduction is post-translationally inhibited by phosphorylation and subsequent binding of 14-3-3 protein to a conserved phosphoserine located in the surface-exposed hinge between the catalytic and heme domain. Here we investigated Arabidopsis thaliana NR activity upon phosphorylation and 14-3-3 binding by using a fully defined in vitro system with purified proteins. We demonstrate that among different calcium-dependent protein kinases (CPKs), CPK-17 efficiently phosphorylates Ser534 in NR. Out of eight purified Arabidopsis 14-3-3 proteins, isoforms ω, κ, and λ exhibited the strongest inhibition of NR. The kinetic parameters of noninhibited, phosphorylated NR (pNR) and pNR in a complex with 14-3-3 were investigated. An 18-fold reduction in k(cat) and a decrease in the apparent K(M)(nitrate) (from 280 to 141 μM) were observed upon binding of 14-3-3 to pNR, suggesting a noncompetitive inhibition with a preferential binding to the substrate-bound state of the enzyme. Recording partial activities of NR demonstrated that the transfer of electrons to the heme is not affected by 14-3-3 binding. The Ser534Ala variant of NR was not inhibited by 14-3-3 proteins. We propose that 14-3-3 binding to Ser534 blocks the transfer of electrons from heme to nitrate by arresting the domain movement via hinge 1.
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Affiliation(s)
- Iris Lambeck
- Institute of Biochemistry, Department of Chemistry, University of Cologne, 50674 Cologne, Germany
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Etezad SM, Khajeh K, Soudi M, Ghazvini PTM, Dabirmanesh B. Evidence on the presence of two distinct enzymes responsible for the reduction of selenate and tellurite in Bacillus sp. STG-83. Enzyme Microb Technol 2009. [DOI: 10.1016/j.enzmictec.2009.04.004] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Yu HQ, Zhang DH, Gu XB, Miyoshi D, Sugimoto N. Regulation of telomerase activity by the thermodynamic stability of a DNA x RNA hybrid. Angew Chem Int Ed Engl 2008; 47:9034-8. [PMID: 18850626 DOI: 10.1002/anie.200803577] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Affiliation(s)
- Hai-Qing Yu
- Frontier Institute for Biomolecular Engineering Research, Konan University, 8-9-1 Okamoto, Higashinada-ku, Kobe 658-8501, Japan
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Yu HQ, Zhang DH, Gu XB, Miyoshi D, Sugimoto N. Regulation of Telomerase Activity by the Thermodynamic Stability of a DNA⋅RNA Hybrid. Angew Chem Int Ed Engl 2008. [DOI: 10.1002/ange.200803577] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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