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Contrôle de l'organisation moléculaire en 2D et 3D par l’utilisation de liaisons hydrogène, de coordination métallique et d'autres interactions

Duong, Adam
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Thèse ou Mémoire numérique / Electronic Thesis or Dissertation
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La stratégie de la tectonique moléculaire a montré durant ces dernières années son utilité dans la construction de nouveaux matériaux. Elle repose sur l’auto-assemblage spontané de molécule dite intelligente appelée tecton. Ces molécules possèdent l’habilité de se reconnaitre entre elles en utilisant diverses interactions intermoléculaires. L'assemblage résultant peut donner lieu à des matériaux moléculaires avec une organisation prévisible. Cette stratégie exige la création de nouveaux tectons, qui sont parfois difficiles à synthétiser et nécessitent dans la plupart des cas de nombreuses étapes de synthèse, ce qui empêche ou limite leur mise en application pratique. De plus, une fois formées, les liaisons unissant le corps central du tecton avec ces groupements de reconnaissance moléculaire ne peuvent plus être rompues, ce qui ne permet pas de remodeler le tecton par une procédure synthétique simple. Afin de contourner ces obstacles, nous proposons d’utiliser une stratégie hybride qui se sert de la coordination métallique pour construire le corps central du tecton, combinée avec l'utilisation des interactions plus faibles pour contrôler l'association. Nous appelons une telle entité métallotecton du fait de la présence du métal. Pour explorer cette stratégie...

Insights into Phosphate Cooperativity and Influence of Substrate Modifications on Binding and Catalysis of Hexameric Purine Nucleoside Phosphorylases

Giuseppe, Priscila O. de; Martins, Nadia H.; Meza, Andreia N.; Santos, Camila R. dos; Pereira, Humberto D'Muniz; Murakami, Mario T.
Fonte: PUBLIC LIBRARY SCIENCE; SAN FRANCISCO Publicador: PUBLIC LIBRARY SCIENCE; SAN FRANCISCO
Tipo: Artigo de Revista Científica
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The hexameric purine nucleoside phosphorylase from Bacillus subtilis (BsPNP233) displays great potential to produce nucleoside analogues in industry and can be exploited in the development of new anti-tumor gene therapies. In order to provide structural basis for enzyme and substrates rational optimization, aiming at those applications, the present work shows a thorough and detailed structural description of the binding mode of substrates and nucleoside analogues to the active site of the hexameric BsPNP233. Here we report the crystal structure of BsPNP233 in the apo form and in complex with 11 ligands, including clinically relevant compounds. The crystal structure of six ligands (adenine, 2'deoxyguanosine, aciclovir, ganciclovir, 8-bromoguanosine, 6-chloroguanosine) in complex with a hexameric PNP are presented for the first time. Our data showed that free bases adopt alternative conformations in the BsPNP233 active site and indicated that binding of the co-substrate (2'deoxy) ribose 1-phosphate might contribute for stabilizing the bases in a favorable orientation for catalysis. The BsPNP233-adenosine complex revealed that a hydrogen bond between the 5' hydroxyl group of adenosine and Arg(43*) side chain contributes for the ribosyl radical to adopt an unusual C3'-endo conformation. The structures with 6-chloroguanosine and 8-bromoguanosine pointed out that the Cl-6 and Br-8 substrate modifications seem to be detrimental for catalysis and can be explored in the design of inhibitors for hexameric PNPs from pathogens. Our data also corroborated the competitive inhibition mechanism of hexameric PNPs by tubercidin and suggested that the acyclic nucleoside ganciclovir is a better inhibitor for hexameric PNPs than aciclovir. Furthermore...

