Sample records for enzyme catalyzed reactions

  1. Thermodynamics of Enzyme-Catalyzed Reactions Database

    National Institute of Standards and Technology Data Gateway

    SRD 74 Thermodynamics of Enzyme-Catalyzed Reactions Database (Web, free access)   The Thermodynamics of Enzyme-Catalyzed Reactions Database contains thermodynamic data on enzyme-catalyzed reactions that have been recently published in the Journal of Physical and Chemical Reference Data (JPCRD). For each reaction the following information is provided: the reference for the data, the reaction studied, the name of the enzyme used and its Enzyme Commission number, the method of measurement, the data and an evaluation thereof.

  2. Stochastic Simulation of Enzyme-Catalyzed Reactions with Disparate Timescales

    E-print Network

    Paul, Mark

    Stochastic Simulation of Enzyme-Catalyzed Reactions with Disparate Timescales Debashis Barik-steady-state approximation'' for enzyme-catalyzed reactions provides a useful framework for efficient and accurate stochastic simulations. The method is applied to three examples: a simple enzyme-catalyzed reaction where enzyme

  3. Microorganisms detected by enzyme-catalyzed reaction

    NASA Technical Reports Server (NTRS)

    Vango, S. P.; Weetall, H. H.; Weliky, N.

    1966-01-01

    Enzymes detect the presence of microorganisms in soils. The enzyme lysozymi is used to release the enzyme catalase from the microorganisms in a soil sample. The catalase catalyzes the decomposition of added hydrogen peroxide to produce oxygen which is detected manometrically. The partial pressure of the oxygen serves as an index of the samples bacteria content.

  4. Representing Rate Equations for Enzyme-Catalyzed Reactions

    ERIC Educational Resources Information Center

    Ault, Addison

    2011-01-01

    Rate equations for enzyme-catalyzed reactions are derived and presented in a way that makes it easier for the nonspecialist to see how the rate of an enzyme-catalyzed reaction depends upon kinetic constants and concentrations. This is done with distribution equations that show how the rate of the reaction depends upon the relative quantities of…

  5. Thermodynamics of Enzyme-Catalyzed Reactions: Part 7--2007 Update Robert N. Goldberg,a...

    E-print Network

    Magee, Joseph W.

    Thermodynamics of Enzyme-Catalyzed Reactions: Part 7--2007 Update Robert N. Goldberg,a... Yadu B evaluations of equilibrium constants and enthalpy changes for enzyme-catalyzed reactions. For each reaction, the following information is given: the reference for the data, the reaction studied, the name of the enzyme

  6. Monitoring Enzyme-catalyzed Reactions in Micromachined Nanoliter Wells using a Conventional Microscope based

    E-print Network

    van Vliet, Lucas J.

    Monitoring Enzyme-catalyzed Reactions in Micromachined Nanoliter Wells using a Conventional to ethanol and carbon dioxide. This pathway consists of 12 enzyme-catalyzed reactions. With the approach × 300µm2 . The depth varies from 20 to 50µm. Enzyme activity levels can be derived by monitoring

  7. Measurement of positional isotope exchange rates in enzyme catalyzed reactions by fast atom bombardment mass spectrometry 

    E-print Network

    Hilscher, Larry Wayne

    1985-01-01

    of the requiremer ts for the degree of MASTEP. QF SCIENCE August 1985 Major Subject: Chemistry MEASUREMENT OF POSITIONAL ISOTOPE EXCHANGE RATES IN ENZYME CATALYZED REACTIONS BY FAST ATOM BOMBARDMENT MASS SPECTROMETRY A Thesis LARRY NAYNE HILSCHER Approved...MEASUREMENT OF POSITIONAL ISOTOPE EXCHANGE RATES IN ENZYME CATALYZED REACTIONS BY FAST ATOM BOMBARDMENT MASS SPECTROMETRY A Thesis by LARRY NAYNE HILSCHER Submitted to the Gradu te College of Texas A&M University in partial fulfil" mert...

  8. Aldol reaction catalyzed by a hydrophilic catalyst in aqueous micelle as an enzyme mimic system.

    PubMed

    Zhang, Hefeng; Zhao, Wenshan; Zou, Jun; Liu, Yi; Li, Runtao; Cui, Yuanchen

    2009-05-01

    Chitosan-supported L-proline complex was synthesized and applied as a catalyst for the direct asymmetric aldol reaction in various organic solvents and water as well. It was found that the novel synthesized catalyst was able to efficiently catalyze the aldol reaction in various media. The catalytic capacity and stereoselectivity of the catalyst were obviously improved with the introduction of aqueous micelle, possibly because the micelle functioned as a hydrophobic pocket, like the hydrophobic portion in enzymes. Moreover, the present synthetic catalyst showed performance similar to that of enzymes and could be used as a model of enzyme catalysis to help better understand the mystic mechanism of enzymes. PMID:18655166

  9. Folylpolyglutamate synthetase: direct evidence for an acyl phosphate intermediate in the enzyme-catalyzed reaction

    SciTech Connect

    Banerjee, R.; McGuire, J.J.; Shane, B.; Coward, J.K.

    1986-05-01

    The nature of the intermediate in the reaction catalyzed by folylpoly-..gamma..-glutamate synthetase (FPGS) has been investigated. Incubation of ..cap alpha..,..gamma..-(/sup 18/O)methotrexate with ATP, glutamate, and FPGS resulted in the formation of (/sup 18/O)phosphate, thus providing strong evidence for the formation of a ..gamma..-glutamyl phosphate during catalysis. The inorganic phosphate formed in the enzyme-catalyzed reaction was separated from other products and substrates by chromatography on DEAE-cellulose, then converted to the trimethyl ester, and analyzed by mass spectroscopy. Stoichiometric formation of (/sup 18/O)phosphate was observed in the case of the E. coli enzyme, isolated from a transformant containing the cloned FPGS-dihydrofolate synthetase (folC) gene. In addition, /sup 31/P-NMR analysis of the phosphate isolated from the reaction using E. coli FPGS showed the expected /sup 18/O-isotopic perturbations due to both singly bonded and doubly bonded P-/sup 18/O species. Similar experiments were carried out with FPGS isolated from hog liver. In this case, the small amounts of pure enzyme available precluded use of the NMR technique. However, mass spectral analysis of the derivatized phosphate product revealed the presence of (/sup 18/O)-trimethyl phosphate, thus indicating that the reaction catalyzed by the mammalian enzyme also proceeds via an acyl phosphate intermediate.

  10. Isotope Effects as Probes for Enzyme Catalyzed Hydrogen-Transfer Reactions

    PubMed Central

    Roston, Daniel; Islam, Zahidul; Kohen, Amnon

    2015-01-01

    Kinetic Isotope effects (KIEs) have long served as a probe for the mechanisms of both enzymatic and solution reactions. Here, we discuss various models for the physical sources of KIEs, how experimentalists can use those models to interpret their data, and how the focus of traditional models has grown to a model that includes motion of the enzyme and quantum mechanical nuclear tunneling. We then present two case studies of enzymes, thymidylate synthase and alcohol dehydrogenase, and discuss how KIEs have shed light on the C-H bond cleavages those enzymes catalyze. We will show how the combination of both experimental and computational studieshas changed our notion of how these enzymes exert their catalytic powers. PMID:23673528

  11. Enzyme-catalyzed organic syntheses: transesterification reactions of chlorophyl a, bacteriochlorophyll a, and derivatives with chlorophyllase

    SciTech Connect

    Michalski, T.J.; Hunt, J.E.; Bradshaw, C.; Wagner, A.M.; Norris, J.R.; Katz, J.J.

    1988-08-17

    The green plant enzyme chlorophyllase (EC 3.1.1.14, chlorophyll chlorophyllido-hydroase) has been used for the synthesis of a variety of primary alcohol and diol esters of chlorophyll a, bacteriochlorophyll a, and pyrobacteriochlorophyll a. Green plant chlorophyllase accepts a much larger range of alcohol and chlorophyll substrates than had previously been realized. Thus, chlorophyllide and bacteriochlorophyllide esters of primary alcohols such as retinol and the detergent Triton X-100 and of dihydric alcohols such as ethylene glycol, butanediol, or 2-hydroxyethyl disulfide can readily be obtained by enzyme-assisted transesterification. The diol chlorophyllide esters are valuable intermediates for the synthesis of reaction center special pair models. Chlorophyllase-assisted reactions can be carried out in media containing up to 95% of organic solvents without the concomitant side reactions that important chlorophyll functional groups readily undergo even under mild conditions in conventional chemical synthetic procedures. In competitive chlorophyllase-catalyzed transesterification reactions, long-chain alcohols such as farnesol and retinol vs simple aliphatic alcohols and diols, the enzyme shows a definite preference for the long-chain alcohol. 37 references, 1 figure, 2 tables.

  12. Local Bifurcations of the Enzyme-Catalyzed Reaction Comprising a Branched Network

    NASA Astrophysics Data System (ADS)

    Zhang, Qiuyan; Liu, Lingling; Zhang, Weinian

    2015-06-01

    An enzyme-catalyzed reaction system with four parameters a, b, c, ? is discussed. The system can be reduced to a quartic polynomial differential system with four parameters, which leads to difficulties in the computation of semi-algebraic systems of large degree polynomials. Those systems have to be discussed on subsets of special biological sense, none of which is closed under operations of the polynomial ring. In this paper, we overcome those difficulties to determine the exact number of equilibria and their qualitative properties. Moreover, we obtain parameter conditions for all codimension-1 bifurcations such as saddle-node, transcritical, pitchfork and Hopf bifurcations. We compute varieties of Lyapunov quantities under the limitations of biological requirements and prove that the weak focus is of at most order 2. We further obtain parameter conditions for exact number of limit cycles arising from Hopf bifurcations.

  13. Structural characterization of tartrate dehydrogenase: a versatile enzyme catalyzing multiple reactions

    SciTech Connect

    Malik, Radhika; Viola, Ronald E. (Toledo)

    2010-10-28

    The first structure of an NAD-dependent tartrate dehydrogenase (TDH) has been solved to 2 {angstrom} resolution by single anomalous diffraction (SAD) phasing as a complex with the intermediate analog oxalate, Mg{sup 2+} and NADH. This TDH structure from Pseudomonas putida has a similar overall fold and domain organization to other structurally characterized members of the hydroxy-acid dehydrogenase family. However, there are considerable differences between TDH and these functionally related enzymes in the regions connecting the core secondary structure and in the relative positioning of important loops and helices. The active site in these complexes is highly ordered, allowing the identification of the substrate-binding and cofactor-binding groups and the ligands to the metal ions. Residues from the adjacent subunit are involved in both the substrate and divalent metal ion binding sites, establishing a dimer as the functional unit and providing structural support for an alternating-site reaction mechanism. The divalent metal ion plays a prominent role in substrate binding and orientation, together with several active-site arginines. Functional groups from both subunits form the cofactor-binding site and the ammonium ion aids in the orientation of the nicotinamide ring of the cofactor. A lysyl amino group (Lys192) is the base responsible for the water-mediated proton abstraction from the C2 hydroxyl group of the substrate that begins the catalytic reaction, followed by hydride transfer to NAD. A tyrosyl hydroxyl group (Tyr141) functions as a general acid to protonate the enolate intermediate. Each substrate undergoes the initial hydride transfer, but differences in substrate orientation are proposed to account for the different reactions catalyzed by TDH.

  14. Structural characterization of tartrate dehydrogenase: a versatile enzyme catalyzing multiple reactions

    PubMed Central

    Malik, Radhika; Viola, Ronald E.

    2010-01-01

    The first structure of an NAD-dependent tartrate dehydrogenase (TDH) has been solved to 2?Å resolution by single anomalous diffraction (SAD) phasing as a complex with the intermediate analog oxalate, Mg2+ and NADH. This TDH structure from Pseudomonas putida has a similar overall fold and domain organization to other structurally characterized members of the hydroxy-acid dehydrogenase family. How­ever, there are considerable differences between TDH and these functionally related enzymes in the regions connecting the core secondary structure and in the relative positioning of important loops and helices. The active site in these complexes is highly ordered, allowing the identification of the substrate-binding and cofactor-binding groups and the ligands to the metal ions. Residues from the adjacent subunit are involved in both the substrate and divalent metal ion binding sites, establishing a dimer as the functional unit and providing structural support for an alternating-site reaction mechanism. The divalent metal ion plays a prominent role in substrate binding and orientation, together with several active-site arginines. Functional groups from both subunits form the cofactor-binding site and the ammonium ion aids in the orientation of the nicotinamide ring of the cofactor. A lysyl amino group (Lys192) is the base responsible for the water-mediated proton abstraction from the C2 hydroxyl group of the substrate that begins the catalytic reaction, followed by hydride transfer to NAD. A tyrosyl hydroxyl group (Tyr141) functions as a general acid to protonate the enolate inter­mediate. Each substrate undergoes the initial hydride transfer, but differences in substrate orientation are proposed to account for the different reactions catalyzed by TDH. PMID:20516620

  15. Reformulation of the Michaelis-Menten Equation: How Enzyme-Catalyzed Reactions Depend on Gibbs Energy

    ERIC Educational Resources Information Center

    Bozlee, Brian J.

    2007-01-01

    The impact of raising Gibbs energy of the enzyme-substrate complex (G[subscript 3]) and the reformulation of the Michaelis-Menten equation are discussed. The maximum velocity of the reaction (v[subscript m]) and characteristic constant for the enzyme (K[subscript M]) will increase with increase in Gibbs energy, indicating that the rate of reaction

  16. Identification of mouse selenomethionine alpha,gamma-elimination enzyme: cystathionine gamma-lyase catalyzes its reaction to generate methylselenol.

    PubMed

    Okuno, Tomofumi; Motobayashi, Shinji; Ueno, Hitoshi; Nakamuro, Katsuhiko

    2005-01-01

    The purpose of this study was to identify the seleno-L-methionine (L-SeMet) alpha,gamma-elimination enzyme that catalyzes L-SeMet to generate methylselenol (CH3SeH), a notable intermediate for the metabolism of selenium compounds, in mammalian tissues. The enzyme purified from ICR mouse liver was separated by one-dimensional gel electrophoresis, and the specific band was subjected to in-gel trypsin digestion followed by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometric analysis. In the peptide mass fingerprinting search, the mass numbers of 14 peptides produced by tryptic digestion of the enzyme were consistent with the theoretical mass numbers calculated from the amino acid sequence of murine cystathionine gamma-lyase (E.C. 4.4.1.1). The peptide sequence tags search was also performed to obtain the amino acid sequence data of five tryptic peptides. These peptides were significantly identical to the partial amino acid sequences of cystathionine gamma-lyase. This enzyme was clearly shown to catalyze the alpha,gamma-elimination reaction of L-cystathionine by the enzymological research. The Km value for the catalysis of L-cystathionine was 0.81 mM and Vmax was 0.0013 unit/mg protein. These results suggested that cystathionine gamma-lyase catalyzes L-SeMet to generate CH3SeH by its alpha,gamma-elimination reaction. PMID:16327076

  17. Assembly of zinc finger motif-fused enzymes on a dsDNA scaffold for catalyzing consecutive reactions with a proximity effect.

    PubMed

    Funabashi, Hisakage; Yanagi, Satoshi; Suzuki, Shigeya; Mie, Masayasu; Kobatake, Eiry

    2015-01-01

    The feasibility of assembling enzymes, catalyzing consecutive reactions, on to a double-stranded DNA (dsDNA) scaffold utilizing zinc finger motifs is described. The catalytic activities of two zinc finger motif-fused enzymes catalyzing a bioluminescence reaction with energy recycling, namely pyruvate phosphate dikinase and firefly luciferase, have been evaluated. Bioluminescence measurements with dsDNA scaffolds coding a different distance between the binding sites for each zinc finger motif-fused enzyme confirmed the effect of the distance, proving the proximity effect of ATP recycling presumed to be the result of efficient intermediate diffusion. Thus, fusion to zinc finger motifs offers a promising option for the assembly of bi-enzymes, catalyzing a consecutive reaction, onto a dsDNA scaffold with a proximity effect. PMID:25216646

  18. Monitoring enzyme-catalyzed reactions in micromachined nanoliter wells using a conventional microscope-based microarray reader

    NASA Astrophysics Data System (ADS)

    van den Doel, L. Richard; Moerman, R.; van Dedem, G. W. K.; Young, Ian T.; van Vliet, Lucas J.

    2002-06-01

    Yeast-Saccharomyces cerevisiae - it widely used as a model system for other higher eukaryotes, including man. One of the basic fermentation processes in yeast is the glycolytic pathway, which is the conversion of glucose to ethanol and carbon dioxide. This pathway consists of 12 enzyme-catalyzed reactions. With the approach of microarray technology we want to explore the metabolic regulation of this pathway in yeast. This paper will focus on the design of a conventional microscope based microarray reader, which is used to monitor these enzymatic reactions in microarrays. These microarrays are fabricated in silicon and have sizes of 300 by 300 micrometers 2. The depth varies from 20 to 50 micrometers . Enzyme activity levels can be derived by monitoring the production or consumption rate of NAD(P)H, which is excited at 360nm and emits around 450nm. This fluorophore is involved in all 12 reactions of the pathway. The microarray reader is equipped with a back-illuminated CCD camera in order to obtain a high quantum efficiency for the lower wavelengths. The dynamic range of our microarray reader varies form 5(mu) Molar to 1mMolar NAD(P)H. With this microarray reader enzyme activity levels down to 0.01 unit per milliliter can be monitored. The acquisition time per well is 0.1s. The total scan cycle time for a 5 X 5 microarray is less than half a minute. The number of cycles for a proper estimation of the enzyme activity is inversely proportional to the enzyme activity: long measurement times are needed to determine low enzyme activity levels.

  19. Enzyme Reactions

    NSDL National Science Digital Library

    Maryland Virtual High School

    The enzyme reaction rate activity allows students to simulate the effects of variables such as temperature and pH on the reaction rate of the enzyme catalase. This computer simulation is best used after the students have done a wet lab experiment. The value of the simulation is that it requires the students to interpret and analyze the graphical representation of data and it enables the running of mutiple experiments in a short amount of time.

  20. Stoichiometry of the Redox Neutral Deamination and Oxidative Dehydrogenation Reactions Catalyzed by the Radical SAM Enzyme DesII

    PubMed Central

    Ruszczycky, Mark W.; Choi, Sei-hyun; Liu, Hung-wen

    2010-01-01

    DesII from Streptomyces venezuelae is a radical SAM (S-adenosyl-l-methionine) enzyme that catalyzes the deamination of TDP-4-amino-4,6-dideoxy-d-glucose to form TDP-3-keto-4,6-dideoxy-d-glucose in the biosynthesis of TDP-d-desosamine. DesII also catalyzes the dehydrogenation of the non-physiological substrate TDP-d-quinovose to TDP-3-keto-6-deoxy-d-glucose. These properties prompted an investigation of how DesII handles SAM in the redox neutral deamination versus the oxidative dehydrogenation reactions. This work was facilitated by the development of an enzymatic synthesis of TDP-4-amino-4,6-dideoxy-d-glucose that couples a transamination equilibrium to the thermodynamically favorable oxidation of formate. In this study, DesII is found to consume SAM versus TDP-sugar with stoichiometries of 0.96 ± 0.05 and 1.01 ± 0.05 in the deamination and dehydrogenation reactions, respectively, using Na2S2O4 as the reductant. Importantly, no significant change in stoichiometry is observed when the flavodoxin/flavodoxin NADP+ oxidoreductase/NADPH reducing system is used in place of Na2S2O4. Moreover, there is no evidence of an uncoupled or abortive process in the deamination reaction, as indicated by the observation that dehydrogenation can take place in the absence of an external source of reductant whereas deamination cannot. Mechanistic and biochemical implications of these results are discussed. PMID:20121093

  1. Enzyme-Catalyzed Processes in Organic Solvents

    Microsoft Academic Search

    Aleksey Zaks; Alexander M. Klibanov

    1985-01-01

    Three different lipases (porcine pancreatic, yeast, and mold) can vigorously act as catalysts in a number of nearly anhydrous organic solvents. Various transesterification reactions catalyzed by porcine pancreatic lipase in hexane obey Michaelis-Menten kinetics. The dependence of the catalytic activity of the enzyme in organic media on the pH of the aqueous solution from which it was recovered is bell-shaped,

  2. The Effect of Temperature on the Enzyme-Catalyzed Reaction: Insights from Thermodynamics

    ERIC Educational Resources Information Center

    Aledo, Juan Carlos; Jimenez-Riveres, Susana; Tena, Manuel

    2010-01-01

    When teaching the effect of temperature on biochemical reactions, the problem is usually oversimplified by confining the thermal effect to the catalytic constant, which is identified with the rate constant of the elementary limiting step. Therefore, only positive values for activation energies and values greater than 1 for temperature coefficients…

  3. Diffusional limitations in liquid-phase reactions catalyzed by enzymes immobilized on porous supports: sucrose inversion by beta-fructooxidase immobilized on IRA-93 resin.

    PubMed

    Toro, L; Gaudioso, D

    1980-08-01

    An experimental procedure has been proposed to study liquid-phase reactions catalyzed by enzymes immobilized on porous supports. The kinetic behavior can be assessed by experimental runs which allow a separate evaluation of the internal diffusion, the surface kinetics, and the fluid-particle mass transfer. The method has been applied in the study of sucrose inversion by beta-fructooxidase immobilized on IRA-93 resin. PMID:7459692

  4. Kinetic studies on enzyme-catalyzed reactions: oxidation of glucose, decomposition of hydrogen peroxide and their combination.

    PubMed

    Tao, Zhimin; Raffel, Ryan A; Souid, Abdul-Kader; Goodisman, Jerry

    2009-04-01

    The kinetics of the glucose oxidase-catalyzed reaction of glucose with O2, which produces gluconic acid and hydrogen peroxide, and the catalase-assisted breakdown of hydrogen peroxide to generate oxygen, have been measured via the rate of O2 depletion or production. The O2 concentrations in air-saturated phosphate-buffered salt solutions were monitored by measuring the decay of phosphorescence from a Pd phosphor in solution; the decay rate was obtained by fitting the tail of the phosphorescence intensity profile to an exponential. For glucose oxidation in the presence of glucose oxidase, the rate constant determined for the rate-limiting step was k = (3.0 +/- 0.7) x 10(4) M(-1) s(-1) at 37 degrees C. For catalase-catalyzed H2O2 breakdown, the reaction order in [H2O2] was somewhat greater than unity at 37 degrees C and well above unity at 25 degrees C, suggesting different temperature dependences of the rate constants for various steps in the reaction. The two reactions were combined in a single experiment: addition of glucose oxidase to glucose-rich cell-free media caused a rapid drop in [O2], and subsequent addition of catalase caused [O2] to rise and then decrease to zero. The best fit of [O2] to a kinetic model is obtained with the rate constants for glucose oxidation and peroxide decomposition equal to 0.116 s(-1) and 0.090 s(-1) respectively. Cellular respiration in the presence of glucose was found to be three times as rapid as that in glucose-deprived cells. Added NaCN inhibited O2 consumption completely, confirming that oxidation occurred in the cellular mitochondrial respiratory chain. PMID:19348778

  5. Janus-faced Enzymes Yeast Tgl3p and Tgl5p Catalyze Lipase and Acyltransferase Reactions

    PubMed Central

    Rajakumari, Sona

    2010-01-01

    In the yeast, mobilization of triacylglycerols (TAGs) is facilitated by the three TAG lipases Tgl3p, Tgl4p, and Tgl5p. Motif search analysis, however, indicated that Tgl3p and Tgl5p do not only contain the TAG lipase motif GXSXG but also an H-(X)4-D acyltransferase motif. Interestingly, lipid analysis revealed that deletion of TGL3 resulted in a decrease and overexpression of TGL3 in an increase of glycerophospholipids. Similar results were obtained with TGL5. Therefore, we tested purified Tgl3p and Tgl5p for acyltransferase activity. Indeed, both enzymes not only exhibited lipase activity but also catalyzed acylation of lysophosphatidylethanolamine and lysophosphatidic acid, respectively. Experiments using variants of Tgl3p created by site-directed mutagenesis clearly demonstrated that the two enzymatic activities act independently of each other. We also showed that Tgl3p is important for efficient sporulation of yeast cells, but rather through its acyltransferase than lipase activity. In summary, our results demonstrate that yeast Tgl3p and Tgl5p play a dual role in lipid metabolism contributing to both anabolic and catabolic processes. PMID:20016004

  6. Strictosidine Synthase: Mechanism of a Pictet–Spengler Catalyzing Enzyme

    PubMed Central

    Maresh, Justin J.; Giddings, Lesley-Ann; Friedrich, Anne; Loris, Elke A.; Panjikar, Santosh; Trout, Bernhardt L.

    2010-01-01

    The Pictet–Spengler reaction, which yields either a ?-carboline or a tetrahydroquinoline product from an aromatic amine and an aldehyde, is widely utilized in plant alkaloid biosynthesis. Here we deconvolute the role that the biosynthetic enzyme strictosidine synthase plays in catalyzing the stereoselective synthesis of a ?-carboline product. Notably, the rate-controlling step of the enzyme mechanism, as identified by the appearance of a primary kinetic isotope effect (KIE), is the rearomatization of a positively charged intermediate. The KIE of a nonenzymatic Pictet–Spengler reaction indicates that rearomatization is also rate-controlling in solution, suggesting that the enzyme does not significantly change the mechanism of the reaction. Additionally, the pH dependence of the solution and enzymatic reactions provides evidence for a sequence of acid–base catalysis steps that catalyze the Pictet–Spengler reaction. An additional acid-catalyzed step, most likely protonation of a carbinolamine intermediate, is also significantly rate controlling. We propose that this step is efficiently catalyzed by the enzyme. Structural analysis of a bisubstrate inhibitor bound to the enzyme suggests that the active site is exquisitely tuned to correctly orient the iminium intermediate for productive cyclization to form the diastereoselective product. Furthermore, ab initio calculations suggest the structures of possible productive transition states involved in the mechanism. Importantly, these calculations suggest that a spiroindolenine intermediate, often invoked in the Pictet–Spengler mechanism, does not occur. A detailed mechanism for enzymatic catalysis of the ?-carboline product is proposed from these data. PMID:18081287

  7. Exchange reactions catalyzed by group-transferring enzymes oppose the quantitation and the unravelling of the identify of the pentose pathway.

    PubMed

    Flanigan, I; Collins, J G; Arora, K K; MacLeod, J K; Williams, J F

    1993-04-01

    1. The distributions and rates of transfer of carbon isotopes from a selection of specifically labelled ketosugar-phosphate substrates by exchange reactions catalyzed by the pentose and photosynthetic carbon-reduction-pathway group-transferring enzymes transketolase, transaldolase and aldolase have been measured using 13C-NMR spectroscopy. 2. The rates of these exchange reactions were 5, 4 and 1.5 mumol min-1 mg-1 for transketolase exchange, transaldolase exchange and aldolase exchange, respectively. 3. A comparison of the exchange capacities contributed by the activities of these enzymes in three in vitro liver preparations with the maximum non-oxidative pentose pathway flux rates of the preparations shows that transketolase and aldolase exchanges exceeded flux by 9-19 times in liver cytosol and acetone powder enzyme preparations and by 5 times in hepatocytes. Transaldolase was less effective in the comparison of exchange versus flux rates: transaldolase exchange exceeded flux by 1.6 and 5 in catalysis by liver cytosol and acetone powder preparations, respectively, but was only 0.6 times the flux in hepatocytes. 4. Values of group enzyme exchange and pathway flux rates in the above three preparations are important because of the feature role of liver and of these particular preparations in the establishment, elucidation and measurement of a proposed reaction scheme for the fat-cell-type pentose pathway in biochemistry. 5. It is the claim of this paper that the excess of exchange rate activity (particularly transketolase exchange) over pathway flux will overturn attempts to unravel, using isotopically labelled sugar substrates, the identity, reaction sequence and quantitative contribution of the pentose pathway to glucose metabolism. 6. The transketolase exchange reactions relative to the pentose pathway flux rates in normal, regenerating and foetal liver, Morris hepatomas, mammary carcinoma, melanoma, colonic epithelium, spinach chloroplasts and epididymal fat tissue show that transketolase exchange may exceed flux in these tissues by factors ranging over 5-600 times. 7. The confusion of pentose pathway theory by the effects of transketolase exchange action is illustrated by the 13C-NMR spectrum of the hexose 6-phosphate products of ribose 5-phosphate dissimilation, formed after 30 min of liver enzyme action, and shows 13C-labelling in carbons 1 and 3 of glucose 6-phosphate with ratios which range over 2.1-6.4 rather than the mandatory value of 2 which is imposed by the theoretical mechanism of the pathway. PMID:8477719

  8. Isotope effects in the transient phases of the reaction catalyzed by ethanolamine ammonia-lyase: determination of the number of exchangeable hydrogens in the enzyme-cofactor complex.

    PubMed

    Bandarian, V; Reed, G H

    2000-10-01

    Transient phases of the reaction catalyzed by ethanolamine ammonia-lyase (EAL) from Salmonella typhimurium have been investigated by stopped-flow visible spectrophotometry and deuterium kinetic isotope effects. The cleavage of adenosylcobalamin (coenzyme B(12)) to form cob(II)alamin (B(12r)) with ethanolamine as the substrate occurred within the dead time of the instrument whenever coenzyme B(12) was preincubated with enzyme prior to mixing with substrate. The rate was, however, slowed sufficiently to be measured with perdeutero ethanolamine as the substrate. Optical spectra indicate that, during the steady states of the reactions with ethanolamine and with S-2-aminopropanol as substrates, approximately 90% of the active sites contain B(12r). Reformation of the carbon-cobalt bond of the cofactor occurs following depletion of substrate in the reaction mixtures, and the rate constant for this process reflects k(cat) of the respective substrates. This late phase of the reaction also exhibits (2)H isotope effects similar to those measured for the overall reaction with (2)H-labeled substrates. With unlabeled substrates, the rate of cofactor reassembly is independent of the number of substrate molecules turned over in the steady-state phase. However, with (2)H-labeled substrates, kinetic isotope effects appear in the reassembly phase, and these isotope effects are maximal after only approximately 2 equiv of substrate/active site are processed. With 5'-deuterated coenzyme B(12) and deuterated substrate, the isotope effect on reassembly is independent of the number of substrate molecules that are turned over. These results indicate that the pool of exchangeable hydrogens in the enzyme-cofactor complex is two-a finding consistent with the hydrogens in the C5' methylene of coenzyme B(12). PMID:11009622

  9. Efficient antibody-catalyzed oxygenation reaction

    SciTech Connect

    Hsieh, L.C.; Stephans, J.C.; Schultz, P.G. (Univ. of California, Berkeley, CA (United States))

    1994-03-09

    Biological oxygen-transfer reactions are essential for the biosynthesis of steroids and neurotransmitters, the degradation of endogenous substances, and the detoxification of xenobiotics. The monooxygenase enzymes responsible for these transformations require biological cofactors such as flavin, heme and non-heme iron, copper, or pterin and typically utilize NADPH for cofactor regeneration. We now report an antibody-catalyzed sulfide oxygenation reaction mediated by the chemical cofactor sodium periodate, with turnover numbers similar to those of the corresponding enzymatic reactions. Sodium periodate NaIO[sub 4]O was chosen as the oxidant, since sulfoxide formation occurs under mild aqueous conditions with minimal overoxidation to the sulfone. Furthermore, compared to the flavin and heme cofactors required by the monooxygenase enzymes, NaIO[sub 4] is very inexpensive, obviating the need for cofactor recycling. Overall, these results raise the possibility of using antibodies as catalysts for regio- and stereoselective sulfide oxidations. 18 refs., 1 fig.

  10. Understanding bistability in complex enzyme-driven reaction networks

    E-print Network

    Craciun, Gheorghe

    Understanding bistability in complex enzyme-driven reaction networks Gheorghe Craciun* , Yangzhong for enzyme catalysis of a single overall reaction. We present a theorem that distinguishes between those mass- ically simple enzyme-catalyzed reaction networks can give rise to bistability. If two experiments under

  11. Controlling reaction specificity in pyridoxal phosphate enzymes.

    PubMed

    Toney, Michael D

    2011-11-01

    Pyridoxal 5'-phosphate enzymes are ubiquitous in the nitrogen metabolism of all organisms. They catalyze a wide variety of reactions including racemization, transamination, decarboxylation, elimination, retro-aldol cleavage, Claisen condensation, and others on substrates containing an amino group, most commonly ?-amino acids. The wide variety of reactions catalyzed by PLP enzymes is enabled by the ability of the covalent aldimine intermediate formed between substrate and PLP to stabilize carbanionic intermediates at C? of the substrate. This review attempts to summarize the mechanisms by which reaction specificity can be achieved in PLP enzymes by focusing on three aspects of these reactions: stereoelectronic effects, protonation state of the external aldimine intermediate, and interaction of the carbanionic intermediate with the protein side chains present in the active site. This article is part of a Special Issue entitled: Pyridoxal Phosphate Enzymology. PMID:21664990

  12. Controlling reaction specificity in pyridoxal phosphate enzymes

    PubMed Central

    Toney, Michael D.

    2012-01-01

    Pyridoxal 5'-phosphate enzymes are ubiquitous in the nitrogen metabolism of all organisms. They catalyze a wide variety of reactions including racemization, transamination, decarboxylation, elimination, retro-aldol cleavage, Claisen condensation, and others on substrates containing an amino group, most commonly ?-amino acids. The wide variety of reactions catalyzed by PLP enzymes is enabled by the ability of the covalent aldimine intermediate formed between substrate and PLP to stabilize carbanionic intermediates at C? of the substrate. This review attempts to summarize the mechanisms by which reaction specificity can be achieved in PLP enzymes by focusing on three aspects of these reactions: stereoelectronic effects, protonation state of the external aldimine intermediate, and interaction of the carbanionic intermediate with the protein side chains present in the active site. PMID:21664990

  13. Reaction specificity in pyridoxal phosphate enzymes.

    PubMed

    Toney, Michael D

    2005-01-01

    Pyridoxal phosphate enzymes catalyze a wide variety of reaction types on amines and amino acids, generally by stabilizing carbanionic intermediates. This makes them very useful in cellular metabolism, but it also creates problems in controlling the reaction pathway that a given enzyme follows, i.e., in controlling reaction specificity. Stereoelectronic effects have been proposed to play a major role in determining the bond to Calpha that gets broken in the external aldimine intermediate that is common to all PLP enzymes. Here, we discuss our work on dialkylglycine decarboxylase aimed at providing direct evidence for stereoelectronic control of external aldimine reactivity. Once a bond to Calpha has been broken to form the carbanionic intermediate, enzymes must also carefully control the fate of this reactive species. Our studies with alanine racemase suggest that the enzyme selectively destabilizes the carbanionic quinonoid intermediate to promote higher racemization specificity by avoiding transamination side reactions. PMID:15581583

  14. Fronts and pulses in an enzymatic reaction catalyzed by glucose oxidase

    E-print Network

    Epstein, Irving R.

    Fronts and pulses in an enzymatic reaction catalyzed by glucose oxidase David G. Míguez* , Vladimir as catalysts and regulators. We present a reaction­diffusion system catalyzed by the enzyme glucose oxidase previously studied the temporal dynamics of the enzymatic autocatalytic reaction between glucose and ferricya

  15. Accelerated Stochastic Simulation of the Stiff Enzyme-Substrate Reaction

    E-print Network

    Cao, Yang

    1 Accelerated Stochastic Simulation of the Stiff Enzyme-Substrate Reaction Yang Cao a) Dept, Santa Barbara, Santa Barbara, CA 93106 Abstract: The enzyme-catalyzed conversion of a substrate this process, the intermediate enzyme-substrate complex is usually much more likely to decay into its original

  16. Unusual Cytochrome P450 Enzymes and Reactions*

    PubMed Central

    Guengerich, F. Peter; Munro, Andrew W.

    2013-01-01

    Cytochrome P450 enzymes primarily catalyze mixed-function oxidation reactions, plus some reductions and rearrangements of oxygenated species, e.g. prostaglandins. Most of these reactions can be rationalized in a paradigm involving Compound I, a high-valent iron-oxygen complex (FeO3+), to explain seemingly unusual reactions, including ring couplings, ring expansion and contraction, and fusion of substrates. Most P450s interact with flavoenzymes or iron-sulfur proteins to receive electrons from NAD(P)H. In some cases, P450s are fused to protein partners. Other P450s catalyze non-redox isomerization reactions. A number of permutations on the P450 theme reveal the diversity of cytochrome P450 form and function. PMID:23632016

  17. Reaction products and intermediates of tryptophan tryptophylquinone enzymes

    Microsoft Academic Search

    Victor L. Davidson; Zhenyu Zhu

    2000-01-01

    Methylamine dehydrogenase and aromatic amine dehydrogenase each possess the tryptophan tryptophylquinone (TTQ) cofactor which catalyzes the oxidative deamination of primary amines and transfer of substrate-derived electrons to type I copper proteins. The reaction steps and intermediates in the overall oxidation–reduction reactions catalyzed by these enzymes are described. An important feature of the reaction mechanism of TTQ-dependent amine dehydrogenases is that

  18. The two types of 3-dehydroquinase have distinct structures but catalyze the same overall reaction 

    E-print Network

    Gourley, David G; Shrive, Annette K; Polikarpov, Igor; Krell, Tino; Coggins, John R; Hawkins, Alastair R; Isaacs, Neil W; Sawyer, Lindsay

    The structures of enzymes catalyzing the reactions in central metabolic pathways are generally well conserved as are their catalytic mechanisms. The two types of 3-dehydroquinate dehydratase (DHQase) are therefore most ...

  19. Gold-catalyzed carbene transfer reactions.

    PubMed

    Shin, Seunghoon

    2015-01-01

    In homogeneous gold catalysis, generations and reactions of metal carbenes have been one of the most rapidly developing areas because of their diverse reactivity under mild conditions. This review covers recent advances in the gold-catalyzed oxygen atom transfer and carbene transfer reactions to alkynes. Atom transfer to an alkyne enables alkynes to function as metal carbene synthons. Many such reactions fulfill redox neutrality starting from safe and easily handled precursors. PMID:25518973

  20. An antibody-catalyzed bimolecular Diels-Alder reaction

    SciTech Connect

    Braisted, A.C.; Schultz, P.G. (Lawrence Berkeley Laboratory, CA (USA))

    1990-09-26

    There exist over 1,500 known enzymes which carry out a vast array of chemical reactions with remarkable specificity and reaction rates. It is surprising then that there are no documented examples of enzyme-catalyzed pericyclic cycloaddition reactions, yet there are among the most powerful and commonly used reactions in synthetic organic chemistry. The most important of these is the Diels-Alder reaction of a diene with a dienophile, which provides a straightforward and highly stereospecific route to cyclohexene derivatives. Given the importance of this reaction in organic chemistry and its novel mechanism, it was of interest to ask whether a Diels-Alderase enzymatic catalyst could be evolved from an antibody combining site. Generation of antibodies to a structure that mimics the pericyclic transition state for a Diels-Alder reaction should result in an antibody combining site that lowers the entropy of activation {Delta}S{sup {double dagger}} by binding both the diene and the dienophile in a reactive conformation. The authors approach toward the design of a transition-state analogue involves incorporation of an ethano bridge, which locks the cyclohexene ring of hapten in a conformation that resembles the proposed pericyclic transition state for the Diels-Alder reaction of cisoid diene with dienophile. The authors now report that antibodies generated to the transition-state analogue catalyze the addition of the acyclic water-soluble diene to the maleimide derivative to give the cyclohexene product.

  1. Atomic Description of an Enzyme Reaction Dominated by Proton Tunneling

    Microsoft Academic Search

    Laura Masgrau; Anna Roujeinikova; Linus O. Johannissen; Parvinder Hothi; Jaswir Basran; Kara E. Ranaghan; Adrian J. Mulholland; Michael J. Sutcliffe; Nigel S. Scrutton; David Leys

    2006-01-01

    We present an atomic-level description of the reaction chemistry of an enzyme-catalyzed reaction dominated by proton tunneling. By solving structures of reaction intermediates at near-atomic resolution, we have identified the reaction pathway for tryptamine oxidation by aromatic amine dehydrogenase. Combining experiment and computer simulation, we show proton transfer occurs predominantly to oxygen O2 of Asp128beta in a reaction dominated by

  2. Deep eutectic solvents (DESs) are viable cosolvents for enzyme-catalyzed epoxide hydrolysis

    Microsoft Academic Search

    Diana Lindberg; Mario de la Fuente Revenga; Mikael Widersten

    2010-01-01

    A special group of ionic liquids, deep eutectic solvents (DESs) have been tested as cosolvents in enzyme-catalyzed hydrolysis of a chiral (1,2)-trans-2-methylstyrene oxide. The choline chloride:ethane diol (ET), choline chloride:glycerol (GLY) and choline:chloride:urea (REL) DESs were included in the reaction mixtures with epoxide and the potato epoxide hydrolase StEH1. The effect of the DESs on enzyme function was primarily elevations

  3. Enantioselective Imidation of Sulfides via Enzyme-Catalyzed Intermolecular Nitrogen-Atom Transfer

    PubMed Central

    2015-01-01

    Engineering enzymes with novel reaction modes promises to expand the applications of biocatalysis in chemical synthesis and will enhance our understanding of how enzymes acquire new functions. The insertion of nitrogen-containing functional groups into unactivated C–H bonds is not catalyzed by known enzymes but was recently demonstrated using engineered variants of cytochrome P450BM3 (CYP102A1) from Bacillus megaterium. Here, we extend this novel P450-catalyzed reaction to include intermolecular insertion of nitrogen into thioethers to form sulfimides. An examination of the reactivity of different P450BM3 variants toward a range of substrates demonstrates that electronic properties of the substrates are important in this novel enzyme-catalyzed reaction. Moreover, amino acid substitutions have a large effect on the rate and stereoselectivity of sulfimidation, demonstrating that the protein plays a key role in determining reactivity and selectivity. These results provide a stepping stone for engineering more complex nitrogen-atom-transfer reactions in P450 enzymes and developing a more comprehensive biocatalytic repertoire. PMID:24901646

  4. Enantioselective imidation of sulfides via enzyme-catalyzed intermolecular nitrogen-atom transfer.

    PubMed

    Farwell, Christopher C; McIntosh, John A; Hyster, Todd K; Wang, Z Jane; Arnold, Frances H

    2014-06-18

    Engineering enzymes with novel reaction modes promises to expand the applications of biocatalysis in chemical synthesis and will enhance our understanding of how enzymes acquire new functions. The insertion of nitrogen-containing functional groups into unactivated C-H bonds is not catalyzed by known enzymes but was recently demonstrated using engineered variants of cytochrome P450BM3 (CYP102A1) from Bacillus megaterium. Here, we extend this novel P450-catalyzed reaction to include intermolecular insertion of nitrogen into thioethers to form sulfimides. An examination of the reactivity of different P450BM3 variants toward a range of substrates demonstrates that electronic properties of the substrates are important in this novel enzyme-catalyzed reaction. Moreover, amino acid substitutions have a large effect on the rate and stereoselectivity of sulfimidation, demonstrating that the protein plays a key role in determining reactivity and selectivity. These results provide a stepping stone for engineering more complex nitrogen-atom-transfer reactions in P450 enzymes and developing a more comprehensive biocatalytic repertoire. PMID:24901646

  5. Biginelli Reaction Catalyzed by Copper Nanoparticles

    PubMed Central

    Dewan, Manika; Kumar, Ajeet; Saxena, Amit; De, Arnab; Mozumdar, Subho

    2012-01-01

    We recently reported a novel synthesis of copper nanoparticles from copper sulphate utilizing the charge-compensatory effect of ionic liquid [bmim]BF4 and ethylene glycol. The nanoparticles were characterized and found to be stable for one year. Here we hypothesize that the stabilized nanoparticles should be able to catalyze one-pot multicomponent organic reactions. We show that the nanoparticles catalyzed Biginelli reaction at room temperature to give the product 3,4-dihydopyrimidinone (>90% yield in ?15 minutes) from aldehydes, ?-diketoester (ethylacetoacetate) and urea (or thiourea). ). Remarkably, such high yields and rapid kinetics was found to be independent of the electronic density on the reactant aryl-aldehyde. This was probably because even the surface-active particles reacted faster in the presence of ionic liquid as compared to conventional methods. The heterocyclic dihydropyrimidinones (DHPMs) and their derivatives are widely used in natural and synthetic organic chemistry due to their wide spectrum of biological and therapeutic properties (resulting from their antibacterial, antiviral, antitumor and anti-inflammatory activities. Our method has an easy work-up procedure and the nanoparticles could be recycled with minimal loss of efficiency. PMID:22912792

  6. Alternative metals for homogeneous catalyzed hydroformylation reactions.

    PubMed

    Pospech, Jola; Fleischer, Ivana; Franke, Robert; Buchholz, Stefan; Beller, Matthias

    2013-03-01

    Transition-metal-catalyzed hydroformylation reactions constitute one of the most powerful tools for C-C bond formation in organic synthesis and represent an outstanding example of the application of homogeneous catalysis on an industrial scale. This process allows for the straightforward conversion of inexpensive chemical feedstock into broadly applicable aldehydes, which serve as major building blocks for numerous chemical products. These products are highly valuable for the chemical industry and used as plasticizers, detergents, and surfactants on a million ton scale. Moreover, aldehydes serve as versatile chemical intermediates for the production of fine chemicals and pharmaceuticals. Currently, most of the bulk hydroformylation processes rely on rhodium-based catalysts. The increasing demand and resulting high cost of this precious metal has resulted in alternative transition-metal catalysts becoming highly desirable. The following Review summarizes the progress achieved utilizing Ru, Ir, Pd, Pt, and Fe catalysts in hydroformylation reactions. PMID:23436281

  7. Two-Dimensional Reaction Free Energy Surfaces of Catalytic Reaction: Effects of Protein Conformational Dynamics on Enzyme Catalysis

    E-print Network

    Xie, Xiaoliang Sunney

    Two-Dimensional Reaction Free Energy Surfaces of Catalytic Reaction: Effects of Protein the reaction free energy surface of the enzyme-catalyzed reaction, as is shown in many biochemistry textbooks Form: October 23, 2007 We introduce a two-dimensional (2D) multisurface reaction free energy

  8. First-principles calculations of Fischer-Tropsch processes catalyzed by nitrogenase enzymes

    NASA Astrophysics Data System (ADS)

    Varley, Joel; Grabow, Lars; Nørskov, Jens

    2012-02-01

    The nitrogenase enzyme system of the bacteria Azotobacter vinelandii, which is used in nature to catalyze ammonia synthesis, has been found recently to catalyze the efficient conversion of carbon monoxide (CO) into hydrocarbons under ambient temperature and pressure [1]. These findings indicate that nitrogenase enzymes could inspire more efficient catalysts for electrochemical CO and CO2 reduction to liquid fuels. The nitrogenase variants, in which vanadium substitutes the molybdenum in the active site of the enzyme, show distinct features in their reaction pathways to hydrocarbon production. To compare and contrast the catalytic properties of these nitrogenase enzymes, we perform first-principles calculations to map out the reaction pathways for both nitrogen fixation and for the reduction of CO to higher-order hydrocarbons. We discuss the trends and differences between the two enzymes and detail the relevant chemical species and rate-limiting steps involved in the reactions. By utilizing this information, we predict the electrochemical conditions necessary for the catalytic reduction of CO into fuels by the nitrogenase active sites, analogous to a Fischer-Tropsch process requiring less extreme conditions. [4pt] [1] Y. Hu, C.C. Lee, M.W. Ribbe, Science 333, 753 (2011)

  9. Pressure effects on enzyme-catalyzed quantum tunneling events arise from protein-specific structural and dynamic changes.

    PubMed

    Hay, Sam; Johannissen, Linus O; Hothi, Parvinder; Sutcliffe, Michael J; Scrutton, Nigel S

    2012-06-13

    The rate and kinetic isotope effect (KIE) on proton transfer during the aromatic amine dehydrogenase-catalyzed reaction with phenylethylamine shows complex pressure and temperature dependences. We are able to rationalize these effects within an environmentally coupled tunneling model based on constant pressure molecular dynamics (MD) simulations. As pressure appears to act anisotropically on the enzyme, perturbation of the reaction coordinate (donor-acceptor compression) is, in this case, marginal. Therefore, while we have previously demonstrated that pressure and temperature dependences can be used to infer H-tunneling and the involvement of promoting vibrations, these effects should not be used in the absence of atomistic insight, as they can vary greatly for different enzymes. We show that a pressure-dependent KIE is not a definitive hallmark of quantum mechanical H-tunneling during an enzyme-catalyzed reaction and that pressure-independent KIEs cannot be used to exclude tunneling contributions or a role for promoting vibrations in the enzyme-catalyzed reaction. We conclude that coupling of MD calculations with experimental rate and KIE studies is required to provide atomistic understanding of pressure effects in enzyme-catalyzed reactions. PMID:22632111

  10. Enzyme-catalyzed removal of phenol from refinery wastewater: feasibility studies.

    PubMed

    Ibrahim, M S; Ali, H I; Taylor, K E; Biswas, N; Bewtra, J K

    2001-01-01

    Phenols are present in petroleum refining wastewater. An enzymatic method for removing phenols from industrial aqueous effluent has been developed in the past several years. In this method, a peroxidase enzyme catalyzes the oxidation of phenol by hydrogen peroxide generation of phenoxyl radicals. These radicals diffuse from the active center of the enzyme into solution and react nonenzymatically to eventually form higher oligomers and polymers, which can be removed from wastewater by conventional coagulation and sedimentation or filtration. In this study, Arthromyces ramosus peroxidase (ARP) was applied to treat a petroleum refining wastewater containing 2 mM (188 mg/L) phenol in a batch and continuous-flow system. The latter consisted of a plug-flow reactor (PFR) where the reaction took place between phenol and hydrogen peroxide catalyzed by the enzyme in the presence of polyethylene glycol (PEG). A flocculation tank followed the PFR where alum and sodium hydroxide were added and then the polymers formed were settled in a sedimentation tank and removed from the system. Most (95 to 99%) of the phenol was removed by the same dose of ARP required for the treatment of synthetic wastewater containing an equal amount of phenol. Polyethylene glycol, as an additive, reduced enzyme inactivation and consequently reduced the enzyme dose and the cost of the treatment process. Step feeding of hydrogen peroxide was not effective in reducing the enzyme requirement. A significant removal of chemical oxygen demand was achieved when using PEG to reduce the enzyme dose. PMID:11563376

  11. Activity of formylphosphate in the reaction catalyzed by formyltetrahydrofolate synthetase

    SciTech Connect

    Jahansouz, H.; Kofron, J.L.; Smithers, G.W.; Himes, R.H.; Reed, G.H.