Catalysis of tubulin heterodimerization in vivo; Catalysis of tubulin heterodimer reassembly

Doll, John M., 1976-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 150 leaves; 5159976 bytes; 5157414 bytes; application/pdf; application/pdf
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The heterodimerization of α- and β-tubulin represents a critical early step in microtubule morphogenesis. In vitro studies have defined a pathway that mediates the incorporation of monomeric tubulin polypeptides into heterodimer. The components of this pathway, tubulin cofactors, are dispensable for growth in Saccharomyces cerevisiae under laboratory conditions. Yet, these proteins are required for survival under conditions of stress or in the presence of a weakened tubulin heterodimer. This finding suggests cofactors may function in vivo to promote reformation of dissociated tubulin heterodimer. In order to carry out this activity, cofactors are thought to facilitate the association of tubulin monomers without likewise promoting the dissociation of tubulin heterodimer. However, the mechanism of cofactor activity in vivo and the method by which these proteins achieve vectorial catalysis of heterodimerization has remained obscure. In this study, we present evidence that several endogenous tubulin cofactors associate with one another in vivo and bind tubulin monomer under conditions of stress. We also provide physical and genetic data suggesting that Cin4p, an ARF family GTPase, associates with the tubulin cofactor Cin1 p (cofactor D) and promotes tubulin heterodimerization by modulating Cin1 p's association with β-tubulin. Through site-directed mutagenesis...

Identification of phosphates involved in catalysis by the ribozyme RNase P RNA.

Harris, M E; Pace, N R
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/1995 Português
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The RNA subunit of ribonuclease P (RNase P RNA) is a catalytic RNA that cleaves precursor tRNAs to generate mature tRNA 5' ends. Little is known concerning the identity and arrangement of functional groups that constitute the active site of this ribozyme. We have used an RNase P RNA-substrate conjugate that undergoes rapid, accurate, and efficient self-cleavage in vitro to probe, by phosphorothioate modification-interference, functional groups required for catalysis. We identify four phosphate oxygens where substitution by sulfur significantly reduces the catalytic rate (50-200-fold). Interference at one site was partially rescued in the presence of manganese, suggesting a direct involvement in binding divalent metal ion cofactors required for catalysis. All sites are located in conserved sequence and secondary structure, and positioned adjacent to the substrate phosphate in a tertiary structure model of the ribozyme-substrate complex. The spatial arrangement of phosphorothioate-sensitive sites in RNase P RNA was found to resemble the distribution of analogous positions in the secondary and potential tertiary structures of other large catalytic RNAs.

Multifunctional Role of His159in the Catalytic Reaction of Serine Palmitoyltransferase*

Shiraiwa, Yuka; Ikushiro, Hiroko; Hayashi, Hideyuki
Fonte: American Society for Biochemistry and Molecular Biology Publicador: American Society for Biochemistry and Molecular Biology
Tipo: Artigo de Revista Científica
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Serine palmitoyltransferase (SPT) belongs to the fold type I family of the pyridoxal 5′-phosphate (PLP)-dependent enzyme and forms 3-ketodihydrosphingosine (KDS) from l-serine and palmitoyl-CoA. Like other α-oxamine synthase subfamily enzymes, SPT is different from most of the fold type I enzymes in that its re face of the PLP-Lys aldimine is occupied by a His residue (His159) instead of an aromatic amino acid residue. His159 was changed into alanine or aromatic amino acid residues to examine its role during catalysis. All mutant SPTs formed the PLP-l-serine aldimine with dissociation constants several 10-fold higher than that of the wild type SPT and catalyzed the abortive transamination of l-serine. These results indicate that His159 is not only the anchoring site for l-serine but regulates the α-deprotonation of l-serine by fixing the conformation of the PLP-l-serine aldimine to prevent unwanted side reactions. Only H159A SPT retained activity and showed a prominent 505-nm absorption band of the quinonoid species during catalysis. Global analysis of the time-resolved spectra suggested the presence of the two quinonoid intermediates, the first formed from the PLP-l-serine aldimine and the second from the PLP-KDS aldimine. Accumulation of these quinonoid intermediates indicated that His159 promotes both the Claisen-type condensation as an acid catalyst and the protonation at Cα of the second quinonoid to form the PLP-KDS aldimine. These results...

Prebiotic RNA Synthesis by Montmorillonite Catalysis

Jheeta, Sohan; Joshi, Prakash C.
Fonte: MDPI Publicador: MDPI
Tipo: Artigo de Revista Científica
Publicado em 05/08/2014 Português
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This review summarizes our recent findings on the role of mineral salts in prebiotic RNA synthesis, which is catalyzed by montmorillonite clay minerals. The clay minerals not only catalyze the synthesis of RNA but also facilitate homochiral selection. Preliminary data of these findings have been presented at the “Horizontal Gene Transfer and the Last Universal Common Ancestor (LUCA)” conference at the Open University, Milton Keynes, UK, 5–6 September 2013. The objective of this meeting was to recognize the significance of RNA in LUCA. We believe that the prebiotic RNA synthesis from its monomers must have been a simple process. As a first step, it may have required activation of the 5'-end of the mononucleotide with a leaving group, e.g., imidazole in our model reaction (Figure 1). Wide ranges of activating groups are produced from HCN under plausible prebiotic Earth conditions. The final step is clay mineral catalysis in the presence of mineral salts to facilitate selective production of functional RNA. Both the clay minerals and mineral salts would have been abundant on early Earth. We have demonstrated that while montmorillonite (pH 7) produced only dimers from its monomers in water, addition of sodium chloride (1 M) enhanced the chain length multifold...

Thermodynamic Analysis Reveals a Temperature-dependent Change in the Catalytic Mechanism of Bacillus stearothermophilus Tyrosyl-tRNA Synthetase*S⃞

Sharma, Gyanesh; First, Eric A.
Fonte: American Society for Biochemistry and Molecular Biology Publicador: American Society for Biochemistry and Molecular Biology
Tipo: Artigo de Revista Científica
Publicado em 13/02/2009 Português
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Catalysis of tRNATyr aminoacylation by tyrosyl-tRNA synthetase can be divided into two steps. In the first step, tyrosine is activated by ATP to form the tyrosyl-adenylate intermediate. In the second step, the tyrosyl moiety is transferred to the 3′ end of tRNA. To investigate the roles that enthalpic and entropic contributions play in catalysis by Bacillus stearothermophilus tyrosyl-tRNA synthetase (TyrRS), the temperature dependence for the activation of tyrosine and subsequent transfer to tRNATyr has been determined using single turnover kinetic methods. A van't Hoff plot for binding of ATP to the TyrRS·Tyr complex reveals three distinct regions. Particularly striking is the change occurring at 25 °C, where the values of ΔH0 and ΔS0 go from –144 kJ/mol and –438 J/mol K below 25 °C to +137.9 kJ/mol and +507 J/mol K above 25 °C. Nonlinear Eyring and van't Hoff plots are also observed for formation of the TyrRS·[Tyr-ATP]‡ and TyrRS·Tyr-AMP complexes. Comparing the van't Hoff plots for the binding of ATP to tyrosyl-tRNA synthetase in the absence and presence of saturating tyrosine concentrations indicates that the temperature-dependent changes in ΔH0 and ΔS0 for the binding of ATP only occur when tyrosine is bound to the enzyme. Previous investigations revealed a similar synergistic interaction between the tyrosine and ATP substrates when the “KMSKS” signature sequence is deleted or replaced by a nonfunctional sequence. We propose that the temperature-dependent changes in ΔH0 and ΔS0 are because of the KMSKS signature sequence being conformationally constrained and unable to disrupt this synergistic interaction below 25 °C.

The roles of the conserved pyrimidine bases in hammerhead ribozyme catalysis: evidence for a magnesium ion-binding site.