    1986-05-01

    Formylphosphate (FP), a putative enzyme-bound intermediate in the reaction catalyzed by N/sup 10/-formylH/sub 4/folate synthetase, was synthesized from formylfluoride and Pi. Measurement of hydrolysis rates by /sup 31/P NMR showed that FP is very unstable with a half-life of 48 min at 20/sup 0/C and pH 7. At pH 7 hydrolysis occurs with O-P bond cleavage as shown by /sup 18/O incorporation from /sup 18/O-H/sub 2/O into Pi. The substrate activity of FP was tested in the reaction catalyzed by N/sup 10/-formylH/sub 4/folate synthetase isolated from Clostridium cylindrosporum. MgATP + H/sub 4/folate + HCOO/sup -/ in equilibrium MgADP + Pi +N/sup 10/-formylH/sub 4/folate FP supports the reaction in both the forward and reverse directions. Thus, N/sup 10/-formylH/sub 4/folate is produced from H/sub 4/-folate and FP but only if ADP is present, and ATP is produced from FP and ADP but only if H/sub 4/folate is present. The requirements for H/sub 4/folate in the synthesis of ATP from ADP and FP and for ADP in the synthesis of N/sup 10/-formylH/sub 4/folate from FP and H/sub 4/folate, are consistent with past kinetic and isotope exchange studies which showed that the reaction proceeds by a sequential mechanism and that all three substrates must be present for any reaction to occur.

  12. Microcalorimetric study of the enzymatic hydrolysis of starch: An ?-amylase catalyzed reaction

    Microsoft Academic Search

    G. Salieri; G. Vinci; M. L. Antonelli

    1995-01-01

    Microcalorimetric studies of enzyme activities have been made on the hydrolysis of starch catalyzed by ?-amylase. The best conditions for the hydrolysis of starch in the presence of ?-amylase have been pointed out and the ?-amylase activity was determined by isothermal batch microcalorimetry. The heat changes involved during the hydrolytic reaction can be related to the starch concentrations in a

  13. Enzyme-catalyzed synthesis and kinetics of ultrasonic-assisted biodiesel production from waste tallow.

    PubMed

    Adewale, Peter; Dumont, Marie-Josée; Ngadi, Michael

    2015-11-01

    The use of ultrasonic processing was evaluated for its ability to achieve adequate mixing while providing sufficient activation energy for the enzymatic transesterification of waste tallow. The effects of ultrasonic parameters (amplitude, cycle and pulse) and major reaction factors (molar ratio and enzyme concentration) on the reaction kinetics of biodiesel generation from waste tallow bio-catalyzed by immobilized lipase [Candida antarctica lipase B (CALB)] were investigated. Three sets of experiments namely A, B, and C were conducted. In experiment set A, two factors (ultrasonic amplitude and cycle) were investigated at three levels; in experiment set B, two factors (molar ratio and enzyme concentration) were examined at three levels; and in experiment set C, two factors (ultrasonic amplitude and reaction time) were investigated at five levels. A Ping Pong Bi Bi kinetic model approach was employed to study the effect of ultrasonic amplitude on the enzymatic transesterification. Kinetic constants of transesterification reaction were determined at different ultrasonic amplitudes (30%, 35%, 40%, 45%, and 50%) and enzyme concentrations (4, 6, and 8wt.% of fat) at constant molar ratio (fat:methanol); 1:6, and ultrasonic cycle; 5Hz. Optimal conditions for ultrasound-assisted biodiesel production from waste tallow were fat:methanol molar ratio, 1:4; catalyst level 6% (w/w of fat); reaction time, 20min (30 times less than conventional batch processes); ultrasonic amplitude 40% at 5Hz. The kinetic model results revealed interesting features of ultrasound assisted enzyme-catalyzed transesterification (as compared to conventional system): at ultrasonic amplitude 40%, the reaction activities within the system seemed to be steady after 20min which means the reaction could proceed with or without ultrasonic mixing. Reversed phase high performance liquid chromatography indicated the biodiesel yield to be 85.6±0.08%. PMID:26186814

  14. Enzyme-catalyzed oxidation facilitates the return of fluorescence for single-walled carbon nanotubes.

    PubMed

    Chiu, Cheuk Fai; Barth, Brian A; Kotchey, Gregg P; Zhao, Yong; Gogick, Kristy A; Saidi, Wissam A; Petoud, Stéphane; Star, Alexander

    2013-09-11

    In this work, we studied enzyme-catalyzed oxidation of single-walled carbon nanotubes (SWCNTs) produced by the high-pressure carbon monoxide (HiPco) method. While oxidation via strong acids introduced defect sites on SWCNTs and suppressed their near-infrared (NIR) fluorescence, our results indicated that the fluorescence of SWCNTs was restored upon enzymatic oxidation, providing new evidence that the reaction catalyzed by horseradish peroxidase (HRP) in the presence of H2O2 is mainly a defect-consuming step. These results were further supported by both UV-vis-NIR and Raman spectroscopy. Therefore, when acid oxidation followed by HRP-catalyzed enzyme oxidation was employed, shortened (<300 nm in length) and NIR-fluorescent SWCNTs were produced. In contrast, upon treatment with myeloperoxidase, H2O2, and NaCl, the oxidized HiPco SWCNTs underwent complete oxidation (i.e., degradation). The shortened, NIR-fluorescent SWCNTs resulting from HRP-catalyzed oxidation of acid-cut HiPco SWCNTs may find applications in cellular NIR imaging and drug delivery systems. PMID:23672715

  15. ~ristalsof bovine chyrnotrypsin. Enzymes are proteins specialized to catalyze biological reac-

    E-print Network

    Vallino, Joseph J.

    Figure 8-1 ~ristalsof bovine chyrnotrypsin. 1 Enzymes are proteins specialized to catalyze of biochemistry is the history of en- zyme research. The name enzyme ("in yeast") was not used until 1877- furic acid. Although Louis Pasteur recognized that fermentation is catalyzed by enzymes, he postulated

  16. Reaction pathways and free energy profiles for cholinesterase-catalyzed hydrolysis of 6-monoacetylmorphine.

    PubMed

    Qiao, Yan; Han, Keli; Zhan, Chang-Guo

    2014-04-14

    As the most active metabolite of heroin, 6-monoacetylmorphine (6-MAM) can penetrate into the brain for the rapid onset of heroin effects. The primary enzymes responsible for the metabolism of 6-MAM to the less potent morphine in humans are acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). The detailed reaction pathways for AChE- and BChE-catalyzed hydrolysis of 6-MAM to morphine have been explored, for the first time, in the present study by performing first-principles quantum mechanical/molecular mechanical free energy calculations. It has been demonstrated that the two enzymatic reaction processes follow similar catalytic reaction mechanisms, and the whole catalytic reaction pathway for each enzyme consists of four reaction steps. According to the calculated results, the second reaction step associated with the transition state TS2(a)/TS2(b) should be rate-determining for the AChE/BChE-catalyzed hydrolysis, and the free energy barrier calculated for the AChE-catalyzed hydrolysis (18.3 kcal mol(-1)) is 2.5 kcal mol(-1) lower than that for the BChE-catalyzed hydrolysis (20.8 kcal mol(-1)). The free energy barriers calculated for the AChE- and BChE-catalyzed reactions are in good agreement with the experimentally derived activation free energies (17.5 and 20.7 kcal mol(-1) for the AChE- and BChE-catalyzed reactions, respectively). Further structural analysis reveals that the aromatic residues Phe295 and Phe297 in the acyl pocket of AChE (corresponding to Leu286 and Val288 in BChE) contribute to the lower energy of TS2(a) relative to TS2(b). The obtained structural and mechanistic insights could be valuable for use in future rational design of a novel therapeutic treatment of heroin abuse. PMID:24595354

  17. Ultrasound assisted enzyme catalyzed synthesis of glycerol carbonate from glycerol and dimethyl carbonate.

    PubMed

    Waghmare, Govind V; Vetal, Mangesh D; Rathod, Virendra K

    2015-01-01

    The present work illustrates the transesterification of glycerol to glycerol carbonate (GlyC) from dimethyl carbonate (DMC) using commercial immobilized lipase (Novozym 435) under ultrasonic irradiation. The experiments were performed in a batch reactor placed in an ultrasonic water bath using a sequence of experimental protocol to evaluate the effects of temperature, molar ratios of substrates, enzyme loading, duty cycle and ultrasound power on the conversion of glycerol to GlyC. It has been found that ultrasound-assisted lipase-catalyzed transesterification of glycerol would be a potential alternative to conventional alkali-catalyzed method, as high conversion (99.75%) was obtained at mild operating conditions: molar ratio of DMC to glycerol 3:1, catalyst amount of 13% (w/w), lower power input (100W), duty cycle 50% and temperature (60°C) in a relatively short reaction time (4h) using Novozym 435 as catalyst. Ultrasound reduces the reaction time up to 4h as compared to conventional stirring method (14h) catalyzed by Novozym 435. The repeated use of the catalyst under the optimum experimental condition resulted in decay in both enzyme activity and product conversion. PMID:25069889

  18. The enzymatic reaction catalyzed by lactate dehydrogenase exhibits one dominant reaction path

    NASA Astrophysics Data System (ADS)

    Masterson, Jean E.; Schwartz, Steven D.

    2014-10-01

    Enzymes are the most efficient chemical catalysts known, but the exact nature of chemical barrier crossing in enzymes is not fully understood. Application of transition state theory to enzymatic reactions indicates that the rates of all possible reaction paths, weighted by their relative probabilities, must be considered in order to achieve an accurate calculation of the overall rate. Previous studies in our group have shown a single mechanism for enzymatic barrier passage in human heart lactate dehydrogenase (LDH). To ensure that this result was not due to our methodology insufficiently sampling reactive phase space, we implement high-perturbation transition path sampling in both microcanonical and canonical regimes for the reaction catalyzed by human heart LDH. We find that, although multiple, distinct paths through reactive phase space are possible for this enzymatic reaction, one specific reaction path is dominant. Since the frequency of these paths in a canonical ensemble is inversely proportional to the free energy barriers separating them from other regions of phase space, we conclude that the rarer reaction paths are likely to have a negligible contribution. Furthermore, the non-dominate reaction paths correspond to altered reactive conformations and only occur after multiple steps of high perturbation, suggesting that these paths may be the result of non-biologically significant changes to the structure of the enzymatic active site.

  19. Complex Biotransformations Catalyzed by Radical S-Adenosylmethionine Enzymes*

    PubMed Central

    Zhang, Qi; Liu, Wen

    2011-01-01

    The radical S-adenosylmethionine (AdoMet) superfamily currently comprises thousands of proteins that participate in numerous biochemical processes across all kingdoms of life. These proteins share a common mechanism to generate a powerful 5?-deoxyadenosyl radical, which initiates a highly diverse array of biotransformations. Recent studies are beginning to reveal the role of radical AdoMet proteins in the catalysis of highly complex and chemically unusual transformations, e.g. the ThiC-catalyzed complex rearrangement reaction. The unique features and intriguing chemistries of these proteins thus demonstrate the remarkable versatility and sophistication of radical enzymology. PMID:21771780

  20. Effect of additives on enzyme-catalyzed polymerization of phenols and aromatic amines.

    PubMed

    D'Annibale, Alessandro; Stazi, Silvia Rita; Petruccioli, Maurizio

    2012-01-01

    Among biological approaches to the removal of aromatic amines and phenols from wastewater, the so-called enzyme-catalyzed polymerization and precipitation (ECPP) process relies on the use of oxidoreductases acting via radical mechanisms and characterized by a rather relaxed substrate specificity, such as laccase, tyrosinase and peroxidases. The main technical constraints of ECPP processes are due to a variety of enzyme deactivation phenomena occurring during catalysis and to the incomplete removal of oxidation products from solution. In order to put ECPP into practice, these drawbacks have to be either counteracted or minimized. Although several approaches, such as enzyme immobilization and reaction engineering, have been proposed to limit these constraints, this review is intended to provide a wide survey on some chemical additives with either protective or coagulating effects that have been so far employed for these purposes. PMID:22652869

  1. Toward cell circuitry: Topological analysis of enzyme reaction networks via reaction route graphs

    NASA Astrophysics Data System (ADS)

    Datta, Ravindra; Vilekar, Saurabh A.; Fishtik, Ilie; Dittami, James P.

    2008-05-01

    The first step toward developing complete cell circuitry is to build quantitative networks for enzyme reactions. The conventional King-Altman-Hill (KAH) algorithm for topological analysis of enzyme networks, adapted from electrical networks, is based on “Reaction Graphs” that, unlike electrical circuits, are not quantitative, being straightforward renderings of conventional schematics of reaction mechanisms. Therefore, we propose the use of “Reaction Route (RR) Graphs” instead, as a more suitable graph-theoretical representation for topological analysis of enzyme reaction networks. The RR Graphs are drawn such that they are not only useful for visualizing the various reaction routes or pathways, but unlike Reaction Graphs possess network properties consistent with requisite kinetic, mass balance, and thermodynamic constraints. Therefore, they are better than the conventional Reaction Graphs for topological representation and analysis of enzyme reactions, both via the KAH methodology as well as via numerical matrix inversion. The difference between the two is highlighted based on the example of a single enzyme reaction network for the conversion of 7,8-dihydrofolate and NADPH into 5,6,7,8-tetrahydrofolate and NADP +, catalyzed by the enzyme dihydrofolate reductase.

  2. Influencing Enzymes: A Lesson on Enzyme Reactions

    NSDL National Science Digital Library

    Camia Steinmann (Clear Creek High School)

    2007-08-01

    This teaching resource was developed by a K-12 science teacher in the American Physiological SocietyÂ?s 2007 Frontiers in Physiology Program. For more information on this program, please visit www.frontiersinphys.org. Students will investigate the catabolic properties of the enzyme amylase and its role in digestion of breaking down starch molecules. Prior to this activity, students should be able to identify the structural and functional properties of carbohydrates and proteins. Upon completion of this activity, students will be able to predict the effect of different environments on enzyme activity.

  3. The Biginelli Reaction Is a Urea-Catalyzed Organocatalytic Multicomponent Reaction.

    PubMed

    Puripat, Maneeporn; Ramozzi, Romain; Hatanaka, Miho; Parasuk, Waraporn; Parasuk, Vudhichai; Morokuma, Keiji

    2015-07-17

    The recently developed artificial force induced reaction (AFIR) method was applied to search systematically all possible multicomponent pathways for the Biginelli reaction mechanism. The most favorable pathway starts with the condensation of the urea and benzaldehyde, followed by the addition of ethyl acetoacetate. Remarkably, a second urea molecule catalyzes nearly every step of the reaction. Thus, the Biginelli reaction is a urea-catalyzed multicomponent reaction. The reaction mechanism was found to be identical in both protic and aprotic solvents. PMID:26066623

  4. Copper-Catalyzed Oxidative Heck Reactions between Alkyltrifluoroborates and Vinylarenes

    PubMed Central

    Liwosz, Timothy W.; Chemler, Sherry R.

    2013-01-01

    We report herein that potassium alkyltrifluoroborates can be utilized in oxidative Heck-type reactions with vinyl arenes. The reaction is catalyzed by a Cu(OTf)2/1,10-phenanthroline with MnO2 as the stoichiometric oxidant. In addition to the alkyl Heck, amination, esterification and dimerization reactions of alkyltrifluoroborates are demonstrated under analogous reaction conditions. Evidence for an alkyl radical intermediate is presented. PMID:23734764

  5. Hydroxyatrazine N-Ethylaminohydrolase (AtzB): an Amidohydrolase Superfamily Enzyme Catalyzing Deamination and Dechlorination?

    PubMed Central

    Seffernick, Jennifer L.; Aleem, Asma; Osborne, Jeffrey P.; Johnson, Gilbert; Sadowsky, Michael J.; Wackett, Lawrence P.

    2007-01-01

    Hydroxyatrazine [2-(N-ethylamino)-4-hydroxy-6-(N-isopropylamino)-1,3,5-triazine] N-ethylaminohydrolase (AtzB) is the sole enzyme known to catalyze the hydrolytic conversion of hydroxyatrazine to N-isopropylammelide. AtzB, therefore, serves as the point of intersection of multiple s-triazine biodegradative pathways and is completely essential for microbial growth on s-triazine herbicides. Here, atzB was cloned from Pseudomonas sp. strain ADP and its product was purified to homogeneity and characterized. AtzB was found to be dimeric, with subunit and holoenzyme molecular masses of 52 kDa and 105 kDa, respectively. The kcat and Km of AtzB with hydroxyatrazine as a substrate were 3 s?1 and 20 ?M, respectively. Purified AtzB had a 1:1 zinc-to-subunit stoichiometry. Sequence analysis revealed that AtzB contained the conserved mononuclear amidohydrolase superfamily active-site residues His74, His76, His245, Glu248, His280, and Asp331. An intensive in vitro investigation into the substrate specificity of AtzB revealed that 20 of the 51 compounds tested were substrates for AtzB; this allowed for the identification of specific substrate structural features required for catalysis. Substrates required a monohydroxylated s-triazine ring with a minimum of one primary or secondary amine substituent and either a chloride or amine leaving group. AtzB catalyzed both deamination and dechlorination reactions with rates within a range of one order of magnitude. This differs from AtzA and TrzN, which do not catalyze deamination reactions, and AtzC, which is not known to catalyze dechlorination reactions. PMID:17660279

  6. Mechanistic Imperatives for Deprotonation of Carbon Catalyzed by Triosephosphate Isomerase: Enzyme-Activation by Phosphite Dianion

    PubMed Central

    Zhai, Xiang; Malabanan, M. Merced; Amyes, Tina L.; Richard, John P.

    2013-01-01

    The mechanistic imperatives for catalysis of deprotonation of ?–carbonyl carbon by triosephosphate isomerase (TIM) are discussed. There is a strong imperative to reduce the large thermodynamic barrier for deprotonation of carbon to form an enediolate reaction intermediate; and, a strong imperative for specificity in the expression of the intrinsic phosphodianion binding energy at the transition state for the enzyme-catalyzed reaction. Binding energies of 2 and 6 kcal/mol, respectively, have been determined for formation of phosphite dianion complexes to TIM and to the transition state for TIM-catalyzed deprotonation of the truncated substrate glycolaldehyde [T. L. Amyes, J. P. Richard, Biochemistry 2007, 46, 5841]. We propose that the phosphite dianion binding energy, which is specifically expressed at the transition state complex, is utilized to stabilize a rare catalytically active loop-closed form of TIM. The results of experiments to probe the role of the side chains of Ile172 and Leu232 in activating the loop-closed form of TIM for catalysis of substrate deprotonation are discussed. Evidence is presented that the hydrophobic side chain of Ile172 assists in activating TIM for catalysis of substrate deprotonation through an enhancement of the basicity of the carboxylate side-chain of Glu167. Our experiments link the two imperatives for TIM-catalyzed deprotonation of carbon by providing evidence that the phosphodianion binding energy is utilized to drive an enzyme conformational change, which results in a reduction in the thermodynamic barrier to deprotonation of the carbon acid substrate at TIM compared with the barrier for deprotonation in water. The effects of a P168A mutation on the kinetic parameters for the reactions of whole and truncated substrates are discussed. PMID:24729658

  7. Adenosyl radical: reagent and catalyst in enzyme reactions

    PubMed Central

    Patterson, Dustin P.

    2010-01-01

    Lead in Adenosine is undoubtedly an ancient biological molecule that is a component of many enzyme cofactors; ATP, FADH, NAD(P)H, and coenzyme A, to name but a few, and, of course, of RNA. Here we present an overview of the role of adenosine in its most reactive form: as an organic radical formed either by homolytic cleavage of adenosylcobalamin (coenzyme B12, AdoCbl) or by single-electron reduction of S-adenosylmethionine (AdoMet) complexed to an iron-sulfur cluster. Although many of the enzymes we discuss are newly discovered, adenosine’s role as a radical cofactor most likely arose very early in evolution, before the advent of photosynthesis and the production of molecular oxygen which rapidly inactivates many radical enzymes. AdoCbl-dependent enzymes appear to be confined to a rather narrow repertoire of rearrangement reactions involving 1,2-hydrogen atom migrations. In contrast, there has been a recent explosion in the number radical AdoMet enzymes discovered that catalyze a remarkably wide range of chemically challenging reactions. Although all the radical AdoMet enzymes so far characterized come from anaerobically growing microbes and are very oxygen sensitive, there is tantalizing evidence that some of these enzymes may be active in aerobic organisms including humans. PMID:20191656

  8. Ligand Intermediates in Metal-Catalyzed Reactions

    SciTech Connect

    Gladysz, John A.

    1999-07-31

    The longest-running goal of this project has been the synthesis, isolation, and physical chemical characterization of homogeneous transition metal complexes containing ligand types believed to be intermediates in the metal-catalyzed conversion of CO/H{sub 2}, CO{sub 2}, CH{sub 4}, and similar raw materials to organic fuels, feedstocks, etc. In the current project period, complexes that contain unusual new types of C{sub x}(carbide) and C{sub x}O{sub y} (carbon oxide) ligands have been emphasized. A new program in homogeneous fluorous phase catalysis has been launched as described in the final report.

  9. The sporulation-specific enzymes encoded by the DIT1 and DIT2 genes catalyze a two-step reaction leading to a soluble LL-dityrosine-containing precursor of the yeast spore wall.

    PubMed Central

    Briza, P; Eckerstorfer, M; Breitenbach, M

    1994-01-01

    Dityrosine is a sporulation-specific component of the yeast ascospore wall that is essential for the resistance of the spores to adverse environmental conditions. Dityrosine in vivo exists in both the LL and DL configurations and is part of an insoluble macromolecule of unknown structure. Here we present data indicating that dityrosine of the yeast spore wall is biosynthesized by a different mechanism than dityrosine in other biological systems--e.g., the hard fertilization membrane of the sea urchin egg. We identified two soluble, low molecular weight LL-dityrosine-containing spore wall precursors in extracts of sporulating cells and one precursor containing L-tyrosine. By expression of the previously described sporulation-specific genes DIT1 and DIT2 in vegetative cells, it was shown that DIT1 catalyzes the reaction leading from L-tyrosine to the tyrosine-containing precursor. DIT2, which is a member of the cytochrome P450 superfamily, is responsible for the dimerization reaction leading to the dityrosine-containing precursors. Epimerization of LL- to DL-dityrosine is one of the latest steps in spore wall formation and takes place after the dityrosine-containing precursors are incorporated into the spore wall. On the basis of these findings we suggest a biosynthetic pathway for the top layer of the yeast spore wall. Images PMID:8183942

  10. Development of a Lewis Base Catalyzed Selenocyclization Reaction

    ERIC Educational Resources Information Center

    Collins, William

    2009-01-01

    The concept of Lewis base activation of selenium Lewis acids has been effectively reduced to practice in the Lewis base catalyzed selenofunctionalization of unactivated olefins. In this reaction, the weakly acidic species, "N"-phenylselenyl succinimide, is cooperatively activated by the addition of a "soft" Lewis base donor (phosphine sulfides,…

  11. ENZYME-CATALYZED GEL-FORMATION OF GELATIN AND CHITOSAN. POTENTIAL FOR IN SITU APPLICATIONS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    We compared the ability of two enzymes to catalyze the formation of gels from solutions of gelatin and chitosan. A microbial transglutaminase, currently under investigation for food applications, was observed to catalyze the formation of strong and permanent gels from gelatin solutions. Chitosan w...

  12. Cross-ligation and exchange reactions catalyzed by hairpin ribozymes.

    PubMed Central

    Komatsu, Y; Koizumi, M; Sekiguchi, A; Ohtsuka, E

    1993-01-01

    The negative strand of the satellite RNA of tobacco ringspot virus (sTobRV(-)) contains a hairpin catalytic domain that shows self-cleavage and self-ligation activities in the presence of magnesium ions. We describe here that the minimal catalytic domain can catalyze a cross-ligation reaction between two kinds of substrates in trans. The cross-ligated product increased when the reaction temperature was decreased during the reaction from 37 degrees C to 4 degrees C. A two-stranded hairpin ribozyme, divided into two fragments between G45 and U46 in a hairpin loop, showed higher ligation activity than the nondivided ribozyme. The two stranded ribozyme also catalyzed an exchange reaction of the 3'-portion of the cleavage site. Images PMID:8441626

  13. LIGAND: chemical database of enzyme reactions

    PubMed Central

    Goto, Susumu; Nishioka, Takaaki; Kanehisa, Minoru

    2000-01-01

    LIGAND is a composite database comprising three sections: ENZYME for the information of enzyme molecules and enzymatic reactions, COMPOUND for the information of metabolites and other chemical compounds, and REACTION for the collection of substrate–product relations. The current release includes 3390 enzymes, 5645 compounds and 5207 reactions. The database is indispensable for the reconstruction of metabolic pathways in the completely sequenced organisms. The LIGAND database can be accessed through the WWW (http://www.genome.ad.jp/dbget/ligand.html ) or may be downloaded by anonymous FTP (ftp://kegg.genome.ad.jp/molecules/ligand/ ). PMID:10592281

  14. Cascade reactions catalyzed by metal organic frameworks.

    PubMed

    Dhakshinamoorthy, Amarajothi; Garcia, Hermenegildo

    2014-09-01

    Cascade or tandem reactions where two or more individual reactions are carried out in one pot constitute a clear example of process intensification, targeting the maximization of spatial and temporal productivity with mobilization of minimum resources. In the case of catalytic reactions, cascade processes require bi-/multifunctional catalysts that contain different classes of active sites. Herein, we show that the features and properties of metal-organic frameworks (MOFs) make these solids very appropriate materials for the development of catalysts for cascade reactions. Due to composition and structure, MOFs can incorporate different types of sites at the metal nodes, organic linkers, or at the empty internal pores, allowing the flexible design and synthesis of multifunctional catalysts. After some introductory sections on the relevance of cascade reactions from the point of view of competitiveness, sustainability, and environmental friendliness, the main part of the text provides a comprehensive review of the literature reporting the use of MOFs as heterogeneous catalysts for cascade reactions including those that combine in different ways acid/base, oxidation/reduction, and metal-organic centers. The final section summarizes the current state of the art, indicating that the development of a first commercial synthesis of a high-added-value fine chemical will be a crucial milestone in this area. PMID:25082205

  15. List-Barbas-Mannich reaction catalyzed by modularly designed organocatalysts.

    PubMed

    Perera, Sandun; Sinha, Debarshi; Rana, Nirmal K; Trieu-Do, Van; Zhao, John Cong-Gui

    2013-11-01

    The List-Barbas-Mannich reaction of ethyl (p-methoxyphenylimino)acetate (p-methoxyphenyl = PMP) with unmodified aldehydes or ketones catalyzed by modularly designed organocatalysts (MDOs) that are self-assembled from proline and cinchona alkaloid thioureas (such as a quinidine-derived thiourea) produces the corresponding ?-oxo-?-amino acid derivatives in high yields and excellent stereoselectivities. No solvent is necessary for this reaction. Aldehydes are especially good substrates for this reaction: The reaction takes only a few minutes to yield the corresponding List-Barbas-Mannich products in excellent dr (up to >99:1) and ee values (up to >99% ee). PMID:24106958

  16. Enzyme Reactions in Nanoporous, Picoliter Volume Containers

    SciTech Connect

    Siuti, Piro [ORNL; Retterer, Scott T [ORNL; Choi, Chang Kyoung [Michigan Technological University; Doktycz, Mitchel John [ORNL

    2012-01-01

    Advancements in nanoscale fabrication allow creation of small volume reaction containers that can facilitate the screening and characterization of enzymes. A porous, ~19 pL volume vessel has been used in this work to carry out enzyme reactions under varying substrate concentrations. Glucose oxidase and horseradish peroxidase can be contained in these structures and diffusively fed with a solution containing glucose and the fluorogenic substrate Amplex Red through the engineered nanoscale pore structure. Fluorescent microscopy was used to monitor the reaction, which was carried out under microfluidic control. Kinetic characteristics of the enzyme were evaluated and compared with results from conventional scale reactions. These picoliter, nanoporous containers can facilitate quick determination of enzyme kinetics in microfluidic systems without the requirement of surface tethering and can be used for applications in drug discovery, clinical diagnostics and high-throughput screening.

  17. Stau-catalyzed big-bang nucleosynthesis reactions

    SciTech Connect

    Kamimura, Masayasu [Department of Physics, Kyushu University, Fukuoka 812-8581 (Japan); Kino, Yasushi [Department of Physics, Tohoku University, Sendai 980-8578 (Japan); Hiyama, Emiko [RIKEN Nishina Center, Wako 351-0198 (Japan)

    2010-06-01

    We study the new type of big-bang nucleosynthesis (BBN) reactions that are catalyzed by a hypothetical long-lived negatively charged, massive leptonic particle (called X{sup -}) such as the supersymmetric (SUSY) particle stau, the scalar partner of the tau lepton. It is known that if the X{sup -} particle has a lifetime of tau{sub X} > or approx. 10{sup 3} s, it can capture a light element previously synthesized in standard BBN and form a Coulombic bound state and induces various types of reactions in which X{sup -} acts as a catalyst. Some of these X{sup -} catalyzed reactions have significantly large cross sections so that the inclusion of the reactions into the BBN network calculation can markedly change the abundances of some elements. We use a high-accuracy three-body calculation method developed by the authors and provide precise cross sections and rates of these catalyzed BBN reactions for use in the BBN network calculation.

  18. 9422 Stratospheric ice catalyzes chlorine reactions 9428 Fusing silk and silica

    E-print Network

    McFadden, Geoff

    9422 Stratospheric ice catalyzes chlorine reactions 9428 Fusing silk and silica 9482 Identifying deteriorates with age CHEMISTRY Stratospheric ice catalyzes chlorine reactions To explain how ice crystals can catalyze chlorine reactions in the stratosphere, Faye McNeill et al. report that small amounts

  19. Reversible H atom abstraction catalyzed by the radical S-adenosylmethionine enzyme HydG.

    PubMed

    Duffus, Benjamin R; Ghose, Shourjo; Peters, John W; Broderick, Joan B

    2014-09-24

    The organometallic H-cluster at the active site of [FeFe]-hydrogenases is synthesized by three accessory proteins, two of which are radical S-adenosylmethionine enzymes (HydE, HydG) and one of which is a GTPase (HydF). In this work we probed the specific role of H atom abstraction in HydG-catalyzed carbon monoxide and cyanide production from tyrosine. The isotope distributions of 5'-deoxyadenosine and p-cresol were evaluated using deuterium-labeled tyrosine substrates in H2O and D2O. The observation of multiply deuterated 5'-deoxyadenosine and deuterated S-adenosylmethionine when the reaction is carried out in D2O provides evidence for a 5'-deoxyadenosyl radical-mediated abstraction of a hydrogen atom from a solvent-exchangeable position as a reversible event. PMID:25099480

  20. Signal enhancement strategy for a micro-arrayed polydiacetylene (PDA) immunosensor using enzyme-catalyzed precipitation.

    PubMed

    Lee, Jong Uk; Jeong, Ji Hoon; Lee, Doo Sung; Sim, Sang Jun

    2014-11-15

    This paper describes a signal enhancement strategy to improve the sensitivity of an antibody-based immunosensor that uses polydiacetylene (PDA) liposomes to detect a target protein (human immunoglobulin E [hIgE]). To achieve ultrasensitive detection, multiple stimuli applied to PDA immunosensor chips offer a signal enhancement method that combines the primary immune reaction between antigen and antibody with the sandwich method of polyclonal antibody (pAb)-conjugated horseradish peroxidase (HRP). In the second step, fluorescence is enhanced by the mechanical pressure from the precipitate formed by enzyme catalysis. In order to detect hIgE, the surface of immobilized PDA liposomes was conjugated with monoclonal antibodies against hIgE, and fluorescence signals were detected after the antigen-antibody reaction. In this step, hIgE concentrations as low as 10 ng/mL were detected. Fluorescence signals slightly increased when anti-hIgE pAb-HRP was used as an amplifying agent after primary immunoresponse. After secondary immunoresponse, HRP-catalyzed oxidation of 3,3'-diaminobenzidine produced an insoluble precipitate that strongly stimulated PDA liposomes by their weight and pressure, thereby dramatically increasing the fluorescence signal. Thus, PDA liposome immunosensor could detect hIgE concentrations as low as 0.01 ng/mL, representing a 1000-fold increase in sensitivity over the signal generated by the primary immunoresponse. This study indicates that increasing the external mechanical force applied to PDA liposomes by enzyme-catalyzed precipitate formation enhanced the sensitivity of the PDA liposome immunosensor chip. This strategy can be applied to the detection of other biomolecules in experimental or clinical settings where ultrasensitive and highly specific biosensing is required. PMID:24907539

  1. Substrate activity of synthetic formyl phosphate in the reaction catalyzed by formyltetrahydrofolate synthetase

    SciTech Connect

    Smithers, G.W.; Jahansouz, H.; Kofron, J.L.; Himes, R.H.; Reed, G.H.

    1987-06-30

    Formyl phosphate, a putative enzyme-bound intermediate in the reaction catalyzed by formyltetrahydrofolate synthetase (EC 6.3.4.3), was synthesized from formyl fluoride and inorganic phosphate, and the product was characterized by /sup 31/P, /sup 1/H, and /sup 13/C nuclear magnetic resonance (NMR). Measurement of hydrolysis rates by /sup 31/P NMR indicates that formyl phosphate is particularly labile, with a half-life of 48 min in a buffered neutral solution at 20 /sup 0/C. At pH 7, hydrolysis occurs with P-O bond cleavage, as demonstrated by /sup 18/O incorporation from H/sub 2//sup 18/O into P/sub i/, while at pH 1 and pH 13 hydrolysis occurs with C-O bond cleavage. The substrate activity of formyl phosphate was tested in the reaction catalyzed by formyltetrahydrofolate synthetase isolated from Clostridium cylindrosporum. Formyl phosphate supports the reaction in both the forward and reverse directions. Thus, N/sup 10/-formyltetrahydrofolate is produced from tetrahydrofolate and formyl phosphate in a reaction mixture that contains enzyme, Mg(II), and ADP, and ATP is produced from formyl phosphate and ADP with enzyme, Mg(II), and tetrahydrofolate present. The requirements for ADP and for tetrahydrofolate as cofactors in these reactions are consistent with previous steady-state kinetic and isotope exchange studies, which demonstrated that all substrate subsites must be occupied prior to catalysis. The k/sub cat/ values for both the forward and reverse directions, with formyl phosphate as the substrate, are much lower than those for the normal forward and reverse reactions. Kinetic analysis of the formyl phosphate supported reactions indicates that the low steady-state rates observed for the synthetic intermediate are most likely due to the sequential nature of the normal reaction.

  2. Removal of benzene from wastewater via Fenton pre-treatment followed by enzyme catalyzed polymerization.

    PubMed

    Saha, Beeta; Taylor, K E; Bewtra, J K; Biswas, N

    2011-01-01

    This study investigated the feasibility of a two-step process for the removal of benzene from buffered synthetic wastewater. Benzene is outside the scope of enzymatic removal. In order to remove it from wastewater using enzyme, its pretreatment by modified Fenton reaction was employed to generate the corresponding phenolic compounds. In the first phase, the optimum pH, H2O2 and Fe2+ concentrations and reaction time for the Fenton reaction were determined to maximize the conversion of benzene to phenolic compounds without causing significant mineralization. The pretreatment process was followed by oxidative polymerization of the phenolic compounds catalyzed by a laccase from Trametes villosa. Factors of interest for the three-hour enzymatic treatment were pH and laccase concentration. Under optimum Fenton reaction conditions, 80% conversion of the initial benzene concentration was achieved, giving a mixture containing oxidative dimerization product (biphenyl) and hydroxylation products (phenol, catechol, resorcinol, benzoquinone and hydroquinone). Enzymatic removal of biphenyl and benzoquinone was not possible but 2.5 U/mL laccase was successful in removal of the rest of the phenolic PMID:21866766

  3. Investigations into Transition Metal Catalyzed Arene Trifluoromethylation Reactions

    PubMed Central

    Ye, Yingda; Sanford, Melanie S.

    2015-01-01

    Trifluoromethyl-substituted arenes and heteroarenes are widely prevalent in pharmaceuticals and agrochemicals. As a result, the development of practical methods for the formation of aryl–CF3 bonds has become an active field of research. Over the past five years, transition metal catalyzed cross-coupling between aryl–X (X = halide, organometallic, or H) and various “CF3” reagents has emerged as a particularly exciting approach for generating aryl–CF3 bonds. Despite many recent advances in this area, current methods generally suffer from limitations such as poor generality, harsh reaction conditions, the requirement for stoichiometric quantities of metals, and/or the use of costly CF3 sources. This Account describes our recent efforts to address some of these challenges by: (1) developing aryl trifluoromethylation reactions involving high oxidation state Pd intermediates, (2) exploiting AgCF3 for C–H trifluoromethylation, and (3) achieving Cu-catalyzed trifluoromethylation with photogenerated CF3•. PMID:25838638

  4. Direct evidence for an acyl phosphate intermediate in the folylpoly-. gamma. -glutamate synthetase and dihydrofolate synthetase-catalyzed reactions

    SciTech Connect

    Banerjee, R.

    1987-01-01

    The mechanism of the reactions catalyzed by two enzymes, namely dihydrofolate synthetase (DHFS) and folylpoly-..gamma..-glutamate synthetase (FPGS), has been investigated. The nature of the intermediate in each of the two reactions was monitored simultaneously in the multifunctional enzyme, FPGS/DHFS from E. coli. The latter was isolated from a transformant containing the cloned FPGS/DHFS gene. Incubation of (/sup 18/O)-H/sub 2/Pte and (/sup 17/O)-glutamate with ATP and the enzyme, resulted in the formation of (/sup 18/O)- and (/sup 17/O)-P/sub i/, thus providing strong evidence for the formation of an acyl phosphate species during catalysis of each reaction. The inorganic phosphate formed in the enzyme-catalyzed reaction was purified by chromatography on DEAE-cellulose, then converted to the trimethyl ester and analyzed by mass spectroscopy /sup 17/O NMR and /sup 31/P NMR. Stoichiometric formation of (/sup 17/O)- and (/sup 18/O)-Pi was observed. /sup 31/P NMR analysis showed the expected /sup 18/O-induced isotopic perturbations. The presence of (/sup 17/O)-trimethyl phosphate was revealed by /sup 17/O NMR. The mechanism of the FPGS-catalyzed reaction was also investigated with the antifolate (/sup 18/O)-methotrexate.

  5. Enzyme catalysis Enzyme catalysis is the catalysis of chemical reactions by

    E-print Network

    Cavanagh, John

    Enzyme catalysis Enzyme catalysis is the catalysis of chemical reactions by specialized proteins known as enzymes. Catalysis of biochemical reactions in the cell is vital due to the very low reaction rates of the uncatalysed reactions. The mechanism of enzyme catalysis is similar in principle to other

  6. Criteria for identifying homogeneous transition metal cluster-catalyzed reactions

    SciTech Connect

    Laine, R.M.

    1980-01-01

    Four criteria were developed for distinguishing homogeneous cluster from mononuclear catalysis. A criterion based on reaction kinetics, which distinguishes catalysis by clusters from catalysis by mononuclear complexes in equilibrium with the clusters, is illustrated with the hydroformylation of 1-pentene by Ru/sub 3/(CO)/sub 12/ clusters in equilibrium with 3Ru(CO)/sub 5/ complexes in the presence of CO. A criterion based on selectivity is illustrated by the water gas shift and deuterium-exchange reactions catalyzed by ruthenium and rhodium carbonyl clusters in methanol and triethylamine; the scope of this criterion is limited to deuterium exchange reactions. A criterion based on mixed-metal catalysis, in which a mixed-metal system has higher catalytic activity than each transition metal cluster alone, is illustrated with hydroformylation of 1-pentene and the water gas shift reaction catalyzed by Ru/sub 3/(CO)/sub 12//Fe/sub 3/(CO)/sub 2/ and Rh/sub 6/(CO)/sub 16//Fe/sub 3/(CO)/sub 12/. A criterion based on changes in asymmetric induction is a special case of the selectivity criterion, in which specific starting metal complexes may produce either of two enantiomers. Catalysis by metal clusters is an analytical tool for modeling heterogeneous catalytic mechanisms.

  7. Kinetics of Imidazole Catalyzed Ester Hydrolysis: Use of Buffer Dilutions to Determine Spontaneous Rate, Catalyzed Rate, and Reaction Order.

    ERIC Educational Resources Information Center

    Lombardo, Anthony

    1982-01-01

    Described is an advanced undergraduate kinetics experiment using buffer dilutions to determine spontaneous rate, catalyzed rate, and reaction order. The reaction utilized is hydrolysis of p-nitro-phenyl acetate in presence of imidazole, which has been shown to enhance rate of the reaction. (Author/JN)

  8. Ruthenium(II)-catalyzed reactions of 1,4-epiperoxides

    SciTech Connect

    Suzuki, Masaaki; Ohtake, Hiroaki; Kameya, Yoshimi; Noyori, Ryoji (Nagoya Univ. (Japan)); Hamanaka, Nobuyuki (Ono Pharmaceutical Co., Osaka (Japan))

    1989-10-27

    The behavior of 1,4-epiperoxides in the presence of transition-metal complexes is highly dependent on the structures of the substrates and the nature of the metal catalysts. Reaction of saturated epiperoxides such as 1,3-epiperoxycyclopentane, 1,4-epiperoxycyclohexane, or dihydroascaridole catalyzed by RuCl{sub 2}(PPh{sub 3}){sub 3} in dichloromethane gives a mixture of products arising from fragmentation, rearrangement, reduction, disproportionation, etc. Prostaglandin H{sub 2} methyl ester undergoes clean and stereospecific fragmentation to afford methyl (5Z,8E,10E,12S)-12-hydroxy-5,8,10-heptadecatrienoate and malonaldehyde. Bicyclic 2,3-didehydro 1,4-epiperoxides give the syn-1,2:3,4-diepoxides by the same catalyst. The monocyclic analogues are transformed to a mixture of diepoxides and furan products. The stereochemical outcome of the epoxide formation reflects unique differences in the ground-state geometry of the starting epiperoxide substrates. FeCl{sub 2}(PPh{sub 3}){sub 2} serves as a useful catalyst for the skeletal change of sterically hindered bicyclic 2,3-didehydro 1,4-epiperoxides to the syn-diepoxides. In addition, the Fe complex best effects the conversion of 1,4-unsubstituted 2,3-didehydro epiperoxides to furans. The Ru-catalyzed reactions are interpreted in terms of the intermediacy of inner-sphere radicals formed by atom transfer of the Ru(II) species to peroxy substrates, in contrast to the Fe-catalyzed reactions proceeding via free, outer-sphere radicals generated by an electron-transfer mechanism.

  9. Mathematical Analysis of Activation Thresholds in Enzyme-Catalyzed Positive Feedbacks: Application to the Feedbacks of Blood Coagulation

    Microsoft Academic Search

    Edward Beltrami; Jolyon Jesty

    1995-01-01

    A hierarchy of enzyme-catalyzed positive feedback loops is examined by mathematical and numerical analysis. Four systems are described, from the simplest, in which an enzyme catalyzes its own formation from an inactive precursor, to the most complex, in which two sequential feedback loops act in a cascade. In the latter we also examine the function of a long-range feedback, in

  10. A Bovine Pancreatic Enzyme Catalyzing the Conversion of Proinsulin to Insulin

    PubMed Central

    Yip, C. C.

    1971-01-01

    An enzyme that catalyzes the conversion of bovine proinsulin to insulin has been purified from a bovine pancreatic extract. The product of conversion was identified as insulin by aminoacid analysis and determination of carboxyl terminal aminoacid residues. The purified enzyme preparation showed one major protein band on polyacrylamide gel disc electrophoresis; it had a molecular weight of about 70,000 and an isoelectric point (pI) at a pH of 4.82. Images PMID:5288380

  11. THE TRIACYLGLYCEROL SYNTHESIS ENZYME DGAT1 ALSO CATALYZES THE SYNTHESIS OF DIACYLGLYCEROLS, WAXES, AND RETINYL ESTERS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The final step of triacylglycerol biosynthesis is catalyzed by acyl CoA:diacylglycerol acyltransferase (DGAT) enzymes. The two known DGATs, DGAT1 and DGAT2, are encoded by unrelated genes. Although both DGAT1 and DGAT2 knockout mice have reduced tissue triacylglycerol contents, they have disparate p...

  12. Ultrasound assisted enzyme catalyzed degradation of Cetirizine dihydrochloride.

    PubMed

    Sutar, Rahul S; Rathod, Virendra K

    2015-05-01

    Cetirizine dihydrochloride, a pharmaceutical drug of the class antihistamines is frequently detected in wastewater samples. In the present work, the degradation of Cetirizine dihydrochloride is carried out using a novel technique of laccase enzyme as a catalyst under the influence of ultrasound irradiation. Effect of various process parameters such as enzyme loading, temperature, power, duty cycle, frequency and speed of agitation has been studied along with identification of the degradation intermediates. The maximum degradation of 91% is achieved at optimized experimental parameters such as 0.02% enzyme loading (w/v), 50°C temperature, power input of 100 W, 25 kHz frequency and 50% duty cycle with agitation speed of 200 rpm. It is observed that enzymatic degradation of Cetirizine dihydrochloride under the influence of ultrasound irradiation not only enhances the degradation but also reduces the time of degradation as compared to conventional enzymatic degradation technique. PMID:25515235

  13. Reactions of ethyl diazoacetate catalyzed by methylrhenium trioxide

    SciTech Connect

    Zhu, Z.; Espenson, H. [Iowa State Univ., Ames, IA (United States)

    1995-11-03

    Methylrhenium trioxide (CH{sub 3}ReO{sub 3} or MTO) has found wise use in catalysis, including the epoxidation and metathesis of olefins, aldehyde olefination, and oxygen transfer. Extensive reports have now appeared in the area of MTO-catalyzed substrate oxidations with hydrogen peroxide. Certain catalytic applications of MTO for organic reactions that do not utilize peroxide have now been realized. In particular, a catalytic amount of MTO with ethyl diazoacetate (EDA) will convert aromatic imines to aziridines and convert aldehydes and ketones to epoxides. The aziridine preparation proceeds in high yields under anaerobic conditions more conveniently than with existing methods. Compounds with a three-membered heterocyclic ring can be obtained with the EDA/MTO catalytic system. Aromatic imines undergo cycloaddition reactions to give aziridines under mild conditions.

  14. Nickel-catalyzed coupling reactions and synthetic studies toward ent-dioxepandehydrothyrsiferol via an epoxide-opening cascade

    E-print Network

    Ng, Sze-Sze

    2008-01-01

    Nickel-Catalyzed Coupling Reactions. Nickel-catalyzed allene--aldehyde coupling and alkene--aldehyde coupling represent two methods of preparing allylic alcohols. Most asymmetric transition metal-catalyzed methods of ...

  15. Mechanistic studies of the catalyzed carbon gasification reactions

    SciTech Connect

    Goethel, P.J.

    1989-01-01

    The catalyzed graphite hydrogenation reaction was studied employing the Etch Decoration Transmission Electron Microscope technique to view the monolayer channeling action of nickel and ruthenium catalysts. The results indicate a carbidic catalyst surface carbon reacting with surface hydrogen to form methane as the rate limiting step of the mechanism. The mechanism is compared to the methanation reaction from CO + H{sub 2} feedstocks and also to the catalytic growth of carbon filaments. A new mode of catalytic action termed tunneling was shown to exist for Pt, Ni, and Ru in the graphite hydrogenation reaction. For monolayer channeling and tunneling the overall contribution to bulk gasification is shown to be significant. A TGA technique for measuring the solubility and diffusion coefficient of carbon in metals is presented. The technique is shown to be accurate and to give quick results in comparison to other techniques. The monolayer channeling action of Pt, Cu, V{sub 2}O{sub 5}, V and Mo{sub 2}C was examined in the graphite oxidation reaction. Pt and Cu show C-C bond breakage as the rate limiting step while V, V{sub 2}O{sub 5} and Mo{sub 2}C reveal a gas-catalyst interface reaction limiting the process. V{sub 2}O{sub 5}, V and Mo{sub 2}C were also found to participate in monolayer edge recession thus forming elongated hexagon pits.

  16. Ab initio study of ice catalyzation of HOCl + HCl reaction

    SciTech Connect

    Zhou, Y.F.; Liu, C.B.

    2000-06-15

    The observations by Farman et al. revealed remarkable depletions in the total atmospheric ozone content in Antarctica. The observed total ozone decreased smoothing during the spring season from about 1975. Satellite observations have proved Antarctic ozone depletions over a very extended region, in general agreement with the local ground-based data of Farman et al. It was suggested that heterogeneous reactions occurring on particles in polar stratospheric clouds (PSCs) play a central role in the depletion of stratospheric ozone. Experiments proved that the reaction of HOCl + HCl was very slow in the gas phase, but on ice surface it was rapid. In this work the ice catalysis of HOCl + HCl reaction was investigated by using ab initio molecular orbital theory. The authors applied the Hartree-Fock self-consistent field and the second-order Moeller-Plesset perturbation theory with the basis sets of 6-31G* to the model system. The complexes and transition state were obtained along the reaction with and without the presence of ice surface. By comparing the results, a possible catalyzation mechanism of ice on the reaction is proposed.

  17. Structure of a Novel Enzyme That Catalyzes Acyl Transfer to Alcohols in Aqueous Conditions

    SciTech Connect

    Mathews, I.; Soltis, M.; Saldajeno, M.; Ganshaw, G.; Sala, R.; Weyler, W.; Cervin, M.A.; Whited, G.; Bott, R.