Murray, J B; Adams, C J; Arnold, J R; Stockley, P G
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/10/1995 Português
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We report details of the synthesis and characterization of oligoribonucleotides containing 4-thiouridine or 2-pyrimidinone ribonucleoside (4HC). We have used these probes to examine the roles of the conserved pyrimidines in the central core of the hammerhead ribozyme. The effects on catalysis of singly-substituted hammerhead ribozyme and substrate strands were quantified in multiple-turnover reactions. Various effects were observed on kcat. and Km, with up to a 7-fold decrease and a 3-fold increase respectively. For substitutions with 4HC at positions 3 or 17, catalytic activity in single turnover reactions can be increased up to 8-fold equivalent to 40% of wild-type activity, by increasing the concentration of the Mg2+ cofactor, implying that these substitutions had a deleterious effect on Mg2+ binding. Calculations of the change in the apparent free energy of binding for variants at positions 3, 4 or 17 are each consistent with deletion of a single hydrogen-bond to an uncharged group in the ribozyme. The cytidine 5' to the scissile phosphate had not previously been thought to play a direct role in catalysis, however, removal of the exocyclic amino group decreased kcat. 4-fold. Recently, the crystal structures of a hammerhead ribozyme bound to either a non-cleavable 2'-deoxy substrate strand or a ribo-substrate strand have been reported. The kinetic properties of the variants described here are consistent with several key interactions seen in the crystals...

Use of binding energy by an RNA enzyme for catalysis by positioning and substrate destabilization.

Narlikar, G J; Gopalakrishnan, V; McConnell, T S; Usman, N; Herschlag, D
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 25/04/1995 Português
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A fundamental catalytic principle for protein enzymes in the use of binding interactions away from the site of chemical transformation for catalysis. We have compared the binding and reactivity of a series of oligonucleotide substrates and products of the Tetrahymena ribozyme, which catalyzes a site-specific phosphodiester cleavage reaction: CCCUCUpA+G<-->CCCUCU-OH+GpA. The results suggest that this RNA enzyme, like protein enzymes, can utilize binding interactions to achieve substantial catalysis via entropic fixation and substrate destabilization. The stronger binding of the all-ribose oligonucleotide product compared to an analog with a terminal 3' deoxyribose residue gives an effective concentration of 2200 M for the 3' hydroxyl group, a value approaching those obtained with protein enzymes and suggesting the presence of a structurally well defined active site capable of precise positioning. The stabilization from tertiary binding interactions is 40-fold less for the oligonucleotide substrate than the oligonucleotide product, despite the presence of the reactive phosphoryl group in the substrate. This destabilization is accounted for by a model in which tertiary interactions away from the site of bond cleavage position the electron-deficient 3' bridging phosphoryl oxygen of the oligonucleotide substrate next to an electropositive Mg ion. As the phosphodiester bond breaks and this 3' oxygen atom develops a negative charge in the transition state...

Contrasting observations on buffer catalysis of guanosine amino proton exchange.

McConnell, B
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 10/12/1987 Português
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The two amino protons of 3', 5'-cyclic guanosine monophosphate are shown to differ drastically in their solvent exchange properties: One is rapidly exchanging and sensitive to buffer catalysis; the other slow and insensitive. This observation accounts for the marked contrast between stopped-flow and NMR observations on buffer catalysis of amino proton exchange in guanosine monophosphates. The amino protons of guanine compounds traverse a "fast" solvent exchange position through the process of amino rotation, which together with kinetic considerations and comparative data on adenine and cytosine compounds, supports proposals of solvent exchange mediated by events at the guanine (N-3) site, rather than the (N-7) site. Exchange does not conform to rate expressions used by different workers for amino proton exchange.