    2009-06-03

    The unusual architecture of the enzyme (MsAcT) isolated from Mycobacterium smegmatis forms the mechanistic basis for favoring alcoholysis over hydrolysis in water. Unlike hydrolases that perform alcoholysis only under anhydrous conditions, MsAcT demonstrates alcoholysis in substantially aqueous media and, in the presence of hydrogen peroxide, has a perhydrolysis:hydrolysis ratio 50-fold greater than that of the best lipase tested. The crystal structures of the apoenzyme and an inhibitor-bound form have been determined to 1.5 {angstrom} resolution. MsAcT is an octamer in the asymmetric unit and forms a tightly associated aggregate in solution. Relative to other structurally similar monomers, MsAcT contains several insertions that contribute to the oligomerization and greatly restrict the shape of the active site, thereby limiting its accessibility. These properties create an environment by which MsAcT can catalyze transesterification reactions in an aqueous medium and suggests how a serine hydrolase can be engineered to be an efficient acyltransferase.

  18. Stereochemistry and mechanism of a new single-turnover, half-transamination reaction catalyzed by the tryptophan synthase alpha 2 beta 2 complex.

    PubMed

    Miles, E W

    1987-01-27

    Tryptophan synthase is a versatile enzyme that catalyzes a wide variety of pyridoxal phosphate dependent reactions that are also catalyzed in model systems. These include beta-replacement, beta-elimination, racemization, and transamination reactions. We now show that the apo-alpha 2 beta 2 complex of tryptophan synthase will bind two unnatural substrates, pyridoxamine phosphate and indole-3-pyruvic acid, and will convert them by a single-turnover, half-transamination reaction to pyridoxal phosphate and L-tryptophan, the natural coenzyme and a natural product, respectively. This enzyme-catalyzed reaction is more rapid and more stereospecific than an analogous model reaction. The pro-S 4'-methylene proton of pyridoxamine phosphate is removed during the reaction, and the product is primarily L-tryptophan. We conclude that pyridoxal phosphate enzymes may be able to catalyze some unnatural reactions involving bound reactants and bound coenzyme since the coenzyme itself has the intrinsic ability to promote a variety of reactions. PMID:3548822

  19. Acid-catalyzed Heterogeneous Reactions in SOA Formation

    NASA Astrophysics Data System (ADS)

    Ng, N.; Keywood, M.; Varutbangkul, V.; Gao, S.; Loewer, E.; Surratt, J.; Richard, F. C.; John, S. H.

    2003-12-01

    The importance of heterogeneous reactions in secondary organic aerosol (SOA) formation has recently excited a great deal of interest in the aerosol community. Jang and Kamens (2001) showed enhanced aerosol yield from aldehydes, which can be produced by atmospheric photochemical reactions, in the presence of acidic seed. They suggest that the carbonyl functional groups of the aldehydes further react in the aerosol phase via hydration, polymerization, and hemiacetal/acetal formation with alcohols at an accelerated rate in the presence of acid. Jang et al. (2003) demonstrated similar results using a flow reactor and Czoschke et al. (in press) qualitatively showed increased yields for isoprene and alpha-pinene ozonolysis in the presence of acidic seed. While these findings are intriguing and important, the conditions under which the experiments were carried out were atmospherically unrealistic. A series of SOA formation experiments have been carried out in the Caltech Indoor Chamber Facility, which is comprised of dual 28 m3 FEP Teflon chambers, with the flexibility to carry out both dark ozonolysis and photochemical OH oxidation reactions. Cycloheptene and alpha-pinene were oxidized in the presence of neutral seed under dry (<10% RH) and humid (50% RH) conditions and in the presence of acidic seed under humid (50% RH) conditions. The SOA yields for these experiments will be presented, and the extent of the influence of acid-catalyzed reactions on SOA yield will be discussed. Reference List 1. Cocker, D. R. III. and R. C. Flagan and J. H. Seinfeld, State-of-the-art chamber facility for studying atmospheric aerosol chemistry, Environmental Science and Technology, 35, 2594-2601, 2001. 2. Czoschke, N. M., M. Jang, and R. M. Kamens, Effect of acid seed on biogenic sceondary organic aerosol growth, Atmospheric Environment, In press. 3. Jang, M., S. Lee, and R. M. Kamens, Organic aerosol growth by acid-catalyzed heterogeneous reactions of octanal in a flow reactor, Atmospheric Environment, 37, 2125-2138, 2003. 4. Jang, M. S. and R. M Kamens, Atmospheric secondary aerosol formation by heterogeneous reactions of aldehydes in the presence of a sulfuric acid aerosol catalyst. Environmental Science and Technology, 35, 4758-4766,2001.

  20. RNA size is a critical factor for U-containing substrate selectivity and permanent pseudouridylated product release during the RNA:?-synthase reaction catalyzed by box H/ACA sRNP enzyme at high temperature.

    PubMed

    Tillault, Anne-Sophie; Fourmann, Jean-Baptiste; Loegler, Christine; Blaud, Magali; Branlant, Christiane; Charpentier, Bruno

    2015-06-01

    The box H/ACA small ribonucleoprotein particles (H/ACA sRNPs) are RNP enzymes that isomerize uridines (U) into pseudouridines (?) in archaeal RNAs. The RNA component acts as a guide by forming base-pair interactions with the substrate RNA to specify the target nucleotide of the modification to the catalytic subunit Cbf5. Here, we have analyzed association of an H/ACA sRNP enzyme from the hyperthermophilic archaeon Pyrococcus abyssi with synthetic substrate RNAs of different length and with target nucleotide variants, and estimated their turnover at high temperature. In these conditions, we found that a short substrate, which length is restricted to the interaction with RNA guide sequence, has higher turnover rate. However, the longer substrate with additional 5' and 3' sequences non-complementary to the guide RNA is better discriminated by the U to ? conversion allowing the RNP enzyme to distinguish the modified product from the substrate. In addition, we identified that the conserved residue Y179 in the catalytic center of Cbf5 is crucial for substrate selectivity. PMID:25896443

  1. Palladium-catalyzed reaction of allyl halides with a-diazocarbonyl Shufeng Chen and Jianbo Wang*

    E-print Network

    Wang, Jianbo

    Palladium-catalyzed reaction of allyl halides with a-diazocarbonyl compoundsw Shufeng Chen-diazocarbonyl compounds and allyl bromides or chlorides leads to the forma- tion of 1,3-diene derivatives. p-Allylic palladium complexes are important intermediates in palladium-catalyzed reactions.1 The p-allylic palladium

  2. Amine-catalyzed direct Diels–Alder reactions of ?,?-unsaturated ketones with nitro olefins

    Microsoft Academic Search

    Rajeswari Thayumanavan; Buchiramachary Dhevalapally; Kandasamy Sakthivel; Fujie Tanaka; Carlos F Barbas

    2002-01-01

    Amine-catalyzed Diels–Alder reactions of ?,?-unsaturated ketones with dienophiles have been developed. Either (S)-1-(2-pyrrolidinylmethyl)pyrrolidine or l-proline catalyzed the in situ-generation and reaction of 2-amino-1,3-dienes to provide cyclohexanone derivatives in good yield (up to 87%) in one step with modest enantioselectivity.

  3. Atmospheric Environment 40 (2006) 68636878 Acid-catalyzed reactions of hexanal on sulfuric acid particles

    E-print Network

    Elrod, Matthew J.

    2006-01-01

    Atmospheric Environment 40 (2006) 6863­6878 Acid-catalyzed reactions of hexanal on sulfuric acid are incorporated into atmospheric aerosols are not well understood. Acid-catalyzed reactions of compounds into acidic aerosols. In the present study, we use the aerodyne aerosol mass spectrometer (AMS) to probe

  4. Gold-Catalyzed Cycloisomerization of 1,5-Allenynes via Dual Activation of an Ene Reaction

    E-print Network

    Toste, Dean

    Gold-Catalyzed Cycloisomerization of 1,5-Allenynes via Dual Activation of an Ene Reaction Paul Ha an atom-economical entry into polyunsaturated carbo- and heterocycles.1-3 These reactions involving Rh, Pd an increase in the formal oxidation state of the metal.1,4 On the other hand, gold(I)- catalyzed enyne5

  5. Exploration Into Copper Catalyzed and Copper-less Click Reactions with Re(CO)3 Complexes

    E-print Network

    Collins, Gary S.

    Exploration Into Copper Catalyzed and Copper-less Click Reactions with Re(CO)3 Complexes Nicholas that combines a alkyne and an oxime to generate a isoxazole cycloaddtion product. Compared to the copper and then proceeding with the typical copper(I) catalyzed "click" reaction procedure, while the other approach involves

  6. A review on lipase-catalyzed reactions in ultrasound-assisted systems.

    PubMed

    Lerin, Lindomar A; Loss, Raquel A; Remonatto, Daniela; Zenevicz, Mara Cristina; Balen, Manuela; Netto, Vendelino Oenning; Ninow, Jorge L; Trentin, Cláudia M; Oliveira, J Vladimir; de Oliveira, Débora

    2014-12-01

    The named "green chemistry" has been receiving increasing prominence due to its environmentally friendly characteristics. The use of enzymes as catalysts in processes of synthesis to replace the traditional use of chemical catalysts present as main advantage the fact of following the principles of the green chemistry. However, processes of enzymatic nature generally provide lower yields when compared to the conventional chemical processes. Therefore, in the last years, the ultrasound has been extensively used in enzymatic processes, such as the production of esters with desirable characteristics for the pharmaceutical, cosmetics, and food industry, for the hydrolysis and glycerolysis of vegetable oils, production of biodiesel, etc. Several works found in the open literature suggest that the energy released by the ultrasound during the cavitation phenomena can be used to enhance mass transfer (substrate/enzyme), hence increasing the rate of products formation, and also contributing to enhance the enzyme catalytic activity. Furthermore, the ultrasound is considered a "green" technology due to its high efficiency, low instrumental requirement and significant reduction of the processing time in comparison to other techniques. The main goal of this review was to summarize studies available to date regarding the application of ultrasound in enzyme-catalyzed esterification, hydrolysis, glycerolysis and transesterification reactions. PMID:24906428

  7. Nickel-catalyzed reductive coupling reactions of 1,6-enynes and the total synthesis of (+)-acutiphycin

    E-print Network

    Moslin, Ryan Thomas McLeod

    2007-01-01

    Nickel-Catalyzed Reductive Coupling Reactions of Aldehydes and Chiral 1,6-Enynes. A study of nickel-catalyzed reductive coupling reactions of aldehydes and chiral 1,6-enynes has provided evidence for stereospecific ligand ...

  8. Adrenodoxin supports reactions catalyzed by microsomal steroidogenic cytochrome P450s

    SciTech Connect

    Pechurskaya, Tatiana A. [Institute of Bioorganic Chemistry, Academy of Sciences of Belarus, Kuprevicha st., 5/2, Minsk 220141 (Belarus); Harnastai, Ivan N. [Institute of Bioorganic Chemistry, Academy of Sciences of Belarus, Kuprevicha st., 5/2, Minsk 220141 (Belarus); Grabovec, Irina P. [Institute of Bioorganic Chemistry, Academy of Sciences of Belarus, Kuprevicha st., 5/2, Minsk 220141 (Belarus); Gilep, Andrei A. [Institute of Bioorganic Chemistry, Academy of Sciences of Belarus, Kuprevicha st., 5/2, Minsk 220141 (Belarus); Usanov, Sergey A. [Institute of Bioorganic Chemistry, Academy of Sciences of Belarus, Kuprevicha st., 5/2, Minsk 220141 (Belarus)]. E-mail: usanov@iboch.bas-net.by

    2007-02-16

    The interaction of adrenodoxin (Adx) and NADPH cytochrome P450 reductase (CPR) with human microsomal steroidogenic cytochrome P450s was studied. It is found that Adx, mitochondrial electron transfer protein, is able to support reactions catalyzed by human microsomal P450s: full length CYP17, truncated CYP17, and truncated CYP21. CPR, but not Adx, supports activity of truncated CYP19. Truncated and the full length CYP17s show distinct preference for electron donor proteins. Truncated CYP17 has higher activity with Adx compared to CPR. The alteration in preference to electron donor does not change product profile for truncated enzymes. The electrostatic contacts play a major role in the interaction of truncated CYP17 with either CPR or Adx. Similarly electrostatic contacts are predominant in the interaction of full length CYP17 with Adx. We speculate that Adx might serve as an alternative electron donor for CYP17 at the conditions of CPR deficiency in human.

  9. Predicting enzyme targets for cancer drugs by profiling human Metabolic reactions in NCI-60 cell lines

    PubMed Central

    2010-01-01

    Background Drugs can influence the whole metabolic system by targeting enzymes which catalyze metabolic reactions. The existence of interactions between drugs and metabolic reactions suggests a potential way to discover drug targets. Results In this paper, we present a computational method to predict new targets for approved anti-cancer drugs by exploring drug-reaction interactions. We construct a Drug-Reaction Network to provide a global view of drug-reaction interactions and drug-pathway interactions. The recent reconstruction of the human metabolic network and development of flux analysis approaches make it possible to predict each metabolic reaction's cell line-specific flux state based on the cell line-specific gene expressions. We first profile each reaction by its flux states in NCI-60 cancer cell lines, and then propose a kernel k-nearest neighbor model to predict related metabolic reactions and enzyme targets for approved cancer drugs. We also integrate the target structure data with reaction flux profiles to predict drug targets and the area under curves can reach 0.92. Conclusions The cross validations using the methods with and without metabolic network indicate that the former method is significantly better than the latter. Further experiments show the synergism of reaction flux profiles and target structure for drug target prediction. It also implies the significant contribution of metabolic network to predict drug targets. Finally, we apply our method to predict new reactions and possible enzyme targets for cancer drugs. PMID:20932284

  10. 2,3-Migration in Rh(II)-Catalyzed Reactions of -Trifluoroacetamido

    E-print Network

    Wang, Jianbo

    2,3-Migration in Rh(II)-Catalyzed Reactions of -Trifluoroacetamido r-Diazocarbonyl Compounds Feng(II)-catalyzed reactions of these diazo compounds gave 2,3-migration products in high yields. 1,2-Migration is one,2-migration reactions, the 1,2-hydride migration is generally predominant, but 1,2-alkyl, 1,2-aryl, 1,2-thio

  11. Minor Modifications of the C-terminal Helix Reschedule the Favored Chemical Reactions Catalyzed by Theta Class Glutathione Transferase T1-1*

    PubMed Central

    Shokeer, Abeer; Mannervik, Bengt

    2010-01-01

    Adaptive responses to novel toxic challenges provide selective advantages to organisms in evolution. Glutathione transferases (GSTs) play a pivotal role in the cellular defense because they are main contributors to the inactivation of genotoxic compounds of exogenous as well as of endogenous origins. GSTs are promiscuous enzymes catalyzing a variety of chemical reactions with numerous alternative substrates. Despite broad substrate acceptance, individual GSTs display pronounced selectivities such that only a limited number of substrates are transformed with high catalytic efficiency. The present study shows that minor structural changes in the C-terminal helix of mouse GST T1-1 induce major changes in the substrate-activity profile of the enzyme to favor novel chemical reactions and to suppress other reactions catalyzed by the parental enzyme. PMID:20022951

  12. Enzyme-catalyzed acylation of homoserine: mechanistic characterization of the Haemophilus influenzae met2-encoded homoserine transacetylase.

    PubMed

    Born, T L; Franklin, M; Blanchard, J S

    2000-07-25

    The first unique step in bacterial and plant methionine biosynthesis involves the acylation of the gamma-hydroxyl of homoserine. In Haemophilus influenzae, acylation is accomplished via an acetyl-CoA-dependent acetylation catalyzed by homoserine transacetylase. The activity of this enzyme regulates flux of homoserine into multiple biosynthetic pathways and, therefore, represents a critical control point for cell growth and viability. We have cloned homoserine transacetylase from H. influenzae and present the first detailed enzymatic study of this enzyme. Steady-state kinetic experiments demonstrate that the enzyme utilizes a ping-pong kinetic mechanism in which the acetyl group of acetyl-CoA is initially transferred to an enzyme nucleophile before subsequent transfer to homoserine to form the final product, O-acetylhomoserine. The maximal velocity and V/K(homoserine) were independent of pH over the range of values tested, while V/K(acetyl)(-)(CoA) was dependent upon the ionization state of a single group exhibiting a pK value of 8.6, which was required to be protonated. Solvent kinetic isotope effect studies yielded inverse effects of 0.75 on V and 0.74 on V/K(CoA) on the reverse reaction and effects of 1.2 on V and 1.7 on V/K(homoserine) on the forward reaction. Direct evidence for the formation of an acetyl-enzyme intermediate was obtained using rapid-quench labeling studies. On the basis of these observations, we propose a chemical mechanism for this important member of the acyltransferase family and contrast its mechanism with that of homoserine transsuccinylase. PMID:10913262

  13. Scanning electrochemical impedance microscopy for investigation of glucose oxidase catalyzed reaction.

    PubMed

    Morkvenaite-Vilkonciene, I; Genys, P; Ramanaviciene, A; Ramanavicius, A

    2015-02-01

    In this research biointerface based on immobilized glucose oxidase (GOx) was evaluated by scanning electrochemical impedance microscopy (SEIM), which consisted of merged scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy (EIS). The gluconolactone, which is quickly hydrolyzed to gluconic acid, is produced during the enzyme-catalyzed glucose oxidation reaction. Gluconic acid formed above an enzyme-modified not-conducting plastic surface, was evaluated by EIS technique. A two electrode cell consisting of a scanning probe, which was based on 10 ?m diameter ultramicroelectrode and stationary platinum counter/reference electrode was applied for the measurement. Locally measured solution impedance depends on the gluconic acid concentration close to the ultramicroelectrode surface and on the ion diffusion, which is hindered when the electrode is approaching close to the GOx-modified surface. EIS results were evaluated by applying an equivalent circuit consisting of elements representing solution resistance, double-layer capacitance, charge-transfer resistance and Warburg impedance. Solution resistance was calculated and showed to be dependent on the position of ultramicroelectrode. Also it was observed that the thickness of the conducting layer and gluconic acid concentration both are changing in time. The results indicate that here proposed SEIM technique could become a valuable tool for the investigation and characterization of enzyme-modified surfaces of biosensors and biofuel cells. PMID:25620444

  14. Organic reactions catalyzed by methylrhenium trioxide: Reactions of ethyl diazoacetate and organic azides

    SciTech Connect

    Zhu, Z.; Espenson, J.H. [Ames Lab., IA (United States)] [Ames Lab., IA (United States); [Iowa State Univ., Ames, IA (United States)

    1996-10-16

    Methylrhenium trioxide (CH{sub 3}ReO{sub 3} or MTO) catalyzes several classes of reactions of ethyl diazoacetate, EDA. It is the first high valent oxo complex for carbene transfer. Under mild conditions and in the absence of other substrates, EDA was converted to a 9:1 mixture of diethyl maleate and diethyl fumarate. In the presence of alcohols, {alpha}-alkoxy ethyl acetates were obtained in good yield. The yields dropped for the larger and more branched alcohols, the balance of material being diethyl maleate and fumarate. An electron-donating group in the para position of phenols favors the formation of {alpha}-phenoxy ethyl acetates. The use of EDA to form {alpha}-thio ethyl acetates and N-substituted glycine ethyl esters, on the other hand, is hardly affected by the size or structure of the parent thiol or amine, with all of these reactions proceeding in high yield. MTO-catalyzed cycloaddition reactions occur between EDA and aromatic imines, olefins, and carbonyl compounds. Three-membered ring products are formed: aziridines, cyclopropanes, and epoxides, respectively. The reactions favor the formation of trans products, and provide a convenient route for the preparation of aziridines. Intermediate carbenoid and nitrenoid species have been proposed. In the presence of an oxygen source such as an epoxide, ethyl diazoacetate and azibenzil are converted to an oxalic acid monoethyl ester and to benzil; at the same time the epoxide was converted to an olefin. 75 refs., 1 fig., 7 tabs.

  15. Identification and characterization of the two-enzyme system catalyzing oxidation of EDTA in the EDTA-degrading bacterial strain DSM 9103.

    PubMed

    Witschel, M; Nagel, S; Egli, T

    1997-11-01

    In a gram-negative isolate (DSM 9103) able to grow with EDTA as the sole source of carbon, nitrogen, and energy, the first two steps of the catabolic pathway for EDTA were elucidated. They consisted of the sequential oxidative removal of two acetyl groups, resulting in the formation of glyoxylate. An enzyme complex that catalyzes the removal of two acetyl groups was purified and characterized. In the reaction, ethylenediaminetriacetate (ED3A) was formed as an intermediate and N,N'-ethylenediaminediacetate was the end product. The enzyme complex consisted of two components: component A' (cA'), most likely a monooxygenase, which catalyzes the cleavage of EDTA and ED3A while consuming oxygen and reduced flavin mononucleotide (FMN)-H2, and component B' (cB'), an NADH2:FMN oxidoreductase that provides FMNH2 for cA'. cB' could be replaced by other NADH2:FMN oxidoreductases such as component B of the nitrilotriacetate monooxygenase or the NADH2:FMN oxidoreductase from Photobacterium fischeri. The EDTA-oxidizing enzyme complex accepted EDTA as a substrate only when it was complexed with Mg2+, Zn2+, Mn2+, Co2+, or Cu2+. Moreover, the enzyme complex catalyzed the removal of acetyl groups from several other aminopolycarboxylic acids that possess three or more acetyl groups. PMID:9371437

  16. Modelling as a tool of enzyme reaction engineering for enzyme reactor development

    Microsoft Academic Search

    Durda Vasi?-Ra?ki; Zvjezdana Findrik; Ana Vrsalovi? Prese?ki

    2011-01-01

    Strategy of the development of model for enzyme reactor at laboratory scale with respect to the modelling of kinetics is presented.\\u000a The recent literature on the mathematic modelling on enzyme reaction rate is emphasized.

  17. Synthesis of (-)-?9-trans-Tetrahydrocannabinol - Stereocontrol via Mo-catalyzed Asymmetric Allylic Alkylation Reaction

    PubMed Central

    Trost, Barry M.; Dogra, Kalindi

    2008-01-01

    ?9-THC is synthesized in enantiomericaly pure form, where all of the stereochemistry is derived from the molybdenum catalyzed asymmetric alkylation reaction of the extremely sterically congested bis-ortho substituted cinnamyl carbonate in high regio- and enantioselectivity. PMID:17266321

  18. Development of novel transition metal-catalyzed cross-coupling reactions and applications thereof

    E-print Network

    Teverovskiy, Georgiy

    2013-01-01

    Chapter 1 The first example of Pd(0)/(II) catalyzed fluorination of aryl bromides is reported herein. Based on these data, an analogous method was developed for the fluorination of aryl triflates. The reaction proceeds ...

  19. Mechanistic studies on metal-catalyzed carbon-nitrogen bond forming reactions

    E-print Network

    Strieter, Eric R

    2005-01-01

    Mechanistic studies on copper and palladium-catalyzed C-N bond forming reactions are described. To understand the mechanistic details of these processes, several principles of physical organic chemistry have been employed. ...

  20. Cu-catalyzed cross-coupling reactions of epoxides with organoboron compounds.

    PubMed

    Lu, Xiao-Yu; Yang, Chu-Ting; Liu, Jing-Hui; Zhang, Zheng-Qi; Lu, Xi; Lou, Xin; Xiao, Bin; Fu, Yao

    2015-02-11

    A copper-catalyzed cross-coupling reaction of epoxides with arylboronates is described. This reaction is not limited to aromatic epoxides, because aliphatic epoxides are also suitable substrates. In addition, N-sulfonyl aziridines can be successfully converted into the products. This reaction provides convenient access to ?-phenethyl alcohols, which are valuable synthetic intermediates. PMID:25564373

  1. Enzyme-catalyzed conversion of chemical structures on the surface of gold nanorods.

    PubMed

    Kusaka, Eriko; Ito, Takeo; Tanabe, Kazuhito; Nishimoto, Sei-ichi

    2013-09-18

    For developing metal nanoparticles of which surface chemical structures could be altered by enzymes in the cells, functional linkers caged by coumaric acids have been synthesized. Synthesized gold nanorod (GNR) conjugates possessing coumaric acid precursors underwent (porcine liver) esterase-catalyzed hydrolysis on their surface to afford GNRs coated with amino-functionalized polyethylene glycol and fluorescent coumarins as reporter molecules for monitoring the conversion. The chemical structural conversion on the GNR surfaces was successfully observed inside cells by fluorescence microscopy when GNR conjugates were incubated with tumor cells. PMID:23889000

  2. Computational Study of a Model System of Enzyme-Mediated [4+2] Cycloaddition Reaction

    PubMed Central

    2015-01-01

    A possible mechanistic pathway related to an enzyme-catalyzed [4+2] cycloaddition reac-tion was studied by theoretical calculations at density functional (B3LYP, O3LYP, M062X) and semiempirical levels (PM6-DH2, PM6) performed on a model system. The calculations were carried out for the key [4+2] cycloaddition step considering enzyme-catalyzed biosynthesis of Spinosyn A in a model reaction, where a reliable example of a biological Diels-Alder reaction was reported experimentally. In the present study it was demonstrated that the [4+2] cycloaddition reaction may benefit from moving along the energetically balanced reaction coordinate, which enabled the catalytic rate enhancement of the [4+2] cycloaddition pathway involving a single transition state. Modeling of such a system with coordination of three amino acids indicated a reliable decrease of activation energy by ~18.0 kcal/mol as compared to a non-catalytic transformation. PMID:25853669

  3. The Radical S-Adenosyl-L-methionine Enzyme QhpD Catalyzes Sequential Formation of Intra-protein Sulfur-to-Methylene Carbon Thioether Bonds.

    PubMed

    Nakai, Tadashi; Ito, Hiroto; Kobayashi, Kazuo; Takahashi, Yasuhiro; Hori, Hiroshi; Tsubaki, Motonari; Tanizawa, Katsuyuki; Okajima, Toshihide

    2015-04-24

    The bacterial enzyme designated QhpD belongs to the radical S-adenosyl-L-methionine (SAM) superfamily of enzymes and participates in the post-translational processing of quinohemoprotein amine dehydrogenase. QhpD is essential for the formation of intra-protein thioether bonds within the small subunit (maturated QhpC) of quinohemoprotein amine dehydrogenase. We overproduced QhpD from Paracoccus denitrificans as a stable complex with its substrate QhpC, carrying the 28-residue leader peptide that is essential for the complex formation. Absorption and electron paramagnetic resonance spectra together with the analyses of iron and sulfur contents suggested the presence of multiple (likely three) [4Fe-4S] clusters in the purified and reconstituted QhpD. In the presence of a reducing agent (sodium dithionite), QhpD catalyzed the multiple-turnover reaction of reductive cleavage of SAM into methionine and 5'-deoxyadenosine and also the single-turnover reaction of intra-protein sulfur-to-methylene carbon thioether bond formation in QhpC bound to QhpD, producing a multiknotted structure of the polypeptide chain. Homology modeling and mutagenic analysis revealed several conserved residues indispensable for both in vivo and in vitro activities of QhpD. Our findings uncover another challenging reaction catalyzed by a radical SAM enzyme acting on a ribosomally translated protein substrate. PMID:25778402

  4. A natural vanishing act: the enzyme-catalyzed degradation of carbon nanomaterials.

    PubMed

    Kotchey, Gregg P; Hasan, Saad A; Kapralov, Alexander A; Ha, Seung Han; Kim, Kang; Shvedova, Anna A; Kagan, Valerian E; Star, Alexander

    2012-10-16

    Over the past three decades, revolutionary research in nanotechnology by the scientific, medical, and engineering communities has yielded a treasure trove of discoveries with diverse applications that promise to benefit humanity. With their unique electronic and mechanical properties, carbon nanomaterials (CNMs) represent a prime example of the promise of nanotechnology with applications in areas that include electronics, fuel cells, composites, and nanomedicine. Because of toxicological issues associated with CNMs, however, their full commercial potential may not be achieved. The ex vitro, in vitro, and in vivo data presented in this Account provide fundamental insights into the biopersistence of CNMs, such as carbon nanotubes and graphene, and their oxidation/biodegradation processes as catalyzed by peroxidase enzymes. We also communicate our current understanding of the mechanism for the enzymatic oxidation and biodegradation. Finally, we outline potential future directions that could enhance our mechanistic understanding of the CNM oxidation and biodegradation and could yield benefits in terms of human health and environmental safety. The conclusions presented in this Account may catalyze a rational rethinking of CNM incorporation in diverse applications. For example, armed with an understanding of how and why CNMs undergo enzyme-catalyzed oxidation and biodegradation, researchers can tailor the structure of CNMs to either promote or inhibit these processes. In nanomedical applications such as drug delivery, the incorporation of carboxylate functional groups could facilitate biodegradation of the nanomaterial after delivery of the cargo. On the other hand, in the construction of aircraft, a CNM composite should be stable to oxidizing conditions in the environment. Therefore, pristine, inert CNMs would be ideal for this application. Finally, the incorporation of CNMs with defect sites in consumer goods could provide a facile mechanism that promotes the degradation of these materials once these products reach landfills. PMID:22824066

  5. Identification of critical parameters in liquid enzyme-catalyzed biodiesel production.

    PubMed

    Nordblad, Mathias; Silva, Vanessa T L; Nielsen, Per Munk; Woodley, John M

    2014-12-01

    Callera™ Trans L, a liquid formulation of Thermomyces lanuginosus lipase, has recently shown great promise as a cost-efficient catalyst for methanolysis of triglyceride substrates, specifically in the BioFAME process. However, identifying the right combination of temperature and concentrations of catalyst, water and methanol to realize the full potential of the reaction system has remained a challenge. This study presents an investigation of the impact of temperature, enzyme and water concentration on the reaction, as well as the effect of methanol feed rate for the conversion of rapeseed oil in a fed-batch reaction system. It was observed that the reaction can be divided into two distinct parts. The first part of the reaction, during which primarily tri- and diglycerides are converted, proceeded at a high rate and thus required a high rate of methanol supply. The second part of the reaction, where the remaining di- and monoglycerides are converted, proceeded at a much lower rate. Consequently, it is necessary to reduce the methanol feed rate during the latter part of the reaction to avoid inhibition or even inactivation of the enzyme. Since the second part of the reaction occupied most of the 24-h reaction time, it was concluded that this is the part of the process where further development efforts should be targeted. This point was demonstrated by partially substituting the catalyst with a lipase with a different specificity, which enhanced the performance during the second phase of the reaction. PMID:24902824

  6. REACTION MECHANISMS OF 15-HYDROPEROXYEICOSATETRAENOIC ACID CATALYZED BY HUMAN PROSTACYCLIN AND THROMBOXANE SYNTHASES

    PubMed Central

    Yeh, Hui-Chun; Tsai, Ah-Lim; Wang, Lee-Ho

    2007-01-01

    Prostacyclin synthase (PGIS) and thromboxane synthase (TXAS) are atypical cytochrome P450s. They do not require NADPH or dioxygen for isomerization of prostaglandin H2 (PGH2) to produce prostacyclin (PGI2) and thromboxane A2 (TXA2). PGI2 and TXA2 have opposing actions on platelet aggregation and blood vessel tone. In this report, we use a lipid hydroperoxide, 15-hydroperoxyeicosatetraenoic acid (15-HPETE), to explore the active site characteristics of PGIS and TXAS. The two enzymes transformed 15-HPETE not only into 13-hydroxy-14,15-epoxy-5,8,11-eicosatrienoic acid (13-OH-14,15-EET), like many microsomal P450s, but also to 15-ketoeicosatetraenoic acid (15-KETE) and 15-hydroxyeicosatetraenoic acid (15-HETE). 13-OH-14,15-EET and 15-KETE result from homolytic cleavage of the O–O bond, whereas 15-HETE results from heterolytic cleavage, a common peroxidase pathway. About 80% of 15-HPETE was homolytically cleaved by PGIS and 60% was homolytically cleaved by TXAS. The Vmax of homolytic cleavage is 3.5-fold faster than heterolytic cleavage for PGIS-catalyzed reactions (1100 min?1 vs. 320 min?1) and 1.4-fold faster for TXAS (170 min?1 vs. 120 min?1). Similar KM values for homolytic and heterolytic cleavages were found for PGIS (?60 ?M 15-HPETE) and TXAS (?80 ?M 15-HPETE), making PGIS a more efficient catalyst for the 15-HPETE reaction. PMID:17459323

  7. Role of long-range protein dynamics in different thymidylate synthase catalyzed reactions.

    PubMed

    Abeysinghe, Thelma; Kohen, Amnon

    2015-01-01

    Recent studies of Escherichia coli thymidylate synthase (ecTSase) showed that a highly conserved residue, Y209, that is located 8 Å away from the reaction site, plays a key role in the protein's dynamics. Those crystallographic studies indicated that Y209W mutant is a structurally identical but dynamically altered relative to the wild type (WT) enzyme, and that its turnover catalytic rate governed by a slow hydride-transfer has been affected. The most challenging test of an examination of a fast chemical conversion that precedes the rate-limiting step has been achieved here. The physical nature of both fast and slow C-H bond activations have been compared between the WT and mutant by means of observed and intrinsic kinetic isotope effects (KIEs) and their temperature dependence. The findings indicate that the proton abstraction step has not been altered as much as the hydride transfer step. Additionally, the comparison indicated that other kinetic steps in the TSase catalyzed reaction were substantially affected, including the order of the substrate binding. Enigmatically, although Y209 is H-bonded to 3'-OH of 2'-deoxyuridine-5'-mono-phosphate (dUMP), its altered dynamics is more pronounced on the binding of the remote cofactor, (6R)-N5,N10-methylene-5,6,7,8-tetrahydrofolate (CH2H4folate), revealing the importance of long-range dynamics of the enzymatic complex and its catalytic function. PMID:25837629

  8. Modified enzymes for reactions in organic solvents

    Microsoft Academic Search

    A. B. Salleh; M. Basri; M. Taib; H. Jasmani; R. N. Z. A. Rahman; M. B. A. Rahman; C. N. A. Razak

    2002-01-01

    Recent studies on biocatalysis in water—organic solvent biphasic systems have shown that many enzymes retain their catalytic\\u000a activities in the presence of high concentrations of organic solvents. However, not all enzymes are organic solvent tolerant,\\u000a and most have limited and selective tolerance to particular organic solvents. Protein modification or protein tailoring is\\u000a an approach to alter the characteristics of enzymes,

  9. CYP4F Enzymes Are the Major Enzymes in Human Liver Microsomes That Catalyze the O-Demethylation of the Antiparasitic Prodrug DB289 [2,5-Bis(4-amidinophenyl)furan-bis-O-methylamidoxime

    PubMed Central

    Wang, Michael Zhuo; Saulter, Janelle Y.; Usuki, Etsuko; Cheung, Yen-Ling; Hall, Michael; Bridges, Arlene S.; Loewen, Greg; Parkinson, Oliver T.; Stephens, Chad E.; Allen, James L.; Zeldin, Darryl C.; Boykin, David W.; Tidwell, Richard R.; Parkinson, Andrew; Paine, Mary F.; Hall, James Edwin

    2007-01-01

    DB289 [2,5-bis(4-amidinophenyl)furan-bis-O-methylamidoxime] is biotransformed to the potent antiparasitic diamidine DB75 [2,5-bis(4-amidinophenyl) furan] by sequential oxidative O-demethylation and reductive N-dehydroxylation reactions. Previous work demonstrated that the N-dehydroxylation reactions are catalyzed by cytochrome b5/NADH-cytochrome b5 reductase. Enzymes responsible for catalyzing the DB289 O-demethylation pathway have not been identified. We report an in vitro metabolism study to characterize enzymes in human liver microsomes (HLMs) that catalyze the initial O-demethylation of DB289 (M1 formation). Potent inhibition by 1-aminobenzotriazole confirmed that M1 formation is catalyzed by P450 enzymes. M1 formation by HLMs was NADPH-dependent, with a Km and Vmax of 0.5 ?M and 3.8 nmol/min/mg protein, respectively. Initial screening showed that recombinant CYP1A1, CYP1A2, and CYP1B1 were efficient catalysts of M1 formation. However, none of these three enzymes was responsible for M1 formation by HLMs. Further screening showed that recombinant CYP2J2, CYP4F2, and CYP4F3B could also catalyze M1 formation. An antibody against CYP4F2, which inhibited both CYP4F2 and CYP4F3B, inhibited 91% of M1 formation by HLMs. Two inhibitors of P450-mediated arachidonic acid metabolism, HET0016 (N-hydroxy-N?-(4-n-butyl-2-methylphenyl)formamidine) and 17-octadecynoic acid, effectively inhibited M1 formation by HLMs. Inhibition studies with ebastine and antibodies against CYP2J2 suggested that CYP2J2 was not involved in M1 formation by HLMs. Additionally, ketoconazole preferentially inhibited CYP4F2, but not CYP4F3B, and partially inhibited M1 formation by HLMs. We conclude that CYP4F enzymes (e.g., CYP4F2, CYP4F3B) are the major enzymes responsible for M1 formation by HLMs. These findings indicate that, in human liver, members of the CYP4F subfamily biotransform not only endogenous compounds but also xenobiotics. PMID:16997912

  10. Model analysis for enhancement of enzyme-catalyzed alcohol oxidation by solvent extraction of product

    SciTech Connect

    Hidaka, Nobuyuki; Matsumoto, Toshitatsu [Kagoshima Univ. (Japan). Dept. of Applied Chemistry and Chemical Engineering; Morooka, Shigeharu [Kyushu Univ., Fukuoka (Japan). Dept. of Chemical Science and Technology

    1995-07-01

    Enzymatic oxidation of ethanol and butanol was conducted with alcohol oxidase in a one-phase system of water and a two-phase system of water and toluene. The conversion of the reaction in the two-phase system was higher than that in the one-phase system. The inhibition of the enzyme was relieved in the two-phase system by extracting the aldehyde product into the organic phase. The dissolved oxygen concentration in the water phase also affected the reaction rate. A kinetic model of the reaction was developed by considering both the inhibition of enzyme activity and the dissolved oxygen concentration. Parameters used in the model were evaluated experimentally. The reaction rate calculated using the model was in good agreement with the data.

  11. Nickel-catalyzed carboannulation reaction of o-bromobenzyl zinc bromide with unsaturated compounds.

    PubMed

    Deng, Ruixue; Sun, Liangdong; Li, Zhi

    2007-12-01

    A number of indenes have been prepared in good yields by treating o-bromobenzyl zinc bromide 1 with various terminal and internal alkynes in the presence of a nickel catalyst. The nickel-catalyzed carboannulation reaction was successfully extended to the synthesis of indane derivatives by reaction of 1 with acrylates and styrene. PMID:17990889

  12. Sequential Au(I)-catalyzed reaction of water with o-acetylenyl-substituted phenyldiazoacetates

    PubMed Central

    Zhou, Lei; Liu, Yizhou; Zhang, Yan

    2011-01-01

    Summary The gold(I)-catalyzed reaction of water with o-acetylenyl-substituted phenyldiazoacetates provides 1H-isochromene derivatives in good yields. The reaction follows a catalytic sequence of gold carbene formation/water O–H insertion/alcohol-alkyne cyclization. The gold(I) complex is the only catalyst in each of these steps. PMID:21647254

  13. Fischer chromium carbene complexes as nucleophiles in palladium-catalyzed allylic substitution reactions

    Microsoft Academic Search

    Dušan Draho?ovský; Vincent Borgo; Dalimil Dvo?ák

    2002-01-01

    The Pd-catalyzed reaction of carbanions derived from chromium aminocarbene complexes with allylic acetates and carbonates smoothly affords the corresponding allyl-substituted aminocarbenes. On the contrary, the same reaction of the anion derived from pentacarbonyl[(methoxy)methylcarbene]chromium(0) with cinnamyl acetate affords 5-methoxy-1-phenylhexa-1,5-diene, the product of 1-methoxyethen-1-yl group transfer.

  14. Iron and xanthine oxidase catalyze formation of an oxidant species distinguishable from OH. : comparison with the Haber-Weiss reaction

    SciTech Connect

    Winterbourn, C.C.; Sutton, H.C.

    1986-01-01

    O2- was produced by gamma irradiation of formate solutions, by the action of xanthine oxidase on hypoxanthine and O2, and by the action of ferredoxin reductase on NADPH and paraquat in the presence of O2. Its reaction with H2O2 and various iron chelates was studied. Oxidation of deoxyribose to thiobarbituric acid-reactive products that was appropriately inhibited by OH. scavengers, or formate oxidation to CO2, was used to detect OH(.). With each source of O2-, and by these criteria, Fe(EDTA) efficiently catalyzed this (Haber-Weiss) reaction, but little catalysis was detectable with iron bound to DTPA, citrate, ADP, ATP, or pyrophosphate, or without chelator in phosphate buffer. O2- produced from xanthine oxidase, but not from the other sources, underwent another iron-dependent reaction with H2O2, to produce an oxidant that did not behave as free OH(.). It was formed in phosphate or bicarbonate buffer, and caused deoxyribose oxidation that was readily inhibited by mannitol or Tris, but not by benzoate, formate, or dimethyl sulfoxide. It did not oxidize formate to CO2. Addition of EDTA changed the pattern of inhibition to that expected for a reaction of OH(.). The other chelators all inhibited deoxyribose oxidation, provided their concentrations were high enough. The results are compatible with iron bound to xanthine oxidase catalyzing production of a strong oxidant (which is not free OH.) from H2O2 and O2- produced by the enzyme.

  15. Continuous In Vitro Evolution of a Ribozyme that Catalyzes Three Successive Nucleotidyl Addition Reactions

    NASA Technical Reports Server (NTRS)

    McGinness, Kathleen E.; Wright, Martin C.; Joyce, Gerald F.

    2002-01-01

    Variants of the class I ligase ribozyme, which catalyzes joining of the 3' end of a template bound oligonucleotide to its own 5' end, have been made to evolve in a continuous manner by a simple serial transfer procedure that can be carried out indefinitely. This process was expanded to allow the evolution of ribozymes that catalyze three successive nucleotidyl addition reactions, two template-directed mononucleotide additions followed by RNA ligation. During the development of this behavior, a population of ribozymes was maintained against an overall dilution of more than 10(exp 406). The resulting ribozymes were capable of catalyzing the three-step reaction pathway, with nucleotide addition occurring in either a 5' yieldig 3' or a 3' yielding 5' direction. This purely chemical system provides a functional model of a multi-step reaction pathway that is undergoing Darwinian evolution.

  16. [Analogs of pyrophosphate in a pyrophosphorolysis reaction catalyzed by DNA polymerases].

    PubMed

    Rozovskaia, T A; Tarusova, N B; Minasian, Sh Kh; Atrazhev, A M; Kukhanova, M K

    1989-01-01

    The reaction of pyrophosphorolysis catalyzed by Escherichia coli DNA polymerase I Klenov fragment, calf thymus DNA polymerase alpha, rat liver DNA polymerase beta and AMV reverse transcriptase was studied. Some pyrophosphate (PPi) analogs were taken as low molecular weight substrates. It was shown that only imidodiphosphonic acid acted as the PPi substrate analog for the reactions catalyzed by DNA polymerases I and alpha, both imidodiphosphonic acid and methylenediphosphonic acid were active in the case of DNA polymerase beta and reverse transcriptase. Other analogs tested were neither nucleotide residue acceptors, nor inhibitors of the pyrophosphorolysis reaction with PPi. The abilities of some PPi analogs to inhibit the DNA elongation catalyzed by reverse transcriptase were investigated. The principles of specificity of low molecular substrates recognition by DNA polymerases and some problems concerning the mechanisms of DNA synthesis inhibition by PPi analogues are discussed. PMID:2549402

  17. Penicillin acylase-catalyzed synthesis of ?-lactam antibiotics in water-methanol mixtures: effect of cosolvent content and chemical nature of substrate on reaction rates and yields

    Microsoft Academic Search

    Min Gon Kim; Sun Bok Lee

    1996-01-01

    The synthesis of four ?-lactam antibiotics (penicillin G, pivaloyloxymethyl ester of penicillin G, ampicillin and pivampicillin) catalyzed byEscherichia coli penicillin acylase has been investigated in water-methanol mixtures. The enzyme reactions were either thermodynamically or kinetically controlled at the same conditions using phenylacetic acid andd-?-phenylglycine methyl ester as acyl donors and 6-aminopenicillanic acid and pivaloyloxymethyl 6-aminopenicillanic acid as acyl acceptors. It

  18. Ultrasound assisted lipase catalyzed synthesis of cinnamyl acetate via transesterification reaction in a solvent free medium.

    PubMed

    Tomke, Prerana D; Rathod, Virendra K

    2015-11-01

    Cinnamyl acetate is known for its use as flavor and fragrance material in different industries such as food, pharmaceutical, cosmetic etc. This work focuses on ultrasound assisted lipase (Novozym 435) catalyzed synthesis of cinnamyl acetate via transesterification of cinnamyl alcohol and vinyl acetate in non-aqueous, solvent free system. Optimization of various parameters shows that a higher yield of 99.99% can be obtained at cinnamyl alcohol to vinyl acetate ratio of 1:2 with 0.2% of catalyst, at 40°C and 150rpm, with lower ultrasound power input of 50W (Ultrasound intensity 0.81W/cm(2)), at 25kHz frequency, 50% duty cycle. Further, the time required for the maximum conversion is reduced to 20min as compared to 60min of conventional process. Similarly, the enzyme can be successfully reused seven times without loss of enzyme activity. Thus, ultrasound helps to enhance the enzyme catalyzed synthesis of flavors. PMID:26186841

  19. Zinc Enzymes.

    ERIC Educational Resources Information Center

    Bertini, I.; And Others

    1985-01-01

    Discusses the role of zinc in various enzymes concerned with hydration, hydrolysis, and redox reactions. The binding of zinc to protein residues, properties of noncatalytic zinc(II) and catalytic zinc, and the reactions catalyzed by zinc are among the topics considered. (JN)

  20. A sensitive electrochemical aptasensor for thrombin detection based on exonuclease-catalyzed target recycling and enzyme-catalysis.

    PubMed

    Yi, Huayu; Xu, Wenju; Yuan, Yali; Wu, Yongmei; Chai, Yaqin; Yuan, Ruo

    2013-09-15

    In the present study, a sensitive electrochemical aptasensor based on exonuclease-catalyzed target recycling and enzyme-catalysis was developed for thrombin (TB) detection. Firstly, the alcohol dehydrogenase (ADH) was abundantly embedded in the 3-(mercaptopropyl)trimethoxysilane (MPTS) sol with a 3-D network that exhibited tunable porosity and high thermal stability. ADH, as an alcohol oxidase, catalyzed the conversation of alcohol into acetaldehyde coupling with the production of NADH in the presence of NAD(+). Then the immobilized gold nanoparticles (AuNPs) could electrocatalyze the oxidation of NADH, finally promoting the redox reaction of the electroactive material methylene blue (MB) labeled on the hybrid double strand DNA (dsDNA). Furthermore, when the mixture of TB and RecJf exonuclease was introduced, TB combined with the thrombin aptamer II (TBA II) and the aptamer-TB complex was formed. And then, the RecJf exonuclease selectively degraded the TBA II from 5'?3', releasing the target TB into the solution. The free TB was reused to combine with other TBA II to accomplish the target recycling and realize the electrochemical signal amplification. In this way, excellent sensitivity of the aptasensor was obtained. The thrombin aptasensor achieved a detection limit of 1.7pM (defined as S/N=3) with a linear range from 5pM to 100nM. In addition, the proposed aptasensor had good stability and sensitivity, and would become a promising choice for the protein diagnostics in clinical analysis. PMID:23603135

  1. An NADPH and FAD dependent enzyme catalyzes hydroxylation of flavonoids in position 8.

    PubMed

    Halbwirth, Heidrun; Stich, Karl

    2006-06-01

    Yellow flavonols contribute to flower pigmentation in Asteraceae. In contrast to common flavonols, they show additional hydroxyl groups in position 6 and/or 8 of the aromatic A-ring in addition to the basic 5,7-hydroxylation pattern. An enzyme introducing a hydroxyl group in position 8 of flavonols and flavones was demonstrated for the first time with enzyme preparations from petals of Chrysanthemum segetum. Flavanones, dihydroflavonols and glucosylated flavonols and flavones were not accepted as substrates. The enzyme was localized in the microsomal fraction and uses NADPH and FAD as cofactors. Experiments with carbon monoxide/blue light and with antibodies specific for cytochrome P450 reductase did not indicate the involvement of a classical cytochrome P450 dependent monooxygenase in the reaction. Thus, the flavonoid 8-hydroxylase represents a novel type of hydroxylating enzyme in the flavonoid pathway. Apart from flavonoid 8-hydroxylase activity, the presence of all enzymes involved in the formation of flavonoid 7-O-glucosides in C. segetum was demonstrated. The pathway leading to 8-hydroxyflavonoids in C. segetum has been derived from enzyme activities and substrate specificities observed. PMID:16678869

  2. The Enolase Superfamily: A General Strategy for Enzyme-Catalyzed Abstraction of the R-Protons of Carboxylic Acids

    E-print Network

    Rayment, Ivan

    -Protons of Carboxylic Acids Patricia C. Babbitt,*, Miriam S. Hasson,§,| Joseph E. Wedekind,,# David R. J. Palmer by their ability to catalyze the abstraction of the R-proton of a carboxylic acid to form an enolic intermediate specialized enzymes: mandelate racemase, galactonate dehydratase, glucarate dehydratase, muconate

  3. Ultrasensitive electrochemical detection of breast cancer cells based on DNA-rolling-circle-amplification-directed enzyme-catalyzed polymerization.

    PubMed

    Sheng, Qinglin; Cheng, Ni; Bai, Wushuang; Zheng, Jianbin

    2015-02-01

    An ultrasensitive cytosensor based on DNA-rolling-circle-amplification-directed enzyme-catalyzed polymerization is demonstrated. As a proof of concept, the cytosensor shows excellent sensitivity for MCF-7 cell detection with a lower detection limit of 12 cells per mL. PMID:25536491

  4. Nonperfect Synchronization of Reaction Center Rehybridization in the Transition State of the Hydride Transfer Catalyzed by Dihydrofolate Reductase

    PubMed Central

    Pu, Jingzhi; Ma, Shuhua; Garcia-Viloca, Mireia; Gao, Jiali; Truhlar, Donald G.; Kohen, Amnon

    2015-01-01

    It has been suggested that the magnitudes of secondary kinetic isotope effects (2° KIEs) of enzyme-catalyzed reactions are an indicator of the extent of reaction-center rehybridization at the transition state. A 2° KIE value close to the corresponding secondary equilibrium isotope effects (2° EIE) is conventionally interpreted as indicating a late transition state that resembles the final product. The reliability of using this criterion to infer the structure of the transition state is examined by carrying out a theoretical investigation of the hybridization states of the hydride donor and acceptor in the Escherichia coli dihydrofolate reductase (ecDHFR)-catalyzed reaction for which a 2° KIE close to the 2° EIE was reported. Our results show that the donor carbon at the hydride transfer transition state resembles the reactant state more than the product state, whereas the acceptor carbon is more productlike, which is a symptom of transition state imbalance. The conclusion that the isotopically substituted carbon is reactant-like disagrees with the conclusion that would have been derived from the criterion of 2° KIEs and 2° EIEs, but the breakdown of the correlation with the equilibrium isotope effect can be explained by considering the effect of tunneling. PMID:16231943

  5. Non-contact photothermal control of enzyme reactions on a microchip by using a compact diode laser

    Microsoft Academic Search

    Yuki Tanaka; Maxim N Slyadnev; Akihide Hibara; Manabu Tokeshi; Takehiko Kitamori

    2000-01-01

    Photothermal temperature control of an enzyme-catalyzed reaction in a microchip using a diode laser was demonstrated. A laser beam with energy of 10 mW was used to irradiate an absorbing target placed on top of the microchip cover plate. Theoretical calculations have shown that temperature in the microchannel can be locally increased by 5–7°C during short time intervals, due to

  6. Enzymes in Analytical Chemistry.

    ERIC Educational Resources Information Center

    Fishman, Myer M.

    1980-01-01

    Presents tabular information concerning recent research in the field of enzymes in analytic chemistry, with methods, substrate or reaction catalyzed, assay, comments and references listed. The table refers to 128 references. Also listed are 13 general citations. (CS)

  7. Molybdopterin Biosynthesis: Trapping of Intermediates for the MoaA-Catalyzed Reaction Using 2?-DeoxyGTP and 2?-ChloroGTP as Substrate Analogues.

    PubMed Central

    2015-01-01

    MoaA is a radical S-adenosylmethionine (AdoMet) enzyme that catalyzes a complex rearrangement of guanosine-5'-triphosphate (GTP) in the first step of molybdopterin biosynthesis. In this paper, we provide additional characterization of the MoaA reaction product, describe the use of 2?-chloroGTP to trap the GTP C3? radical, generated by hydrogen atom transfer to the 5?-deoxyadenosyl radical, and the use of 2?-deoxyGTP to block a late step in the reaction sequence. These probes, coupled with the previously reported trapping of an intermediate in which C3? of the ribose is linked to C8 of the purine, allow us to propose a plausible mechanism for the MoaA-catalyzed reaction. PMID:24955657

  8. Chromium-Catalyzed Homoaldol Equivalent Reaction, Indium-Mediated Cycloisomerization, and Palladium-Catalyzed Cross-Coupling Reaction 

    E-print Network

    Kang, Jun

    2011-10-21

    yield in many cases. A highly efficient and catalytic cycloisomerization reaction that transforms acetylenic ?,?-epoxides to 2,3,5-tri-substituted furans under InCl3 catalysis was developed. This reaction sequence allows access to rapid construction...

  9. Micellar catalysis using a photochromic surfactant: application to the Pd-catalyzed Tsuji-Trost reaction in water.

    PubMed

    Billamboz, Muriel; Mangin, Floriane; Drillaud, Nicolas; Chevrin-Villette, Carole; Banaszak-Léonard, Estelle; Len, Christophe

    2014-01-17

    The first example of a Pd-catalyzed Tsuji-Trost reaction, applied in a photochromic micellar media under conventional heating and microwave irradiation, is reported. The surfactant activity and recycling ability were investigated and compared with those of a few commercially available surfactants. The synthetic photochromic surfactant proved to be efficient, recyclable, and versatile for Pd-catalyzed coupling reactions. PMID:24295431

  10. Enantioselective direct Mannich reactions of cyclic ?-ketoesters catalyzed by chiral phosphine via a novel dual-reagent catalysis.

    PubMed

    Lou, Yan-Peng; Zheng, Chang-Wu; Pan, Ren-Ming; Jin, Qiao-Wen; Zhao, Gang; Li, Zhong

    2015-02-01

    A combination of an amino acid derived chiral phosphine catalyst and methyl acrylate efficiently catalyzed the direct Mannich reaction of cyclic ?-ketoesters and N-Boc-aldimines. The dual-reagent catalysis was presumed to function through the formation of a zwitterion, which catalyzed the reaction with excellent stereocontrol via a hydrogen-bonding assisted chiral ion-pair pathway. PMID:25621822

  11. Purification and characterization of cannabidiolic-acid synthase from Cannabis sativa L.. Biochemical analysis of a novel enzyme that catalyzes the oxidocyclization of cannabigerolic acid to cannabidiolic acid.

    PubMed

    Taura, F; Morimoto, S; Shoyama, Y

    1996-07-19

    We identified a unique enzyme that catalyzes the oxidocyclization of cannabigerolic acid to cannabidiolic acid (CBDA) in Cannabis sativa L. (CBDA strain). The enzyme, named CBDA synthase, was purified to apparent homogeneity by a four-step procedure: ammonium sulfate precipitation followed by chromatography on DEAE-cellulose, phenyl-Sepharose CL-4B, and hydroxylapatite. The active enzyme consists of a single polypeptide with a molecular mass of 74 kDa and a pI of 6.1. The NH2-terminal amino acid sequence of CBDA synthase is similar to that of Delta1-tetrahydrocannabinolic-acid synthase. CBDA synthase does not require coenzymes, molecular oxygen, hydrogen peroxide, and metal ion cofactors for the oxidocyclization reaction. These results indicate that CBDA synthase is neither an oxygenase nor a peroxidase and that the enzymatic cyclization does not proceed via oxygenated intermediates. CBDA synthase catalyzes the formation of CBDA from cannabinerolic acid as well as cannabigerolic acid, although the kcat for the former (0.03 s-1) is lower than that for the latter (0.19 s-1). Therefore, we conclude that CBDA is predominantly biosynthesized from cannabigerolic acid rather than cannabinerolic acid. PMID:8663284

  12. Direct Detection and Kinetic Analysis of Covalent Intermediate Formation in the 4-Amino-4-deoxychorismate Synthase Catalyzed Reaction

    E-print Network

    Toney, Michael

    with isochorismate synthase (IS) and anthranilate synthase (AS), in which nucleophile addition at C2 initiates- aminobenzoate (PABA). ADCS catalyzes the first step of PABA biosynthesis, which starts from chorismate. It adds they catalyze. This group of enzymes includes anthranilate synthase (AS) (6), isochoris- mate synthase (IS) (7

  13. Enzyme Catalysis and the Gibbs Energy

    ERIC Educational Resources Information Center

    Ault, Addison

    2009-01-01

    Gibbs-energy profiles are often introduced during the first semester of organic chemistry, but are less often presented in connection with enzyme-catalyzed reactions. In this article I show how the Gibbs-energy profile corresponds to the characteristic kinetics of a simple enzyme-catalyzed reaction. (Contains 1 figure and 1 note.)

  14. Efficient chromium(II)-catalyzed cross-coupling reactions between Csp2 centers.

    PubMed

    Steib, Andreas K; Kuzmina, Olesya M; Fernandez, Sarah; Flubacher, Dietmar; Knochel, Paul

    2013-10-16

    Low-toxicity chromium(II) chloride catalyzes at 25 °C within minutes the coupling reactions of various (hetero)arylmagnesium reagents with N-heterocyclic halides, aromatic halogenated ketones or imines, and alkenyl iodides. Remarkably, much lower amounts of homo-coupling side products are obtained compared to related iron, cobalt, or manganese cross-couplings. PMID:24053764

  15. Synthesis of Polycyclic Nitrogen Heterocycles via Cascade Pd-Catalyzed Alkene Carboamination/Diels-Alder Reactions.

    PubMed

    White, Derick R; Wolfe, John P

    2015-05-15

    Cascade Pd-catalyzed alkene carboamination/Diels-Alder reactions between bromodienes and amines bearing two pendant alkenes are described. These transformations generate 4 bonds, 3 rings, and 3-5 stereocenters to afford polycyclic nitrogen heterocycles with high diastereoselectivity. PMID:25946563

  16. Pd-Catalyzed Cross-Coupling Reactions of Amides and Aryl Mesylates

    PubMed Central

    Dooleweerdt, Karin; Fors, Brett P.; Buchwald, Stephen L.

    2010-01-01

    A catalyst, based on a biarylphosphine ligand, for the Pd-catalyzed cross-coupling reactions of amides and aryl mesylates is described. This system allows an array of aryl and heteroaryl mesylates to be transformed into the corresponding N-arylamides in moderate to excellent yields. PMID:20420379

  17. Acid-catalyzed heterogeneous reaction of 3-methyl-2-buten-1-ol with hydrogen peroxide.

    PubMed

    Liu, Qifan; Wang, Weigang; Ge, Maofa

    2015-05-01

    Acid-catalyzed heterogeneous oxidation with hydrogen peroxide (H2O2) has been suggested to be a potential pathway for secondary organic aerosol (SOA) formation from isoprene and its oxidation products. However, knowledge of the chemical mechanism and kinetics for this process is still incomplete. 3-Methyl-2-buten-1-ol (MBO321), an aliphatic alcohol structurally similar to isoprene, is emitted by pine forests and widely used in the manufacturing industries. Herein the uptake of MBO321 into H2SO4-H2O2 mixed solution was investigated using a flow-tube reactor coupled to a mass spectrometer. The reactive uptake coefficients (?) were acquired for the first time and were found to increase rapidly with increasing acid concentration. Corresponding aqueous-phase reactions were performed to further study the mechanism of this acid-catalyzed reaction. MBO321 could convert to 2-methyl-3-buten-2-ol (MBO232) and yield isoprene in acidic media. Organic hydroperoxides (ROOHs) were found to be generated through the acid-catalyzed route, which could undergo a rearrangement reaction and result in the formation of acetone and acetaldehyde. Organosulfates, which have been proposed to be SOA tracer compounds in the atmosphere, were also produced during the oxidation process. These results suggest that the heterogeneous acid-catalyzed reaction of MBO321 with H2O2 may contribute to SOA mass under certain atmospheric conditions. PMID:25968263

  18. Synthesis of biaryls via AlCl3 catalyzed domino reaction involving cyclization, dehydration, and oxidation.

    PubMed

    Narender, Tadigoppula; Sarkar, Satinath; Rajendar, Kandikonda; Tiwari, Sriniwas

    2011-12-01

    A new chemical access has been developed to synthesize biaryls from substituted acetophenones, phenylacetones, dihydrochalcone, and 2-acetylnaphthalene in reasonably good yields at room temperature via a domino reaction sequence of AlCl(3) catalyzed cyclization, dehydration, and then oxidation. PMID:22040063

  19. The effect of Mg/2+/ and Ca/2+/ on urea-catalyzed phosphorylation reactions

    NASA Technical Reports Server (NTRS)

    Handschuk, G. J.; Lohrmann, R.; Orgel, L. E.

    1973-01-01

    The effect of Mg(2+) and Ca(2+) on phosphorylation reactions catalyzed by urea is investigated, showing that Mg(2+) improves markedly the yield of products containing pyrophosphate bonds. Yields of up to 25% of uridine diphosphate can be obtained with struvite at temperatures as low as 65 C.

  20. Textured catalysts, methods of making textured catalysts, and methods of catalyzing reactions conducted in hydrothermal conditions

    DOEpatents

    Werpy, Todd [West Richland, WA; Wang, Yong [Richland, WA

    2003-12-30

    A textured catalyst having a hydrothermally-stable support, a metal oxide and a catalyst component is described. Methods of conducting aqueous phase reactions that are catalyzed by a textured catalyst are also described. The invention also provides methods of making textured catalysts and methods of making chemical products using a textured catalyst.

  1. Synthesis of 6,7,8-trisubstituted purines via a copper-catalyzed amidation reaction.

    PubMed

    Ibrahim, Nada; Legraverend, Michel

    2009-01-01

    We report herein an efficient method for the synthesis of 6,7,8-trisubstituted purines via a copper-catalyzed amidation reaction from easily accessible starting materials. Furthermore, the resulting 6-benzylsulfanyl-substituted purine derivatives may be readily oxidized for substitution by nucleophiles to give access to 6,7,8-trisubstituted purines for biological screening purposes. PMID:19012431

  2. Copper-catalyzed multicomponent reaction: synthesis of 4-arylsulfonylimino-4,5-dihydrofuran derivatives.

    PubMed

    Shang, Yongjia; Ju, Kai; He, Xinwei; Hu, Jinsong; Yu, Shuyan; Zhang, Min; Liao, Kaisheng; Wang, Lifen; Zhang, Ping

    2010-08-20

    A series of 4-arylsulfonylimino-4,5-dihydrofurans (14 examples) were efficiently synthesized in good to excellent yields by using the copper-catalyzed three-component reaction between sulfonyl azides, phenylacetylene, and beta-ketoesters in tetrahydrofuran (THF) at 40 degrees C for 8 h in the presence of triethylamine (TEA). A plausible mechanism for this process is proposed. PMID:20704448

  3. Reaction mechanism of epoxide cycloaddition to CO? catalyzed by salen-M (M = Co, Al, Zn).

    PubMed

    Wang, Ting-Ting; Xie, Yong; Deng, Wei-Qiao

    2014-10-01

    We propose a catalytic mechanism for the cycloaddition of epoxide to carbon dioxide catalyzed by salen-M (M = Co, Zn, Al) based on density functional theory calculations. The catalytic reaction follows a single-site mechanism rather than a bimetallic-site mechanism, which includes four steps: epoxide adsorption by salen-M, ring opening of epoxide, CO2 insertion, and intramolecular rearrangement. Our calculation results showed that the highest reaction barrier for salen-Co catalyst is only 9.94 kcal/mol, which is lower than that of salen-Al (14.38 kcal/mol) and salen-Zn (13.05 kcal/mol). The results indicate that the reaction catalyzed by salen-Al, salen-Co, or salen-Zn can occur at room temperature and atmospheric pressure, which is in agreement with experimental results. The mechanism can be used for the design of a novel catalyst for this reaction. PMID:25046346

  4. An Iodine-Catalyzed Hofmann-Löffler Reaction.

    PubMed

    Martínez, Claudio; Muñiz, Kilian

    2015-07-01

    Iodine reagents have been identified as economically and ecologically benign alternatives to transition metals, although their application as molecular catalysts in challenging C?H oxidation reactions has remained elusive. An attractive iodine oxidation catalysis is now shown to promote the convenient conversion of carbon-hydrogen bonds into carbon-nitrogen bonds with unprecedented complete selectivity. The reaction proceeds by two interlocked catalytic cycles comprising a radical chain reaction, which is initiated by visible light as energy source. This unorthodox synthetic strategy for the direct oxidative amination of alkyl groups has no biosynthetic precedence and provides an efficient and straightforward access to a general class of saturated nitrogenated heterocycles. PMID:26016458

  5. Metal enzymes in "impossible" microorganisms catalyzing the anaerobic oxidation of ammonium and methane.

    PubMed

    Reimann, Joachim; Jetten, Mike S M; Keltjens, Jan T

    2015-01-01

    Ammonium and methane are inert molecules and dedicated enzymes are required to break up the N-H and C-H bonds. Until recently, only aerobic microorganisms were known to grow by the oxidation of ammonium or methane. Apart from respiration, oxygen was specifically utilized to activate the inert substrates. The presumed obligatory need for oxygen may have resisted the search for microorganisms that are capable of the anaerobic oxidation of ammonium and of methane. However extremely slowly growing, these "impossible" organisms exist and they found other means to tackle ammonium and methane. Anaerobic ammonium-oxidizing (anammox) bacteria use the oxidative power of nitric oxide (NO) by forging this molecule to ammonium, thereby making hydrazine (N2H4). Nitrite-dependent anaerobic methane oxidizers (N-DAMO) again take advantage of NO, but now apparently disproportionating the compound into dinitrogen and dioxygen gas. This intracellularly produced dioxygen enables N-DAMO bacteria to adopt an aerobic mechanism for methane oxidation.Although our understanding is only emerging how hydrazine synthase and the NO dismutase act, it seems clear that reactions fully rely on metal-based catalyses known from other enzymes. Metal-dependent conversions not only hold for these key enzymes, but for most other reactions in the central catabolic pathways, again supported by well-studied enzymes from model organisms, but adapted to own specific needs. Remarkably, those accessory catabolic enzymes are not unique for anammox bacteria and N-DAMO. Close homologs are found in protein databases where those homologs derive from (partly) known, but in most cases unknown species that together comprise an only poorly comprehended microbial world. PMID:25707470

  6. Recyclable Polystyrene-Supported Siloxane-Transfer Agent for Palladium-Catalyzed Cross-Coupling Reactions

    PubMed Central

    2015-01-01

    The rational design, synthesis, and validation of a significantly improved insoluble polymer-supported siloxane-transfer agent has been achieved that permits efficient palladium-catalyzed cross-coupling reactions. The cross-linked polystyrene support facilitates product purification with excellent siloxane recycling. Drawbacks of a previous polymer-supported siloxane-transfer agent, relating to reaction efficiency and polymer stability after repeated cycles, have been addressed. PMID:24661113

  7. Indium(III) bromide-catalyzed preparation of dihydropyrimidinones: improved protocol conditions for the Biginelli reaction

    Microsoft Academic Search

    Nan-Yan Fu; Yao-Feng Yuan; Zhong Cao; Shan-Wei Wang; Ji-Tao Wang; Clovis Peppe

    2002-01-01

    Indium(III) bromide efficiently catalyzes the three-component coupling of ?-keto esters, aldehydes and urea (or thiourea) to afford the corresponding dihydropyrimidinones. This new protocol for the Biginelli reaction includes the following important features: produces excellent yields, allows the recycling of catalyst with no loss in its activity, and leads to zero-discharge during the process. The reaction of ethyl acetoacetate, salicylaldehyde and

  8. Synthesis of Substituted Tetrahydroindoloisoquinoline Derivatives via Intramolecular Pd-Catalyzed Alkene Carboamination Reactions

    PubMed Central

    2015-01-01

    Intramolecular Pd-catalyzed alkene carboamination reactions of substituted 2-allyl-N-(2-bromobenzyl)anilines are described. The substrates for these reactions are generated in two steps from readily available 2-allylanilines and 2-bromobenzaldehyde derivatives. The transformations afford substituted tetrahydroindoloisoquinolines, an uncommon class of fused bicyclic heterocycles, in good yield. The mechanism of these transformations is described, and a model that accounts for the observed product stereochemistry is proposed. PMID:24724560

  9. Copper(I)-catalyzed multicomponent reaction providing a new access to fully substituted thiophene derivatives.

    PubMed

    Jiang, Bo; Tu, Xing-Jun; Wang, Xue; Tu, Shu-Jiang; Li, Guigen

    2014-07-18

    Readily available triethylammonium 1-(2-oxoindolin-3-ylidene)-2-aroylethanethiolates are efficiently converted into a variety of fully substituted thiophene derivatives by copper(I)-catalyzed denitrogenative reactions with terminal alkynes and N-sulfonyl azides. This new reaction simultaneously installs C-N, C-S, and C-C bonds, allowing direct formation of highly functionalized thiophenes with a wide diversity in substituents in a one-pot manner. A plausible mechanism for the domino process is proposed. PMID:24988049

  10. Amine-catalyzed direct asymmetric Mannich-type reactions

    Microsoft Academic Search

    Wolfgang Notz; Kandasamy Sakthivel; Tommy Bui; Guofu Zhong; Carlos F Barbas

    2001-01-01

    Three chiral cyclic secondary amines are shown to be catalysts for the direct asymmetric Mannich-type reaction of acetone with a variety of preformed aldimines derived from o-anisidine. A simple one-pot three-component reaction procedure consisting of aldehyde, acetone, p-anisidine and an amine catalyst provides the corresponding ?-amino ketones with 50–89% ee under very mild conditions.

  11. A new paradigm for electrostatic catalysis of radical reactions in vitamin B12 enzymes

    PubMed Central

    Sharma, Pankaz K.; Chu, Zhen T.; Olsson, Mats H. M.; Warshel, Arieh

    2007-01-01

    The catalytic power of enzymes containing coenzyme B12 cofactor has been, in some respects, the “last bastion” for the strain hypothesis. The present work explores the origin of this effect by using simulation methods that overcome the sampling difficulties of previous energy minimization studies. It is found that the major part of the catalytic effect is due to the electrostatic interaction between the ribose and the protein, and that the strain contribution is very small. Remarkably, enzymes can use electrostatic effects even in a radical process, when the charge distribution of the reacting fragments does not change significantly during the reaction. Electrostatic catalysis can, in such cases, be obtained by attaching a polar group to the leaving fragment and designing an active site that interacts more strongly with this group in the product state than in the reactant state. The finding that evolution had to use this trick provides further evidence to the observation that it is extremely hard to catalyze enzymatic reactions by nonelectrostatic factors. The trick used by B12 enzymes may, in fact, be a very powerful new strategy in enzyme design. PMID:17517615

  12. Experimental and theoretical methods in kinetic studies of heterogeneously catalyzed reactions.

    PubMed

    Reyniers, Marie-Françoise; Marin, Guy B

    2014-01-01

    This review aims to illustrate the potential of kinetic analysis in general and microkinetic modeling in particular for rational catalyst design. Both ab initio calculations and experiments providing intrinsic kinetic data allow us to assess the effects of catalytic properties and reaction conditions on the activity and selectivity of the targeted reactions. Three complementary approaches for kinetic analysis of complex reaction networks are illustrated, using select examples of acid zeolite-catalyzed reactions from the authors' recent work. Challenges for future research aimed at defining targets for synthesis strategies that enable us to tune zeolite properties are identified. PMID:24910922

  13. Palladium-catalyzed allyl cross-coupling reactions with in situ generated organoindium reagents.

    PubMed

    Lee, Kooyeon; Kim, Hyunseok; Mo, Juntae; Lee, Phil Ho

    2011-08-01

    Inter- and intramolecular palladium-catalyzed allyl cross-coupling reactions, using allylindium generated in situ from allyl halides and indium, is demonstrated. Allylindium compounds may be effective nucleophilic coupling partners in palladium-catalyzed cross-coupling reactions. A variety of allyl halides, such as allyl iodide, allyl bromide, crotyl bromide, prenyl bromide, geranyl bromide, and 3-bromocyclohexene afforded the allylic cross-coupling products in good to excellent yields. Stereochemistry of the double bond is retained in the allylic cross-coupling reactions. Electrophilic cross-coupling partners, such as aryl and vinyl halides, dibromoolefin, alkynyl iodide, and aryl and vinyl triflates participate in these reactions. The presence of various substituents, such as n-butyl, ketal, acetyl, ethoxycarbonyl, nitrile, N-phenylamido, nitro, and chloride groups on the aromatic ring of electrophilic coupling partners showed little effect on the efficiency of the reactions. The present conditions work equally well for not only intermolecular but also intramolecular palladium-catalyzed cross-coupling reactions. These methods provide an efficient synthetic method for the introduction of an allyl group, which can be easily further functionalized to afford an sp(2)- and sp-hybridized carbon. The present method complements existing synthetic methods as a result of advantageous features such as easy preparation and handling, thermal stability, high reactivity and selectivity, operational simplicity, and low toxicity of allylindium reagents. PMID:21538904

  14. Big-Bang Nucleosynthesis Reactions Catalyzed by a Long-Lived Negatively Charged Leptonic Particle

    E-print Network

    Masayasu Kamimura; Yasushi Kino; Emiko Hiyama

    2009-06-13

    An accurate quantum three-body calculation is performed for the new type of big-bang nucleosynthesis (BBN) reactions that are catalyzed by a long-lived negatively-charged, massive leptonic particle (called X^-) such as the supersymmetric (SUSY) particle stau. The reactions studied here includes, i) 4He-transfer reactions such as (4He X)+d --> 6Li+X, ii) radiative capture reactions such as (7Be X)+ p --> (8B X) + gamma, iii) three-body breakup reactions such as (7Li X)+ p --> 4He+4He+X, iv) charge-exchange reactions such as (p X)+4He -->(4He X) +p, and v) neutron induced reactions such as (8Be X)+ n -->9Be+X, where (A X) denotes a Coulombic bound state of a nucleus A and X^-. In recent papers it has been claimed that some of the catalyzed BBN reactions have significantly large cross sections so as to markedly change the abundances of some elements, not only giving a solution to the 6Li-7Li problem (calculated underproduction of 6Li by a factor of 1000 and overproduction of 7Li+7Be by a factor of nearly 3) but also imposing strong restrictions on the lifetime and the primordial abundance of X^-. However, most of the calculations of these reaction cross sections in the literature were performed assuming too naive models or approximations that are unsuitable for the complicated low-energy nuclear reactions. We use a high-accuracy few-body calculational method developed by the authors, and provide precise cross sections and rates of these catalyzed BBN reactions for use in the BBN network calculation.

  15. Quantum Transition State Theory for proton transfer reactions in enzymes

    E-print Network

    Bothma, Jacques P; McKenzie, Ross H

    2009-01-01

    We consider the role of quantum effects in the transfer of hyrogen-like species in enzyme-catalysed reactions. This study is stimulated by claims that the observed magnitude and temperature dependence of kinetic isotope effects imply that quantum tunneling below the energy barrier associated with the transition state significantly enhances the reaction rate in many enzymes. We use a path integral approach which provides a general framework to understand tunneling in a quantum system which interacts with an environment at non-zero temperature. Here the quantum system is the active site of the enzyme and the environment is the surrounding protein and water. Tunneling well below the barrier only occurs for temperatures less than a temperature $T_0$ which is determined by the curvature of potential energy surface near the top of the barrier. We argue that for most enzymes this temperature is less than room temperature. For physically reasonable parameters quantum transition state theory gives a quantitative descr...

  16. Evidence for the formation of an enamine species during aldol and Michael-type addition reactions promiscuously catalyzed by 4-oxalocrotonate tautomerase.

    PubMed

    Poddar, Harshwardhan; Rahimi, Mehran; Geertsema, Edzard M; Thunnissen, Andy-Mark W H; Poelarends, Gerrit J

    2015-03-23

    The enzyme 4-oxalocrotonate tautomerase (4-OT), which has a catalytic N-terminal proline residue (Pro1), can promiscuously catalyze various carbon-carbon bond-forming reactions, including aldol condensation of acetaldehyde with benzaldehyde to yield cinnamaldehyde, and Michael-type addition of acetaldehyde to a wide variety of nitroalkenes to yield valuable ?-nitroaldehydes. To gain insight into how 4-OT catalyzes these unnatural reactions, we carried out exchange studies in D2 O, and X-ray crystallography studies. The former established that H-D exchange within acetaldehyde is catalyzed by 4-OT and that the Pro1 residue is crucial for this activity. The latter showed that Pro1 of 4-OT had reacted with acetaldehyde to give an enamine species. These results provide evidence of the mechanism of the 4-OT-catalyzed aldol and Michael-type addition reactions in which acetaldehyde is activated for nucleophilic addition by Pro1-dependent formation of an enamine intermediate. PMID:25728471

  17. Extracellular Enzymes Lab Biochemistry

    E-print Network

    Vallino, Joseph J.

    Extracellular Enzymes Lab Biochemistry · All organisms convert small organic compounds shown here: All of these reactions, of which there are more than 1000, are catalyzed by enzymes. Glucose Phosphate PathwayEMP Pathway #12;Amino Acids #12;More Complete Metabolic Network TOP #12;#12;Enzymes

  18. Understanding Lignin-Degrading Reactions of Ligninolytic Enzymes: Binding Affinity and Interactional Profile

    PubMed Central

    Chen, Ming; Zeng, Guangming; Tan, Zhongyang; Jiang, Min; Li, Hui; Liu, Lifeng; Zhu, Yi; Yu, Zhen; Wei, Zhen; Liu, Yuanyuan; Xie, Gengxin

    2011-01-01

    Previous works have demonstrated that ligninolytic enzymes mediated effective degradation of lignin wastes. The degrading ability greatly relied on the interactions of ligninolytic enzymes with lignin. Ligninolytic enzymes mainly contain laccase (Lac), lignin peroxidase (LiP) and manganese peroxidase (MnP). In the present study, the binding modes of lignin to Lac, LiP and MnP were systematically determined, respectively. Robustness of these modes was further verified by molecular dynamics (MD) simulations. Residues GLU460, PRO346 and SER113 in Lac, residues ARG43, ALA180 and ASP183 in LiP and residues ARG42, HIS173 and ARG177 in MnP were most crucial in binding of lignin, respectively. Interactional analyses showed hydrophobic contacts were most abundant, playing an important role in the determination of substrate specificity. This information is an important contribution to the details of enzyme-catalyzed reactions in the process of lignin biodegradation, which can be used as references for designing enzyme mutants with a better lignin-degrading activity. PMID:21980516

  19. Graphene cover-promoted metal-catalyzed reactions

    PubMed Central

    Yao, Yunxi; Fu, Qiang; Zhang, Y. Y.; Weng, Xuefei; Li, Huan; Chen, Mingshu; Jin, Li; Dong, Aiyi; Mu, Rentao; Jiang, Peng; Liu, Li; Bluhm, Hendrik; Liu, Zhi; Zhang, S. B.; Bao, Xinhe

    2014-01-01

    Graphitic overlayers on metals have commonly been considered as inhibitors for surface reactions due to their chemical inertness and physical blockage of surface active sites. In this work, however, we find that surface reactions, for instance, CO adsorption/desorption and CO oxidation, can take place on Pt(111) surface covered by monolayer graphene sheets. Surface science measurements combined with density functional calculations show that the graphene overlayer weakens the strong interaction between CO and Pt and, consequently, facilitates the CO oxidation with lower apparent activation energy. These results suggest that interfaces between graphitic overlayers and metal surfaces act as 2D confined nanoreactors, in which catalytic reactions are promoted. The finding contrasts with the conventional knowledge that graphitic carbon poisons a catalyst surface but opens up an avenue to enhance catalytic performance through coating of metal catalysts with controlled graphitic covers. PMID:25404332

  20. Eutectic Salt Catalyzed Environmentally Benign and Highly Efficient Biginelli Reaction

    PubMed Central

    Azizi, Najmadin; Dezfuli, Sahar; Hahsemi, Mohmmad Mahmoodi

    2012-01-01

    A simple deep eutectic solvent based on tin (II) chloride was used as a dual catalyst and environmentally benign reaction medium for an efficient synthesis of 3,4-dihydropyrimidin-2(1H)-one derivatives, from aromatic and aliphatic aldehydes, 1,3-dicarbonyl compounds, and urea in good-to-excellent yields and short reaction time. This simple ammonium deep eutectic solvent, easily synthesized from choline chloride and tin chloride, is relatively inexpensive and recyclable, making it applicable for industrial applications. PMID:22649326

  1. Rhodium-catalyzed redox allylation reactions of ketones.

    PubMed

    Williams, Florence J; Grote, Robin E; Jarvo, Elizabeth R

    2012-02-01

    Ketones react with allyl acetate to generate tertiary homoallylic alcohols in the presence of a rhodium catalyst and bis(pinacolato)diboron. A range of substrates, including aryl, alkyl and cyclic ketones react smoothly under these conditions. Diastereoselective allylation reactions of functionalized ketones such as pregnenolone acetate are also reported. PMID:21984365

  2. A new family of enzymes catalyzing the first committed step of the methylerythritol 4-phosphate (MEP) pathway for isoprenoid biosynthesis in bacteria

    PubMed Central

    Sangari, Félix J.; Pérez-Gil, Jordi; Carretero-Paulet, Lorenzo; García-Lobo, Juan M.; Rodríguez-Concepción, Manuel

    2010-01-01

    Isoprenoids are a large family of compounds with essential functions in all domains of life. Most eubacteria synthesize their isoprenoids using the methylerythritol 4-phosphate (MEP) pathway, whereas a minority uses the unrelated mevalonate pathway and only a few have both. Interestingly, Brucella abortus and some other bacteria that only use the MEP pathway lack deoxyxylulose 5-phosphate (DXP) reductoisomerase (DXR), the enzyme catalyzing the NADPH-dependent production of MEP from DXP in the first committed step of the pathway. Fosmidomycin, a specific competitive inhibitor of DXR, inhibited growth of B. abortus cells expressing the Escherichia coli GlpT transporter (required for fosmidomycin uptake), confirming that a DXR-like (DRL) activity exists in these bacteria. The B. abortus DRL protein was found to belong to a family of uncharacterized proteins similar to homoserine dehydrogenase. Subsequent experiments confirmed that DRL and DXR catalyze the same biochemical reaction. DRL homologues shown to complement a DXR-deficient E. coli strain grouped within the same phylogenetic clade. The scattered taxonomic distribution of sequences from the DRL clade and the occurrence of several paralogues in some bacterial strains might be the result of lateral gene transfer and lineage-specific gene duplications and/or losses, similar to that described for typical mevalonate and MEP pathway genes. These results reveal the existence of a novel class of oxidoreductases catalyzing the conversion of DXP into MEP in prokaryotic cells, underscoring the biochemical and genetic plasticity achieved by bacteria to synthesize essential compounds such as isoprenoids. PMID:20660776

  3. A new family of enzymes catalyzing the first committed step of the methylerythritol 4-phosphate (MEP) pathway for isoprenoid biosynthesis in bacteria.

    PubMed

    Sangari, Félix J; Pérez-Gil, Jordi; Carretero-Paulet, Lorenzo; García-Lobo, Juan M; Rodríguez-Concepción, Manuel

    2010-08-10

    Isoprenoids are a large family of compounds with essential functions in all domains of life. Most eubacteria synthesize their isoprenoids using the methylerythritol 4-phosphate (MEP) pathway, whereas a minority uses the unrelated mevalonate pathway and only a few have both. Interestingly, Brucella abortus and some other bacteria that only use the MEP pathway lack deoxyxylulose 5-phosphate (DXP) reductoisomerase (DXR), the enzyme catalyzing the NADPH-dependent production of MEP from DXP in the first committed step of the pathway. Fosmidomycin, a specific competitive inhibitor of DXR, inhibited growth of B. abortus cells expressing the Escherichia coli GlpT transporter (required for fosmidomycin uptake), confirming that a DXR-like (DRL) activity exists in these bacteria. The B. abortus DRL protein was found to belong to a family of uncharacterized proteins similar to homoserine dehydrogenase. Subsequent experiments confirmed that DRL and DXR catalyze the same biochemical reaction. DRL homologues shown to complement a DXR-deficient E. coli strain grouped within the same phylogenetic clade. The scattered taxonomic distribution of sequences from the DRL clade and the occurrence of several paralogues in some bacterial strains might be the result of lateral gene transfer and lineage-specific gene duplications and/or losses, similar to that described for typical mevalonate and MEP pathway genes. These results reveal the existence of a novel class of oxidoreductases catalyzing the conversion of DXP into MEP in prokaryotic cells, underscoring the biochemical and genetic plasticity achieved by bacteria to synthesize essential compounds such as isoprenoids. PMID:20660776

  4. Crystal structure of glycogen synthase: homologous enzymes catalyze glycogen synthesis and degradation

    PubMed Central

    Buschiazzo, Alejandro; Ugalde, Juan E; Guerin, Marcelo E; Shepard, William; Ugalde, Rodolfo A; Alzari, Pedro M

    2004-01-01

    Glycogen and starch are the major readily accessible energy storage compounds in nearly all living organisms. Glycogen is a very large branched glucose homopolymer containing about 90% ?-1,4-glucosidic linkages and 10% ?-1,6 linkages. Its synthesis and degradation constitute central pathways in the metabolism of living cells regulating a global carbon/energy buffer compartment. Glycogen biosynthesis involves the action of several enzymes among which glycogen synthase catalyzes the synthesis of the ?-1,4-glucose backbone. We now report the first crystal structure of glycogen synthase in the presence and absence of adenosine diphosphate. The overall fold and the active site architecture of the protein are remarkably similar to those of glycogen phosphorylase, indicating a common catalytic mechanism and comparable substrate-binding properties. In contrast to glycogen phosphorylase, glycogen synthase has a much wider catalytic cleft, which is predicted to undergo an important interdomain ‘closure' movement during the catalytic cycle. The structures also provide useful hints to shed light on the allosteric regulation mechanisms of yeast/mammalian glycogen synthases. PMID:15272305

  5. Gas Phase Studies of N-Heterocyclic Carbene-Catalyzed Condensation Reactions.

    PubMed

    Tian, Yuan; Lee, Jeehiun K

    2015-07-01

    N-Heterocyclic carbenes (NHCs) catalyze Umpolung condensation reactions of carbonyl compounds, including the Stetter reaction. These types of reactions have not heretofore been examined in the gas phase. Herein, we explore the feasibility of examining these reactions in the absence of solvent. A charge-tagged thiazolylidene catalyst is used to track the reactions by mass spectrometry. We find that the first Umpolung step, the addition of the NHC catalyst to a carbonyl compound to form the "Breslow intermediate", does not readily proceed in the gas phase, contrary to the case in solution. The use of acylsilanes in place of the carbonyl compounds appears to solve this issue, presumably because of a favorable Brook rearrangement. The second addition reaction, with enones, does not occur under our gas phase conditions. These reactions do occur in solution; the differential reactivity between the condensed and gas phases is discussed, and calculations are used to aid in the interpretation of the results. PMID:26066314

  6. The structure of SpnF, a standalone enzyme that catalyzes [4 + 2] cycloaddition.

    PubMed

    Fage, Christopher D; Isiorho, Eta A; Liu, Yungnan; Wagner, Drew T; Liu, Hung-wen; Keatinge-Clay, Adrian T

    2015-04-01

    In the biosynthetic pathway of the spinosyn insecticides, the tailoring enzyme SpnF performs a [4 + 2] cycloaddition on a 22-membered macrolactone to forge an embedded cyclohexene ring. To learn more about this reaction, which could potentially proceed through a Diels-Alder mechanism, we determined the 1.50-Å-resolution crystal structure of SpnF bound to S-adenosylhomocysteine. This sets the stage for advanced experimental and computational studies to determine the precise mechanism of SpnF-mediated cyclization. PMID:25730549

  7. Reaction Kinetics of Substrate Transglycosylation Catalyzed by TreX of Sulfolobus solfataricus and Effects on Glycogen Breakdown

    PubMed Central

    Nguyen, Dang Hai Dang; Park, Jong-Tae; Shim, Jae-Hoon; Tran, Phuong Lan; Oktavina, Ershita Fitria; Nguyen, Thi Lan Huong; Lee, Sung-Jae; Park, Cheon-Seok; Li, Dan; Park, Sung-Hoon; Stapleton, David; Lee, Jin-Sil

    2014-01-01

    We studied the activity of a debranching enzyme (TreX) from Sulfolobus solfataricus on glycogen-mimic substrates, branched maltotetraosyl-?-cyclodextrin (Glc4-?-CD), and natural glycogen to better understand substrate transglycosylation and the effect thereof on glycogen debranching in microorganisms. The validation test of Glc4-?-CD as a glycogen mimic substrate showed that it followed the breakdown process of the well-known yeast and rat liver extract. TreX catalyzed both hydrolysis of ?-1,6-glycosidic linkages and transglycosylation at relatively high (>0.5 mM) substrate concentrations. TreX transferred maltotetraosyl moieties from the donor substrate to acceptor molecules, resulting in the formation of two positional isomers of dimaltotetraosyl-?-1,6-?-cyclodextrin [(Glc4)2-?-CD]; these were 61,63- and 61,64-dimaltotetraosyl-?-1,6-?-CD. Use of a modified Michaelis-Menten equation to study substrate transglycosylation revealed that the kcat and Km values for transglycosylation were 1.78 × 103 s?1 and 3.30 mM, respectively, whereas the values for hydrolysis were 2.57 × 103 s?1 and 0.206 mM, respectively. Also, enzyme catalytic efficiency (the kcat/Km ratio) increased as the degree of polymerization of branch chains rose. In the model reaction system of Escherichia coli, glucose-1-phosphate production from glycogen by the glycogen phosphorylase was elevated ?1.45-fold in the presence of TreX compared to that produced in the absence of TreX. The results suggest that outward shifting of glycogen branch chains via transglycosylation increases the number of exposed chains susceptible to phosphorylase action. We developed a model of the glycogen breakdown process featuring both hydrolysis and transglycosylation catalyzed by the debranching enzyme. PMID:24610710

  8. Reaction kinetics of substrate transglycosylation catalyzed by TreX of Sulfolobus solfataricus and effects on glycogen breakdown.

    PubMed

    Nguyen, Dang Hai Dang; Park, Jong-Tae; Shim, Jae-Hoon; Tran, Phuong Lan; Oktavina, Ershita Fitria; Nguyen, Thi Lan Huong; Lee, Sung-Jae; Park, Cheon-Seok; Li, Dan; Park, Sung-Hoon; Stapleton, David; Lee, Jin-Sil; Park, Kwan-Hwa

    2014-06-01

    We studied the activity of a debranching enzyme (TreX) from Sulfolobus solfataricus on glycogen-mimic substrates, branched maltotetraosyl-?-cyclodextrin (Glc?-?-CD), and natural glycogen to better understand substrate transglycosylation and the effect thereof on glycogen debranching in microorganisms. The validation test of Glc?-?-CD as a glycogen mimic substrate showed that it followed the breakdown process of the well-known yeast and rat liver extract. TreX catalyzed both hydrolysis of ?-1,6-glycosidic linkages and transglycosylation at relatively high (>0.5 mM) substrate concentrations. TreX transferred maltotetraosyl moieties from the donor substrate to acceptor molecules, resulting in the formation of two positional isomers of dimaltotetraosyl-?-1,6-?-cyclodextrin [(Glc?)?-?-CD]; these were 6(1),6(3)- and 6(1),6(4)-dimaltotetraosyl-?-1,6-?-CD. Use of a modified Michaelis-Menten equation to study substrate transglycosylation revealed that the kcat and Km values for transglycosylation were 1.78 × 10(3) s(-1) and 3.30 mM, respectively, whereas the values for hydrolysis were 2.57 × 10(3) s(-1) and 0.206 mM, respectively. Also, enzyme catalytic efficiency (the kcat/Km ratio) increased as the degree of polymerization of branch chains rose. In the model reaction system of Escherichia coli, glucose-1-phosphate production from glycogen by the glycogen phosphorylase was elevated ?1.45-fold in the presence of TreX compared to that produced in the absence of TreX. The results suggest that outward shifting of glycogen branch chains via transglycosylation increases the number of exposed chains susceptible to phosphorylase action. We developed a model of the glycogen breakdown process featuring both hydrolysis and transglycosylation catalyzed by the debranching enzyme. PMID:24610710

  9. Disproportionation reactions catalyzed by Leuconostoc and Streptococcus glucansucrases.

    PubMed

    Binder, T P; Côté, G L; Robyt, J F

    1983-12-23

    Glucansucrases from Leuconostoc mesenteroides NRRL B-512F and Streptococcus mutans 6715 were found to utilize a number of D-gluco-oligosaccharides as D-glucosyl donors and as acceptors. These donors included isomaltotriose and its homologs, panose, maltotriose, and dextran. In each case, D-glucosyl groups were transferred from the donor to an acceptor sugar. When the donor sugar also acted as an acceptor, disproportionation reactions occurred. Isomaltotriose, for example, gave rise to isomaltose and isomaltotetraose initially, and to a series of isomalto-oligosaccharides eventually. In addition to forming alpha-D-(1----6) linkages in the reactions, dextransucrase from S. mutans 6715 was capable of forming alpha-D-(1----3)-linked products. PMID:6671200

  10. Acid-catalyzed transformation of ionophore veterinary antibiotics: reaction mechanism and product implications.

    PubMed

    Sun, Peizhe; Yao, Hong; Minakata, Daisuke; Crittenden, John C; Pavlostathis, Spyros G; Huang, Ching-Hua

    2013-07-01

    Ionophore antibiotics (IPAs) are polyether antimicrobials widely used in the livestock industry and may enter the environment via land application of animal waste and agricultural runoff. Information is scarce regarding potential transformation of IPAs under environmental conditions. This study is among the first to identify the propensity of IPAs to undergo acid-catalyzed transformation in mildly acidic aquatic systems and characterize the reactions in depth. The study focused on the most widely used monensin (MON) and salinomycin (SAL), and also included narasin (NAR) in the investigation. All three IPAs are susceptible to acid-catalyzed transformation. MON reacts much more slowly than SAL and NAR and exhibits a different kinetic behavior that is further evaluated by a reversible reaction kinetic model. Extensive product characterization identifies that the spiro-ketal group of IPAs is the reactive site for the acid-catalyzed hydrolytic transformation, yielding predominantly isomeric and other products. Toxicity evaluation of the transformation products shows that the products retain some antimicrobial properties. The occurrence of IPAs and isomeric transformation products is also observed in poultry litter and agricultural runoff samples. Considering the common presence of mildly acidic environments (pH 4-7) in soils and waters, the acid-catalyzed transformation identified in this study likely plays an important role in the environmental fate of IPAs. PMID:23373828

  11. Enzyme-Catalyzed Oxidation of 17?-Estradiol Using Immobilized Laccase from Trametes versicolor

    PubMed Central

    Cardinal-Watkins, Chantale; Nicell, Jim A.

    2011-01-01

    Many natural and synthetic estrogens are amenable to oxidation through the catalytic action of oxidative enzymes such as the fungal laccase Trametes versicolor. This study focused on characterizing the conversion of estradiol (E2) using laccase that had been immobilized by covalent bonding onto silica beads contained in a bench-scale continuous-flow packed bed reactor. Conversion of E2 accomplished in the reactor declined when the temperature of the system was changed from room temperature to just above freezing at pH 5 as a result of a reduced rate of reaction rather than inactivation of the enzyme. Similarly, conversion increased when the system was brought to warmer temperatures. E2 conversion increased when the pH of the influent to the immobilized laccase reactor was changed from pH 7 to pH 5, but longer-term experiments showed that the enzyme is more stable at pH 7. Results also showed that the immobilized laccase maintained its activity when treating a constant supply of aqueous E2 at a low mean residence time over a 12-hour period and when treating a constant supply of aqueous E2 at a high mean residence time over a period of 9 days. PMID:21869925

  12. The oxidative fermentation of ethanol in Gluconacetobacter diazotrophicus is a two-step pathway catalyzed by a single enzyme: alcohol-aldehyde Dehydrogenase (ADHa).

    PubMed

    Gómez-Manzo, Saúl; Escamilla, José E; González-Valdez, Abigail; López-Velázquez, Gabriel; Vanoye-Carlo, América; Marcial-Quino, Jaime; de la Mora-de la Mora, Ignacio; Garcia-Torres, Itzhel; Enríquez-Flores, Sergio; Contreras-Zentella, Martha Lucinda; Arreguín-Espinosa, Roberto; Kroneck, Peter M H; Sosa-Torres, Martha Elena

    2015-01-01

    Gluconacetobacter diazotrophicus is a N2-fixing bacterium endophyte from sugar cane. The oxidation of ethanol to acetic acid of this organism takes place in the periplasmic space, and this reaction is catalyzed by two membrane-bound enzymes complexes: the alcohol dehydrogenase (ADH) and the aldehyde dehydrogenase (ALDH). We present strong evidence showing that the well-known membrane-bound Alcohol dehydrogenase (ADHa) of Ga. diazotrophicus is indeed a double function enzyme, which is able to use primary alcohols (C2-C6) and its respective aldehydes as alternate substrates. Moreover, the enzyme utilizes ethanol as a substrate in a reaction mechanism where this is subjected to a two-step oxidation process to produce acetic acid without releasing the acetaldehyde intermediary to the media. Moreover, we propose a mechanism that, under physiological conditions, might permit a massive conversion of ethanol to acetic acid, as usually occurs in the acetic acid bacteria, but without the transient accumulation of the highly toxic acetaldehyde. PMID:25574602

  13. The Oxidative Fermentation of Ethanol in Gluconacetobacter diazotrophicus Is a Two-Step Pathway Catalyzed by a Single Enzyme: Alcohol-Aldehyde Dehydrogenase (ADHa)

    PubMed Central

    Gómez-Manzo, Saúl; Escamilla, José E.; González-Valdez, Abigail; López-Velázquez, Gabriel; Vanoye-Carlo, América; Marcial-Quino, Jaime; de la Mora-de la Mora, Ignacio; Garcia-Torres, Itzhel; Enríquez-Flores, Sergio; Contreras-Zentella, Martha Lucinda; Arreguín-Espinosa, Roberto; Kroneck, Peter M. H.; Sosa-Torres, Martha Elena

    2015-01-01

    Gluconacetobacter diazotrophicus is a N2-fixing bacterium endophyte from sugar cane. The oxidation of ethanol to acetic acid of this organism takes place in the periplasmic space, and this reaction is catalyzed by two membrane-bound enzymes complexes: the alcohol dehydrogenase (ADH) and the aldehyde dehydrogenase (ALDH). We present strong evidence showing that the well-known membrane-bound Alcohol dehydrogenase (ADHa) of Ga. diazotrophicus is indeed a double function enzyme, which is able to use primary alcohols (C2–C6) and its respective aldehydes as alternate substrates. Moreover, the enzyme utilizes ethanol as a substrate in a reaction mechanism where this is subjected to a two-step oxidation process to produce acetic acid without releasing the acetaldehyde intermediary to the media. Moreover, we propose a mechanism that, under physiological conditions, might permit a massive conversion of ethanol to acetic acid, as usually occurs in the acetic acid bacteria, but without the transient accumulation of the highly toxic acetaldehyde. PMID:25574602

  14. Nickel-Catalyzed Reactions Directed toward the Formation of Heterocycles.

    PubMed

    Kurahashi, Takuya; Matsubara, Seijiro

    2015-06-16

    Heterocycles have garnered significant attention because they are important functional building blocks in various useful molecules, such as pharmaceuticals, agricultural chemicals, pesticides, and materials. Several studies have been conducted regarding the preparation of heterocyclic skeletons with an emphasis on selectivity and efficiency. Three strategies are typically employed to construct cyclic molecules, namely, cyclization, cycloaddition, and ring-size alterations. Although each method has certain advantages, cycloaddition may be superior from the viewpoint of divergence. Specifically, cycloadditions enable the construction of rings from several pieces. However, the construction of heterocycles via cycloadditions is more challenging than the construction of carbocycles. For heterocycle construction, simple pericyclic reactions rarely work smoothly because of the large HOMO-LUMO gap unless well-designed combinations, such as electron-rich dienes and aldehydes, are utilized. Thus, a different approach should be employed to prepare heterocycles via cycloadditions. To this end, the use of metallacycles containing heteroatoms is expected to serve as a promising solution. In this study, we focused on the preparation of heteroatom-containing nickelacycles. Because nickel possesses a relatively high redox potential and an affinity for heteroatoms, several methods were developed to synthesize heteronickelacycles from various starting materials. The prepared nickelacycles were demonstrated to be reasonable intermediates in cycloaddition reactions, which were used to prepare various heterocycles. In this Account, we introduce the following four methods to prepare heterocycles via heteronickelacycles. (1) Direct oxidative insertion of Ni(0) to ?,?-unsaturated enone derivatives: treatment of 3-ethoxycarbonyl-4-phenyl-3-buten-2-one with Ni(0) afforded an oxa-nickelacycle, which reacted with alkynes to give pyrans. (2) Substitution of a part of a cyclic compound with low-valent nickel, accompanied by elimination of small molecules such as CO, CO2, and acetophenone: treatment of phthalic anhydride with Ni(0) in the presence of ZnCl2 afforded the oxanickelacycle, which was formed via decarbonylative insertion of Ni(0) and reacted with alkynes to give isocumarins. (3) Cyclization to a nickelacycle, accompanied by two C-C ?-bond activations: insertion of Ni(0) into an arylnitrile, followed by aryl cyanation of an alkyne, gave alkenylnickel as an intermediate. The alkenylnickel species subsequently underwent an intramolecular nucleophilic attack with an arylcarbonyl group to form a cyclized product with concomitant cleavage of the C-C ?-bond between the carbonyl and aryl groups. (4) Assembly of several components to form a heteroatom-containing nickelacycle via cycloaddition: a new [2 + 2 + 1] cyclization reaction was carried out using an ?,?-unsaturated ester, isocyanate, and alkyne via a nickelacycle. On the basis of these four strategies, we developed new methods to prepare heterocyclic compounds using nickelacycles as the key active species. PMID:25989256

  15. Asymmetric copper-catalyzed Diels-Alder reaction revisited: control of the structure of bis(oxazoline) ligands.

    E-print Network

    Paris-Sud XI, Université de

    1 Asymmetric copper-catalyzed Diels-Alder reaction revisited: control of the structure of bis,R)-dihydroethano trans-dicarboxylic acid, a complete series of ligands was evaluated in the copper-catalyzed Diels[2.2.2] backbone; Diels-Alder catalysis; Copper; Enantioselectivity. * Corresponding author. E

  16. Amino Alcohols as Ligands for Nickel-Catalyzed Suzuki Reactions of Unactivated Alkyl Halides, Including Secondary Alkyl Chlorides, with

    E-print Network

    Fu, Gregory C.