Selectivity of Fungal Sesquiterpene Synthases: Role of the Active Site's H-1α Loop in Catalysis▿ †

López-Gallego, Fernando; Wawrzyn, GraysonT.; Schmidt-Dannert, Claudia
Fonte: American Society for Microbiology (ASM) Publicador: American Society for Microbiology (ASM)
Tipo: Artigo de Revista Científica
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Sesquiterpene synthases are responsible for the cyclization of farnesyl pyrophosphate into a myriad of structurally diverse compounds with various biological activities. We examine here the role of the conserved active site H-α1 loop in catalysis in three previously characterized fungal sesquiterpene synthases. The H-α1 loops of Cop3, Cop4, and Cop6 from Coprinus cinereus were altered by site-directed mutagenesis and the resultant product profiles were analyzed by gas chromatography-mass spectrometry and compared to the wild-type enzymes. In addition, we examine the effect of swapping the H-α1 loop from the promiscuous enzyme Cop4 with the more selective Cop6 and the effect of acidic or basic conditions on loop mutations in Cop4. Directed mutations of the H-α1 loop had a marked effect on the product profile of Cop3 and Cop4, while little to no change was shown in Cop6. Swapping of the Cop4 and Cop6 loops with one another was again shown to influence the product profile of Cop4, while the product profile of Cop6 remained identical to the wild-type enzyme. The loop mutations in Cop4 also implicate specific residues responsible for the pH sensitivity of the enzyme. These results affirm the role of the H-α1 loop in catalysis and provide a potential target to increase the product diversity of terpene synthases.

Mechanistic studies on the phosphoramidite coupling reaction in oligonucleotide synthesis. I. Evidence for nucleophilic catalysis by tetrazole and rate variations with the phosphorus substituents.

Dahl, B H; Nielsen, J; Dahl, O
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 25/02/1987 Português
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Tetrazole catalyzed reactions of a series of phosphoramidites, 5'-O-DMTdT-3'-O-P(OR1)NR2(2) (1a-h), with 3'-O-SiButPh2-6-N-benzoyl-dA (2a) in acetonitrile solution have been studied. It is found that the coupling rate depends very much on whether tetrazole is added before or after 2a, and that dialkylammonium tetrazolide salts are inhibitors. These and other facts are evidence that the reactions are subjected to nucleophilic catalysis by tetrazole, in addition to acid catalysis. The rate variations with phosphorus substituents of 1a-h are NEt2 greater than NPri2 greater than N(CH2CH2)O greater than NMePh, and OMe greater than OCH2CH2CN greater than OCHMeCH2CN greater than OCMe2CH2CN much greater than OC6H4Cl. The inhibitor properties of dialkylammonium tetrazolides have practical consequences for the efficiency of DNA syntheses, when in situ prepared phosphoramidites are used; the same would apply for segmented, simultaneous syntheses or syntheses where recycling is performed.

Binding to thermolysin of phenolate-containing inhibitors necessitates a revised mechanism of catalysis.

Mock, W L; Aksamawati, M
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/08/1994 Português
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Competitive inhibition as a function of pH for the metalloendoprotease thermolysin by derivatives of L-alpha-(2-hydroxyphenyl)benzenepropanoyl-L- tryptophanylglycylglycine exhibits a diagnostic bell shape. Binding is maximal between two pKa values: on the acidic limb the apparent Ki value is regulated by an unchanging enzymic ionization (pKa 5.3) which is also seen in the substrate-hydrolysis kinetics (kcat/Km), whereas the alkaline limb for inhibition varies and depends specifically on the pKa of the phenolic group in the inhibitor. Although it should be the phenolate form of the inhibitor that co-ordinates more efficiently to the active-site Zn2+, the apparent Ki shifts from pH-independent at pH values immediately below the inhibitor's pKa to progressively weaker binding at higher pH. This is explained by an anomalous acidity for the exchangeable solvent molecule that is attached to enzymic Zn2+ in the absence of substrate or inhibitor. Since OH- cannot be displaced from the enzyme as readily as H2O, a compensating pKa of 5.3 possessed by Zn(2+)-bound water rationalizes the binding characteristics, yielding the level pH profile exhibited at intermediate pH values. Recognition of the implicit heightened Lewis acidity of the metal ion in thermolysin leads to a revision of the mechanism of catalysis. The substrate amide bond becomes activated for hydrolysis by carbonyl-group co-ordination to the especially acidic Zn2+ ion (completely displacing the H2O/OH- species otherwise bound). The imidazole group of enzymic residue His-231...