    Amino Alcohols as Ligands for Nickel-Catalyzed Suzuki Reactions of Unactivated Alkyl Halides February 27, 2006; E-mail: gcf@mit.edu Early work in the area of palladium- and nickel-catalyzed cross of unactivated secondary alkyl halides is based on nickel/bathophenanthroline.4 This method can be applied

  17. Organic reactions catalyzed by methylrhenium trioxide: Dehydration, amination, and disproportionation of alcohols

    SciTech Connect

    Zhu, Zuolin; Espenson, J.H. [Iowa State Univ., Ames, IA (United States)] [Iowa State Univ., Ames, IA (United States)

    1996-01-12

    Methylrhenium trioxide (MTO) is the first transition metal complex in trace quantity to catalyze the direct formation of ethers from alcohols. The reactions are independent of the solvents used: benzene, toluene, dichloromethane, chloroform, acetone, and in the alcohols themselves. Aromatic alcohols gave better yields than aliphatic. Reactions between two different alcohols could also be used to prepare unsymmetric ethers, the best yields being obtained when one of the alcohols is aromatic alcohols proceeding in better yield. When primary (secondary) amines were used as the limiting reagent, direct amination of alcohols catalyzed by MTO gave good yields of the expected secondary (tertiary) amines at room temperature. Disproportionation of alcohols to alkanes and carbonyl compounds was also observed for aromatic alcohols in the presence of MTO. On the basis of the results of this investigation and a comparison with the interaction between MTO and water, a concerted process and a mechanism involving carbocation intermediates have been suggested. 5 tabs.

  18. Mechanistic insights into a BINOL-derived phosphoric acid-catalyzed asymmetric Pictet-Spengler reaction

    E-print Network

    Overvoorde, Lois M.; Grayson, Matthew N.; Luo, Yi; Goodman, Jonathan M.

    2015-02-05

    Mechanistic Insights into a BINOL-Derived Phosphoric Acid- Catalyzed Asymmetric Pictet?Spengler Reaction Lois M. Overvoorde,† Matthew N. Grayson,† Yi Luo,§ and Jonathan M. Goodman*,† †Centre for Molecular Informatics, Department of Chemistry... unrestricted use, distribution and reproduction in any medium, provided the author and source are cited. considerably higher in energy than the five- and six-membered ring formation TSs. They therefore concluded that the five- membered intermediate would not go...

  19. Isotope Effects and Mechanism of the Asymmetric BOROX Brønsted Acid Catalyzed Aziridination Reaction

    PubMed Central

    Vetticatt, Mathew J.; Desai, Aman A.; Wulff, William D.

    2013-01-01

    The mechanism of the chiral VANOL-BOROX Brønsted acid catalyzed aziridination reaction of imines and ethyldiazoacetate has been studied using a combination of experimental kinetic isotope effects and theoretical calculations. A stepwise mechanism where reversible formation of a diazonium ion intermediate precedes rate-limiting ring-closure to form the cis-aziridine is implicated. A revised model for the origin of enantio- and diastereoselectivity is proposed based on relative energies of the ring closing transition structures. PMID:23687986

  20. Studies of fundamental factors controlling catalyzation of reactions of gases with carbonaceous solids. First progress report

    Microsoft Academic Search

    R. M. Fisher; C. G. Shirley; A. Szirmae; J. V. Mahoney; F. C. Schwerer

    1977-01-01

    Flakes of natural graphite exposed to various Hâ-HâO-He atmospheres at temperatures from 650 to 1100°C after deposition of small particles of iron have been examined in the SEM and MVEM. The characteristics of surface channels resulting from iron-catalyzed reactions producing CO and\\/or CHâ appear to depend on temperature and to a lesser extent on P\\/sub HâO\\/ level. Very narrow, parallel-sided

  1. Identification and Quantitation of Reaction Intermediates and Residuals in Lipase-Catalyzed Transesterified Oils by HPLC

    Microsoft Academic Search

    Alberta N. A. Aryee; Leroy E. Phillip; Roger I. Cue; Benjamin K. Simpson

    A high-performance liquid chromatography (HPLC) unit equipped with size exclusion column and a refractive index detector was\\u000a used for simultaneous monitoring, identification, and quantitation of the reaction components from lipase-catalyzed transesterification\\u000a of three oils. The procedure simultaneously separated and detected the unreacted triacylglycerols (TAG), diacyl-, and monoacyl-glycerol\\u000a (DAG and MAG) co-products, residual alcohol as well as free fatty acid (FFA)

  2. Continuous reaction performances of benzene alkylation with long chain olefins catalyzed by ionic liquid

    Microsoft Academic Search

    Congzhen Qiao; Chengyue Li

    2008-01-01

    Based on a compulsive mixing-reacting-separating-recycling small experimental setup,the continuous reaction performances of\\u000a benzene alkylation with long chain olefins catalyzed by [BMIM]Cl-AlCl3 ionic liquid were investigated. Three different situations including normal continuous operation mode (reagent materials),\\u000a sidetrack feeding from different axial positions along the static mixing reactor (reagent materials) and normal continuous\\u000a alkylation using industrial paraffin and olefins materials were examined.

  3. Water-dependent reaction pathways: an essential factor for the catalysis in HEPD enzyme.

    PubMed

    Du, Likai; Gao, Jun; Liu, Yongjun; Liu, Chengbu

    2012-10-01

    The hydroxyethylphosphonate dioxygenase (HEPD) catalyzes the critical carbon-carbon bond cleavage step in the phosphinothricin (PT) biosynthetic pathway. The experimental research suggests that water molecules play an important role in the catalytic reaction process of HEPD. This work proposes a water involved reaction mechanism where water molecules serve as an oxygen source in the generation of mononuclear nonheme iron oxo complexes. These molecules can take part in the catalytic cycle before the carbon-carbon bond cleavage process. The properties of trapped water molecules are also discussed. Meanwhile, water molecules seem to be responsible for converting the reactive hydroxyl radical group ((-)OH) to the ferric hydroxide (Fe(III)-OH) in a specific way. This converting reaction may prevent the enzyme from damages caused by the hydroxyl radical groups. So, water molecules may serve as biological catalysts just like the work in the heme enzyme P450 StaP. This work could provide a better interpretation on how the intermediates interact with water molecules and a further understanding on the O(18) label experimental evidence in which only a relatively smaller ratio of oxygen atoms in water molecules (?40%) are incorporated into the final product HMP. PMID:22950439

  4. Site-Specific Bioconjugation of a Murine Dihydrofolate Reductase Enzyme by Copper(I)-Catalyzed Azide-Alkyne Cycloaddition with Retained Activity

    PubMed Central

    Lim, Sung In; Mizuta, Yukina; Takasu, Akinori; Kim, Yong Hwan; Kwon, Inchan

    2014-01-01

    Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) is an efficient reaction linking an azido and an alkynyl group in the presence of copper catalyst. Incorporation of a non-natural amino acid (NAA) containing either an azido or an alkynyl group into a protein allows site-specific bioconjugation in mild conditions via CuAAC. Despite its great potential, bioconjugation of an enzyme has been hampered by several issues including low yield, poor solubility of a ligand, and protein structural/functional perturbation by CuAAC components. In the present study, we incorporated an alkyne-bearing NAA into an enzyme, murine dihydrofolate reductase (mDHFR), in high cell density cultivation of Escherichia coli, and performed CuAAC conjugation with fluorescent azide dyes to evaluate enzyme compatibility of various CuAAC conditions comprising combination of commercially available Cu(I)-chelating ligands and reductants. The condensed culture improves the protein yield 19-fold based on the same amount of non-natural amino acid, and the enzyme incubation under the optimized reaction condition did not lead to any activity loss but allowed a fast and high-yield bioconjugation. Using the established conditions, a biotin-azide spacer was efficiently conjugated to mDHFR with retained activity leading to the site-specific immobilization of the biotin-conjugated mDHFR on a streptavidin-coated plate. These results demonstrate that the combination of reactive non-natural amino acid incorporation and the optimized CuAAC can be used to bioconjugate enzymes with retained enzymatic activity. PMID:24887377

  5. EzCatDB: the enzyme reaction database, 2015 update

    PubMed Central

    Nagano, Nozomi; Nakayama, Naoko; Ikeda, Kazuyoshi; Fukuie, Masaru; Yokota, Kiyonobu; Doi, Takuo; Kato, Tsuyoshi; Tomii, Kentaro

    2015-01-01

    The EzCatDB database (http://ezcatdb.cbrc.jp/EzCatDB/) has emphasized manual classification of enzyme reactions from the viewpoints of enzyme active-site structures and their catalytic mechanisms based on literature information, amino acid sequences of enzymes (UniProtKB) and the corresponding tertiary structures from the Protein Data Bank (PDB). Reaction types such as hydrolysis, transfer, addition, elimination, isomerization, hydride transfer and electron transfer have been included in the reaction classification, RLCP. This database includes information related to ligand molecules on the enzyme structures in the PDB data, classified in terms of cofactors, substrates, products and intermediates, which are also necessary to elucidate the catalytic mechanisms. Recently, the database system was updated. The 3D structures of active sites for each PDB entry can be viewed using Jmol or Rasmol software. Moreover, sequence search systems of two types were developed for the EzCatDB database: EzCat-BLAST and EzCat-FORTE. EzCat-BLAST is suitable for quick searches, adopting the BLAST algorithm, whereas EzCat-FORTE is more suitable for detecting remote homologues, adopting the algorithm for FORTE protein structure prediction software. Another system, EzMetAct, is also available to searching for major active-site structures in EzCatDB, for which PDB-formatted queries can be searched. PMID:25324316

  6. EzCatDB: the enzyme reaction database, 2015 update.

    PubMed

    Nagano, Nozomi; Nakayama, Naoko; Ikeda, Kazuyoshi; Fukuie, Masaru; Yokota, Kiyonobu; Doi, Takuo; Kato, Tsuyoshi; Tomii, Kentaro

    2015-01-01

    The EzCatDB database (http://ezcatdb.cbrc.jp/EzCatDB/) has emphasized manual classification of enzyme reactions from the viewpoints of enzyme active-site structures and their catalytic mechanisms based on literature information, amino acid sequences of enzymes (UniProtKB) and the corresponding tertiary structures from the Protein Data Bank (PDB). Reaction types such as hydrolysis, transfer, addition, elimination, isomerization, hydride transfer and electron transfer have been included in the reaction classification, RLCP. This database includes information related to ligand molecules on the enzyme structures in the PDB data, classified in terms of cofactors, substrates, products and intermediates, which are also necessary to elucidate the catalytic mechanisms. Recently, the database system was updated. The 3D structures of active sites for each PDB entry can be viewed using Jmol or Rasmol software. Moreover, sequence search systems of two types were developed for the EzCatDB database: EzCat-BLAST and EzCat-FORTE. EzCat-BLAST is suitable for quick searches, adopting the BLAST algorithm, whereas EzCat-FORTE is more suitable for detecting remote homologues, adopting the algorithm for FORTE protein structure prediction software. Another system, EzMetAct, is also available to searching for major active-site structures in EzCatDB, for which PDB-formatted queries can be searched. PMID:25324316

  7. A palladium - catalyzed domino reaction of 3-acetyl-5-hexyn-2-one with aryl iodides under carbon monoxide

    Microsoft Academic Search

    Antonio Arcadi; Elisabetta Rossi

    1996-01-01

    The palladium-catalyzed reaction of 3-acetyl-5-hexyn-2-one with aryl iodides under a carbon monoxide atmosphere produces different 2,3,5-trisubstituted furans depending on the alkyne\\/aryl iodide ratio.

  8. Palladium-catalyzed C-N cross-coupling reactions toward the synthesis of drug-like molecules

    E-print Network

    McAvoy, Camille Z

    2012-01-01

    The development of methodologies for C-N bond formation reactions is an important scientific challenge because of many academic and industrial applications. This work will focus particularly on palladium-catalyzed ...

  9. Nickel-catalyzed reductive coupling reactions : application to the total syntheses of pumiliotoxins 209F and 251D

    E-print Network

    Woodin, Katrina Sue

    2007-01-01

    Catalytic Asymmetric Reductive Coupling of 1,3-Enynes and Aromatic Aldehydes Nickel-catalyzed reductive coupling reactions of 1,3-enynes and aromatic aldehydes efficiently afford conjugated dienols in excellent regioselectivity ...

  10. Quantum Transition State Theory for proton transfer reactions in enzymes

    E-print Network

    Jacques P. Bothma; Joel Gilmore; Ross H. McKenzie

    2009-10-07

    We consider the role of quantum effects in the transfer of hyrogen-like species in enzyme-catalysed reactions. This study is stimulated by claims that the observed magnitude and temperature dependence of kinetic isotope effects imply that quantum tunneling below the energy barrier associated with the transition state significantly enhances the reaction rate in many enzymes. We use a path integral approach which provides a general framework to understand tunneling in a quantum system which interacts with an environment at non-zero temperature. Here the quantum system is the active site of the enzyme and the environment is the surrounding protein and water. Tunneling well below the barrier only occurs for temperatures less than a temperature $T_0$ which is determined by the curvature of potential energy surface near the top of the barrier. We argue that for most enzymes this temperature is less than room temperature. For physically reasonable parameters quantum transition state theory gives a quantitative description of the temperature dependence and magnitude of kinetic isotope effects for two classes of enzymes which have been claimed to exhibit signatures of quantum tunneling. The only quantum effects are those associated with the transition state, both reflection at the barrier top and tunneling just below the barrier. We establish that the friction due to the environment is weak and only slightly modifies the reaction rate. Furthermore, at room temperature and for typical energy barriers environmental degrees of freedom with frequencies much less than 1000 cm$^{-1}$ do not have a significant effect on quantum corrections to the reaction rate.

  11. Stereoselective Synthesis of Saturated Heterocycles via Pd-Catalyzed Alkene Carboetherification and Carboamination Reactions

    PubMed Central

    Wolfe, John P.

    2009-01-01

    The development of Pd-catalyzed carboetherification and carboamination reactions between aryl/alkenyl halides and alkenes bearing pendant heteroatoms is described. These transformations effect the stereoselective construction of useful heterocycles such as tetrahydrofurans, pyrrolidines, imidazolidin-2-ones, isoxazolidines, and piperazines. The scope, limitations, and applications of these reactions are presented, and current stereochemical models are described. The mechanism of product formation, which involves an unusual intramolecular syn-insertion of an alkene into a Pd-Heteroatom bond is also discussed in detail. PMID:19183704

  12. Transition-Metal-Catalyzed Laboratory-Scale Carbon–Carbon Bond-Forming Reactions of Ethylene

    PubMed Central

    Saini, Vaneet; Stokes, Benjamin J.; Sigman, Matthew S.

    2014-01-01

    Ethylene, the simplest alkene, is the most abundantly synthesized organic molecule by volume. It is readily incorporated into transitionmetal–catalyzed carbon-carbon bond-forming reactions through migratory insertions into alkylmetal intermediates. Because of its D2h symmetry, only one insertion outcome is possible. This limits byproduct formation and greatly simplifies analysis. As described within this Minireview, many carbon–carbon bond-forming reactions incorporate a molecule (or more) of ethylene at ambient pressure and temperature. In many cases, a useful substituted alkene is incorporated into the product. PMID:24105881

  13. Synthesis of fullerene glycoconjugates via a copper-catalyzed Huisgen cycloaddition reaction.

    PubMed

    Isobe, Hiroyuki; Cho, Kaimei; Solin, Niclas; Werz, Daniel B; Seeberger, Peter H; Nakamura, Eiichi

    2007-10-25

    The synthesis of fullerene-carbohydrate conjugates using a copper-catalyzed [3+2] cycloaddition reaction to facilitate the union of an azido-functionalized sugar and a pentaalkynyl[60]fullerene is straightforward. Thus, fullerenes bearing five oligosaccharides such as Gb3-trisaccharide can be readily accessed. Nanometer-scale molecular architectures presenting as many as 15 sugar moieties in C5-symmetry are readily produced. The cycloaddition reaction proceeds quantitatively under mild conditions without the need to protect the sugar hydroxyl groups. PMID:17915889

  14. The first dehydration and the competing reaction pathways of glucose homogeneously and heterogeneously catalyzed by acids.

    PubMed

    Lin, Xufeng; Qu, Yuanyuan; Lv, Yanhong; Xi, Yanyan; Phillips, David Lee; Liu, Chenguang

    2013-02-28

    The dehydration mechanisms for glucose in ?-pyranose (BP) and in open-chain (OC) forms, catalyzed by acids homogeneously and heterogeneously, were investigated using density functional and two-layer ONIOM calculations. The first dehydration reaction and competing reaction pathways are the main focus of the present study. The energetics of five dehydration and two isomerization pathways were examined for the protonated form of BP in acidic aqueous solutions and the most favorable pathway of these was found to be the dehydration at the anomeric site. No dehydration pathway of OC glucose is favored over its isomerization to BP or to fructose. The relative ease of dehydration over isomerization depends on the selection of the reaction media for the protonated form of BP. These two reaction pathways catalyzed by a surface Brönsted acid site were then examined and the isomerization pathway was found to be more favorable than dehydration at the anomeric site on a surface acid site. These mechanistic insights provide an important guide for the catalyst design/selection of the reaction media for glucose dehydration. PMID:23340797

  15. Enantioselective nickel-catalyzed reductive coupling reactions of alkynes and aldehydes. Synthesis of amphidinolides T1 and T4 via catalytic, stereoselective macrocyclizations

    E-print Network

    Colby Davie, Elizabeth A. (Elizabeth Anne)

    2005-01-01

    I. Enantioselective Nickel-Catalyzed Reductive Couplings of Alkynes and Aldehydes Allylic alcohol synthesis via a nickel-catalyzed reductive coupling reaction of alkylsubstituted alkynes and aldehydes was studied for ligand ...

  16. Nickel-catalyzed Suzuki-Miyaura reactions of unactivated halides with alkyl boranes and planar-chiral borabenzene catalysts for Diels-Alder reactions

    E-print Network

    Lu, Zhe

    2010-01-01

    Part I describes the expansion in scope of a nickel-catalyzed coupling reaction of unactivated alkyl bromides and alkyl boranes to include unactivated alkyl chlorides. The new method is adapted for use outside of a glove ...

  17. Effect of tritium on luminous marine bacteria and enzyme reactions.

    PubMed

    Selivanova, M A; Mogilnaya, O A; Badun, G A; Vydryakova, G A; Kuznetsov, A M; Kudryasheva, N S

    2013-06-01

    The paper studies chronic effect of tritiated water, HTO, (0.0002-200 MBq/L) on bioluminescent assay systems: marine bacteria Photobacterium phosphoreum (intact and lyophilized) and coupled enzyme reactions. Bioluminescence intensity serves as a marker of physiological activity. Linear dependencies of bioluminescent intensity on exposure time or radioactivity were not revealed. Three successive stages in bacterial bioluminescence response to HTO were found: (1) absence of the effect, (2) activation, and (3) inhibition. They were interpreted in terms of reaction of organisms to stress-factor i.e. stress recognition, adaptive response/syndrome, and suppression of physiological function. In enzyme system, in contrast, the kinetic stages mentioned above were not revealed, but the dependence of bioluminescence intensity on HTO specific radioactivity was found. Damage of bacteria cells in HTO (100 MBq/L) was visualized by electron microscopy. Time of bioluminescence inhibition is suggested as a parameter to evaluate the bacterial sensitivity to ionizing radiation. PMID:23410594

  18. Simulating feedback and reversibility in substrate-enzyme reactions

    NASA Astrophysics Data System (ADS)

    van Zwieten, D. A. J.; Rooda, J. E.; Armbruster, D.; Nagy, J. D.

    2011-12-01

    We extend discrete event models (DEM) of substrate-enzyme reactions to include regulatory feedback and reversible reactions. Steady state as well as transient systems are modeled and validated against ordinary differential equation (ODE) models. The approach is exemplified in a model of the first steps of glycolysis with the most common regulatory mechanisms. We find that in glycolysis, feedback and reversibility together act as a significant damper on the stochastic variations of the intermediate products as well as for the stochastic variation of the transit times. This suggests that these feedbacks have evolved to control both the overall rate of, as well as stochastic fluctuations in, glycolysis.

  19. Enhancement of enzyme activity and enantioselectivity by cyclopentyl methyl ether in the transesterification catalyzed by Pseudomonas cepacia lipase co-lyophilized with cyclodextrins.

    PubMed

    Mine, Yurie; Zhang, Lin; Fukunaga, Kimitoshi; Sugimura, Yoshiaki

    2005-03-01

    The solvent effects of cyclopentyl methyl ether (CPME) on the reaction rates and enzyme enantioselectivity in the enantioselective transesterifications of racemic 6-methyl-5-hepten-2-ol (racemic sulcatol: SUL) and racemic 2,2-dimethyl-1,3-dioxolane-4-methanol (racemic solketal: SOL) with a series of enol esters catalyzed by Pseudomonas cepacia lipase co-lyophilized with cyclodextrins (alpha-, beta-, gamma-, partially methylated beta-, and 2,3,6-tri-O-methyl-beta-cyclodextrin: alphaCyD; betaCyD; gammaCyD; Me1.78betaCyD; Me3betaCyD) were investigated and compared with those in diisopropyl ether (IPE). In the case of SUL, enzyme activities of the co-lyophilizate with Me1.78betaCyD in CPME were lower than those in IPE with every acyl source, however, the absolute enantiopreference was shown in the transesterification with vinyl butyrate (VBR) in IPME. When the substrates were SOL and VBR, the enzyme activities in CPME were greatly enhanced as high as 1.6-9.8-fold, while the enantioselectivities in CPME were comparable to those in IPE. PMID:15834802

  20. ?,?-Unsaturated Acyl Azoliums from N-Heterocyclic Carbene Catalyzed Reactions: Observation and Mechanistic Investigation**

    PubMed Central

    Mahatthananchai, Jessada; Zheng, Pinguan; Bode, Jeffrey W.

    2011-01-01

    Catalytically generated acyl azoliums I and their ?,?-unsaturated counterparts II are thought to be key reactive intermediates in a rapidly growing number of transformations promoted by N-heterocyclic carbene (NHC) catalysts.[1] Acyl azoliums are invoked in the postulated catalytic cycles of nearly all of the new NHC-catalyzed reactions of ?-functionalized aldehydes reported since 2004, in which they are generally assumed to possess the reactivity of an activated carboxylic acid, that is, analogous to an activated ester.[2] In NHC-catalyzed processes, they are most often obtained through internal redox reactions of functionalized aldehydes but have also been prepared by oxidations of the Breslow intermediates[3] or additions to ketenes.[4] Acyl azoliums I are important intermediates in thiamine pyrophosphate (ThPP) dependent enzymatic reactions.[5] Townsend et al. have recently proposed that unsaturated acyl azolium III is the key intermediate in clavulanic acid biosynthesis;[6] despite careful efforts, III or its analogues II have never been characterized or independently synthesized. Here, we document the observation and characterization of ?,?-unsaturated acyl azoliums 1 and 2 (Scheme 1) and demonstrate that their corresponding hemiacetals (1? and 2”) are the kinetically important intermediates in both their acylation and annulation reactions. PMID:21308930

  1. Exploiting Acyl and Enol Azolium Intermediates via NHeterocyclic Carbene Catalyzed Reactions of Alpha-Reducible Aldehydes

    PubMed Central

    Vora, Harit U.; Wheeler, Philip

    2013-01-01

    N-heterocyclic carbenes are well known for their role in catalyzing benzoin and Stetter reactions: the generation of acyl anion equivalents from simple aldehydes to react with a variety of electrophiles. However, when an aldehyde bearing a leaving group or unsaturation adjacent to the acyl anion equivalent is subjected to an NHC, a new avenue of reactivity is unlocked, leading to a number of novel transformations which can generate highly complex products from simple starting materials, many of which are assembled through unconventional bond disconnections. The field of these new reactions - those utilizing ?-reducible aldehydes to access previously unexplored catalytic intermediates – has expanded rapidly in the past eight years. This review aims to provide the reader with a historical perspective on the underlying discoveries that led to the current state of the art, a mechanistic description of these reactions, and a summary of the recent advances in this area. PMID:23538785

  2. Cyclones in the Diels-Alder reaction catalyzed by aluminum chloride

    SciTech Connect

    Kiselev, V.D.; Shakirov, I.M.; Konovalov, A.I.

    1986-07-10

    A comparison was made of the kinetic parameters for the uncatalyzed and catalyzed (with aluminum chloride) Diels-Alder reaction between N-arylmaleimides and acrylic, methacrylic, and fumaric esters as dienophiles and phencyclone and tetracyclone as dienes. By thermochemical and spectrophotometric experiments it was shown that the aluminum chloride coordinates with the dienophile in a ratio of 1:1. With a larger concentration of the catalyst coordination also takes place at the carbonyl of the diene. For the complexes of N-arylmaleimides the rate constants for the reaction with free tetracyclone and phencyclone increase by not more than 60 times, those for the esters of the unsaturated acids increase by 300-600 times, whereas those in the reaction with anthracene increase by 10/sup 5/ times. The results are discussed form the standpoint of the change in the energy of the molecular orbitals of the reagents.

  3. Role of Valine 464 in the Flavin Oxidation Reaction Catalyzed by Choline Oxidase

    SciTech Connect

    Finnegan, Steffan; Agniswamy, Johnson; Weber, Irene T.; Gadda, Giovanni (GSU)

    2010-11-03

    The oxidation of reduced flavin cofactors by oxygen is a very important reaction that is central to the chemical versatility of hundreds of flavoproteins classified as monooxygenases and oxidases. These enzymes are characterized by bimolecular rate constants {ge} 10{sup 5} M{sup -1} s{sup -1} and produce water and hydrogen peroxide, respectively. A hydrophobic cavity close to the reactive flavin C(4a) atom has been previously identified in the 3D structure of monooxygenases but not in flavoprotein oxidases. In the present study, we have investigated by X-ray crystallography, mutagenesis, steady-state, and rapid reaction approaches the role of Val464, which is <6 {angstrom} from the flavin C(4a) atom in choline oxidase. The 3D structure of the Val464Ala enzyme was essentially identical to that of the wild-type enzyme as shown by X-ray crystallography. Time-resolved anaerobic substrate reduction of the enzymes showed that replacement of Val464 with alanine or threonine did not affect the reductive half-reaction. Steady-state and rapid kinetics as well as enzyme-monitored turnovers indicated that the oxidative half-reaction in the Ala464 and Thr464 enzymes was decreased by 50-fold with respect to the wild-type enzyme. We propose that the side chain of Val464 in choline oxidase provides a nonpolar site that is required to guide oxygen in proximity of the C(4a) atom of the flavin, where it will subsequently react via electrostatic catalysis. Visual analysis of available structures suggests that analogous nonpolar sites are likely present in most flavoprotein oxidases. Mechanistic considerations provide rationalization for the differences between sites in monooxygenases and oxidases.

  4. Penicillin acylase-catalyzed synthesis of pivampicillin: Effect of reaction variables and organic cosolvents

    Microsoft Academic Search

    Min Gon Kim; Sun Bok Lee

    1996-01-01

    Enzymatic synthesis of pivampicillin (PVM) from D-?-phenylglycine methyl ester (PGM) and pivaloyloxymethyl 6-aminopenicillanic acid (POM-6-APA) was investigated using an immobilized Escherichia coli penicillin acylase. The effects of reaction variables such as enzyme concentration, pH, temperature, and molar ratio of the substrates on PVM synthesis were investigated. The time-course profiles of the PVM synthesis reaction followed a typical pattern of the

  5. Synthesis of tetrasubstituted alkenes through a palladium-catalyzed domino carbopalladation/C-H-activation reaction.

    PubMed

    Tietze, Lutz F; Hungerland, Tim; Düfert, Alexander; Objartel, Ina; Stalke, Dietmar

    2012-03-12

    Helical tetrasubstituted alkenes (7) were obtained in a highly efficient way through a palladium-catalyzed domino-carbopalladation/CH-activation reaction of propargylic alcohols 6 in good to excellent yields. Electron-withdrawing- and electron-donating substituents can be introduced onto the upper and lower aromatic rings. The substrates (6) for the domino process were synthesized by addition of the lithiated alkyne (20) to various aldehydes (19); moreover, the substrates were accessible enantioselectively (in 95% ee) by reduction of the corresponding ketone using the Noyori procedure. PMID:22259072

  6. Direct aminoalkylation of arenes, heteroarenes, and alkenes via Ni-catalyzed Negishi cross-coupling reactions.

    PubMed

    Melzig, Laurin; Dennenwaldt, Teresa; Gavryushin, Andrey; Knochel, Paul

    2011-11-01

    A room-temperature Ni-catalyzed cross-coupling of aryl, heteroaryl, and alkenyl electrophiles with aminoalkylzinc bromides, readily available from the corresponding aminoalkyl chlorides via Grignard reagents, was developed. The reaction allows a convenient one-step preparation of various aminoalkyl products, including piperidine and tropane derivatives. Such functionalized amine moieties are widely present in various biologically active molecules. Aryl, heteroaryl, and alkenyl iodides, bromides, chlorides and triflates are suitable electrophiles. A short total synthesis of two natural products, (±)-galipinine and (±)-cusparine, is also reported. PMID:21923124

  7. Structure and function of metal cations in light alkane reactions catalyzed by modified H-ZSM5

    Microsoft Academic Search

    Joseph A. Biscardi; Enrique Iglesia

    1996-01-01

    The rate of propane dehydrocyclodimerization to form C6 aromatics is limited by a sequence of irreversible dehydrogenation reactions leading to propene, higher alkenes, dienes, trienes, and aromatics. Quasi-equilibrated acid—catalyzed cracking, oligometization, and cyclization reactions of alkene intermediates occur in sequence with these dehydrogenation reactions. Each dehydrogenation reaction is in turn limited by the rate of elementary steps that dispose of

  8. Regioselective acylation of nucleosides and their analogs catalyzed by Pseudomonas cepacia lipase: enzyme substrate recognition

    E-print Network

    Bao, Xinhe

    Regioselective acylation of nucleosides and their analogs catalyzed by Pseudomonas cepacia lipase: Floxuridine Lipase Nucleosides Regioselective acylation Substrate recognition a b s t r a c t The substrate recognition of Pseudomonas cepacia lipase in the acylation of nucleosides was investigated by means

  9. Lipase-catalyzed transesterification of rapeseed oils for biodiesel production with a novel organic solvent as the reaction medium

    Microsoft Academic Search

    Lilin Li; Wei Du; Dehua Liu; Li Wang; Zebo Li

    2006-01-01

    tert-Butanol, as a novel reaction medium, has been adopted for lipase-catalyzed transesterification of rapeseed oil for biodiesel production, with which both the negative effects caused by excessive methanol and by-product glycerol could be eliminated. Combined use of Lipozyme TL IM and Novozym 435 was proposed further to catalyze the methanolysis and the highest biodiesel yield of 95% could be achieved

  10. Enzyme-functionalized vascular grafts catalyze in-situ release of nitric oxide from exogenous NO prodrug.

    PubMed

    Wang, Zhihong; Lu, Yaxin; Qin, Kang; Wu, Yifan; Tian, Yingping; Wang, Jianing; Zhang, Jimin; Hou, Jingli; Cui, Yun; Wang, Kai; Shen, Jie; Xu, Qingbo; Kong, Deling; Zhao, Qiang

    2015-07-28

    Nitric oxide (NO) is an important signaling molecule in cardiovascular system, and the sustained release of NO by endothelial cells plays a vital role in maintaining patency and homeostasis. In contrast, lack of endogenous NO in artificial blood vessel is believed to be the main cause of thrombus formation. In this study, enzyme prodrug therapy (EPT) technique was employed to construct a functional vascular graft by immobilization of galactosidase on the graft surface. The enzyme-functionalized grafts exhibited excellent catalytic property in decomposition of the exogenously administrated NO prodrug. Localized and on-demand release of NO was demonstrated by in vitro release assay and fluorescent probe tracing in an ex vivo model. The immobilized enzyme retained catalytic property even after subcutaneous implantation of the grafts for one month. The functional vascular grafts were implanted into the rat abdominal aorta with a 1-month monitoring period. Results showed effective inhibition of thrombus formation in vivo and enhancement of vascular tissue regeneration and remodeling on the grafts. Thus, we create an enzyme-functionalized vascular graft that can catalyze prodrug to release NO locally and sustainably, indicating that this approach may be useful to develop new cell-free vascular grafts for treatment of vascular diseases. PMID:26004323

  11. Surface-catalyzed air oxidation reactions of hydrazines: Tubular reactor studies

    NASA Technical Reports Server (NTRS)

    Kilduff, Jan E.; Davis, Dennis D.; Koontz, Steven L.

    1988-01-01

    The surface-catalyzed air oxidation reactions of hydrazine, monomethylhydrazine, unsymmetrical dimethylhydrazine, symmetrical dimethylhydrazine, trimethylhydrazine and tetramethylhydrazine were investigated in a metal-powder packed turbular flow reactor at 55 plus or minus 3 C. Hydrazine was completely reacted on all surfaces studied. The major products of monomethylhydrazine (MMH) oxidation were methanol, methane and methyldiazene. The di-, tri- and tetra-methyl hydrazines were essentially unreactive under these conditions. The relative catalytic reactivities toward MMH are: Fe greater than Al2O3 greater than Ti greater than Zn greater than 316 SS greater than Cr greater than Ni greater than Al greater than 304L SS. A kinetic scheme and mechanism involving adsorption, oxidative dehydrogenation and reductive elimination reactions on a metal oxide surface are proposed.

  12. Alkali-Stabilized Pt-OHx Species Catalyze Low-Temperature Water-Gas Shift Reactions

    SciTech Connect

    Zhai, Y.; Pierre, D; Si, R; Deng, W; Ferrin, P; Nilekar, A; Peng, G; Herron, J; Bell, D; et. al.

    2010-01-01

    We report that alkali ions (sodium or potassium) added in small amounts activate platinum adsorbed on alumina or silica for the low-temperature water-gas shift (WGS) reaction (H{sub 2}O + CO {yields} H{sub 2} + CO{sub 2}) used for producing H{sub 2}. The alkali ion-associated surface OH groups are activated by CO at low temperatures ({approx}100 C) in the presence of atomically dispersed platinum. Both experimental evidence and density functional theory calculations suggest that a partially oxidized Pt-alkali-O{sub x}(OH){sub y} species is the active site for the low-temperature Pt-catalyzed WGS reaction. These findings are useful for the design of highly active and stable WGS catalysts that contain only trace amounts of a precious metal without the need for a reducible oxide support such as ceria.

  13. Difructosan anhydrides III preparation from sucrose by coupled enzyme reaction.

    PubMed

    Hang, Hua; Miao, Ming; Li, Yungao; Jiang, Bo; Mu, Wanmeng; Zhang, Tao

    2013-02-15

    Difructosan anhydrides III (DFA III) preparation was usually obtained by inulin hydrolysis with inulin fructotransferase (IFTase). The fructofuranosidic linkages of inulin were the same as fructooligosaccharides (FOS), which was synthesized by sucrose with fructosyltransferase (FTase). FOS was mainly composed of 1-kestose (GF(2)), nystose (GF(3)) and fructofuranosylnystose (GF(4)), and nystose was observed to be the smallest substrate for IFTase to synthesize DFA III. So sucrose, much cheaper than inulin, was considered to produce DFA III by coupled FTase and IFTase reaction. DFA III yield was obtained about 100mg/g (DFA III weight/sucrose weight) through this method. The results demonstrated the high potential of the coupled enzyme reaction as a novel DFA III producing method. PMID:23399196

  14. The reaction mechanism of methyl-coenzyme M reductase: how an enzyme enforces strict binding order.

    PubMed

    Wongnate, Thanyaporn; Ragsdale, Stephen W

    2015-04-10

    Methyl-coenzyme M reductase (MCR) is a nickel tetrahydrocorphinoid (coenzyme F430) containing enzyme involved in the biological synthesis and anaerobic oxidation of methane. MCR catalyzes the conversion of methyl-2-mercaptoethanesulfonate (methyl-SCoM) and N-7-mercaptoheptanoylthreonine phosphate (CoB7SH) to CH4 and the mixed disulfide CoBS-SCoM. In this study, the reaction of MCR from Methanothermobacter marburgensis, with its native substrates was investigated using static binding, chemical quench, and stopped-flow techniques. Rate constants were measured for each step in this strictly ordered ternary complex catalytic mechanism. Surprisingly, in the absence of the other substrate, MCR can bind either substrate; however, only one binary complex (MCR·methyl-SCoM) is productive whereas the other (MCR·CoB7SH) is inhibitory. Moreover, the kinetic data demonstrate that binding of methyl-SCoM to the inhibitory MCR·CoB7SH complex is highly disfavored (Kd = 56 mM). However, binding of CoB7SH to the productive MCR·methyl-SCoM complex to form the active ternary complex (CoB7SH·MCR(Ni(I))·CH3SCoM) is highly favored (Kd = 79 ?M). Only then can the chemical reaction occur (kobs = 20 s(-1) at 25 °C), leading to rapid formation and dissociation of CH4 leaving the binary product complex (MCR(Ni(II))·CoB7S(-)·SCoM), which undergoes electron transfer to regenerate Ni(I) and the final product CoBS-SCoM. This first rapid kinetics study of MCR with its natural substrates describes how an enzyme can enforce a strictly ordered ternary complex mechanism and serves as a template for identification of the reaction intermediates. PMID:25691570

  15. Synergistic effect of two E2 ubiquitin conjugating enzymes in SCFhFBH1 catalyzed polyubiquitination

    PubMed Central

    Choi, Jin Sun; Kim, Sunhong; Kim, Kidae; Myung, Pyung Keun; Park, Sung Goo; Seo, Yeon-Soo; Park, Byoung Chul

    2015-01-01

    Ubiquitination is a post translational modification which mostly links with proteasome dependent protein degradation. This process has been known to play pivotal roles in the number of biological events including apoptosis, cell signaling, transcription and translation. Although the process of ubiquitination has been studied extensively, the mechanism of polyubiquitination by multi protein E3 ubiquitin ligase, SCF complex remains elusive. In the present study, we identified UbcH5a as a novel stimulating factor for poly-ubiquitination catalyzed by SCFhFBH1 using biochemical fractionations and MALDI-TOF. Moreover, we showed that recombinant UbcH5a and Cdc34 synergistically stimulate SCFhFBH1 catalyzed polyubiquitination in vitro. These data may provide an important cue to understand the mechanism how the SCF complex efficiently polyubiquitinates target substrates. [BMB Reports 2015; 48(1): 25-29] PMID:24667174

  16. Efficient approach to 4-sulfonamidoquinolines via copper(I)-catalyzed cascade reaction of sulfonyl azides with alkynyl imines.

    PubMed

    Cheng, Guolin; Cui, Xiuling

    2013-04-01

    A novel and efficient approach to 4-sulfonamidoquinolines via copper-catalyzed cascade reaction of sulfonyl azides with alkynyl imines has been developed in which a 1,3-dipole cycloaddition/ketenimine formation/6?-electrocyclization/[1,3]-H shift cascade reaction was involved. Various 4-sulfonamidoquinolines were afforded in up to 84% yield for 19 examples. This synthetic strategy features with atom economy, concise steps, easy operation, and mild reaction conditions. PMID:23521106

  17. Mechanistic variety in zirconium-catalyzed bond-forming reaction of arsines.

    PubMed

    Roering, Andrew J; Davidson, Jillian J; MacMillan, Samantha N; Tanski, Joseph M; Waterman, Rory

    2008-09-01

    Triamidoamine-supported zirconium complexes have been demonstrated to catalyze a range of bond-forming events utilizing arsines. Three different mechanisms have been observed in these reactions. In the first mechanism, triamidoamine-supported zirconium complexes of the general type (N3N)ZrX (N3N =N(CH2CH2NSiMe3)33-; X = monoanionic ligand) catalyzed the dehydrogenative dimerization of diphenylarsine. Mechanistic analysis revealed that As-As bond formation proceeds via sigma-bond metathesis steps similar to the previously reported dehydrocoupling of phosphines by the same catalysts. In the second mechanism, sterically encumbered primary arsines appear to be dehydrocoupled via alpha elimination of an arsinidene fragment. Dehydrocoupling of dmpAsH2 (dmp = 2,6-dimesitylphenyl) to form (dmp)As = As(dmp) by (N3N)Zr-complexes appeared to proceed via elimination of dmpAs: from the arsenido intermediate, (N3N)ZrAsH(dmp). Further support for -arsinidene elimination came from the thermal decomposition of (N3N)ZrAsHMes (9) to (MesAs)4 (10), which obeyed first-order kinetics. In the third mechanism, the observation of stoichiometric insertion reactivity of the Zr-As bond with polar substrates, PhCH2NC, PhCN, (1-napthyl)NCS, and CS2, led to the development of intermolecular hydroarsination catalysis of terminal alkynes. Here, (N3N)ZrAsPh2 (2) catalyzed the addition of diphenylarsine to phenylacetylene and 1-hexyne to give the respective vinylarsine products. Arsenido complexes 2 and 9 and tetraarsine 10 have been structurally characterized. PMID:18698453

  18. Bioluminescence reaction catalyzed by membrane-bound luciferase in the "firefly squid," Watasenia scintillans.

    PubMed

    Tsuji, Frederick I

    2002-08-19

    The small Japanese "firefly squid," Watasenia scintillans, emits a bluish luminescence from dermal photogenic organs distributed along the ventral aspects of the head, mantle, funnel, arms and eyes. The brightest light is emitted by a cluster of three tiny organs located at the tip of each of the fourth pair of arms. Studies of extracts of the arm organs show that the light is due to a luciferin-luciferase reaction in which the luciferase is membrane-bound. The other components of the reaction are coelenterazine disulfate (luciferin), ATP, Mg(2+), and molecular oxygen. Based on the results, a reaction scheme is proposed which involves a rapid base/luciferase-catalyzed enolization of the keto group of the C-3 carbon of luciferin, followed by an adenylation of the enol group by ATP. The AMP serves as a recognition moiety for docking the substrate molecule to a luciferase bound to membrane, after which AMP is cleaved and a four-membered dioxetanone intermediate is formed by the addition of molecular oxygen. The intermediate then spontaneously decomposes to yield CO(2) and coelenteramide disulfate (oxyluciferin) in the excited state, which serves as the light emitter in the reaction. PMID:12101012

  19. Fenton-Like Reaction Catalyzed by the Rare Earth Inner Transition Metal Cerium

    PubMed Central

    HECKERT, ERIC G.; SEAL, SUDIPTA; SELF, WILLIAM T.

    2011-01-01

    Cerium (Ce) is a rare earth metal that is not known to have any biological role. Cerium oxide materials of several sizes and shapes have been developed in recent years as a scaffold for catalysts. Indeed even cerium oxide nanoparticles themselves have displayed catalytic activities and antioxidant properties in tissue culture and animal models. Because of ceria's ability to cycle between the +3 and +4 states at oxygen vacancy sites, we investigated whether cerium metal would catalyze a Fenton-like reaction with hydrogen peroxide. Indeed, cerium chloride did exhibit radical production in the presence of hydrogen peroxide, as assessed by relaxation of supercoiled plasmid DNA. Radical production in this reaction was also followed by production of radical cation of 2,2?-azinobis-(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS). Radical scavengers and spin traps were capable of competing with ABTS for radicals produced in this cerium dependent Fenton-like reaction. Electron paramagnetic resonance experiments reveal both hydroxyl radical and superoxide anion in a reaction containing cerium and hydrogen peroxide. Based on these results we propose that cerium is capable of redox-cycling with peroxide to generate damaging oxygen radicals. PMID:18678042

  20. [Conformation aspects of peptide interaction with proteolytic enzymes. Alpha-chymotrypsin catalyzed hydrolysis of the cyclopeptides containing leucyltyrosyl fragments].

    PubMed

    Tsetlin, M M; Ivanov, V T; Ovchinnikov, Y A; Klyosov, A A

    1975-01-01

    The studies were made on the interaction of alpha-chymotrypsin with a series of cyclopeptides cyclo(-L-leucyl-L-tyrosyl-glycyln-), n=4, 6 and 8 (I, II and III respectively), and cyclo(-L-leucyl-L-tryosyl-beta-aminovalero-yl2-) (IV). Compounds I and IV are resistant to enzyme action whereas cyclopeptides II and III proved to be the substrates, their kinetic constants being Km=15.4 and 13.2 mM and kcat=0.54 and 9.53 sec-1 respectively. The binding capacity of cyclopeptides I-IV is evaluated by their competitive inhibition of alpha-chymotrypsin catalyzed hydrolysis of N-acetyl-L-tyrosine methyl ester. PMID:1203366

  1. Molybdenum-catalyzed reduction of molecular dinitrogen under mild reaction conditions.

    PubMed

    Nishibayashi, Yoshiaki

    2012-07-01

    Quite recently we have found two nitrogen fixation systems catalyzed by molybdenum-dinitrogen complexes under mild reaction conditions; one is the transformation of molecular dinitrogen into its synthetic equivalent of ammonia and the other is that into ammonia. A molybdenum-dinitrogen complex bearing two ferrocenyl diphosphines works as a good catalyst in the transformation of molecular dinitrogen into silylamine, where up to 226 equiv are produced based on the catalyst. A dinitrogen-bridged dimolybdenum complex bearing a PNP-type pincer ligand works as a good catalyst in the direct transformation of molecular dinitrogen into ammonia, where up to 23 equiv are produced based on the catalyst. We believe that both systems provide a new aspect in the development of novel nitrogen fixation. PMID:22437849

  2. Multiple mechanisms in Pd(II)-catalyzed S(N)2' reactions of allylic alcohols.

    PubMed

    Ghebreghiorgis, Thomas; Kirk, Brian H; Aponick, Aaron; Ess, Daniel H

    2013-08-01

    Density functional calculations and experiments were used to examine mechanisms of Pd(II) catalyzed intramolecular cyclization and dehydration in acyclic and bicyclic monoallylic diols, a formal S(N)2' reaction. In contrast to the previously proposed syn-oxypalladation mechanism for acyclic monoallylic diols, calculations and experiments strongly suggest that hydrogen bonding templates a hydroxyl group and Pd addition across the alkene and provides a low energy pathway via anti-addition (anti-oxypalladation) followed by intramolecular proton transfer and anti-elimination of water. This anti-addition, anti-elimination pathway also provides a simple rationale for the observed stereospecificity. For bicyclic monoallylic diol compounds, Pd(II) is capable of promoting either anti- or syn-addition. In addition, palladium chloride ligands can mediate proton transfer to promote dehydration when direct intramolecular proton transfer between diol groups is impossible. PMID:23862564

  3. Transition Metal Catalyzed Reactions of Carbohydrates: a Nonoxidative Approach to Oxygenated Organics

    SciTech Connect

    Andrews, Mark

    1997-01-08

    There is a critical need for new environmentally friendly processes in the United States chemical industry as legislative and economic pressures push the industry to zero-waste and cradle-to-grave responsibility for the products they produce. Carbohydrates represent a plentiful, renewable resource, which for some processes might economically replace fossil feedstocks. While the conversion of biomass to fuels, is still not generally economical, the selective synthesis of a commodity or fine chemical, however, could compete effectively if appropriate catalytic conversion systems can be found. Oxygenated organics, found in a variety of products such as nylon and polyester, are particularly attractive targets. We believe that with concerted research efforts, homogeneous transition metal catalyzed reactions could play a significant role in bringing about this future green chemistry technology.

  4. The base catalyzed hydrolysis and condensation reactions of dilute and concentrated TEOS (Tetraethylorthosilicate) solutions: Draft

    SciTech Connect

    Harris, M.T.; Byers, C.H.; Brunson, R.R.

    1989-01-01

    The synthesis of submicron silica particles by the hydrolysis and condensation of dilute and concentrated solutions of tetraethylorthosiliate (TEOS) has been studied in low-molecular weight alcohols (C/sub 1/--C/sub 4/). A base (ammonia) is used to catalyze the reaction. Raman spectroscopy, gas chromatography and the molybdate method are used to establish the hydrolysis and condensation kinetics. Dynamic and classical light-scattering techniques are employed to monitor particle growth and particle number concentration kinetics, and particle size distribution. The effects of solvent and TEOS concentration on the degree of monodispersity of the particles will be discussed. Furthermore, the chemical and particle growth data will be used to test the theories of homogeneous nucleation and coagulative nucleation, which have been proposed as the mechanisms that govern the growth of submicron monodisperse silica particle by TEOS hydrolysis. 13 refs., 4 figs., 1 tab.

  5. Transition-metal-catalyzed carbonylation reactions of olefins and alkynes: a personal account.

    PubMed

    Wu, Xiao-Feng; Fang, Xianjie; Wu, Lipeng; Jackstell, Ralf; Neumann, Helfried; Beller, Matthias

    2014-04-15

    Carbon monoxide was discovered and identified in the 18th century. Since the first applications in industry 80 years ago, academic and industrial laboratories have broadly explored CO's use in chemical reactions. Today organic chemists routinely employ CO in organic chemistry to synthesize all kinds of carbonyl compounds. Despite all these achievements and a century of carbonylation catalysis, many important research questions and challenges remain. Notably, apart from academic developments, industry applies carbonylation reactions with CO on bulk scale. In fact, today the largest applications of homogeneous catalysis (regarding scale) are carbonylation reactions, especially hydroformylations. In addition, the vast majority of acetic acid is produced via carbonylation of methanol (Monsanto or Cativa process). The carbonylation of olefins/alkynes with nucleophiles, such as alcohols and amines, represent another important type of such reactions. In this Account, we discuss our work on various carbonylations of unsaturated compounds and related reactions. Rhodium-catalyzed isomerization and hydroformylation reactions of internal olefins provide straightforward access to higher value aldehydes. Catalytic hydroaminomethylations offer an ideal way to synthesize substituted amines and even heterocycles directly. More recently, our group has also developed so-called alternative metal catalysts based on iridium, ruthenium, and iron. What about the future of carbonylation reactions? CO is already one of the most versatile C1 building blocks for organic synthesis and is widely used in industry. However, because of CO's high toxicity and gaseous nature, organic chemists are often reluctant to apply carbonylations more frequently. In addition, new regulations have recently made the transportation of carbon monoxide more difficult. Hence, researchers will need to develop and more frequently use practical and benign CO-generating reagents. Apart from formates, alcohols, and metal carbonyls, carbon dioxide also offers interesting options. Industrial chemists seek easy to prepare catalysts and patent-free ligands/complexes. In addition, non-noble metal complexes will interest both academic and industrial researchers. The novel Lucite process for methyl methacrylate is an important example of an improved catalyst. This reaction makes use of a specific palladium/bisphosphine catalyst, which led to the successful implementation of the technology. More active and productive catalysts for related carbonylations of less reactive olefins would allow for other large scale applications of this methodology. From an academic point of view, researchers continue to look for selective reactions with more functionalized olefins. Finally, because of the volatility of simple metal carbonyl complexes, carbonylation reactions today remain a domain of homogeneous catalysis. The invention of more stable and recyclable heterogeneous catalysts or metal-free carbonylations (radical carbonylations) will be difficult, but could offer interesting challenges for young chemists. PMID:24564478

  6. Use of the Extraordinary Infrared Transmission of Metallic Subwavelength Arrays To Study the Catalyzed Reaction of Methanol to Formaldehyde on Copper Oxide

    E-print Network

    the Catalyzed Reaction of Methanol to Formaldehyde on Copper Oxide Shaun M. Williams, Kenneth R. Rodriguez scattered out of an incident beam. Commercial nickel mesh has been coated with copper to reduce the hole processes on the Cu surface. The copper oxide catalyzed reaction of methanol has been studied by recording

  7. Enzyme immunoassays as screening tools for catalysts and reaction discovery.

    PubMed

    Créminon, Christophe; Taran, Frédéric

    2015-05-11

    Enzyme immunoassays are incredibly powerful analytical tools for the quantifiable detection of target molecules in complex media. These techniques, which exploit the fantastic specific binding properties of antibodies, are fast, precise, selective and highly sensitive and thus perfectly adapted to high-throughput detection of important analytes. Although immunoassays have been used routinely by biologists for more than 50 years, especially for diagnostic purposes, it is only recently that chemists have used them to address pure chemical problems. In this feature article, we provide an overview of progress in the development of immunoassays and their use in two main fields of organic chemistry: the identification of efficient catalysts in libraries and the discovery of new chemical reactions. PMID:25765583

  8. Nickel-Catalyzed Mizoroki-Heck Reaction of Aryl Sulfonates and Chlorides with Electronically Unbiased Terminal Olefins: High Selectivity for Branched Products

    E-print Network

    Tasker, Sarah Z.

    Achieving high selectivity in the Heck reaction of electronically unbiased alkenes has been a longstanding challenge. Using a nickel-catalyzed cationic Heck reaction, we were able to achieve excellent selectivity for ...

  9. Choline Monooxygenase, an Unusual Iron-Sulfur Enzyme Catalyzing the First Step of Glycine Betaine Synthesis in Plants: Prosthetic Group Characterization and cDNA Cloning

    Microsoft Academic Search

    Bala Rathinasabapathi; Michael Burnet; Brenda L. Russell; Douglas A. Gage; Pao-Chi Liao; Gordon J. Nye; Paul Scott; John H. Golbeck; Andrew D. Hanson

    1997-01-01

    Plants synthesize the osmoprotectant glycine betaine via the route choline --> betaine aldehyde --> glycine betaine. In spinach, the first step is catalyzed by choline monooxygenase (CMO), a ferredoxin-dependent stromal enzyme that has been hypothesized to be an oligomer of identical subunits and to be an Fe-S protein. Analysis by HPLC and matrix-assisted laser desorption ionization MS confirmed that native

  10. A preliminary investigation of acid-catalyzed polymerization reactions of shale oil distillates

    SciTech Connect

    Netzel, D.A.

    1991-04-01

    Sinor (1989) reported that a major specialty market may exist for shale oil as an asphalt blending material. Shale oil can be converted to an asphalt blending material by acid catalyzed condensation and polymerization reactions of the many molecular species comprising the composition of shale oil. To simplify the investigation, crude shale oil was separated by distillation into three distillates of different hydrocarbon and heteroaromatic compositions. These distillates were then treated with two different types of acids to determine the effect of acid type on the end products. Three western shale oil distillates, a naphtha, a middle distillate, and an atmospheric gas oil, were reacted with anhydrous AlCl{sub 3} and 85% H{sub 2}SO{sub 4} under low-severity conditions. At relatively low temperatures, little change in the hydrocarbon composition was noted for the AlCl{sub 3} reactions. AlCl{sub 3}{center_dot} (a polymerized product and/or complex) was formed. However, it is assumed that the sludge was mainly the result of heteroaromatic-AlCl{sub 3} reactions.

  11. A preliminary investigation of acid-catalyzed polymerization reactions of shale oil distillates

    SciTech Connect

    Netzel, D.A.

    1991-04-01

    Sinor (1989) reported that a major specialty market may exist for shale oil as an asphalt blending material. Shale oil can be converted to an asphalt blending material by acid catalyzed condensation and polymerization reactions of the many molecular species comprising the composition of shale oil. To simplify the investigation, crude shale oil was separated by distillation into three distillates of different hydrocarbon and heteroaromatic compositions. These distillates were then treated with two different types of acids to determine the effect of acid type on the end products. Three western shale oil distillates, a naphtha, a middle distillate, and an atmospheric gas oil, were reacted with anhydrous AlCl{sub 3} and 85% H{sub 2}SO{sub 4} under low-severity conditions. At relatively low temperatures, little change in the hydrocarbon composition was noted for the AlCl{sub 3} reactions. AlCl{sub 3}{center dot} (a polymerized product and/or complex) was formed. However, it is assumed that the sludge was mainly the result of heteroaromatic-AlCl{sub 3} reactions.

  12. Probing the Diastereoselectivity of Staudinger Reactions Catalyzed by N-Heterocyclic Carbenes.

    PubMed

    Hans, Morgan; Wouters, Johan; Demonceau, Albert; Delaude, Lionel

    2015-07-20

    The reaction of ethylphenylketene with 1,3-dimesitylimidazol-2-ylidene (IMes) or 1,3-dimesitylimidazolin-2-ylidene (SIMes) afforded the corresponding azolium enolates in high yields. The two zwitterions were fully characterized by various analytical techniques. Their thermal stabilities were monitored by thermogravimetric analysis and the molecular structure of SIMes?EtPhC?C?O was determined by means of X-ray crystallography. A mechanism was proposed to account for the trans-diastereoselectivity observed in the [2+2] cycloaddition of ketenes and N-protected imines catalyzed by N-heterocyclic carbenes and an extensive catalytic screening was performed to test its validity. The steric bulk of the NHC catalyst markedly affected the cis/trans ratio of the model ?-lactam product. The nature of the solvent used to carry out the Staudinger reaction also significantly influenced its diastereoselectivity. Conversely, the nature of the substituent on the N-sulfonated imine reagent and the reaction temperature were less critical parameters. PMID:26073307

  13. Gold atoms stabilized on various supports catalyze the water-gas shift reaction.

    PubMed

    Flytzani-Stephanopoulos, Maria

    2014-03-18

    For important chemical reactions that are catalyzed by single-site metal centers, such as the water-gas shift (WGS) reaction that converts carbon monoxide and water to hydrogen and carbon dioxide, atomically dispersed supported metal catalysts offer maximum atom efficiency. Researchers have found that for platinum metal supported on ceria and doped ceria in the automobile exhaust catalyst, atomic Pt-Ox-Ce species are the active WGS reaction sites. More recently, preparations of gold at the nanoscale have shown that this relatively "new material" is an active and often more selective catalyst than platinum for a variety of reactions, including the WGS reaction. The activity of gold is typically attributed to a size effect, while the interface of gold with the support has also been reported as important for oxidation reactions, but exactly how this comes about has not been probed satisfactorily. Typical supported metal catalysts prepared by traditional techniques have a heterogeneous population of particles, nanoclusters, subnanometer species, and isolated atoms/ions on the support surfaces, making the identification of the active sites difficult. Both we and other researchers have clearly shown that gold nanoparticles are spectator species in the WGS reaction. Evidence has now amassed that the gold active site for the WGS reaction is atomic, that is, Au-Ox species catalyze the reaction, similar to Pt-Ox. In this Account, we review the relevant literature to conclude that the intrinsic activity of the Au-Ox(OH)-S site, where S is a support, is the same for any S. The support effect is indirect, through its carrying (or binding) capacity for the active sites. Destabilization of the gold under reducing conditions through the formation of clusters and nanoparticles is accompanied by a measurable activity loss. Therefore, it is necessary to investigate the destabilizing effect of different reaction gas mixtures on the gold atom sites and to consider regeneration methods that effectively redisperse the gold clusters into atoms. For gold catalysts, we can remove weakly bound clusters and nanoparticles from certain supports by leaching techniques. Because of this, we can prepare a uniform dispersion of gold atoms/ions strongly bound to the support surface by this two-step (loading followed by leaching) approach. Presently, one-step preparation methods to maximize the number of the single atom sites on various supports need to be developed, specific to the type of the selected support. Often, it will be beneficial to alter the surface properties of the support to enhance metal ion anchoring, for example, by shape and size control of the support or by the use of light-assisted deposition and anchoring of the metal on photoresponsive supports. Because of their importance for practical catalyst development, synthesis methods are discussed at some length in this Account. PMID:24266870

  14. Lewis Acid and/or Lewis Base catalyzed [3+2] cycloaddition reaction: Synthesis of pyrazoles and pyrazolines

    E-print Network

    Paris-Sud XI, Université de

    1 Lewis Acid and/or Lewis Base catalyzed [3+2] cycloaddition reaction: Synthesis of pyrazoles-Hillman adducts, activated and simple alkynes to afford 3,5-disubstituted pyrazolines and pyrazoles respectively trichloride, activated olefins, Baylis- Hillman adducts, pyrazolines, pyrazoles. Formation of heterocycles

  15. Nickel-Catalyzed C?O/C?H Cross-Coupling Reactions for C?C Bond Formation.

    PubMed

    Chen, Tieqiao; Han, Li-Biao

    2015-07-20

    Halides not required: Nickel-catalyzed C?O/C?H cross-couplings for the construction of C?C bonds have recently been disclosed. By carefully optimizing the nickel catalyst, new C?C bond-forming reactions were developed, and even quaternary stereogenic centers are now accessible in high yields from readily available phenoxide derivatives and hydrocarbons. PMID:26073575

  16. N-Heterocyclic carbene-catalyzed diastereoselective synthesis of ?-lactone-fused cyclopentanes using homoenolate annulation reaction.

    PubMed

    Mukherjee, Subrata; Mondal, Santigopal; Patra, Atanu; Gonnade, Rajesh G; Biju, Akkattu T

    2015-05-26

    NHC-catalyzed annulation of enals with 2-enoylpyridines or 2-enoylpyridine N-oxides leading to the diastereoselective synthesis of ?-lactone-fused cyclopentanes is reported. The reaction proceeds via the generation of homoenolate equivalent intermediates and tolerates a broad range of functional groups. PMID:25972189

  17. Hybrid single nanoreactor for in situ SERS monitoring of plasmon-driven and small Au nanoparticles catalyzed reactions.

    PubMed

    Li, Pan; Ma, Bingbing; Yang, Liangbao; Liu, Jinhuai

    2015-07-01

    A hybrid single nanoreactor composed of small Au nanoparticles (NPs) and a long Ag nanowire (NW) with a length of 10 ?m can be conveniently located by optical microscopy, allowing us to monitor by in situ surface enhanced Raman spectroscopy (SERS) the plasmon-driven and small Au NPs catalyzed reactions with high sensitivity and reproducibility. PMID:26087227

  18. Iron- and indium-catalyzed reactions toward nitrogen- and oxygen-containing saturated heterocycles.

    PubMed

    Cornil, Johan; Gonnard, Laurine; Bensoussan, Charlélie; Serra-Muns, Anna; Gnamm, Christian; Commandeur, Claude; Commandeur, Malgorzata; Reymond, Sébastien; Guérinot, Amandine; Cossy, Janine

    2015-03-17

    A myriad of natural and/or biologically active products include nitrogen- and oxygen-containing saturated heterocycles, which are thus considered as attractive scaffolds in the drug discovery process. As a consequence, a wide range of reactions has been developed for the construction of these frameworks, much effort being specially devoted to the formation of substituted tetrahydropyrans and piperidines. Among the existing methods to form these heterocycles, the metal-catalyzed heterocyclization of amino- or hydroxy-allylic alcohol derivatives has emerged as a powerful and stereoselective strategy that is particularly interesting in terms of both atom-economy and ecocompatibility. For a long time, palladium catalysts have widely dominated this area either in Tsuji-Trost reactions [Pd(0)] or in an electrophilic activation process [Pd(II)]. More recently, gold-catalyzed formation of saturated N- and O-heterocycles has received growing attention because it generally exhibits high efficiency and diastereoselectivity. Despite their demonstrated utility, Pd- and Au-complexes suffer from high costs, toxicity, and limited natural abundance, which can be barriers to their widespread use in industrial processes. Thus, the replacement of precious metals with less expensive and more environmentally benign catalysts has become a challenging issue for organic chemists. In 2010, our group took advantage of the ability of the low-toxicity and inexpensive FeCl3 in activating allylic or benzylic alcohols to develop iron-catalyzed N- and O-heterocylizations. We first focused on N-heterocycles, and a variety of 2,6-disubstituted piperidines as well as pyrrolidines were synthesized in a highly diastereoselective fashion in favor of the cis-compounds. The reaction was further extended to the construction of substituted tetrahydropyrans. Besides triggering the formation of heterocycles, the iron salts were shown to induce a thermodynamic epimerization, which is the key to reach the high diastereoselectivities observed in favor of the most stable cis-isomers. It is worth noting that spiroketals could be prepared by using this method, which was successfully applied to a synthetic approach toward natural products belonging to the bistramide family. We then turned our attention to heterocycles incorporating two heteroatoms such as isoxazolidines. These frameworks can be found in biologically active natural products, and in addition, they can be transformed into 1,3-amino alcohols, which are of importance in organic chemistry. The use of FeCl3·6H2O allowed the access to a large variety of 3,5-disubstituted isoxazolidines from ?-hydroxylamino allylic alcohol derivatives with good yields and diastereoselectivities in favor of the cis-isomer. Recently, a Lewis acid-catalyzed synthesis of six- and five-membered ring carbonates starting from linear tert-butyl carbonates was reported. In some cases, the mild and chemoselective InCl3 was preferred over FeCl3·6H2O to avoid side-product formation. The resulting cyclic carbonates were easily transformed into 1,3- or 1,2-diols, and a total synthesis of (3S,5S)-alpinikatin was achieved. PMID:25674664

  19. Inactivation of Key Metabolic Enzymes by Mixed-Function Oxidation Reactions: Possible Implication in Protein Turnover and Ageing

    Microsoft Academic Search

    Laura Fucci; Cynthia N. Oliver; Minor J. Coon; Earl R. Stadtman

    1983-01-01

    Several mixed-function oxidation systems catalyze the inactivation of Escherichia coli glutamine synthetase. Inactivation involves modification of a single histidine residue in each enzyme subunit and makes the enzyme susceptible to proteolytic degradation. We show here that 10 key enzymes in metabolism are inactivated by a bacterial NADH oxidase and by an oxidase system comprised of NADPH, cytochrome P-450 reductase, and

  20. Can laccases catalyze bond cleavage in lignin?

    PubMed

    Munk, Line; Sitarz, Anna K; Kalyani, Dayanand C; Mikkelsen, J Dalgaard; Meyer, Anne S

    2015-01-01

    Modification of lignin is recognized as an important aspect of the successful refining of lignocellulosic biomass, and enzyme-assisted processing and upcycling of lignin is receiving significant attention in the literature. Laccases (EC 1.10.3.2) are taking the centerstage of this attention, since these enzymes may help degrading lignin, using oxygen as the oxidant. Laccases can catalyze polymerization of lignin, but the question is whether and how laccases can directly catalyze modification of lignin via catalytic bond cleavage. Via a thorough review of the available literature and detailed illustrations of the putative laccase catalyzed reactions, including the possible reactions of the reactive radical intermediates taking place after the initial oxidation of the phenol-hydroxyl groups, we show that i) Laccase activity is able to catalyze bond cleavage in low molecular weight phenolic lignin model compounds; ii) For laccases to catalyze inter-unit bond cleavage in lignin substrates, the presence of a mediator system is required. Clearly, the higher the redox potential of the laccase enzyme, the broader the range of substrates, including o- and p-diphenols, aminophenols, methoxy-substituted phenols, benzenethiols, polyphenols, and polyamines, which may be oxidized. In addition, the currently available analytical methods that can be used to detect enzyme catalyzed changes in lignin are summarized, and an improved nomenclature for unequivocal interpretation of the action of laccases on lignin is proposed. PMID:25560931

  1. Biaryl phosphites: new efficient adaptative ligands for Pd-catalyzed asymmetric allylic substitution reactions.

    PubMed

    Diéguez, Montserrat; Pàmies, Oscar

    2010-02-16

    Pharmaceuticals, agrochemicals, fragrances, fine chemicals, and natural product chemistry all rely on the preparation of enantiomerically enriched compounds. The palladium-catalyzed asymmetric allylic substitution, which allows for the enantioselective formation of carbon-carbon and carbon-heteroatom bonds, is a potential synthetic tool for preparing these compounds. To date, most of the successful ligands reported for the Pd-catalyzed allylic substitution reactions have used three main design strategies. The first, developed by Hayashi and co-workers, used a secondary interaction of the nucleophile with a side chain of the ligand to direct the approach of the nucleophile to one of the allylic terminal carbon atoms. The second increased the ligand's bite angle in order to create a chiral cavity in which the allyl system is perfectly embedded. To discriminate electronically between the two allylic terminal carbon atoms, the third strategy employed heterodonor ligands. Although many chiral ligands have been successfully applied in the substitution of several disubstituted substrates, problems generally remain with both substrate specificity and reaction rates using these methods. Other substrates, such as those that are monosubstituted, will require more active and more regio- and enantioselective Pd-catalysts. Overcoming these limitations requires research toward the development of new ligands. This Account discusses the application of homo- and heterodonor biaryl-containing phosphites as new, versatile, and highly effective ligands in the Pd-catalyzed asymmetric allylic substitution of several substrate types. We and others recently demonstrated that the inclusion of biarylphosphite moieties in ligand design is highly advantageous. In these systems, the catalyst's substrate specificity decreases because the chiral pocket created (the chiral cavity with the embedded allyl ligand) is flexible enough to allow the perfect coordination of hindered and unhindered substrates. Reaction rates with these ligands increase because of the larger pi-acceptor ability of these moieties. The ability of the phosphite moiety to accept pi-electrons and enhance the S(N)1 character of the nucleophilic attack increases the regioselectivity of the reactions toward the desired branched isomer in monosubstituted linear substrates. Finally, the easy synthesis of biaryl phosphites from readily available alcohols allows for simple ligand tuning as well as systematic modifications of several important ligand parameters. Taking advantage of these features, we and others have designed highly adaptative biaryl-phosphite-containing ligands for asymmetric Pd-allylic substitution reactions. In this context, several diphosphites, phosphite-oxazolines, and phosphite-phosphoroamidites have recently emerged as extremely effective ligands for this process. Using a broad range of mono- and disubstituted hindered and unhindered linear and cyclic substrates, we have obtained high activities (turnover frequencies up to 22,000 mol substrate x (mol Pd x h)(-1)) unprecedented in the literature along with excellent regio- (up to 99%) and enantioselectivitites (up to >99%) at low catalyst loadings (turnover numbers up to 10,000 mol substrate x (mol Pd x h)(-1)). Appropriate ligand tuning allows access to both enantiomers of the substitution products. PMID:19886655

  2. Reaction mechanism of the direct gas phase synthesis of H2O2 catalyzed by Au3

    Microsoft Academic Search

    Bosiljka Njegic; Mark S. Gordon

    2008-01-01

    The gas phase reaction of molecular oxygen and hydrogen catalyzed by a Au3 cluster to yield H2O2 was investigated theoretically using second order Z-averaged perturbation theory, with the final energies obtained with the fully size extensive completely renormalized CR-CC(2,3) coupled cluster theory. The proposed reaction mechanism is initiated by adsorption and activation of O2 on the Au3 cluster. Molecular hydrogen

  3. Cu-catalyzed oxidative Povarov reactions between N-alkyl N-methylanilines and saturated oxa- and thiacycles.

    PubMed

    Kawade, Rahul Kisan; Huple, Deepak B; Lin, Rong-Jing; Liu, Rai-Shung

    2015-04-18

    Cu-catalyzed oxidative Povarov reactions between N,N-dialkylanilines and saturated oxa- or thiacycles with tert-butyl hydroperoxide (TBHP) are described; notably, the reactions use neither [4?] nor [2?]-motifs as the initial reagents. The use of cheap alkane-based substances as building units is of mechanistic and practical interest as two inert sp(3) C-H bonds are activated. PMID:25777971

  4. A new synthetic approach towards N-alkylated 2- epi-valienamines via palladium-catalyzed coupling reaction

    Microsoft Academic Search

    Stanton H. L Kok; Tony K. M Shing

    2000-01-01

    Preparation of N-alkylated 2-epi-valienamines was accomplished by the palladium-catalyzed coupling reaction of the allylic chloride 5 with various amines in the presence of trimethylolpropane phosphite (TMPP). The 2-epi-valienamine precursor (i.e. allylic chloride 5) was obtained from the reaction of diol 2 with Viehe's salt and the diol 2 was readily prepared from (?)-quinic acid in 10 steps.

  5. Characterization of the reaction product of the oriT nicking reaction catalyzed by Escherichia coli DNA helicase I.

    PubMed Central

    Matson, S W; Nelson, W C; Morton, B S

    1993-01-01

    DNA helicase I, encoded on the Escherichia coli F plasmid, catalyzes a site- and strand-specific nicking reaction within the F plasmid origin of transfer (oriT) to initiate conjugative DNA strand transfer. The product of the nicking reaction contains a single phosphodiester bond interruption as determined by single-nucleotide resolution mapping of both sides of the nick site. This analysis has demonstrated that the nick is located at precisely the same site previously shown to be nicked in vivo (T. L. Thompson, M. B. Centola, and R. C. Deonier, J. Mol. Biol. 207:505-512, 1989). In addition, studies with two oriT point mutants have confirmed the specificity of the in vitro reaction. Characterization of the nicked DNA product has revealed a modified 5' end and a 3' OH available for extension by E. coli DNA polymerase I. Precipitation of nicked DNA with cold KCl in the presence of sodium dodecyl sulfate suggests the existence of protein covalently attached to the nicked DNA molecule. The covalent nature of this interaction has been directly demonstrated by transfer of radiolabeled phosphate from DNA to protein. On the basis of these results, we propose that helicase I becomes covalently bound to the 5' end of the nicked DNA strand as part of the reaction mechanism for phosphodiester bond cleavage. A model is presented to suggest how helicase I could nick the F plasmid at oriT and subsequently unwind the duplex DNA to provide single-stranded DNA for strand transfer during bacterial conjugation. Images PMID:8386720

  6. Atomic layer deposition of SiO 2 at room temperature using NH 3-catalyzed sequential surface reactions

    Microsoft Academic Search

    J. W. Klaus; S. M. George

    2000-01-01

    Ultrathin SiO2 films were deposited at 300–338K with atomic layer control using NH3-catalyzed sequential surface reactions. The SiO2 deposition was achieved by splitting the reaction SiCl4+2H2O?SiO2+4HCl into two separate SiCl4 and H2O half-reactions. Successive application of the half-reactions in an ABAB… sequence produced atomic layer controlled SiO2 growth. The NH3 catalyst dramatically lowered the necessary deposition temperature from >600 to

  7. Several dinucleoside polyphosphates are acceptor substrates in the T4 RNA ligase catalyzed reaction.

    PubMed

    Atencia, E A; Montes, M; Günther Sillero, M A; Sillero, A

    2000-03-01

    Several dinucleoside polyphosphates accept cytidine-3', 5'-bisphosphate from the adenylylated donor 5'-adenylylated cytidine 5',3'-bisphosphate in the T4 RNA ligase catalyzed reaction. The 5'-adenylylated cytidine 5',3'-bisphosphate synthesized in a first step, from ATP and cytidine-3',5'-bisphosphate, is used as a substrate to transfer the cytidine-3',5'-bisphosphate residue to the 3'-OH group(s) of diguanosine tetraphosphate (Gp4G) giving rise to Gp4GpCp and pCpGp4GpCp in a ratio of approximately 10 : 1, respectively. The synthesized Gp4GpCp was characterized by treatment with snake venom phosphodiesterase and alkaline phosphatase and analysis (chromatographic position and UV spectra) of the reaction products by HPLC. The apparent Km values measured for Gp4G and 5'-adenylylated cytidine 5',3'-bisphosphate in this reaction were approximately 4 mM and 0.4 mM, respectively. In the presence of 0.5 mM ATP and 0.5 mM cytidine-3',5'-bisphosphate, the relative efficiencies of the following nucleoside(5')oligophospho(5')nucleosides as acceptors of cytidine-3',5'-bisphosphate from 5'-adenylylated cytidine 5', 3'-bisphosphate are indicated in parentheses: Gp4G (100); Gp5G (101); Ap4G (47); Ap4A (39). Gp2G, Gp3G and Xp4X were not substrates of the reaction. Dinucleotides containing two guanines and at least four inner phosphates were the preferred acceptors of cytidine-3', 5'-bisphosphate at their 3'-OH group(s). PMID:10712602

  8. Selectivity of montmorillonite catalyzed prebiotic reactions of D, L-nucleotides

    NASA Astrophysics Data System (ADS)

    Joshi, Prakash C.; Pitsch, Stefan; Ferris, James P.

    2007-02-01

    The montmorillonite-catalyzed reactions of the 5?-phosphorimidazolides of D, L-adenosine (D, L-ImpA) (Figure 1a. N = A, R = H) and D, L-uridine (Figure 1a., N = U, R = H) yields oligomers that were as long as 7 mers and 6 mers, respectively. The reactions of dilute solutions of D-ImpA and D-ImpU under the same conditions gave oligomers as long as 9 and 8 mers respectively. This demonstrated that oligomer formation is only partially inhibited by incorporation of both the D- and L-enantiomers. The structures of the dimers, trimers and tetramer fractions formed from D, L-ImpA was investigated by selective enzymatic hydrolysis, comparison with authentic samples and mass spectrometry. Homochiral products were present in greater amounts than would be expected if theoretical amounts of each were formed. The ratio of the proportion of homochiral products to that of the amount of each expected for the dimers (cyclic and linear), trimers and tetramers, was 1.3, 1.6, and 2.1, respectively. In the D, L-ImpU reaction homochiral products did not predominate with ratios of dimers (cyclic and linear), trimers and tetramers 0.8, 0.44, and 1.4, respectively. The proportions of cyclic dimers in the dimer fraction were 52 66% with D, L-ImpA and 44 69% with D, L-ImpU. No cyclic dimers were formed in the absence of montmorillonite. The differences in the reaction products of D, L-ImpA and D, L-ImpU are likely to be due to the difference in the orientations of the activated monomers when bound to the catalytic sites on montmorillonite. The consequences of the selectivity of montmorillonite as a prebiotic catalyst are discussed.

  9. Purification, Identification, and Cloning of Lysoplasmalogenase, the Enzyme That Catalyzes Hydrolysis of the Vinyl Ether Bond of Lysoplasmalogen*

    PubMed Central

    Wu, Lai-Chu; Pfeiffer, Douglas R.; Calhoon, Elisabeth A.; Madiai, Francesca; Marcucci, Guido; Liu, Shujun; Jurkowitz, Marianne S.

    2011-01-01

    Lysoplasmalogenase (EC 3.3.2.2 and EC 3.3.2.5) is an enzyme that catalyzes hydrolytic cleavage of the vinyl ether bond of lysoplasmalogen, forming fatty aldehyde and glycerophosphoethanolamine or glycerophosphocholine and is specific for the sn-2-deacylated form of plasmalogen. Here we report the purification, characterization, identification, and cloning of lysoplasmalogenase. Rat liver microsomal lysoplasmalogenase was solubilized with octyl glucoside and purified 500-fold to near homogeneity using four chromatography steps. The purified enzyme has apparent Km values of ?50 ?m for both lysoplasmenylcholine and lysoplasmenylethanolamine and apparent Vm values of 24.5 and 17.5 ?mol/min/mg protein for the two substrates, respectively. The pH optimum was 7.0. Lysoplasmalogenase was competitively inhibited by lysophosphatidic acid (Ki ?20 ?m). The predominant band on a gel at ?19 kDa was subjected to trypsinolysis, and the peptides were identified by mass spectrometry as Tmem86b, a protein of unknown function. Transient transfection of human embryonic kidney (HEK) 293T cells showed that TMEM86b cDNA yielded lysoplasmalogenase activity, and Western blot analyses confirmed the synthesis of TMEM86b protein. The protein was localized in the membrane fractions. The TMEM86b gene was also transformed into Escherichia coli, and its expression was verified by Western blot and activity analyses. Tmem86b is a hydrophobic transmembrane protein of the YhhN family. Northern blot analyses demonstrated that liver expressed the highest level of Tmem86b, which agreed with tissue distribution of activity. Overexpression of TMEM86b in HEK 293T cells resulted in decreased levels of plasmalogens, suggesting that the enzyme may be important in regulating plasmalogen levels in animal cells. PMID:21515882

  10. Molecular cloning and characterization of norcoclaurine synthase, an enzyme catalyzing the first committed step in benzylisoquinoline alkaloid biosynthesis.

    PubMed

    Samanani, Nailish; Liscombe, David K; Facchini, Peter J

    2004-10-01

    (S)-Norcoclaurine synthase (NCS) (EC 4.2.1.78) catalyzes the condensation of 3,4-dihydroxyphenylethylamine (dopamine) and 4-hydroxyphenylacetaldehyde (4-HPAA) as the first committed step in the biosynthesis of benzylisoquinoline alkaloids such as morphine, sanguinarine, and berberine, in plants. A molecular clone encoding NCS was isolated from a meadow rue (Thalictrum flavum ssp. glaucum) cell suspension culture cDNA library. Heterologous expression of the NCS cDNA, truncated to remove a putative signal peptide, produced a recombinant protein with NCS activity. Recombinant NCS showed sigmoidal saturation kinetics for dopamine (Hill coefficient=1.98), hyperbolic saturation kinetics for 4-HPAA (Km of 700 microm), and pH and temperature optima of 7.0 and 40 degrees C, respectively, all similar to the purified, plant-derived enzyme. NCS exhibits 28-38% identity, and putative structural homology, with the Bet v 1 allergen and pathogenesis-related (PR)10 protein families. NCS also displays 35% identity with the enzyme (HYP1) responsible for hypericin biosynthesis in St John's wort (Hypericum perforatum). The novel catalytic functions of NCS and HYP1 define a new class of plant secondary metabolic enzymes within the Bet v 1 and PR10 protein families. Weaker homology was also detected between NCS and proteins identified in the latex of Papaver somniferum (opium poppy), and in Arabidopsis thaliana. A family of three to five NCS genes is abundantly expressed in the rhizome, followed by petioles and roots of T. flavum. NCS transcripts were localized to the immature endodermis and pericycle in roots, and the protoderm of leaf primordia in rhizomes; thus, the sites of NCS gene expression and berberine accumulation are temporally and spatially separated in roots and rhizomes respectively. PMID:15447655

  11. PURIFICATION AND ISOLATION OF THE PHOSPHOGLYCERATE KINASE ENZYME

    E-print Network

    Collins, Gary S.

    PURIFICATION AND ISOLATION OF THE PHOSPHOGLYCERATE KINASE ENZYME IN RICE PLANTS Cynthia Bach (NADH). The enzyme, phosphoglycerate kinase (PGKase), catalyzes the reaction that results to purify the enzyme from developing rice seeds. Isolation of the enzyme was obtained by obtaining a crude

  12. Reaction Pathways and Energetics of Etheric C?O Bond Cleavage Catalyzed by Lanthanide Triflates

    SciTech Connect

    Assary, Rajeev S.; Atesin, Abdurrahman C.; Li, Zhi; Curtiss, Larry A.; Marks, Tobin J.

    2013-07-15

    Efficient and selective cleavage of etheric C?O bonds is crucial for converting biomass into platform chemicals and liquid transportation fuels. In this contribution, computational methods at the DFT B3LYP level of theory are employed to understand the efficacy of lanthanide triflate catalysts (Ln(OTf)3, Ln = La, Ce, Sm, Gd, Yb, and Lu) in cleaving etheric C?O bonds. In agreement with experiment, the calculations indicate that the reaction pathway for C?O cleavage occurs via a C?H ? O?H proton transfer in concert with weakening of the C?O bond of the coordinated ether substrate to ultimately yield a coordinated alkenol. The activation energy for this process falls as the lanthanide ionic radius decreases, reflecting enhanced metal ion electrophilicity. Details of the reaction mechanism for Yb(OTf)3-catalyzed ring opening are explored in depth, and for 1-methyl-d3-butyl phenyl ether, the computed primary kinetic isotope effect of 2.4 is in excellent agreement with experiment (2.7), confirming that etheric ring-opening pathway involves proton transfer from the methyl group alpha to the etheric oxygen atom, which is activated by the electrophilic lanthanide ion. Calculations of the catalytic pathway using eight different ether substrates indicate that the more rapid cleavage of acyclic versus cyclic ethers is largely due to entropic effects, with the former C?O bond scission processes increasing the degrees of freedom/particles as the transition state is approached.

  13. Low temperature iron- and nickel-catalyzed reactions leading to coalbed gas formation

    SciTech Connect

    Medina, J.C.; Butala, S.J.; Bartholomew, C.H.; Lee, M.L.

    2000-02-01

    Hydrocarbon hydrogenolysis and CO{sub 2} hydrogenation in the presence of Fe/SiO{sub 2} and Ni/SiO{sub 2} catalysts were evaluated as potential mechanisms contributing to natural gas formation in coalbeds. The hydrocarbons used as reactants in hydrogenolysis included butane, octane, 1-octene, and 1-dodecene. The reactions carried out in a laboratory batch reactor produced gas that contained methane concentrations greater than 90%, which resembles the composition of natural gas. Reaction temperatures were selected to resemble natural coalbed conditions. Evidence is presented to show that iron and nickel minerals, which can be present in coals at levels of 2,000 and 10 ppm, respectively, can become active under geologic conditions. The oxides (Fe{sub 2}O{sub 3} and NiO) used as precursors of the active catalysts (Fe and Ni metals) were reduced at 200 C under a hydrogen atmosphere. Moessbauer spectroscopy showed that ca. 6% of the iron oxide was converted to the metal; in the case of nickel, oxygen titration showed that the extent of reduction to the metal was ca. 29%. The resultant fractions of the active metals in coals are adequate to catalyze generation of appreciable amounts of methane over geologic time.

  14. Analysis of the HindIII-catalyzed reaction by time-resolved crystallography

    PubMed Central

    Kawamura, Takashi; Kobayashi, Tomoki; Watanabe, Nobuhisa

    2015-01-01

    In order to investigate the mechanism of the reaction catalyzed by HindIII, structures of HindIII–DNA complexes with varying durations of soaking time in cryoprotectant buffer containing manganese ions were determined by the freeze-trap method. In the crystal structures of the complexes obtained after soaking for a longer duration, two manganese ions, indicated by relatively higher electron density, are clearly observed at the two metal ion-binding sites in the active site of HindIII. The increase in the electron density of the two metal-ion peaks followed distinct pathways with increasing soaking times, suggesting variation in the binding rate constant for the two metal sites. DNA cleavage is observed when the second manganese ion appears, suggesting that HindIII uses the two-metal-ion mechanism, or alternatively that its reactivity is enhanced by the binding of the second metal ion. In addition, conformational change in a loop near the active site accompanies the catalytic reaction. PMID:25664735

  15. Low temperature iron- and nickel-catalyzed reactions leading to coalbed gas formation

    NASA Astrophysics Data System (ADS)

    Medina, Juan Carlos; Butala, Steven J.; Bartholomew, Calvin H.; Lee, Milton L.

    2000-02-01

    Hydrocarbon hydrogenolysis and CO 2 hydrogenation in the presence of Fe/SiO 2 and Ni/SiO 2 catalysts were evaluated as potential mechanisms contributing to natural gas formation in coalbeds. The hydrocarbons used as reactants in hydrogenolysis included butane, octane, 1-octene, and 1-dodecene. The reactions carried out in a laboratory batch reactor produced gas that contained methane concentrations greater than 90%, which resembles the composition of natural gas. Reaction temperatures were selected to resemble natural coalbed conditions. Evidence is presented to show that iron and nickel minerals, which can be present in coals at levels of 2000 and 10 ppm, respectively, can become active under geologic conditions. The oxides (Fe 2O 3 and NiO) used as precursors of the active catalysts (Fe and Ni metals) were reduced at 200°C under a hydrogen atmosphere. Mössbauer spectroscopy showed that ca. 6% of the iron oxide was converted to the metal; in the case of nickel, oxygen titration showed that the extent of reduction to the metal was ca. 29%. The resultant fractions of the active metals in coals are adequate to catalyze generation of appreciable amounts of methane over geologic time.

  16. de novo computational enzyme design.

    PubMed

    Zanghellini, Alexandre

    2014-10-01

    Recent advances in systems and synthetic biology as well as metabolic engineering are poised to transform industrial biotechnology by allowing us to design cell factories for the sustainable production of valuable fuels and chemicals. To deliver on their promises, such cell factories, as much as their brick-and-mortar counterparts, will require appropriate catalysts, especially for classes of reactions that are not known to be catalyzed by enzymes in natural organisms. A recently developed methodology, de novo computational enzyme design can be used to create enzymes catalyzing novel reactions. Here we review the different classes of chemical reactions for which active protein catalysts have been designed as well as the results of detailed biochemical and structural characterization studies. We also discuss how combining de novo computational enzyme design with more traditional protein engineering techniques can alleviate the shortcomings of state-of-the-art computational design techniques and create novel enzymes with catalytic proficiencies on par with natural enzymes. PMID:24794534

  17. Metal requirements of the enzymes catalyzing conversion of glutamate to delta-aminolevulinic acid in extracts of Chlorella vulgaris and Synechocystis sp. PCC 6803.

    PubMed

    Mayer, S M; Rieble, S; Beale, S I

    1994-07-01

    In the biosynthetic conversion of glutamate to the tetrapyrrole precursor, delta-aminolevulinic acid (ALA), glutamate is activated at C-1 by glutamyl-tRNA synthetase-catalyzed ligation to tRNAGlu. Glutamyl-tRNA reductase next catalyzes reduction of the activated glutamate to glutamate-1-semialdehyde (GSA), which is then converted to ALA by GSA aminotransferase. Glutamyl-tRNA synthetase is known to require a divalent metal (usually Mg2+) for activity, but it has not been established whether Mg2+ or another metal ion is also required for glutamyl-tRNA reductase or GSA aminotransferase, because these enzymes have previously been assayed in combined incubations containing all factors required for conversion of glutamate to ALA. We now report the metal requirements individually for each of the three enzyme reactions. Glutamyl-tRNA reductase activity in extracts from both Chlorella vulgaris and Synechocystis sp. PCC 6803 was stimulated by Mg2+ and inhibited by EDTA. EDTA-pretreated Chlorella glutamyl-tRNA reductase-containing fraction had very little activity in the absence of added Mg2+, but recovered full activity in incubations containing added Mg2+. The divalent metal requirement could be met by Mg2+, Mn2+, or Ca2+. Maximum activity was reached at approximately 15 mM concentration of each of these metals, and higher concentrations were inhibitory. Zn2+ was inhibitory at micromolar concentrations. Chlorella glutamyl-tRNA synthetase showed a metal requirement that could be met by Mg2+ or Mn2+, but not Ca2+. Maximum activity was reached at approximately 15 mM Mg2+ or Mn2+. Although the presence of 10 mM Ca2+ did not affect the Mg2+ concentration optimum, Ca2+ increased the effectiveness of low concentrations of Mg2+. In contrast to glutamyl-tRNA synthetase and glutamyl-tRNA reductase, Chlorella GSA aminotransferase did not show a metal requirement or inhibition by EDTA. However, EDTA decreased nonenzymatic transformation of GSA to ALA. PMID:7913310

  18. De Novo Computational Design of Retro-Aldol Enzymes

    Microsoft Academic Search

    Lin Jiang; Eric A. Althoff; Fernando R. Clemente; Lindsey Doyle; Daniela Röthlisberger; Alexandre Zanghellini; Jasmine L. Gallaher; Jamie L. Betker; Fujie Tanaka; Carlos F. Barbas; Donald Hilvert; Kendall N. Houk; Barry L. Stoddard; David Baker

    2008-01-01

    The creation of enzymes capable of catalyzing any desired chemical reaction is a grand challenge for computational protein design. Using new algorithms that rely on hashing techniques to construct active sites for multistep reactions, we designed retro-aldolases that use four different catalytic motifs to catalyze the breaking of a carbon-carbon bond in a nonnatural substrate. Of the 72 designs that

  19. Characterization of hydroxylaminobenzene mutase from pNBZ139 cloned from Pseudomonas pseudoalcaligenes JS45. A highly associated SDS-stable enzyme catalyzing an intramolecular transfer of hydroxy groups.

    PubMed

    He, Z; Nadeau, L J; Spain, J C

    2000-02-01

    Hydroxylaminobenzene mutase is the enzyme that converts intermediates formed during initial steps in the degradation of nitrobenzene to a novel ring-fission lower pathway in Pseudomonas pseudoalcaligenes JS45. The mutase catalyzes a rearrangement of hydroxylaminobenzene to 2-aminophenol. The mechanism of the reactions and the properties of the enzymes are unknown. In crude extracts, the hydroxylaminobenzene mutase was stable at SDS concentrations as high as 2%. A procedure including Hitrap-SP, Hitrap-Q and Cu(II)-chelating chromatography was used to partially purify the enzyme from an Escherichia coli clone. The partially purified enzyme was eluted in the void volume of a Superose-12 gel-filtration column even in the presence of 0.05% SDS in 25 mM Tris/HCl buffer, which indicated that it was highly associated. When the enzymatic conversion of hydroxylaminobenzene to 2-aminophenol was carried out in 18O-labeled water, the product did not contain 18O, as determined by GC-MS. The results indicate that the reaction proceeded by intramolecular transfer of the hydroxy group from the nitrogen to the C-2 position of the ring. The mechanism is clearly different from the intermolecular transfer of the hydroxy group in the non-enzymatic Bamberger rearrangement of hydroxylaminobenzene to 4-aminophenol and in the enzymatic hydroxymutation of chorismate to isochorismate. PMID:10672020

  20. Partial Randomization of the Four Sequential Amidation Reactions Catalyzed by Cobyric Acid Synthetase with a Single Point Mutation†

    PubMed Central

    Fresquet, Vicente; Williams, LaKenya; Raushel, Frank M.

    2008-01-01

    Cobyric acid synthetase (CbiP) from Salmonella typhimurium catalyzes the glutamine and ATP-dependent amidation of carboxylates b, d, e, and g within adenosyl cobyrinic acid a,c-diamide. After each round of catalysis the partially amidated intermediates are released into solution and the four carboxylates are amidated in the sequential order of e, d, b, and g for the wild type enzyme. In the presence of [?-18O4]-ATP and adenosyl cobyrinic a,c-diamide the enzyme will catalyze the positional isotope exchange of the ??-bridge oxygen with the two ?-nonbridge oxygens. This results supports the proposal that ATP is used to activate the carboxylate groups via the formation of a phosphorylated intermediate. CbiP catalyzes the hydrolysis of glutamine in the absence of ATP or adenosyl cobyrinic acid a,c-diamide but the rate of glutamine hydrolysis is enhanced by a factor of 60 in the presence of these two substrates together. This result suggests that the formation of the phosphorylated intermediate is coupled to the activation of the site utilized for the hydrolysis of glutamine. However, the rate of glutamine hydrolysis is approximately 2.5 times the rate of ADP formation, indicating that the two active sites are partially uncoupled from one another and that some of the ammonia from glutamine hydrolysis leaks into the bulk solution. The mutation of D146 to either alanine or asparagine results in a protein that is able to catalyze the formation of cobyric acid. However, the strict amidation order observed with the wild type CbiP is partially randomized with carboxylate b being amidated last. With the D146N mutant, the predominant pathway occurs in the sequence d, e, g, and b. It is proposed that this residue enforces the amidation order in the wild type enzyme via charge-charge repulsion between the side chain carboxylate and the carboxylates of the substrate. PMID:18001139

  1. Reverse reaction of malic enzyme for HCO3- fixation into pyruvic acid to synthesize L-malic acid with enzymatic coenzyme regeneration.

    PubMed

    Ohno, Yoko; Nakamori, Toshihiko; Zheng, Haitao; Suye, Shin-ichiro

    2008-05-01

    Malic enzyme [L-malate: NAD(P)(+) oxidoreductase (EC 1.1.1.39)] catalyzes the oxidative decarboxylation of L-malic acid to produce pyruvic acid using the oxidized form of NAD(P) (NAD(P)(+)). We used a reverse reaction of the malic enzyme of Pseudomonas diminuta IFO 13182 for HCO(3)(-) fixation into pyruvic acid to produce L-malic acid with coenzyme (NADH) generation. Glucose-6-phosphate dehydrogenase (EC1.1.1.49) of Leuconostoc mesenteroides was suitable for coenzyme regeneration. Optimum conditions for the carboxylation of pyruvic acid were examined, including pyruvic acid, NAD(+), and both malic enzyme and glucose-6-phosphate dehydrogenase concentrations. Under optimal conditions, the ratio of HCO(3)(-) and pyruvic acid to malic acid was about 38% after 24 h of incubation at 30 degrees C, and the concentration of the accumulated L-malic acid in the reaction mixture was 38 mM. The malic enzyme reverse reaction was also carried out by the conjugated redox enzyme reaction with water-soluble polymer-bound NAD(+). PMID:18460807

  2. Relating localized protein motions to the reaction coordinate in coenzyme B??-dependent enzymes.

    PubMed

    Jones, Alex R; Levy, Colin; Hay, Sam; Scrutton, Nigel S

    2013-07-01

    The classical picture of enzyme catalysis relies on controlling the entropic and enthalpic contributions by manipulating reaction barriers and co-locating reactants and cofactors to facilitate the reaction chemistry. Catalysis is linked inextricably to the geometry of the enzyme-substrate complex and the chemical/physical properties of the active site, and probably to dynamical contributions that guide reactants along the desired reaction coordinate. Coenzyme B??-dependent enzymes have remarkable catalytic power and unique properties that enable detailed analysis of the reaction chemistry and associated dynamics. Here we discuss recent developments that are beginning to provide atomistic insight into how coenzyme B??-dependent enzymes steer reactants along the reaction coordinate. Such insight will ultimately generate 'movies' of the catalytic process across all relevant time scales. In the longer term, this will enable more predictive engineering of this class of enzyme to achieve new and desirable chemical outcomes. PMID:23462350

  3. Esterification kinetics of triglycerides in n-hexane catalyzed by an immobilized lipase 

    E-print Network

    Gomez Ruiz, Alejandro

    1998-01-01

    The kinetics of enzyme-catalyzed esterification of triglycerides over immobilized lipase in n-hexane was investigated. The reaction kinetics were described in terms of a mechanism developed following the Langmuir-Hinshelwood-Hougen-Watson (LHHW...