Plasmon-driven surface catalysis in hybridized plasmonic gap modes

Wang, Hui; Liu, Ting; Huang, Yingzhou; Fang, Yurui; Liu, Ruchuan; Wang, Shuxia; Wen, Weijia; Sun, Mengtao
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 18/11/2014 Português
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Plasmon-driven surface catalytic (PDSC) reaction in Ag/Au nanoparticle monomer or dimer-film gaps are experimentally and theoretically investigated, using surface enhanced Raman scattering (SERS) and finite element method. The variation of SERS spectra in different nano gaps of nanoparticle-film systems indicated the PDSC reaction was largely depended on the number of nanoparticles. The higher Raman intensity of p,p′-dimercaptoazobenzene (DMAB) in dimer-film nanogap was because effective coupling of induced image charge on metal film in hybridized plasmonic gap mode, which was confirmed by the electric field distribution. Furthermore, the influence of material and wavelength was also studied to obtain the optimal experimental condition for best surface catalysis in hybridized plasmonic gap mode. Our studies in this common configuration of plasmonic nanostructure are of great significance not only in the field of catalysis on metal surface but also in other surface plasmon fields such as senor, photon detection, water splitting, etc.

Selective hydrogenation of dimethyl adipate on titania-supported RuSn catalysts.

Silva, Adriana Maria da; Morales, Marco A; Baggio-Saitovitch, Elisa M; Jordão, Elisabete; Fraga, Marco André
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
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Applied Catalysis A: General, 353(2009):101-106; The hydrogenation of dimethyl adipate over RuSn catalysis was studied to examine the effect of tin species and titania on selective production of 1,6-hexanediol.

Nmnat1-Rbp7 Is a Conserved Fusion-Protein That Combines NAD+ Catalysis of Nmnat1 with Subcellular Localization of Rbp7

Chen, Hao; Babino, Darwin; Schoenbichler, Stefan A.; Arkhipova, Valeryia; Töchterle, Sonja; Martin, Fabian; Huck, Christian W.; von Lintig, Johannes; Meyer, Dirk
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 30/11/2015 Português
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Retinol binding proteins (Rbps) are known as carriers for transport and targeting of retinoids to their metabolizing enzymes. Rbps are also reported to function in regulating the homeostatic balance of retinoid metabolism, as their level of retinoid occupancy impacts the activities of retinoid metabolizing enzymes. Here we used zebrafish as a model to study rbp7a function and regulation. We find that early embryonic rbp7a expression is negatively regulated by the Nodal/FoxH1-signaling pathway and we show that Nodal/FoxH1 activity has the opposite effect on aldh1a2, which encodes the major enzyme for early embryonic retinoic acid production. The data are consistent with a Nodal-dependent coordination of the allocation of retinoid precursors to processing enzymes with the catalysis of retinoic acid formation. Further, we describe a novel nmnat1-rbp7 transcript encoding a fusion of Rbp7 and the NAD+ (Nicotinamide adenine dinucleotide) synthesizing enzyme Nmnat1. We show that nmnat1-rbp7 is conserved in fish, mouse and chicken, and that in zebrafish regulation of nmnat1-rbp7a is distinct from that of rbp7a and nmnat1. Injection experiments in zebrafish further revealed that Nmnat1-Rbp7a and Nmnat1 have similar NAD+ catalyzing activities but a different subcellular localization. HPLC measurements and protein localization analysis highlight Nmnat1-Rbp7a as the only known cytoplasmic and presumably endoplasmic reticulum (ER) specific NAD+ catalyzing enzyme. These studies...