  4. Mechanism and stereochemical course at phosphorus of the reaction catalyzed by a bacterial phosphotriesterase

    SciTech Connect

    Lewis, V.E.; Donarski, W.J.; Wild, J.R.; Raushel, F.M.

    1988-03-08

    The reaction mechanism for the phosphotriesterase from Pseudomonas diminuta has been examined. When paraoxon (diethyl 4-nitrophenyl phosphate) is hydrolyzed by this enzyme in oxygen-18-labeled water, the oxygen-18 label is found exclusively in the diethyl phosphate product. The absolute configurations for the (+) and (-) enantiomers of O-ethyl phenylphosphonothioic acid have been determined by X-ray diffraction structural determination of the individual crystalline 1-phenylethylamine salts. The (+) enantiomer of the free acid corresponds to the R/sub P/ configuration. The R/sub P/ enantiomer of O-ethyl phenylphosphonothioic acid has been converted to the S/sub P/ enantiomer of EPN (O-ethyl O-(4-nitrophenyl) phenylphosphonothioate). (S/sub P/)-EPN is hydrolyzed by the phosphotriesterase to the S/sub P/ enantiomer of O-ethyl phenylphosphonothioic acid. The enzymatic reaction therefore proceeds with inversion of configuration. These results have been interpreted as an indication of a single in-line displacement by an activated water molecule directly at the phosphorus center of the phosphotriester substrate. (R/sub P/)-EPN is not hydrolyzed by the enzyme at an appreciable rate.

  5. Stereo-specificity for pro-(R) hydrogen of NAD(P)H during enzyme-catalyzed hydride transfer to CL-20.

    PubMed

    Bhushan, Bharat; Halasz, Annamaria; Hawari, Jalal

    2005-12-01

    A dehydrogenase from Clostridium sp. EDB2 and a diaphorase from Clostridium kluyveri were reacted with CL-20 to gain insights into the enzyme-catalyzed hydride transfer to CL-20, and the enzyme's stereo-specificity for either pro-R or pro-S hydrogens of NAD(P)H. Both enzymes biotransformed CL-20 at rates of 18.5 and 24nmol/h/mg protein, using NADH and NADPH as hydride-source, respectively, to produce a N-denitrohydrogenated product with a molecular weight of 393Da. In enzyme kinetics studies using reduced deuterated pyridine nucleotides, we found a kinetic deuterium isotopic effect of 2-fold on CL-20 biotransformation rate using dehydrogenase enzyme against (R)NADD as a hydride-source compared to either (S)NADD or NADH. Whereas, in case of diaphorase, the kinetic deuterium isotopic effect of about 1.5-fold was observed on CL-20 biotransformation rate using (R)NADPD as hydride-source. In a comparative study with LC-MS, using deuterated and non-deuterated NAD(P)H, we found a positive mass-shift of 1Da in the N-denitrohydrogenated product suggesting the involvement of a deuteride (D(-)) transfer from NAD(P)D. The present study thus revealed that both dehydrogenase and diaphorase enzymes from the two Clostridium species catalyzed a hydride transfer to CL-20 and showed stereo-specificity for pro-R hydrogen of NAD(P)H. PMID:16225844

  6. Stereo-specificity for pro-(R) hydrogen of NAD(P)H during enzyme-catalyzed hydride transfer to CL-20

    SciTech Connect

    Bhushan, Bharat [Biotechnology Research Institute, National Research Council of Canada, 6100 Royalmount Avenue, Montreal, Que., H4P 2R2 (Canada); Halasz, Annamaria [Biotechnology Research Institute, National Research Council of Canada, 6100 Royalmount Avenue, Montreal, Que., H4P 2R2 (Canada); Hawari, Jalal [Biotechnology Research Institute, National Research Council of Canada, 6100 Royalmount Avenue, Montreal, Que., H4P 2R2 (Canada)]. E-mail: jalal.hawari@nrc.ca

    2005-12-02

    A dehydrogenase from Clostridium sp. EDB2 and a diaphorase from Clostridium kluyveri were reacted with CL-20 to gain insights into the enzyme-catalyzed hydride transfer to CL-20, and the enzyme's stereo-specificity for either pro-R or pro-S hydrogens of NAD(P)H. Both enzymes biotransformed CL-20 at rates of 18.5 and 24 nmol/h/mg protein, using NADH and NADPH as hydride-source, respectively, to produce a N-denitrohydrogenated product with a molecular weight of 393 Da. In enzyme kinetics studies using reduced deuterated pyridine nucleotides, we found a kinetic deuterium isotopic effect of 2-fold on CL-20 biotransformation rate using dehydrogenase enzyme against (R)NADD as a hydride-source compared to either (S)NADD or NADH. Whereas, in case of diaphorase, the kinetic deuterium isotopic effect of about 1.5-fold was observed on CL-20 biotransformation rate using (R)NADPD as hydride-source. In a comparative study with LC-MS, using deuterated and non-deuterated NAD(P)H, we found a positive mass-shift of 1 Da in the N-denitrohydrogenated product suggesting the involvement of a deuteride (D{sup -}) transfer from NAD(P)D. The present study thus revealed that both dehydrogenase and diaphorase enzymes from the two Clostridium species catalyzed a hydride transfer to CL-20 and showed stereo-specificity for pro-R hydrogen of NAD(P)H.

  7. 9-Mercaptodethiobiotin is Generated as a Ligand to the [2Fe-2S]+ Cluster During the Reaction Catalyzed by Biotin Synthase from Escherichia coli

    PubMed Central

    Fugate, Corey J.; Stich, Troy A.; Kim, Esther G.; Myers, William K.; Britt, R. David; Jarrett, Joseph T.

    2012-01-01

    Biotin synthase catalyzes formation of the thiophane ring through stepwise substitution of a sulfur atom for hydrogen atoms at the C9 and C6 positions of dethiobiotin. Biotin synthase is a Radical SAM enzyme that reductively cleaves S-adenosylmethionine, generating 5?-deoxyadenosyl radicals that initially abstract a hydrogen atom from the C9 position of dethiobiotin. We have proposed that the resulting dethiobiotinyl radical is quenched by the ?-sulfide of the nearby [2Fe-2S]2+ cluster, resulting in coupled formation of 9-mercaptodethiobiotin and a reduced [2Fe-2S]+ cluster. This reduced FeS cluster is observed by electron paramagnetic resonance spectroscopy as a mixture of two orthorhombic spin systems. In the present work, we use isotopically labeled 9-mercaptodethiobiotin and enzyme to probe the ligand environment of the [2Fe-2S]+ cluster in this reaction intermediate. HYSCORE spectra exhibit strong cross-peaks demonstrating strong isotropic coupling of the nuclear spin with the paramagnetic center. The hyperfine coupling constants are consistent with a structural model for the reaction intermediate in which 9-mercaptodethiobiotin is covalently coordinated to the remnant [2Fe-2S]+ cluster. PMID:22607542

  8. Effect of mass transfer on the oxygen reduction reaction catalyzed by platinum dendrimer encapsulated nanoparticles

    PubMed Central

    Dumitrescu, Ioana; Crooks, Richard M.

    2012-01-01

    Here we report on the effect of the mass transfer rate (kt) on the oxygen reduction reaction (ORR) catalyzed by Pt dendrimer-encapsulated nanoparticles (DENs) comprised of 147 and 55 atoms (Pt147 and Pt55). The experiments were carried out using a dual-electrode microelectrochemical device, which enables the study of the ORR under high kt conditions with simultaneous detection of H2O2. At low kt (0.02 to 0.12 cm s-1) the effective number of electrons involved in ORR, neff, is 3.7 for Pt147 and 3.4 for Pt55. As kt is increased, the mass-transfer-limited current for the ORR becomes significantly lower than the value predicted by the Levich equation for a 4-electron process regardless of catalyst size. However, the percentage of H2O2 detected remains constant, such that neff barely changes over the entire kt range explored (0.02 cm s-1). This suggests that mass transfer does not affect neff, which has implications for the mechanism of the ORR on Pt nanoparticles. Interestingly, there is a significant difference in neff for the two sizes of Pt DENs (neff = 3.7 and 3.5 for Pt147 and Pt55, respectively) that cannot be assigned to mass transfer effects and that we therefore attribute to a particle size effect. PMID:22665772

  9. RING E3-Catalyzed E2 Self-Ubiquitination Attenuates the Activity of Ube2E Ubiquitin-Conjugating Enzymes.

    PubMed

    Banka, Prerana Agarwal; Behera, Adaitya Prasad; Sarkar, Sayani; Datta, Ajit B

    2015-07-01

    Ubiquitination of a target protein is accomplished through sequential actions of the E1, E2s, and the E3s. E2s dictate the modification topology while E3 ligases confer substrate specificity and recruit the cognate E2. Human genome codes for ~35 different E2 proteins; all of which contain the characteristic ubiquitin-conjugating UBC core domain sufficient for catalysis. Many of these E2 enzymes also have N- or C-terminal extensions; roles of which are not very well understood. We show that the N-terminal extension of Ube2E1 undergoes intramolecular auto-ubiquitination. This self-ubiquitination activity is enhanced in the presence of interacting RING E3 ligases and results in a progressive attenuation of the E2 activity toward substrate/E3 modification. We also find that the N-terminal ubiquitination sites are conserved in all the three Ube2Es and replacing them with arginine renders all three full-length Ube2Es equally active as their core UBC domains. Based on these results, we propose that E3-catalyzed self-ubiquitination acts as a key regulatory mechanism that controls the activity of Ube2E class of ubiquitin E2s. PMID:25960396

  10. Evolution of Enzymatic Activities in the Enolase Superfamily: Crystallographic and Mutagenesis Studies of the Reaction Catalyzed by D-Glucarate Dehydratase from

    E-print Network

    Rayment, Ivan

    Studies of the Reaction Catalyzed by D-Glucarate Dehydratase from Escherichia coli, Andrew M. Gulick: D-Glucarate dehydratase (GlucD) from Escherichia coli catalyzes the dehydration of both D-glucarate in the active site of MR. Crystals of GlucD have been obtained into which the substrate D-glucarate and two

  11. Enzymatic synthesis of L-DOPA alpha-glycosides by reaction with sucrose catalyzed by four different glucansucrases from four strains of Leuconostoc mesenteroides.

    PubMed

    Yoon, Seung-Heon; Fulton, D Bruce; Robyt, John F

    2010-08-16

    L-DOPA alpha-glycosides were synthesized by reaction of L-DOPA with sucrose, catalyzed by four different glucansucrases from Leuconostoc mesenteroides B-512FMC, B-742CB, B-1299A, and B-1355C. The glucansucrases catalyzed the transfer of d-glucose from sucrose to the phenolic hydroxyl position-3 and -4 of L-DOPA. The glycosides were fractionated and purified by Bio-Gel P-2 column chromatography, and the structures were determined by (1)H NMR spectroscopy. The major glycoside was 4-O-alpha-d-glucopyranosyl L-DOPA, and the minor glycoside was 3-O-alpha-D-glucopyranosyl L-DOPA. The two glycosides were formed by all four of the glucansucrases. The ratio of the 4-O-alpha-glycoside to the 3-O-alpha-glycoside produced by the B-512FMC dextransucrase was higher than that for the other three glucansucrases. The glycosylation of L-DOPA significantly reduced the oxidation of the phenolic hydroxyl groups, which prevents their methylation, potentially increasing the use of L-DOPA in the treatment of Parkinson's disease. The use of one enzyme, glucansucrase, and sucrose as the D-glucosyl donor makes the synthesis considerably simpler and cheaper than the formerly published procedure using cyclomaltodextrin and cyclomaltodextrin glucanyltransferase, followed by glucoamylase, and beta-amylase hydrolysis. PMID:20579635

  12. Investigations into the metal species of the homogeneous iron(III) catalyzed Michael addition reactions.

    PubMed

    Bauer, Matthias; Kauf, Thomas; Christoffers, Jens; Bertagnolli, Helmut

    2005-07-01

    An investigation into the species formed in the first step of the solvent free homogeneous Michael reaction of alpha,beta-unsaturated ketones with 2-oxocyclopentanecarboxylate (1) is presented. This reaction is catalyzed by FeCl(3).6H(2)O (2) and Fe(ClO(4))(3).9H(2)O (3). EXAFS, XANES, Raman and UV-Vis studies were carried out to explain the experimentally found higher catalytic activity of Fe(ClO(4))(3).9H(2)O (3) compared to FeCl(3).6H(2)O (2). A very intense pre-edge peak is found for a 1.6 mol% solution of FeCl(3).6H(2)O (2) in 1, suggesting a tetrachloroferrate(III) compound to be present in this solution. This is proved by UV-Vis and Raman spectroscopy. The counterion of this anionic complex is an octahedral [Fe(III)(1-H)(2)(H2O2)](+) complex with two deprotonated 2-oxocyclopentanecarboxylate (1) as the chelating ligand, (1-H)(-), as suggested by the examination of the XANES region, the obtained coordination numbers from the EXAFS analysis and by UV-Vis and Raman spectroscopies. In summary, the anion-cation species [Fe(III)Cl(4)](-)[Fe(III)(-H)(2)(H2O2)](+) is formed with FeCl(3).6H(2)O (2), whereas in the case of Fe(ClO(4))(3).9H(2)O (3) XAFS, Raman and UV-Vis investigations suggest the presence of a complex of the form [Fe(III)(1-H)(2)(H2O2)](+)[ClO(4)](-). The obtained results are discussed to explain the reduced catalytic activity of FeCl(3).6H(2)O (2) in comparison to Fe(ClO(4))(3).9H(2)O (3). PMID:16189578

  13. Process optimization of enzyme catalyzed production of dietary diacylglycerol (DAG) using TLIM as biocatalyst.

    PubMed

    Dhara, Rupali; Singhal, Rekha S

    2014-01-01

    Diacylglycerol (DAG)-rich sunflower oil was prepared and the optimal conditions for synthesis of DAG-rich oil by glycerolysis using biocatalyst TLIM was determined. A maximum production of 59.8% DAG was obtained after 5 h of constant reaction under vacuum (756 mm of Hg). The optimum temperature for glycerolysis was found to be 50°C, while stoichiometric molar ratio of sunflower oil:glycerol was 2:1 for this reaction. A minimum acid value of 0.48 mg of KOH.g(-1) of oil was observed under these conditions. The fatty acid composition of DAG-rich oil was found to be similar to the original TAG-rich sunflower oil used in the work. The lipase catalysed glycerolysis using 1,3 specific lipase was used to promote the formation of 1,3 isoform of DAG as this isoform is known to possess anti-obesity effect. DAG content was determined by HPTLC and GCMS. The DAG-rich oil contained 59.75% DAG of which 63.34% was found as 1,3-DAG and 36.65% was 1,2-DAG/2,3-DAG. PMID:24500104

  14. A coumarin-specific prenyltransferase catalyzes the crucial biosynthetic reaction for furanocoumarin formation in parsley.

    PubMed

    Karamat, Fazeelat; Olry, Alexandre; Munakata, Ryosuke; Koeduka, Takao; Sugiyama, Akifumi; Paris, Cedric; Hehn, Alain; Bourgaud, Frédéric; Yazaki, Kazufumi

    2014-02-01

    Furanocoumarins constitute a sub-family of coumarin compounds with important defense properties against pathogens and insects, as well as allelopathic functions in plants. Furanocoumarins are divided into two sub-groups according to the alignment of the furan ring with the lactone structure: linear psoralen and angular angelicin derivatives. Determination of furanocoumarin type is based on the prenylation position of the common precursor of all furanocoumarins, umbelliferone, at C6 or C8, which gives rise to the psoralen or angelicin derivatives, respectively. Here, we identified a membrane-bound prenyltransferase PcPT from parsley (Petroselinum crispum), and characterized the properties of the gene product. PcPT expression in various parsley tissues is increased by UV irradiation, with a concomitant increase in furanocoumarin production. This enzyme has strict substrate specificity towards umbelliferone and dimethylallyl diphosphate, and a strong preference for the C6 position of the prenylated product (demethylsuberosin), leading to linear furanocoumarins. The C8-prenylated derivative (osthenol) is also formed, but to a much lesser extent. The PcPT protein is targeted to the plastids in planta. Introduction of this PcPT into the coumarin-producing plant Ruta graveolens showed increased consumption of endogenous umbelliferone. Expression of PcPT and a 4-coumaroyl CoA 2'-hydroxylase gene in Nicotiana benthamiana, which does not produce furanocoumarins, resulted in formation of demethylsuberosin, indicating that furanocoumarin production may be reconstructed by a metabolic engineering approach. The results demonstrate that a single prenyltransferase, such as PcPT, opens the pathway to linear furanocoumarins in parsley, but may also catalyze the synthesis of osthenol, the first intermediate committed to the angular furanocoumarin pathway, in other plants. PMID:24354545

  15. Enzyme-catalyzed synthesis of poly[(R)-(-)-3-hydroxybutyrate]: Formation of macroscopic granules in vitro

    SciTech Connect

    Gerngross, T.U.; Martin, D.P. [Metabolix, Inc., Cambridge, MA (United States)

    1995-07-03

    A combined chemical and enzymatic procedure has been developed to synthesize macroscopic poly[(R)-(-)-3-hydroxybutyrate] (PHB) granules in vitro. The granules form in a matter of minutes when purified polyhydroxyalkanoate (PHA) synthase from Alcaligenes eutrophus is exposed to synthetically prepared (R)-3-hydroxybutyryl coenzyme A, thereby establishing the minimal requirements for PHB granule formation. The artificial granules are spherical with diameters of up to 3 {mu}m and significantly larger than their native counterparts (0.5 {mu}m). The isolated PHB was characterized by {sup 1}H and {sup 13}C NMR, gel-permeation chromatography, and chemical analysis. The in vitro polymerization system yields PHB with a molecular mass > 10 x 10{sup 6} Da, exceeding by an order of magnitude the mass of PHAs typically extracted from microorganisms. We also demonstrate that the molecular mass of the polymer can be controlled by the initial PHA synthase concentration. Preliminary kinetic analysis of de novo granule formation confirms earlier findings of a lag time for the enzyme but suggests the involvement of an additional granule assembly step. Minimal requirements for substrate recognition were investigated. Since substrate analogs lacking the adenosine 3{prime}, 5{prime}-bisphosphate moiety of (R)-3-hydroxybutyryl coenzyme A were not accepted by the PHA synthase, we provide evidence that this structural element of the substrate is essential for catalysis. PHAs provide a range of natural, renewable, biodegradable thermoplastics with a broad range of useful material properties. 33 refs., 6 figs., 1 tab.

  16. Abstract: Several unsymmetrical heterobiaryls have been synthesized through palladium-catalyzed cross-coupling reactions

    E-print Network

    zincates using only one third equivalent of zinc chloride for the synthesis of 5-aryl-2-furaldehydes from 5 chloride to perform nickel- or palladium-catalyzed couplings of aryl Grignard reagents with aryl halides.10, respectively. Nickel-catalyzed cross-couplings of organozinc compounds have been described.14 However

  17. Metal-Catalyzed Carbon-Carbon Bond Forming Reactions for the Synthesis of Significant Chiral Building Blocks 

    E-print Network

    Bugarin Cervantes, Alejandro

    2011-08-08

    by nucleophilic tertiary amines or phosphines.2 In the seminal report,1 Morita and coworkers reported the first nucleophilic triggered acrylic ?-substitution catalyzed by phosphines. Treatment of acrylonitrile with catalytic amounts of tricyclohexylphosphine... several activated alkenes including alkyl vinyl ketones,5-7 alkyl and aryl acrylates,8-10 acrolien,11,12 allenic esters,13 acrylonitriles,6,14 vinyl sulfones and sulfonates,15,16 as well as vinyl phosphonates17 on reactions with aldehydes at atmospheric...

  18. Chirality transfer in Au-catalyzed cyclization reactions of monoallylic diols: selective access to specific enantiomers based on olefin geometry.

    PubMed

    Aponick, Aaron; Biannic, Berenger

    2011-03-18

    The gold(I)-catalyzed cyclization of monoallylic diols to form tetrahydropyrans is shown to be highly stereoselective when chiral allylic alcohols are employed. Substrates that differ only in olefin geometry provide enantiomeric products from formal S(N)2' reactions in high yields with excellent chirality transfer. The allylic alcohol stereochemistry also efficiently controls the facial selectivity when the substrates include additional stereocenters. PMID:21314106

  19. Accelerated search kinetics mediated by redox reactions of DNA repair enzymes

    E-print Network

    Pak-Wing Fok; Tom Chou

    2009-05-20

    A Charge Transport (CT) mechanism has been proposed in several papers (e.g., Yavin, et al. PNAS, v102 3546 (2005)) to explain the localization of Base Excision Repair (BER) enzymes to lesions on DNA. The CT mechanism relies on redox reactions of iron-sulfur cofactors that modify the enzyme's binding affinity. These redox reactions are mediated by the DNA strand and involve the exchange of electrons between BER enzymes along DNA. We propose a mathematical model that incorporates enzyme binding/unbinding, electron transport, and enzyme diffusion along DNA. Analysis of our model within a range of parameter values suggests that the redox reactions can increase desorption of BER enzymes not already bound to their targets, allowing the enzymes to be recycled, thus accelerating the overall search process. This acceleration mechanism is most effective when enzyme copy numbers and enzyme diffusivity along the DNA are small. Under such conditions, we find that CT BER enzymes find their targets more quickly than simple "passive" enzymes that simply attach to the DNA without desorbing.

  20. Faox enzymes inhibited Maillard reaction development during storage both in protein glucose model system and low lactose UHT milk.

    PubMed

    Troise, Antonio Dario; Dathan, Nina A; Fiore, Alberto; Roviello, Giovanni; Di Fiore, Anna; Caira, Simonetta; Cuollo, Marina; De Simone, Giuseppina; Fogliano, Vincenzo; Monti, Simona M

    2014-02-01

    Fructosamines, also known as Amadori products, are formed by the condensation of glucose with the amino group of amino acids or proteins. These compounds are precursors of advanced glycation end products (AGEs) that can be formed either endogenously during aging and diabetes, and exogenously in heat-processed food. The negative effects of dietary AGEs on human health as well as their negative impact on the quality of dairy products have been widely described, therefore specific tools able to prevent the formation of glycation products are needed. Two fructosamine oxidase enzymes isolated from Aspergillus sp. namely, Faox I and Faox II catalyze the oxidative deglycation of Amadori products representing a potential tool for inhibiting the Maillard reaction in dairy products. In this paper, the ability of recombinant Faox I and II in limiting the formation of carboxy-methyl lysine (CML) and protein-bound hydroxymethyl furfurol (b-HMF) in a commercial UHT low lactose milk and a beta-lactoglobulin (?-LG) glucose model system was investigated. Results show a consistent reduction of CML and b-HMF under all conditions. Faox effects were particularly evident on b-HMF formation in low lactose commercial milk. Peptide analysis of the ?-LG glucose system identified some peptides, derived from cyanogen bromide hydrolysis, as suitable candidates to monitor Faox action in milk-based products. All in all data suggested that non-enzymatic reactions in dairy products might be strongly reduced by implementing Faox enzymes. PMID:23604465

  1. Microassay with the NADH-induced light reaction, technique improved by means of purified enzymes from Achromobacter fischeri.

    PubMed

    Brolin, S E; Hjertén, S

    1977-09-01

    Purification of a commercial preparation of Achromobacter fischeri was carried out by agarose-suspension electrophoresis and by molecular-sieve chromatography. Both the luciferase and an oxidoreductase, catalyzing reduction of FMN with NADH, were obtained in more than one form. Flavins, liable to interfere with the light production in analytical applications, were present in amounts worthy of consideration, but seem to be firmly bound to protein. The major quantity was found in the enzymatically inactive fractions. In free zone electrophoresis of the main luciferase component, the mobility of the zone containing enzyme activity was calculated to -4.0 X 10(-5) cm2 sec-1 V-1 at 12 degrees C. Fractions of the two enzymes were separated and mixed in different proportions to study how the intensity and time course of NADH-induced light emission can be modified. These experiments disclosed how reaction mixtures will have to be composed in appropriate photokinetic assays, using NADH as measurable product. A regenerating system based on the purified fractions is described. Instead of the light flash, following the consumption of NADH, the light is emitted on a well maintained level, permitting assays with a less elaborate equipment than the one required for the recording of fast reactions. PMID:198648

  2. Examining the importance of dynamics, barrier compression and hydrogen tunnelling in enzyme catalysed reactions

    Microsoft Academic Search

    Sam Hay; Nigel S. Scrutton

    2011-01-01

    Nuclear quantum mechanical tunnelling is important in enzyme-catalysed H-transfer reactions. This viewpoint has arisen after a number of experimental studies have described enzymatic reactions with kinetic isotope effects that are significantly larger than the semiclassical limit. Other experimental evidence for tunnelling, and the potential role of promoting vibrations that transiently compress the reaction barrier, is more indirect, being derived from

  3. CuI-catalyzed C1-alkynylation of tetrahydroisoquinolines (THIQs) by A3 reaction with tunable iminium ions.

    PubMed

    Zheng, Qin-Heng; Meng, Wei; Jiang, Guo-Jie; Yu, Zhi-Xiang

    2013-12-01

    A CuI-catalyzed A(3) (amines, aldehydes and alkynes) reaction of tetrahydroisoquinolines (THIQs), aldehydes, and alkynes to give C1-alkynylated THIQ products (endo-yne-THIQs) was developed. This redox neutral C1-alkynylation of THIQs, which was conducted under mild conditions, has a broad scope for the used aldehydes and alkynes. It was proposed that the A(3) reaction first generates in situ exo-iminium ions, which then isomerize to endo-iminium ions and react with copper acetylides to give the endo alkynylated THIQs (endo-yne-THIQs). PMID:24237286

  4. Method for the Synthesis of Phenothiazines via a Domino Iron-Catalyzed C-S/C-N Cross-Coupling Reaction.

    PubMed

    Hu, Weiye; Zhang, Songlin

    2015-06-19

    An environmentally benign and efficient method has been developed for the synthesis of phenothiazines via a tandem iron-catalyzed C-S/C-N cross-coupling reaction. Some of the issues typically encountered during the synthesis of phenothiazines in the presence of palladium and copper catalysts, including poor substrate scope, long reaction times and poor regioselectivity, have been addressed using this newly developed iron-catalyzed method. PMID:26028127

  5. Preparation of Strontium-and Zinc-Doped LaGaO3 Powders via Precipitation in the Presence of Urea and/or Enzyme Urease

    E-print Network

    Tas, A. Cuneyt

    and/or Enzyme Urease A. Cu¨neyt Tas,*, Peter J. Majewski, and Fritz Aldinger* Max-Planck-Institut fuer the decomposition of urea was catalyzed by the enzyme urease. The calcination behavior of the precursor powders by Mati- jevic,36 ­38 and others.39 ­ 43 Synthesis of ceramics by enzyme- catalyzed reactions, which

  6. Aminoglycoside Antibiotic-Inactivating Enzymes in Actinomycetes Similar to those Present in Clinical Isolates of Antibiotic-Resistant Bacteria

    Microsoft Academic Search

    Raoul Benveniste; Julian Davies

    1973-01-01

    Various species of Streptomyces possess aminoglycoside-modifying enzymes. Streptomyces kanamyceticus contains an enzyme that acetylates the 6'-amino group of kanamycin A and B, gentamicin C1a, and neomycin. Streptomyces spectabilis produces an enzyme that acetylates the 2'-amino group of the hexose ring of gentamicin C1a. These enzymes catalyze reactions identical to those catalyzed by enzymes found in gram-negative bacteria containing R (antibiotic

  7. Nickel-Catalyzed Heck-Type Reactions of Benzyl Chlorides and Simple Olefins

    E-print Network

    Matsubara, Ryosuke

    Nickel-catalyzed intermolecular benzylation and heterobenzylation of unactivated alkenes to provide functionalized allylbenzene derivatives are described. A wide range of both the benzyl chloride and alkene coupling partners ...

  8. Synthesis of Unsymmetrical Diarylureas via Pd-Catalyzed C–N Cross-Coupling Reactions

    E-print Network

    Breitler, Simon

    A facile synthesis of unsymmetrical N,N?-diarylureas is described. The utilization of the Pd-catalyzed arylation of ureas enables the synthesis of an array of diarylureas in good to excellent yields from benzylurea via a ...

  9. Esterification and interesterification reactions catalyzed by acetone powder from germinating rapeseed

    Microsoft Academic Search

    I. Jachmanilin; K. D. Mukherjee

    1996-01-01

    Acetone powder from germinating rape (Brassica napus L.) seedlings exhibits essentially similar activity in lipolysis of triacylglycerols as the corresponding seedling homogenates.\\u000a Acetone powder from rape seedlings catalyzes the esterification of a fatty acid, such as oleic acid, withn-butanol or a long-chain alcohol, such as oleyl alcohol. Furthermore, the acetone powder catalyzes alcoholysis of a methyl\\u000a ester, such as methyl

  10. Enzyme catalytic efficiency: a function of bio-nano interface reactions.

    PubMed

    Campbell, Alan S; Dong, Chenbo; Meng, Fanke; Hardinger, Jeremy; Perhinschi, Gabriela; Wu, Nianqiang; Dinu, Cerasela Zoica

    2014-04-23

    Biocatalyst immobilization onto carbon-based nanosupports has been implemented in a variety of applications ranging from biosensing to biotransformation and from decontamination to energy storage. However, retaining enzyme functionality at carbon-based nanosupports was challenged by the non-specific attachment of the enzyme as well as by the enzyme-enzyme interactions at this interface shown to lead to loss of enzyme activity. Herein, we present a systematic study of the interplay reactions that take place upon immobilization of three pure enzymes namely soybean peroxidase, chloroperoxidase, and glucose oxidase at carbon-based nanosupport interfaces. The immobilization conditions involved both single and multipoint single-type enzyme attachment onto single and multi-walled carbon nanotubes and graphene oxide nanomaterials with properties determined by Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray analysis (EDX), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Our analysis showed that the different surface properties of the enzymes as determined by their molecular mapping and size work synergistically with the carbon-based nanosupports physico-chemical properties (i.e., surface chemistry, charge and aspect ratios) to influence enzyme catalytic behavior and activity at nanointerfaces. Knowledge gained from these studies can be used to optimize enzyme-nanosupport symbiotic reactions to provide robust enzyme-based systems with optimum functionality to be used for fermentation, biosensors, or biofuel applications. PMID:24666280

  11. Method of controlled reduction of nitroaromatics by enzymatic reaction with oxygen sensitive nitroreductase enzymes

    DOEpatents

    Shah, M.M.; Campbell, J.A.

    1998-07-07

    A method is described for the controlled reduction of nitroaromatic compounds such as nitrobenzene and 2,4,6-trinitrotoluene by enzymatic reaction with oxygen sensitive nitroreductase enzymes, such as ferredoxin NADP oxidoreductase. 6 figs.

  12. Method of controlled reduction of nitroaromatics by enzymatic reaction with oxygen sensitive nitroreductase enzymes

    DOEpatents

    Shah, Manish M. (Richland, WA); Campbell, James A. (Pasco, WA)

    1998-01-01

    A method for the controlled reduction of nitroaromatic compounds such as nitrobenzene and 2,4,6-trinitrotoluene by enzymatic reaction with oxygen sensitive nitroreductase enzymes, such as ferredoxin NADP oxidoreductase.

  13. Method of reduction of nitroaromatics by enzymatic reaction with redox enzymes

    DOEpatents

    Shah, Manish M. (Richland, WA)

    2000-01-01

    A method for the controlled reduction of nitroaromatic compounds such as nitrobenzene and 2,4,6-trinitrotoluene by enzymatic reaction with redox enzymes, such as Oxyrase (Trademark of Oxyrase, Inc., Mansfield, Ohio).

  14. Low-temperature superacid catalysis: Reactions of n-butane catalyzed by iron- and manganese-promoted sulfated zirconia

    SciTech Connect

    Cheung, T.K.; D`Itri, J.L.; Gates, B.C. [Univ. of California, Davis, CA (United States)] [Univ. of California, Davis, CA (United States)

    1995-02-01

    Environmental concerns are leading to the replacement of aromatic hydrocarbons in gasoline with high-octane-number branched paraffins and oxygenated compounds such as methyl t-butyl ether, which is produced from methanol and isobutylene. The latter can be formed from n-butane by isomerization followed by dehydrogenation. To meet the need for improved catalysts for isomerization of n-butane and other paraffins, researchers identified solid acids that are noncorrosive and active at low temperatures. Sulfated zirconia catalyzes the isomerization of n-butane even at 25{degrees}C, and the addition of Fe and Mn promoters increases its activity by three orders of magnitude. Little is known about this new catalyst. Here the authors provide evidence of its performance for n-butane conversion, demonstrating that isomerization is accompanied by disproportionation and other, less well understood, acid-catalyzed reactions and undergoes rapid deactivation associated with deposition of carbonaceous material. 10 refs., 3 figs.

  15. Efficient Boron-Copper Additions to Aryl-Substituted Alkenes Promoted by NHC–Based Catalysts. Enantioselective Cu-Catalyzed Hydroboration Reactions

    PubMed Central

    Lee, Yunmi; Hoveyda, Amir H.

    2009-01-01

    A Cu-catalyzed method for efficient boron-copper addition processes involving acyclic and cyclic disubstituted aryl olefins are reported. Reactions are promoted with 0.5–5 mol % of a readily available N-heterocyclic carbene (NHC) complex; the presence of MeOH promotes in situ protonation of the C–Cu bond and leads to efficient catalyst turnover, constituting a net Cu-catalyzed hydroboration process. Reactions proceed in >98:<2 site-selectivity, and furnish secondary organoborane isomers that complement those obtained through reactions of boron-hydride reagents or by Rh- or Ir-catalyzed hydroborations (benzylic secondary C–B bonds). Initial observations regarding processes catalyzed by chiral NHC complexes, delivering products in up to 99:1 enantiomeric ratio, are disclosed. PMID:19256564

  16. Efficient boron-copper additions to aryl-substituted alkenes promoted by NHC-based catalysts. enantioselective Cu-catalyzed hydroboration reactions.

    PubMed

    Lee, Yunmi; Hoveyda, Amir H

    2009-03-11

    A Cu-catalyzed method for efficient boron-copper addition processes involving acyclic and cyclic disubstituted aryl olefins are reported. Reactions are promoted with 0.5-5 mol % of a readily available N-heterocyclic carbene (NHC) complex; the presence of MeOH promotes in situ protonation of the C-Cu bond and leads to efficient catalyst turnover, constituting a net Cu-catalyzed hydroboration process. Reactions proceed in >98:<2 site selectivity and furnish secondary organoborane isomers that complement those obtained through reactions of boron-hydride reagents or by Rh- or Ir-catalyzed hydroborations (benzylic secondary C-B bonds). Initial observations regarding processes catalyzed by chiral NHC complexes, delivering products in up to 99:1 enantiomeric ratio, are disclosed. PMID:19256564

  17. Computer simulations of quantum tunnelling in enzyme-catalysed hydrogen transfer reactions

    Microsoft Academic Search

    Kara E. Ranaghan; Adrian J. Mulholland

    2010-01-01

    Transfer of hydrogen as a proton, hydride or hydrogen atom is an important step in many enzymic reactions. Experiments show\\u000a kinetic isotope effects (KIEs) for some enzyme-catalysed hydrogen transfer reactions that deviate significantly from the limits\\u000a imposed by considering the differences in mass of the isotopes alone (i.e. the semiclassical limit). These KIEs can be explained\\u000a if the transfer of

  18. A network perspective on the topological importance of enzymes and their phylogenetic conservation

    Microsoft Academic Search

    Wei-chung Liu; Wen-hsien Lin; Andrew J. Davis; Ferenc Jordán; Hsih-te Yang; Ming-jing Hwang

    2007-01-01

    Background: A metabolic network is the sum of all chemical transformations or reactions in the cell, with the metabolites being interconnected by enzyme-catalyzed reactions. Many enzymes exist in numerous species while others occur only in a few. We ask if there are relationships between the phylogenetic profile of an enzyme, or the number of different bacterial species that contain it,

  19. Structural Bases of Stability–function Tradeoffs in Enzymes

    Microsoft Academic Search

    Beth M. Beadle; Brian K. Shoichet

    2002-01-01

    The structures of enzymes reflect two tendencies that appear opposed. On one hand, they fold into compact, stable structures; on the other hand, they bind a ligand and catalyze a reaction. To be stable, enzymes fold to maximize favorable interactions, forming a tightly packed hydrophobic core, exposing hydrophilic groups, and optimizing intramolecular hydrogen-bonding. To be functional, enzymes carve out an

  20. Detection of glucose via enzyme-coupling reaction based on a DT-diaphorase fluorescence probe.

    PubMed

    Gao, Xinghui; Li, Xiaohua; Wan, Qiongqiong; Li, Zhao; Ma, Huimin

    2014-03-01

    Enzyme-coupling reactions play an important role in the assay of analytes. In this manuscript, we developed a new fluorescent probe for the detection of glucose through the enzyme-coupling reaction of DT-diaphorase (DTD). The probe was synthesized through a mild and simple synthetic procedure, and showed good fluorescence response to DTD. The reactions for the detection of glucose proceed as follows: glucose dehydrogenase oxidizes glucose to gluconolactone with NAD(+) as the electron acceptor to yield NADH, and NADH can be utilized by DTD to further react with the probe releasing resorufin. As a result of these tandem reactions, fluorescence off-on response will occur. The method showed high selectivity for glucose with a detection limit of 0.2 µM, which may provide a potential way for fluorescence detection of glucose through enzyme-coupling reactions. Furthermore, the applicability of the method has been demonstrated by detecting glucose in human urine samples. PMID:24468396

  1. Chemical accuracy in QM/MM calculations on enzyme-catalysed reactions

    PubMed Central

    Mulholland, Adrian J

    2007-01-01

    Combined quantum mechanics/molecular mechanics (QM/MM) modelling has the potential to answer fundamental questions about enzyme mechanisms and catalysis. Calculations using QM/MM methods can now predict barriers for enzyme-catalysed reactions with unprecedented, near chemical accuracy, i.e. to within 1 kcal/mol in the best cases. Quantitative predictions from first-principles calculations were only previously possible for very small molecules. At this level, quantitative, reliable predictions can be made about the mechanisms of enzyme-catalysed reactions. This development signals a new era of computational biochemistry. PMID:17880750

  2. Divergence in the reactivity between amine- and phosphine-catalyzed cycloaddition reactions of allenoates with enynals: one-pot gold-catalyzed synthesis of trisubstituted benzofurans from the [3 + 2] cycloadduct via 1,2-alkyl migration and dehydrogenation.

    PubMed

    Kumari, A Leela Siva; Swamy, K C Kumara

    2015-04-17

    Regioselective synthesis of functionalized dihydropyran derivatives by DABCO-catalyzed [2 + 4] cycloaddition of allenoates with enynals or enynones has been developed. Phosphine-catalyzed [3 + 2] cycloaddition of allenoates with enynals provides 1,1-alkyne (aldehyde)-substituted cyclopentenes wherein enynals act as electrophiles. These alkyne-tethered cyclopentenes upon [Au]/[Ag] catalysis lead to substituted benzofurans via 1,2-alkyl migration and dehydrogenation (aromatization). One-pot reaction of allenoates with enynals using sequential phosphine and gold catalysis is also reported. The cyclopentene obtained from the PPh3-catalyzed reaction of allenoate H2C?C?CH(COO-t-Bu) with enynal undergoes decarboxylation under the [Au]/[Ag] catalysis and forms a carboxylate-free benzofuran. The structures of key products are confirmed by single-crystal X-ray analysis. PMID:25793444

  3. Adverse reactions with angiotensin converting enzyme (ACE) inhibitors.

    PubMed

    DiBianco, R

    1986-01-01

    Teprotide, a nonapeptide isolated from the venom of a Brazilian pit viper, Bothrops jararaca, was the first angiotensin converting enzyme (ACE) inhibitor to be discovered and tested. It was found to be an effective, non-toxic antihypertensive agent as well as an afterload-reducing agent for patients with congestive heart failure (CHF). The primary activity of teprotide resulted from blockade of the angiotensin I converting enzyme--the pivotal step in the renin-angiotensin-aldosterone system (RAAS), and consequent reductions in angiotensin II levels. There was limited clinical testing for teprotide because of: its scarcity; the need for parenteral administration; and the subsequent discovery and synthesis of captopril, the first orally active angiotensin converting enzyme inhibitor. Captopril is the prototype oral angiotensin converting enzyme inhibitor and has been extensively studied since the initiation of formal studies in 1976. Perhaps one of the most closely researched drugs in modern times, the experience with captopril now includes more than 12,000 patients studied in formalized trials and over 4,000,000 patients treated world-wide by physicians for hypertension and congestive heart failure. Enalapril (MK421) is the first of what appears to be a growing number of analogues which are structurally and pharmacodynamically different from captopril; yet, they possess the same capacity for inhibiting the activity of angiotensin converting enzyme. The side effect profile of enalapril (and presumably future) angiotensin converting enzyme inhibitors appears to be similar to captopril, though clearly more experience is needed with newer agents. The initial use of captopril was troubled by a relatively high incidence of side effects which will form the focus of this discussion. Partially the result of incomplete pharmacokinetic information, captopril was administered in early studies at dosages now recognised to be far in excess of those necessary for drug action. In addition, dosages were given without regard for deficiencies of renal function, now known to be the main excretory route of captopril. The population of those patients studied frequently had chronic, treatment-resistant hypertension, often associated with concomitant end-organ disease (especially renal disease); and many additional factors further complicating the clinical setting, e.g. a relatively high incidence of collagen vascular disease and immunosuppressive treatments.(ABSTRACT TRUNCATED AT 400 WORDS) PMID:3023783

  4. A mechanistic study of Pd(OAc)2-catalyzed intramolecular C-H functionalization reaction involving CO/isonitrile insertion.

    PubMed

    Gu, Honghong; Qiu, Zhiping; Zhang, Zhongchao; Li, Juan; Yan, Bo

    2015-05-19

    The mechanism of the Pd(OAc)2-catalyzed intramolecular C-H functionalization reaction involving CO/isonitrile insertion was investigated with the aid of density functional theory calculations at the B3LYP level. The similarity between the CO and isonitrile systems includes the following: (1) the anagostic bonding mechanism rather than the concerted metallation-deprotonation (CMD) mechanism is operative for the C-H cleavage step, (2) the CO/isonitrile insertion step is rate-determining, and (3) the C-H activation and CO/isonitrile insertion steps are accomplished with Pd(ii) and Pd(iii), respectively. For the reaction including isonitrile insertion, the arene C-H activation step occurs after deprotonation of the imino group. However, for reaction including CO insertion, the arene C-H activation step is the first step of the reaction mechanism. The difference between CO and isonitrile systems in the reaction mechanism can be attributed to the difference in the oxidants used. In the reaction including isonitrile insertion, the high endergonicity of the oxidation step suppresses prior C-H activation and favors prior deprotonation of the imino group. In the reactions including CO insertion, the low endergonicity of the oxidation step allows prior C-H activation to occur. PMID:25939250

  5. Asymmetric hetero-Diels-Alder reaction of diazenes catalyzed by chiral silver phosphate: water participates in the catalysis and stereocontrol.

    PubMed

    Liu, Bin; Liu, Tong-Yu; Luo, Shi-Wei; Gong, Liu-Zhu

    2014-12-01

    The chiral silver phosphate was confirmed to efficiently catalyze a highly regio- and enantioselective hetero-Diels-Alder reaction of diazenes to furnish piperazine derivatives in high yields and excellent ee values. DFT calculations revealed that the water molecule participates in the catalysis by coordination to silver phosphate and also found that the hydroxy group of 1-hydroxy-2,3-hexadiene not only formed a hydrogen bond with the oxygen of phosphate but also coordinated to the Ag(I) to simultaneously stabilize the transition states and control the regioselectivity. PMID:25409286

  6. Bulk gold catalyzed oxidation reactions of amines and isocyanides and iron porphyrin catalyzed N-H and O-H bond insertion/cyclization reactions of diamines and aminoalcohols

    SciTech Connect

    Klobukowski, Erik

    2011-12-29

    This work involves two projects. The first project entails the study of bulk gold as a catalyst in oxidation reactions of isocyanides and amines. The main goal of this project was to study the activation and reactions of molecules at metal surfaces in order to assess how organometallic principles for homogeneous processes apply to heterogeneous catalysis. Since previous work had used oxygen as an oxidant in bulk gold catalyzed reactions, the generality of gold catalysis with other oxidants was examined. Amine N-oxides were chosen for study, due to their properties and use in the oxidation of carbonyl ligands in organometallic complexes. When amine N-oxides were used as an oxidant in the reaction of isocyanides with amines, the system was able to produce ureas from a variety of isocyanides, amines, and amine N-oxides. In addition, the rate was found to generally increase as the amine N-oxide concentration increased, and decrease with increased concentrations of the amine. Mechanistic studies revealed that the reaction likely involves transfer of an oxygen atom from the amine N-oxide to the adsorbed isocyanide to generate an isocyanate intermediate. Subsequent nucleophilic attack by the amine yields the urea. This is in contrast to the bulk gold-catalyzed reaction mechanism of isocyanides with amines and oxygen. Formation of urea in this case was proposed to proceed through a diaminocarbene intermediate. Moreover, formation of the proposed isocyanate intermediate is consistent with the reactions of metal carbonyl ligands, which are isoelectronic to isocyanides. Nucleophilic attack at coordinated CO by amine N-oxides produces CO{sub 2} and is analogous to the production of an isocyanate in this gold system. When the bulk gold-catalyzed oxidative dehydrogenation of amines was examined with amine N-oxides, the same products were afforded as when O{sub 2} was used as the oxidant. When the two types of oxidants were directly compared using the same reaction system and conditions, it was found that the oxidative dehydrogenation of dibenzylamine to Nbenzylidenebenzylamine, with N-methylmorpholine N-oxide (NMMO), was nearly quantitative (96%) within 24 h. However, the reaction with oxygen was much slower, with only a 52% yield of imine product over the same time period. Moreover, the rate of reaction was found to be influenced by the nature of the amine N-oxide. For example, the use of the weakly basic pyridine N-oxide (PyNO) led to an imine yield of only 6% after 24 h. A comparison of amine N-oxide and O2 was also examined in the oxidation of PhCH{sub 2}OH to PhCHO catalyzed by bulk gold. In this reaction, a 52% yield of the aldehyde was achieved when NMMO was used, while only a 7% product yield was afforded when O{sub 2} was the oxidant after 48 h. The bulk gold-catalyzed oxidative dehydrogenation of cyclic amines generates amidines, which upon treatment with Aerosil and water were found to undergo hydrolysis to produce lactams. Moreover, 5-, 6-, and 7-membered lactams could be prepared through a one-pot reaction of cyclic amines by treatment with oxygen, water, bulk gold, and Aerosil. This method is much more atom economical than industrial processes, does not require corrosive acids, and does not generate undesired byproducts. Additionally, the gold and Aerosil catalysts can be readily separated from the reaction mixture. The second project involved studying iron(III) tetraphenylporphyrin chloride, Fe(TPP)Cl, as a homogeneous catalyst for the generation of carbenes from diazo reagents and their reaction with heteroatom compounds. Fe(TPP)Cl, efficiently catalyzed the insertion of carbenes derived from methyl 2-phenyldiazoacetates into O-H bonds of aliphatic and aromatic alcohols. Fe(TPP)Cl was also found to be an effective catalyst for tandem N-H and O-H insertion/cyclization reactions when 1,2-diamines and 1,2-alcoholamines were treated with diazo reagents. This approach provides a one-pot process for synthesizing piperazinones and morpholinones and related analogues such as quinoxalinones and benzoxazin-2-ones.

  7. The study of the stereospecificity in enzyme-catalyzed reactions of glyceryl acetonide derivatives

    E-print Network

    Chauvet, Christine Jeanne

    1987-01-01

    ) Christine Jeanne Chauvet, B. S. , Lycee Camille See, . Paris, France. Chairman of Advisory Committee: Dr. Chi-Huey Wong. Both enantiomers of glycerol acetonide are useful chiral C3 synthons; they are used in the synthesis of a various type of molecules...

  8. The study of the stereospecificity in enzyme-catalyzed reactions of glyceryl acetonide derivatives 

    E-print Network

    Chauvet, Christine Jeanne

    1987-01-01

    using sodium borohydridezs instead of using the originally described hydrogenation process. In fact, lower values for the optical rotations of the enantiomeric isopropylidene glycerols were usually found for lead tetraacetate cleavage of 1, 2:5, 6...-glucitol-1, 2 ? acetonide (6) with lead tetraacetate (Figure 4) . 2S The optically active aldehyde thus produced, was then reduced to the corresponding alcohol using sodium borohydride. In this synthesis only a portion of the sozbitol underwent...

  9. pH dependence of the reverse reaction catalyzed by phosphofructokinase I from Escherichia coli: implications for the role of Asp 127.

    PubMed Central

    Auzat, I.; Garel, J. R.