Inverse magnetic catalysis in dense holographic matter

Preis, Florian; Rebhan, Anton; Schmitt, Andreas
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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We study the chiral phase transition in a magnetic field at finite temperature and chemical potential within the Sakai-Sugimoto model, a holographic top-down approach to (large-N_c) QCD. We consider the limit of a small separation of the flavor D8-branes, which corresponds to a dual field theory comparable to a Nambu-Jona Lasinio (NJL) model. Mapping out the surface of the chiral phase transition in the parameter space of magnetic field strength, quark chemical potential, and temperature, we find that for small temperatures the addition of a magnetic field decreases the critical chemical potential for chiral symmetry restoration - in contrast to the case of vanishing chemical potential where, in accordance with the familiar phenomenon of magnetic catalysis, the magnetic field favors the chirally broken phase. This "inverse magnetic catalysis" (IMC) appears to be associated with a previously found magnetic phase transition within the chirally symmetric phase that shows an intriguing similarity to a transition into the lowest Landau level. We estimate IMC to persist up to 10^{19} G at low temperatures.; Comment: 42 pages, 11 figures, v3: extended discussion; new appendix D; references added; version to appear in JHEP

Influence of the inverse magnetic catalysis and the vector interaction in the location of the critical end point

Costa, Pedro; Ferreira, Márcio; Menezes, Débora P.; Moreira, João; Providência, Constança
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 31/08/2015 Português
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The effect of a strong magnetic field on the location of the critical end point (CEP) in the QCD phase diagram is discussed under different scenarios. In particular, we consider the contribution of the vector interaction and take into account the inverse magnetic catalysis obtained in lattice QCD calculations at zero chemical potential. The discussion is realized within the (2+1) Polyakov--Nambu--Jona-Lasinio model. It is shown that the vector interaction and the magnetic field have opposite competing effects, and that the winning effect depends strongly on the intensity of the magnetic field. The inverse magnetic catalysis at zero chemical potential has two distinct effects for magnetic fields above $\gtrsim 0.3$ GeV$^2$: it shifts the CEP to lower chemical potentials, hinders the increase of the CEP temperature and prevents a too large increase of the baryonic density at the CEP. For fields $eB<0.1$ GeV$^2$ the competing effects between the vector contribution and the magnetic field can move the CEP to regions of temperature and density in the phase diagram that could be more easily accessible to experiments.; Comment: 12 pages, 9 figures; PRD version

Inverse Magnetic Catalysis in the three-flavor NJL model with axial-vector interaction

Yu, Lang; Van Doorsselaere, Jos; Huang, Mei
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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In this paper we explore the chiral phase transition in QCD within the three-flavor Nambu-Jona-Lasinio (NJL) model with a negative coupling constant in the isoscalar axial-vector channel, which is associated with a polarized instanton--anti-instanton molecule background. The QCD phase diagram described in this scenario shows a new first order phase transition around the transition temperature $T_c$ toward a phase without chiral condensates, but with nontrivial dynamic chiral chemical potentials for the light quarks, spontaneously giving rise to local $\mathcal {CP}$ violation and local chirality imbalance. The corresponding critical temperature $T_{5c}$ for this phase transition decreases with the magnetic field and it gives a natural explanation to the inverse magnetic catalysis effect for light quarks when incorporating a reasonable value of the coupling constant in the isoscalar axial-vector channel. Furthermore, when the isoscalar axial-vector interaction is dominant in light quark sector and suppressed in strange quark sector, it is found that there is no inverse magnetic catalysis for strange quark condensate, which agrees with lattice results.

Optimal Database Search: Waves and Catalysis

Patel, Apoorva
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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Grover's database search algorithm, although discovered in the context of quantum computation, can be implemented using any system that allows superposition of states. A physical realization of this algorithm is described using coupled simple harmonic oscillators, which can be exactly solved in both classical and quantum domains. Classical wave algorithms are far more stable against decoherence compared to their quantum counterparts. In addition to providing convenient demonstration models, they may have a role in practical situations, such as catalysis.; Comment: 4 pages (v2) 6 pages, RevTeX4. Title changed. Substantially expanded to include stability considerations, quantum domain analysis, application to catalysis. (v3) Version accepted for publication. (v4) Error in Eqs.(10,11) corrected by replacing \omega by \omega^2. No change in implementation and application