    1992-01-01

    The kinetics of the reverse reaction catalyzed by Escherichia coli phosphofructokinase, i.e., the synthesis of ATP and fructose-6-phosphate from ADP and fructose-1,6-bisphosphate, have been studied at different pH values, from pH 6 to pH 9.2. Hyperbolic saturations of the enzyme are observed for both substrates. The affinity for fructose-1,6-bisphosphate decreases with pH following the ionization of a group with a pK of 6.6, whereas the catalytic rate constant and perhaps the affinity for ADP are controlled by the ionization of a group with a pK of 6. Several arguments show that the pK of 6.6 is probably that of the carboxyl group of Asp 127, whereas the pK of 6 is tentatively attributed to the carboxyl group of Asp 103. The pK of 6.6 is assigned to the carboxyl group of Asp 127 in the free enzyme, and a simple model suggests that the same group would have an abnormally high pK, above 9.6, in the complex between phosphofructokinase and fructose-1,6-bisphosphate. It is proposed that the large pK shift of more than 3 pH units upon binding of fructose-1,6-bisphosphate is due to an electrostatic repulsion that could exist between the 1-phosphate group and the carboxyl group of Asp 127, which are close to each other in the crystal structure of phosphofructokinase (Shirakihara, Y. & Evans, P.R., 1988, J. Mol. Biol. 204, 973-994). The same interpretation would also explain the much higher affinity of the enzyme for fructose-1,6-bisphosphate when Asp 127 is protonated.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:1304907

  10. The reaction of amino-oxyacetate with pyridoxal phosphate-dependent enzymes.

    PubMed

    John, R A; Charteris, A

    1978-06-01

    The carbonyl reagent amino-oxyacetate is frequently used in metabolic studies to inhibit individual pyridoxal phosphate enzymes. The reaction of this compound with three such enzymes, aspartate transaminase, 4-aminobutyrate transaminase and dopa (3,4-dihydroxyphenylalanine) decarboxylase, was studied to determine the extent to which the inhibition is reversible and the rates at which it takes place. Reactions were followed by observing changes in the absorption spectra of the bound coenzyme and by measuring loss of enzyme activity. The reactions with aspartate transaminase and aminobutyrate transaminase were not rapidly reversible and had second-order rate constants (21 degrees C) of 400 M-1.s.1 and 1300 M-1.s-1 respectively and all all concentrations studied showed the kinetics of a simple bimolecular reaction. The reaction with 4-aminobutyrate transaminase could not be reversed and that with aspartate transaminase could only be reversed significantly by addition of cysteinesulphinate to convert the enzyme into its pyridoxamine form. The first-order rate constant (21 degrees C) for the reverse reaction was 4 X 10(-5)s-1. Dopa decarboxylase inhibition by amino-oxyacetate was more rapid and more readily reversible, but measurements of rate and equilibrium constants were not obtained for this enzyme. PMID:666736

  11. Synthesis of saturated 1,4-benzodiazepines via Pd-catalyzed carboamination reactions.

    PubMed

    Neukom, Joshua D; Aquino, Alvin S; Wolfe, John P

    2011-05-01

    A new synthesis of 1,4-benzodiazepines and 1,4-benzodiazepin-5-ones is reported. The Pd-catalyzed coupling of N-allyl-2-aminobenzylamine derivatives with aryl bromides affords the heterocyclic products in good yield, and substrates bearing allylic methyl groups are transformed to cis-2,3-disubstituted products with >20:1 dr. PMID:21446677

  12. Synthesis of Saturated 1,4-Benzodiazepines via Pd-Catalyzed Carboamination Reactions

    PubMed Central

    Neukom, Joshua D.; Aquino, Alvin S.; Wolfe, John P.

    2011-01-01

    A new synthesis of 1,4-benzodiazepines and 1,4-benzodiazepin-5-ones is reported. The Pd-catalyzed coupling ofN-allyl-2-aminobenzylamine derivatives with aryl bromides affords the heterocyclic products in good yield, and substrates bearing allylic methyl groups are transformed toc is-2,3-disubstituted products with >20:1 dr. PMID:21446677

  13. The gas phase reaction of singlet dioxygen with water: A water-catalyzed mechanism

    E-print Network

    Goddard III, William A.

    this remarkable and unexpected chemistry, we need to understand how 1 O2 can interact with H2O to produce H2O2­10935] that Abs efficiently catalyze the conversion of molecular singlet oxygen (1O2) plus water to hydrogen peroxide (HOOH), we used quantum chemical methods (B3LYP density functional theory) to delineate the most

  14. Fe-Catalyzed Oxidation Reactions of Olefins, Alkanes, and Alcohols: Involvement of Oxo- and Peroxo Complexes

    NASA Astrophysics Data System (ADS)

    Schröder, Kristin; Junge, Kathrin; Bitterlich, Bianca; Beller, Matthias

    In this review, recent developments of iron-catalyzed oxidations of olefins (epoxidation), alkanes, arenes, and alcohols are summarized. Special focus is given on the ligand systems and the catalytic performance of the iron complexes. In addition, the mechanistic involvement of high-valent iron-oxo species is discussed.

  15. An efficient transformation of primary halides into nitriles through palladium-catalyzed hydrogen transfer reaction.

    PubMed

    Zou, Tao; Yu, Xiaoqiang; Feng, Xiujuan; Bao, Ming

    2015-07-01

    Two-step one-pot transformation of primary halides into corresponding nitriles is successfully achieved. Nucleophilic substitution of primary halides with sodium azide and subsequent palladium-catalyzed hydrogen transfer proceeds smoothly in the presence of sterically bulky ligand dicyclohexyl(2',4',6'-triisopropylbiphenyl-2-yl)phosphine (XPhos) in acetone to produce nitriles in satisfactory to good yields. PMID:26050994

  16. Positional Assembly of Enzymes on Bacterial Outer Membrane Vesicles for Cascade Reactions

    PubMed Central

    Park, Miso; Sun, Qing; Liu, Fang; DeLisa, Matthew P.; Chen, Wilfred

    2014-01-01

    The systematic organization of enzymes is a key feature for the efficient operation of cascade reactions in nature. Here, we demonstrate a facile method to create nanoscale enzyme cascades by using engineered bacterial outer membrane vesicles (OMVs) that are spheroid nanoparticles (roughly 50 nm in diameter) produced by Gram-negative bacteria during all phases of growth. By taking advantage of the fact that OMVs naturally contain proteins found in the outer cell membrane, we displayed a trivalent protein scaffold containing three divergent cohesin domains for the position-specific presentation of a three-enzyme cascade on OMVs through a truncated ice nucleation protein anchoring motif (INP). The positional assembly of three enzymes for cellulose hydrolysis was demonstrated. The enzyme-decorated OMVs provided synergistic cellulose hydrolysis resulting in 23-fold enhancement in glucose production than free enzymes. PMID:24820175

  17. Studies on the oxidation reaction of tyrosine (Tyr) with H 2O 2 catalyzed by horseradish peroxidase (HRP) in alcohol-water medium by spectrofluorimetry and differential spectrophotometry

    NASA Astrophysics Data System (ADS)

    Tang, Bo; Wang, Yan; Liang, Huiling; Chen, Zhenzhen; He, Xiwen; Shen, Hanxi

    2006-03-01

    An oxidation reaction of tyrosine (Tyr) with H 2O 2 catalyzed by horseradish peroxidase (HRP) was studied by spectrofluorimetry and differential spectrophotometry in the alcohol(methanol, ethanol, 1-propanol and isopropanol)-water mutual solubility system. Compared with the enzymatic-catalyzed reaction in the water medium, the fluorescence intensities of the product weakened, even extinguished. Because the addition of alcohols made the conformation of HRP change, the catalytic reaction shifted to the side of polymerization and the polymer (A nH 2, n ? 3) exhibited no fluorescence. The four alcohols cannot deactivate HRP. Moreover isopropanol activated HRP remarkably.

  18. Enzyme

    MedlinePLUS

    Enzymes are complex proteins that cause a specific chemical change in all parts of the body. For ... use them. Blood clotting is another example of enzymes at work. Enzymes are needed for all body ...

  19. Galacto-oligosaccharide production from lactose by an enzymic batch reaction using ?-galactosidase

    Microsoft Academic Search

    Ken-ichi Iwasaki; Mitsutoshi Nakajima; Shin-ichi Nakao

    1996-01-01

    Enzymic reaction of lactose was carried out to produce galacto-oligosaccharide with a high degree of conversion. The reaction process was analysed with a simple model. The reaction involved a batch process operated with initial lactose concentrations ranging from 0·139 to 1·67 mol litre?1 at 40°C and pH 4·5 with ?-galactosidase from Aspergillus oryzae. A maximum oligosaccharide conversion of over 30%

  20. Palladium-catalyzed cross-coupling reaction of diazo compounds and vinyl boronic acids: an approach to 1,3-diene compounds.

    PubMed

    Xia, Yamu; Xia, Ying; Liu, Zhen; Zhang, Yan; Wang, Jianbo

    2014-08-15

    A palladium-catalyzed oxidative cross-coupling of vinyl boronic acids and cyclic ?-diazocarbonyl compounds has been reported. The reaction constitutes an efficient method for the synthesis of 1,3-diene compounds bearing a ring structure. Mechanistically, the reaction involves migratory insertion of palladium carbene as the key step. PMID:25019414

  1. Evolution of Enzymatic Activities in the Enolase Superfamily:  Crystallographic and Mutagenesis Studies of the Reaction Catalyzed by d -Glucarate Dehydratase from Escherichia coli † , ‡

    Microsoft Academic Search

    Andrew M. Gulick; Brian K. Hubbard; John A. Gerlt; Ivan Rayment

    2000-01-01

    D-Glucarate dehydratase (GlucD) from Escherichia coli catalyzes the dehydration of both D-glucarate and L-idarate as well as their interconversion via epimerization. GlucD is a member of the mandelate racemase (MR) subgroup of the enolase superfamily, the members of which catalyze reactions that are initiated by abstraction of the R-proton of a carboxylate anion substrate. Alignment of the sequence of GlucD

  2. Lipase-catalyzed enantioselective esterification of (S)-naproxen hydroxyalkyl ester in organic media.

    PubMed

    Chang, Chun-Sheng; Hsu, Chin-Shuo; Shang, Chun-Sheng

    2003-03-01

    A lipase-catalyzed, enantioselective esterification process in organic solvents was developed for the synthesis of (S)-naproxen hydroxyalkyl ester. With the selection of lipase (Candida rugosa lipase) and reaction medium (isooctane and cyclohexane), a high enantiomeric ratio of > 100 for the enzyme was obtained. 1,4-Butanediol was the best acyl acceptor. The carbon chain length of the alcohol had a major effect on the enzyme activity and enantioselectivity of lipase-catalyzed esterification. PMID:12882564

  3. Real-time investigation of human topoisomerase I reaction kinetics using an optical sensor: a fast method for drug screening and determination of active enzyme concentrations

    NASA Astrophysics Data System (ADS)

    Kristoffersen, Emil L.; Jørgensen, Line A.; Franch, Oskar; Etzerodt, Michael; Frøhlich, Rikke; Bjergbæk, Lotte; Stougaard, Magnus; Ho, Yi-Ping; Knudsen, Birgitta R.

    2015-05-01

    Human DNA topoisomerase I (hTopI) is a nuclear enzyme that catalyzes relaxation of super helical tension that arises in the genome during essential DNA metabolic processes. This is accomplished through a common reaction mechanism shared among the type IB topoisomerase enzymes, including eukaryotic and poxvirus topoisomerase I. The mechanism of hTopI is specifically targeted in cancer treatment using camptothecin derivatives. These drugs convert the hTopI activity into a cellular poison, and hence the cytotoxic effects of camptothecin derivatives correlate with the hTopI activity. Therefore, fast and reliable techniques for high throughput measurements of hTopI activity are of high clinical interest. Here we demonstrate potential applications of a fluorophore-quencher based DNA sensor designed for measurement of hTopI cleavage-ligation activities, which are the catalytic steps affected by camptothecin. The kinetic analysis of the hTopI reaction with the DNA sensor exhibits a characteristic burst profile. This is the result of a two-step ping-pong reaction mechanism, where a fast first reaction, the one creating the signal, is followed by a slower second reaction necessary for completion of the catalytic cycle. Hence, the burst profile holds information about two reactions in the enzymatic mechanism. Moreover, it allows the amount of active enzyme in the reaction to be determined. The presented results pave the way for future high throughput drug screening and the potential of measuring active hTopI concentrations in clinical samples for individualized treatment.Human DNA topoisomerase I (hTopI) is a nuclear enzyme that catalyzes relaxation of super helical tension that arises in the genome during essential DNA metabolic processes. This is accomplished through a common reaction mechanism shared among the type IB topoisomerase enzymes, including eukaryotic and poxvirus topoisomerase I. The mechanism of hTopI is specifically targeted in cancer treatment using camptothecin derivatives. These drugs convert the hTopI activity into a cellular poison, and hence the cytotoxic effects of camptothecin derivatives correlate with the hTopI activity. Therefore, fast and reliable techniques for high throughput measurements of hTopI activity are of high clinical interest. Here we demonstrate potential applications of a fluorophore-quencher based DNA sensor designed for measurement of hTopI cleavage-ligation activities, which are the catalytic steps affected by camptothecin. The kinetic analysis of the hTopI reaction with the DNA sensor exhibits a characteristic burst profile. This is the result of a two-step ping-pong reaction mechanism, where a fast first reaction, the one creating the signal, is followed by a slower second reaction necessary for completion of the catalytic cycle. Hence, the burst profile holds information about two reactions in the enzymatic mechanism. Moreover, it allows the amount of active enzyme in the reaction to be determined. The presented results pave the way for future high throughput drug screening and the potential of measuring active hTopI concentrations in clinical samples for individualized treatment. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr01474c

  4. Facile surface PEGylation via tyrosinase-catalyzed oxidative reaction for the preparation of non-fouling surfaces.

    PubMed

    Lee, Yunki; Park, Kyung Min; Bae, Jin Woo; Park, Ki Dong

    2013-02-01

    The control of biological interactions that occur at material-cell/blood interfaces is of great importance to help maximize in vitro and in vivo performance of biomedical devices. PEGylation has been extensively used as an effective surface modification tool that can alter biological responses on device surfaces. Herein, we report a new surface PEGylation method using a tyrosinase-catalyzed oxidative reaction. Tyramine (TA), an enzymatically active phenolic compound, was chemically conjugated to methoxy poly(ethylene glycol) (mPEG). Surface immobilization of mPEG-TA onto various substrates was accomplished simply and rapidly by adding tyrosinase under mild conditions. It was shown that the water contact angles on all surfaces modified with mPEG-TA were decreased, indicating successful introduction of hydrophilic PEG. In addition, the X-ray photoelectron spectroscopy (XPS) spectra demonstrated the differences in the atomic composition on the TiO(2) surface after treatment with mPEG-TA. Non-fouling surfaces prevent non-specific interactions with proteins and cells; consistently, the PEGylated TiO(2) surface clearly showed a decrease in both levels of bovine serum albumin (BSA) adsorption and NIH3T3 cell attachment. Therefore, the facile surface PEGylation using a tyrosinase-catalyzed oxidative reaction should be useful for designing non-fouling surfaces of biomedical devices. PMID:23104029

  5. The gas phase reaction of singlet dioxygen with water: A water-catalyzed mechanism

    Microsoft Academic Search

    Xin Xu; Richard P. Muller; William A. Goddard III

    2002-01-01

    Stimulated by the recent surprising results from Wentworth et al. [Wentworth, A. D., Jones, L. H., Wentworth, P., Janda, K. D. & Lerner, R. A. (2000) Proc. Natl. Acad. Sci. USA 97, 10930-10935] that Abs efficiently catalyze the conversion of molecular singlet oxygen (1O2) plus water to hydrogen peroxide (HOOH), we used quantum chemical methods (B3LYP density functional theory) to

  6. Real-time investigation of human topoisomerase I reaction kinetics using an optical sensor: a fast method for drug screening and determination of active enzyme concentrations.

    PubMed

    Kristoffersen, Emil L; Jørgensen, Line A; Franch, Oskar; Etzerodt, Michael; Frøhlich, Rikke; Bjergbæk, Lotte; Stougaard, Magnus; Ho, Yi-Ping; Knudsen, Birgitta R

    2015-06-01

    Human DNA topoisomerase I (hTopI) is a nuclear enzyme that catalyzes relaxation of super helical tension that arises in the genome during essential DNA metabolic processes. This is accomplished through a common reaction mechanism shared among the type IB topoisomerase enzymes, including eukaryotic and poxvirus topoisomerase I. The mechanism of hTopI is specifically targeted in cancer treatment using camptothecin derivatives. These drugs convert the hTopI activity into a cellular poison, and hence the cytotoxic effects of camptothecin derivatives correlate with the hTopI activity. Therefore, fast and reliable techniques for high throughput measurements of hTopI activity are of high clinical interest. Here we demonstrate potential applications of a fluorophore-quencher based DNA sensor designed for measurement of hTopI cleavage-ligation activities, which are the catalytic steps affected by camptothecin. The kinetic analysis of the hTopI reaction with the DNA sensor exhibits a characteristic burst profile. This is the result of a two-step ping-pong reaction mechanism, where a fast first reaction, the one creating the signal, is followed by a slower second reaction necessary for completion of the catalytic cycle. Hence, the burst profile holds information about two reactions in the enzymatic mechanism. Moreover, it allows the amount of active enzyme in the reaction to be determined. The presented results pave the way for future high throughput drug screening and the potential of measuring active hTopI concentrations in clinical samples for individualized treatment. PMID:25963854

  7. DFT study on the reaction mechanism of the ring closing enyne metathesis (RCEYM) catalyzed by molybdenum alkylidene complexes.

    PubMed

    Solans-Monfort, Xavier

    2014-03-21

    The ring closing enyne metathesis reaction (RCEYM) catalyzed by molybdenum based monoalkoxy pyrrolyl Schrock type catalysts has been studied by means of DFT (B3LYP-D) calculations. The two potential active alkylidene species as well as the three proposed reaction mechanisms (ene-then-yne, endo-yne-then-ene and exo-yne-then-ene) have been taken into account. Moreover, the influence on the exo- and endo- selectivity of the reactant substituents has also been explored. Results show that, in contrast to what is found for RCEYM processes catalyzed by Ru-based catalysts, the metallacyclobutene is a very short-living reaction intermediate that can be present in two isomeric forms (trigonal bipyramid (TBP) coordination around the metal center and square based pyramid (SPY) coordination). These two isomers are directly involved in the reaction mechanism, and the ring opening takes place from the SPY species. Moreover and regardless of the nature of the reacting metal-alkylidene, the yne-then-ene pathways (endo- or exo-) are computed to present significantly lower energy barriers than the ene-then-yne pathway and thus the latter is computed not to take place. Finally, the exo-/endo- selectivity is predicted to highly depend on the sterics of the two carbon ends of the alkyne fragment. In this way, the carbon bearing the largest group prefers to interact with the carbon end of the metal-alkylidene. This places the bulkiest groups as far away as possible from the metal fragment and overall leads to a generally lower energy barrier for the metallacyclobutene formation, the key step in defining the exo-/endo- selectivity. PMID:24492319

  8. L-myo-inosose-1 as a probable intermediate in the reaction catalyzed by myo-inositol oxygenase

    SciTech Connect

    Naber, N.I.; Swan, J.S.; Hamilton, G.A.

    1986-11-04

    In previous investigations, it was necessary to have Fe(II) and cysteine present in order to assay the catalytic activity of purified hog kidney myo-inositol oxygenase. In the present study it was found that, if this purified nonheme iron enzyme is slowly frozen in solution with glutathione and stored at -20 degrees C, it is fully active in the absence of activators if catalase is present to remove adventitious H/sub 2/O/sub 2/. With this simpler assay system it was possible to clarify the effects of several variables on the enzymic reaction. Thus, the maximum velocity is pH-dependent with a maximum around pH 9.5, but the apparent Km for myo-inositol (air atmosphere) remains constant at 5.0 mM throughout a broad pH range. The enzyme is quite specific for its substrate myo-inositol, is very sensitive to oxidants and reductants, but is not affected by a variety of complexing agents, nucleotides, sulfhydryl reagents, etc. In other experiments it was found that L-myo-inosose-1, a potential intermediate in the enzymic reaction, is a potent competitive inhibitor (Ki = 62 microM), while other inososes and a solution thought to contain D-glucodialdehyde, another potential intermediate, are weak inhibitors. Also, both a kinetic deuterium isotope effect (kH/kD = 2.1) and a tritium isotope effect (kH/kT = 7.5) are observed for the enzymic reaction when (1-2H)- and (1-3H)-myo-inositol are used as reactants. These latter results are considered strong evidence that the oxygenase reaction proceeds by a pathway involving L-myo-inosose-1 as an intermediate rather than by an alternative pathway that would have D-glucodialdehyde as the intermediate.

  9. Mechanisms and stereoselectivities of the Rh(i)-catalyzed carbenoid carbon insertion reaction of benzocyclobutenol with diazoester.

    PubMed

    Wang, Yanyan; Wang, Yang; Zhang, Wenjing; Zhu, Yanyan; Wei, Donghui; Tang, Mingsheng

    2015-06-21

    In this study, a density functional theory (DFT) study has been carried out to investigate the mechanisms of Rh(i)-catalyzed carbenoid carbon insertion into a C-C bond reaction between benzocyclobutenol (R1) and diazoester (R2). The calculated results indicate that the reaction proceeds through five stages: deprotonation of R1, cleavage of the C-C bond, carbenoid carbon insertion, intramolecular aldol reaction, and protonation of the alkoxyl-Rh(i) intermediate. We have suggested and studied two possible pathways according to different coordination patterns (including ketone-type and enol-type coordination forms) in the fourth stage and found that the enol-type pathway is favorable, making the coordination mode of the Rh(i) center in the oxa-?-allyl Rh(i) intermediate clear in this reaction system. Moreover, four possible protonation channels have been calculated in the fifth stage, and the computational results show that the H2O-assisted proton transfer channel is the most favorable. The first step of the third stage is rate-determining, and the first steps in stages 3 and 4 play important roles in determining the stereoselectivities. Moreover, the analyses of distortion/interaction, natural bond orbital (NBO), and molecular orbital (MO) have been performed to better understand this title reaction. Furthermore, the pathway corresponding to the RR configurational product is the most favorable path, which is consistent with the experimental result. This work should be helpful for understanding the detailed reaction mechanism and the origin of stereoselectivities of the title reaction and thus could provide valuable insights into rational design of more efficient catalysts for this type of reactions. PMID:25984684

  10. Barrier Compression and Its Contribution to Both Classical and Quantum Mechanical Aspects of Enzyme Catalysis

    Microsoft Academic Search

    Sam Hay; Linus O. Johannissen; Michael J. Sutcliffe; Nigel S. Scrutton

    2010-01-01

    It is generally accepted that enzymes catalyze reactions by lowering the apparent activation energy by transition state stabilization or through destabilization of ground states. A more controversial proposal is that enzymes can also accelerate reactions through barrier compression—an idea that has emerged from studies of H-tunneling reactions in enzyme systems. The effects of barrier compression on classical (over-the-barrier) reactions, and

  11. Modification of Soybean Protein Hydrolysates by Alcalase-Catalyzed Plastein Reaction and the ACE-Inhibitory Activity of the Modified Product In Vitro

    Microsoft Academic Search

    Bo Gao; Xin-Huai Zhao

    2012-01-01

    Soybean protein hydrolysates were prepared by hydrolyzing soybean protein isolates with a protease alcalase to a degree of hydrolysis of 16.6%, and then modified by alcalase-catalyzed plastein reaction to reveal the impact of plastein reaction on the ACE-inhibitory activity of the modified product in vitro. The suitable conditions of plastein reaction of soybean protein hydrolysates were selected based on the

  12. Enzyme immunoassay by dynamic enhanced vibrational spectroscopy of the enzyme reaction product

    NASA Astrophysics Data System (ADS)

    Zhao, Haiying; Dou, Xiaoming

    2005-01-01

    This paper reports a kind of application of surface-enhanced Raman scattering (SERS) to immunology. In the proposed system, antibody immobilized on a solid substrate reacts with antigen, which binds with another antibody labeled with peroxidase. If this immunocomplex is subjected to reaction with o-phenylenediamine and hydrogenperoxide at 37°C, azoaniline is generated. This azo compound is adsorbed on a silver colloid and only the azo compound gives a strong surface-enhanced resonance Raman (SERRS) spectrum. A linear relationship was observed between the peak intensity of the N=N stretching band and the concentration of antigen, revealing that one can determine the concentration of antigen by the SERRS measurement of the reaction product.

  13. Redox Reactions of Metalloporphyrins and their Role in Catalyzed Reduction of Carbon Dioxide

    SciTech Connect

    Neta, P.

    2002-09-01

    Pulse radiolysis and laser photolysis are used to study redox processes of metalloporphyrins and related complexes in order to evaluate these light absorbing molecules as sensitizers and intermediates in solar energy conversion schemes. The main thrust of the current studies is to investigate the role of reduced metalloporphyrins as intermediates in the catalyzed reduction of carbon dioxide. Studies involve cobalt and iron porphyrins, phthalocyanines, corroles, and corrins as homogeneous catalysts for reduction of carbon dioxide in solution. The main aim is to understand the mechanisms of these photochemical schemes in order to facilitate their potential utilization.

  14. Asymmetric Glyoxylate-Ene Reactions Catalyzed by Chiral Pd(II) Complexes in the Ionic Liquid [bmim][PF6

    PubMed Central

    He, Xi Jun; Shen, Zhen Lu; Mo, Wei Min; Hu, Bao Xiang; Sun, Nan

    2007-01-01

    The room temperature ionic liquid [bmim][PF6] was employed as the reaction medium in the asymmetric glyoxylate-ene reaction of ?-methyl styrene (4a) with ethyl glyoxylate using chiral palladium(II) complexes as the catalysts. [Pd(S-BINAP)(3,5-CF3-PhCN)2](SbF6)2 (1b) showed the highest catalytic activity. Under the reaction conditions of 40 °C, 0.5 h, and 1b/4a molar ratio of 0.05, ethyl ?-hydroxy-4-phenyl-4-pentenoate was obtained in excellent chemical yield (94 %) with high enantioselectivity (70 %). Other ?-hydroxy esters can also be obtained in high chemical yields and enantioselectities through the glyoxylate-ene reactions of alkenes with glyoxylates catalyzed by 1b in [bmim][PF6]. Moreover, the ionic liquid [bmim][PF6] which contained the palladium(II) complex could be recycled and reused several times without significant loss of the catalytic activity.

  15. Mechanism of the EPSP synthase catalyzed reaction: evidence for the lack of a covalent carboxyvinyl intermediate in catalysis

    SciTech Connect

    Wibbenmeyer, J.; Brundage, L.; Padgette, S.R.; Likos, J.J.; Kishore, G.M.

    1988-06-16

    In order to detect covalent reaction intermediates in the 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase reaction, we have investigated the interaction of EPSP synthase with the reaction product EPSP. An exchange of EPSP-methylene protons could be demonstrated by incubating EPSPS with EPSP in D/sub 2/O. Since trace amounts of contaminating Pi would lead to reversal of EPSPS reaction and hence methylene proton exchange, we added pyruvate kinase, ADP, Mg++ and K+. Under these conditions, any contaminating Pi that is converted to PEP is trapped as ATP. No exchange of EPSP protons with those of the solvent could be detected in the presence of this trap system, suggesting that enzyme-bound EPSP is unable to form a covalent tetrahedral complex. Incorporation of (/sup 14/C) from (/sup 14/C)-S3P and (/sup 14/C)-PEP into EPSP could be detected, but only in the absence of a PEP (or Pi) trap system. This indicates that for the exchange reaction, Pi is required, and also indicates the absence of a covalent intermediate, unless the carboxyvinyl-enzyme-bound S3P is completely restricted from exchange.

  16. Inhibition of the Reaction Kinetics of the Enzyme o-Diphenol Oxidase

    Microsoft Academic Search

    Kieran Fergus LIM

    Chemical kinetics is a fundamental component of chemistry: traditional chemistry-laboratory exercises have concentrated on the study of non- biological organic or inorganic reaction kinetics. Many students feel that such studies bear little relationship to the world outside the chemistry laboratory. The aim of this experiment is to investigate the kinetics of a reaction catalysed by the enzyme o-diphenol oxidase (oDPO

  17. Kinetic substrate quantification by fitting the enzyme reaction curve to the integrated Michaelis-Menten equation

    Microsoft Academic Search

    Fei Liao; Kao-Cong Tian; Xiao Yang; Qi-Xin Zhou; Zhao-Chun Zeng; Yu-Ping Zuo

    2003-01-01

    The reliability of kinetic substrate quantification by nonlinear fitting of the enzyme reaction curve to the integrated Michaelis-Menten equation was investigated by both simulation and preliminary experimentation. For simulation, product absorptivity k was 3.00 mmolу L cmу and Km was 0.10 mmol Lу, and uniform absorbance error † was randomly inserted into the error-free reaction curve of product absorbance Ai

  18. Cloning and characterization of oxidosqualene cyclases from Kalanchoe daigremontiana: enzymes catalyzing up to 10 rearrangement steps yielding friedelin and other triterpenoids.

    PubMed

    Wang, Zhonghua; Yeats, Trevor; Han, Hong; Jetter, Reinhard

    2010-09-24

    The first committed step in triterpenoid biosynthesis is the cyclization of oxidosqualene to polycyclic alcohols or ketones C(30)H(50)O. It is catalyzed by single oxidosqualene cyclase (OSC) enzymes that can carry out varying numbers of carbocation rearrangements and, thus, generate triterpenoids with diverse carbon skeletons. OSCs from diverse plant species have been cloned and characterized, the large majority of them catalyzing relatively few rearrangement steps. It was recently predicted that special OSCs must exist that can form friedelin, the pentacyclic triterpenoid whose formation involves the maximum possible number of rearrangement steps. The goal of the present study, therefore, was to clone a friedelin synthase from Kalanchoe daigremontiana, a plant species known to accumulate this triterpenoid in its leaf surface waxes. Five OSC cDNAs were isolated, encoding proteins with 761-779 amino acids and sharing between 57.4 and 94.3% nucleotide sequence identity. Heterologous expression in yeast and GC-MS analyses showed that one of the OSCs generated the steroid cycloartenol together with minor side products, whereas the other four enzymes produced mixtures of pentacyclic triterpenoids dominated by lupeol (93%), taraxerol (60%), glutinol (66%), and friedelin (71%), respectively. The cycloartenol synthase was found expressed in all leaf tissues, whereas the lupeol, taraxerol, glutinol, and friedelin synthases were expressed only in the epidermis layers lining the upper and lower surfaces of the leaf blade. It is concluded that the function of these enzymes is to form respective triterpenoid aglycones destined to coat the leaf exterior, probably as defense compounds against pathogens or herbivores. PMID:20610397

  19. Benzoyl-coenzyme A reductase (dearomatizing), a key enzyme of anaerobic aromatic metabolism. ATP dependence of the reaction, purification and some properties of the enzyme from Thauera aromatica strain K172.

    PubMed

    Boll, M; Fuchs, G

    1995-12-15

    Anoxic metabolism of many aromatic compounds proceeds via the common intermediate benzoyl-CoA. Benzoyl-CoA is dearomatized by benzoyl-CoA reductase (dearomatizing) in a two-electron reduction step, possibly yielding cyclohex-1,5-diene-1-carboxyl-CoA. This process has to overcome a high activation energy and is considered a biological Birch reduction. The central, aromatic-ring-reducing enzyme was investigated for the first time in the denitrifying bacterium Thauera aromatica strain K172. A spectrophotometric assay was developed which was strictly dependent on MgATP, both with cell extract and with purified enzyme. The oxygen-sensitive new enzyme was purified 35-fold with 20% yield under anaerobic conditions in the presence of 0.25 mM dithionite. It had a native molecular mass of approximately 170 kDa and consisted of four subunits a,b,c,d of 48, 45, 38 and 32 kDa. The oligomer composition of the protein most likely is abcd. The ultraviolet/visible spectrum of the protein as isolated, but without dithionite, was characteristic for an iron-sulfur protein with an absorption maximum at 279 nm and a broad shoulder at 390 nm. The estimated molar absorption coefficient at 390 nm was 35,000 M-1 cm-1. Reduction of the enzyme by dithionite resulted in a decrease of absorbance at 390 nm, and the colour turned from greenish-brown to red-brown. The enzyme contained 10.8 +/- 1.5 mol Fe and 10.5 +/- 1.5 mol acid-labile sulfur/mol. Besides zinc (0.5 mol/mol protein) no other metals nor selenium could be detected in significant amounts. The enzyme preparation contained a flavin or flavin-like compound; the estimated content was 0.3 mol/mol enzyme. The enzyme reaction required MgATP and a strong reductant such as Ti(III). The reaction catalyzed is: benzoyl-CoA + 2 Ti(III) + n ATP-->non-aromatic acyl-CoA + 2 Ti(IV) + n ADP + n Pi. The estimated number n of ATP molecules hydrolyzed/two electrons transferred in benzoyl-CoA reduction is 2-4. In the absence of benzoyl-CoA the enzyme exhibited oxygen-sensitive ATPase activity. The enzyme was specific for Mg(2+)-ATP, other nucleoside triphosphates being inactive (< 1%). Mg2+ could be substituted to some extent by Mn2+, Fe2+ and less efficiently by Co2+. Benzoate was not reduced, whereas some fluoro, hydroxy, amino and methyl analogues of the activated benzoic acid were reduced, albeit at much lower rate; the products remain to be identified. The specific activity with reduced methyl viologen as the electron donor was 0.55 mumol min-1 mg-1 corresponding to a catalytic number of 1.6 s-1. The apparent Km values under the assay conditions (0.5 mM for both reduced and oxidized methyl viologen) of benzoyl-CoA and ATP were 15 microM and 0.6 mM, respectively. The enzyme was inactivated by ethylene, bipyridyl and, in higher concentrations, by acetylene. Benzoyl-CoA reductase also catalyzed the ATP-dependent two-electron reduction of hydroxylamine (Km 0.15 mM) and azide. Some of the properties of the enzyme are reminiscent of those of nitrogenase which similarly overcomes the high activation energy for dinitrogen reduction by coupling electron transfer to the hydrolysis of ATP. PMID:8575453

  20. Computer simulations of quantum tunnelling in enzyme-catalysed hydrogen transfer reactions.

    PubMed

    Ranaghan, Kara E; Mulholland, Adrian J

    2010-03-01

    Transfer of hydrogen as a proton, hydride or hydrogen atom is an important step in many enzymic reactions. Experiments show kinetic isotope effects (KIEs) for some enzyme-catalysed hydrogen transfer reactions that deviate significantly from the limits imposed by considering the differences in mass of the isotopes alone (i.e. the semiclassical limit). These KIEs can be explained if the transfer of the hydrogen species occurs via a quantum mechanical tunnelling mechanism. The unusual temperature dependence of some KIEs has led to suggestions that enzymes have evolved to promote tunnelling through dynamics - a highly controversial hypothesis. Molecular simulations have a vital role in resolving these questions, providing a level of detail of analysis not possible through experiments alone. Here, we review computational molecular modelling studies of quantum tunnelling in enzymes, in particular focusing on the enzymes soybean lipoxygenase-1 (SLO-1), dihydrofolate reductase (DHFR), methylamine dehydrogenase (MADH) and aromatic amine dehydrogenase (AADH) to illustrate the current controversy regarding the importance of quantum effects in enzyme catalysis. PMID:20640799

  1. From homogeneously to heterogeneously catalyzed cyclopropanation reactions: New polymeric membranes embedding cobalt chiral schiff base complexes

    Microsoft Academic Search

    Alessandro Caselli; Maria Giovanna Buonomenna; Federico de Baldironi; Luca Laera; Simone Fantauzzi; Fabio Ragaini; Emma Gallo; Giovanni Golemme; Sergio Cenini; Enrico Drioli

    2010-01-01

    In this paper we report the preparation of catalytic polymeric membranes having the complex [(N,N?-bis(3-tert-butyl-5-(heptadecafluorooctyl)salicylidene)-trans-1,2-cyclohexanediamine)Co] embedded into Hyflon AD60X, PES and PSf and their use in the cyclopropanation reaction of olefins with ethyl diazoacetate (EDA). A study of the reaction in the homogeneous phase was also performed. The kinetics of the cyclopropanation reaction is first-order in the diazoacetate and the

  2. Importance of glutamate 87 and the substrate ?-amine for the reaction catalyzed by D-arginine dehydrogenase.

    PubMed

    Ball, Jacob; Bui, Quan V V; Gannavaram, Swathi; Gadda, Giovanni

    2015-02-15

    Pseudomonas aeruginosa D-arginine dehydrogenase (PaDADH) catalyzes the oxidation of D-arginine to iminoarginine, which is non-enzymatically hydrolyzed to 2-ketoarginine and ammonia. Here, site-directed mutagenesis and pH effects were used to investigate binding and catalysis of zwitterionic and cationic substrates for the enzyme. An unprotonated group with apparent pKa value ?7.9 is required for binding D-arginine or D-lysine, but not D-methionine or D-leucine. This group is E87, as suggested by its replacement with leucine. An unprotonated group with pKa of 9.5, which persists in the H48F and E87L variants, is required for amine oxidation with all substrates. Since Y53 and Y249 were previously ruled out, the pKa is assigned to the substrate ?-NH3(+) group, which previous QM/MM and Kd pH-profile demonstrated to be protonated for preferred binding to the enzyme. Lack of pH effects on the (D)kred with D-leucine established 9.5 as the intrinsic pKa, and D-leucine as a non-sticky substrate. D-Arginine, D-lysine and D-methionine and their corresponding iminoproducts were significantly stickier than D-leucine, as indicated by apparent pKa values <9.5 in both kcat/Km and kcat. Restricted proton movements in catalysis were established from hollowed kcat pH profiles in wild-type PaDADH with D-lysine and in the H48F and E87L enzymes with D-arginine. PMID:25637657

  3. The enantioselective construction of tetracyclic diterpene skeletons with Friedel-Crafts alkylation and palladium-catalyzed cycloalkenylation reactions.

    PubMed

    Burke, Sarah J; Malachowski, William P; Mehta, Sharan K; Appenteng, Roselyn

    2015-03-01

    Due to the profound extent to which natural products inspire medicinal chemists in drug discovery, there is demand for innovative syntheses of these often complex materials. This article describes the synthesis of tricarbocyclic natural product architectures through an extension of the enantioselective Birch-Cope sequence with intramolecular Friedel-Crafts alkylation reactions. Additionally, palladium-catalyzed enol silane cycloalkenylation of the tricarbocyclic structures afforded the challenging bicyclo[3.2.1]octane C/D ring system found in the gibberellins and the ent-kauranes, two natural products with diverse medicinal value. In the case of the ent-kaurane derivative, an unprecedented alkene rearrangement converted four alkene isomers to one final product. PMID:25598198

  4. Small Temperature Dependence of the Kinetic Isotope Effect for the Hydride Transfer Reaction Catalyzed by Escherichia coli Dihydrofolate Reductase

    PubMed Central

    Pu, Jingzhi; Ma, Shuhua; Gao, Jiali; Truhlar, Donald G.

    2015-01-01

    The H/D primary kinetic isotope effect (KIE) for the hydride transfer reaction catalyzed by Escherichia coli dihydrofolate reductase (ecDHFR) is calculated as a function of temperature employing ensemble-averaged variational transition-state theory with multidimensional tunneling. The calculated KIEs display only a small temperature dependence over the temperature range of 5 to 45 °C. We identify two key features that contribute to canceling most of the temperature dependence of the KIE that would be expected on the basis of simpler models. Related issues such as the isotope effects on Arrhenius preexponential factors, large differences between free energies of activation and Arrhenius activation energy, and fluctuations of effective barriers are also discussed. PMID:16852008

  5. Structural basis of the divergent oxygenation reactions catalyzed by the rieske nonheme iron oxygenase carbazole 1,9a-dioxygenase.

    PubMed

    Inoue, Kengo; Usami, Yusuke; Ashikawa, Yuji; Noguchi, Haruko; Umeda, Takashi; Yamagami-Ashikawa, Aiko; Horisaki, Tadafumi; Uchimura, Hiromasa; Terada, Tohru; Nakamura, Shugo; Shimizu, Kentaro; Habe, Hiroshi; Yamane, Hisakazu; Fujimoto, Zui; Nojiri, Hideaki

    2014-05-01

    Carbazole 1,9a-dioxygenase (CARDO), a Rieske nonheme iron oxygenase (RO), is a three-component system composed of a terminal oxygenase (Oxy), ferredoxin, and a ferredoxin reductase. Oxy has angular dioxygenation activity against carbazole. Previously, site-directed mutagenesis of the Oxy-encoding gene from Janthinobacterium sp. strain J3 generated the I262V, F275W, Q282N, and Q282Y Oxy derivatives, which showed oxygenation capabilities different from those of the wild-type enzyme. To understand the structural features resulting in the different oxidation reactions, we determined the crystal structures of the derivatives, both free and complexed with substrates. The I262V, F275W, and Q282Y derivatives catalyze the lateral dioxygenation of carbazole with higher yields than the wild type. A previous study determined the crystal structure of Oxy complexed with carbazole and revealed that the carbonyl oxygen of Gly178 hydrogen bonds with the imino nitrogen of carbazole. In these derivatives, the carbazole was rotated approximately 15, 25, and 25°, respectively, compared to the wild type, creating space for a water molecule, which hydrogen bonds with the carbonyl oxygen of Gly178 and the imino nitrogen of carbazole. In the crystal structure of the F275W derivative complexed with fluorene, C-9 of fluorene, which corresponds to the imino nitrogen of carbazole, was oriented close to the mutated residue Trp275, which is on the opposite side of the binding pocket from the carbonyl oxygen of Gly178. Our structural analyses demonstrate that the fine-tuning of hydrophobic residues on the surface of the substrate-binding pocket in ROs causes a slight shift in the substrate-binding position that, in turn, favors specific oxygenation reactions toward various substrates. PMID:24584240

  6. Low-temperature superacid catalysis: Reactions of n - butane and propane catalyzed by iron- and manganese-promoted sulfated zirconia

    SciTech Connect

    Tsz-Keung, Cheung; d`Itri, J.L.; Lange, F.C.; Gates, B.C. [Univ. of California, Davis, CA (United States)

    1995-12-31

    The primary goal of this project is to evaluate the potential value of solid superacid catalysts of the sulfated zirconia type for light hydrocarbon conversion. The key experiments catalytic testing of the performance of such catalysts in a flow reactor fed with streams containing, for example, n-butane or propane. Fe- and Mn-promoted sulfated zirconia was used to catalyze the conversion of n-butane at atmospheric pressure, 225-450{degrees}C, and n-butane partial pressures in the range of 0.0025-0.01 atm. At temperatures <225{degrees}C, these reactions were accompanied by cracking; at temperatures >350{degrees}C, cracking and isomerization occurred. Catalyst deactivation, resulting at least in part from coke formation, was rapid. The primary cracking products were methane, ethane, ethylene, and propylene. The observation of these products along with an ethane/ethylene molar ratio of nearly 1 at 450{degrees}C is consistent with cracking occurring, at least in part, by the Haag-Dessau mechanism, whereby the strongly acidic catalyst protonates n-butane to give carbonium ions. The rate of methane formation from n-butane cracking catalyzed by Fe- and Mn-promoted sulfated zirconia at 450{degrees}C was about 3 x 10{sup -8} mol/(g of catalyst {center_dot}s). The observation of butanes, pentanes, and methane as products is consistent with Olah superacid chemistry, whereby propane is first protonated by a very strong acid to form a carbonium ion. The carbonium ion then decomposes into methane and an ethyl cation which undergoes oligocondensation reactions with propane to form higher molecular weight alkanes. The results are consistent with the identification of iron- and manganese-promoted sulfated zirconia as a superacid.

  7. Rapid identification of mycobacteria to the species level by polymerase chain reaction and restriction enzyme analysis.

    PubMed Central

    Telenti, A; Marchesi, F; Balz, M; Bally, F; Böttger, E C; Bodmer, T

    1993-01-01

    A method for the rapid identification of mycobacteria to the species level was developed on the basis of evaluation by the polymerase chain reaction (PCR) of the gene encoding for the 65-kDa protein. The method involves restriction enzyme analysis of PCR products obtained with primers common to all mycobacteria. Using two restriction enzymes, BstEII and HaeIII, medically relevant and other frequent laboratory isolates were differentiated to the species or subspecies level by PCR-restriction enzyme pattern analysis. PCR-restriction enzyme pattern analysis was performed on isolates (n = 330) from solid and fluid culture media, including BACTEC, or from frozen and lyophilized stocks. The procedure does not involve hybridization steps or the use of radioactivity and can be completed within 1 working day. Images PMID:8381805

  8. Chiral N,N'-dioxide-FeCl3 complex-catalyzed asymmetric intramolecular Cannizzaro reaction.

    PubMed

    Wu, Wangbin; Liu, Xiaohua; Zhang, Yuheng; Ji, Jie; Huang, Tianyu; Lin, Lili; Feng, Xiaoming

    2015-07-25

    An environmentally benign catalyst, the N,N'-dioxide-FeCl3 complex, has been developed for the asymmetric intramolecular Cannizzaro reaction. Aryl and alkyl glyoxal monohydrates were applied to obtain ?-hydroxy acid esters with excellent results. Deuterium-label and control experiments shed light on the reaction mechanism. PMID:26098988

  9. Synthesis of dopamine and L-DOPA-alpha-glycosides by reaction with cyclomaltohexaose catalyzed by cyclomaltodextrin glucanyltransferase.

    PubMed

    Yoon, Seung-Heon; Bruce Fulton, D; Robyt, John F

    2009-11-23

    Dopamine-HCl and L-DOPA-alpha-glycosides were prepared by reaction with cyclomaltohexaose, catalyzed by Bacillus macerans cyclomaltodextrin glucanyltransferase. The reaction gave maltodextrins attached to dopamine and L-DOPA; the maltodextrins were trimmed by reactions with glucoamylase and beta-amylase to produce alpha-glucosyl- and alpha-maltosyl-glycosides, respectively. The glucoamylase- or beta-amylase-treated dopamine- and L-DOPA-alpha-glycosides were fractionated and purified by BioGel P-2 gel-filtration column chromatography and preparative descending paper chromatography. Analysis by MALDI-TOF mass spectrometry and one- and two-dimensional NMR showed that the purified glycosides of dopamine and L-DOPA were glycosylated at the hydroxyl groups of positions 3 and 4 of the catechol ring. The major product was found to be 4-O-alpha-glycopyranosyl L-DOPA, and it was shown to be more resistant to oxidative tolerance experiments, involving hydrogen peroxide and ferrous ion, than L-DOPA. L-DOPA-alpha-glycosides are possibly more effective substitutes for L-DOPA in treating Parkinson's disease in that they are more resistant to oxidation and methylation, which renders L-DOPA ineffective and deleterious. PMID:19793583

  10. Specificity of Carica papaya latex in lipase-catalyzed interesterification reactions

    Microsoft Academic Search

    P. Villeneuve; M. Pina; A. Skarbek; J. Graille; T. A. Foglia

    1997-01-01

    Enzymatic interesterification of the chiral triacylglycerol, 1-butyroyl-2-stearoyl-3-palmitoyl-sn-glycerol (sn-BSP) with trimyristin indicated that the lipase present in Carica papaya latex exhibits an sn3 stereoselectivity. Other interesterification experiments with homogeneous triacylglycerols of varying chain length with tricaprylin showed that this enzyme also has a typoselectivity for short chain fatty acids.

  11. Biodegradation of Chlorinated Solvents: Reactions near DNAPL and Enzyme Function

    SciTech Connect

    McCarty, P. L.; Spormann, Alfred M.; Criddle, Craig, S.

    2003-12-11

    Chlorinated solvents are among the most widespread groundwater contaminants in the country, contamination which is also among the most difficult and expensive for remediation. These solvents are biodegradable in the absence of oxygen, but this biodegradation requires both a food source for the organisms (electron donor) and the presence of chlorinated solvent biodegrading organisms. These two requirements are present naturally at some contamination sites, leading to natural attenuation of the solvents. If one or both requirements are absent, then engineered bioremediation either through addition of an external electron donor or through bioaugmentation with appropriate microorganisms, or both, may be used for site remediation. The most difficult case for cleanup is when a large residual of undissolved chlorinated solvents are present, residing as dense -non-aqueous-phase- liquid ( DNAPL). A major focus of this study was on the potential for biodegradation of the solvents when pre sent as DNAPL where concentrations are very high and potential for toxicity to microorganisms exist. Another focus was on a better understanding of the biological mechanisms involved in chlorinated solvent biodegradation . These studies were directed towards the chlorinated solvents, trichloroethene (TCE), tetrachloroethene or perchloroethene (PCE), and carbon tetrachloride (CT). The potential for biodegradation of TCE and PCE DNAPL was clearly demonstrated in this research. From column soil studies and batch studies we found there to be a clear advantage in focusing efforts at bioremediation near the DNAPL. Here, chlorinated solvent concentrations are the highest, both because of more favorable reaction kinetics and because such high solvent concentrations are toxic to microorganisms, such as methanogens, which compete with dehalogenators for the electron donor. Additionally, biodegradation near a PCE DNAPL results in an enhanced dissolution rate for the chlorinated solvent, by factors of three to five times, leading to a more rapid clean-up of the DNAPL zone. The most favored electron donor to add is one which partitions well with the chlorinated solvent or can be concentrated near it. Unfortunately, an ideal electron donor, such as vegetable oil, is difficult to introduce and mix with DNAPL in the ground, doing this properly remains an engineering challenge. Numerical model studies have indicated that several factors may significantly influence the rate and extent of enhancement, including the inhibitory effects of PCE and cDCE, the level of ED concentration, DNAPL configuration, and competition for ED. Such factors need to be considered when contemplating engineered DNAPL bioremediation. Pseudomonas stuzeri KC is an organism that transforms CT to carbon dioxide and chloride without the formation of the hazardous intermediate, chloroform. This is accomplished by production and secretion of a molecule called PDTC. This study was direct ed towards determining how PDTC works. Cu (II) at a ratio of 1:1 Cu to PDTC was found to result in the most rapid CT transformation, confirming that the PDTC-Cu complex is both a reactant and a catalyst in CT transformation. CT degradation requires that the PDTC be in a reduced form, which is generated by contact with cell components. Fe(II) inhibits CT transformation by PDTC. Studies indicated that this inhibition is enhanced by some compound or factor in the supernatant with molecular weight greater than 10,000 Da. We have made progress in determining what this factor might be, but have not yet been able to identify it. In related studies, we found that CT transformation by another organism, Shewanella oneidensis MR1, also involves an excreted factor, but this factor is different from PDTC and results in chloroform transformation as an intermediate. Our studies have indicated that this factor is similar to vitamin K2, and we have also confirmed that vitamin K2 does transform C T into chloroform.

  12. Chiral diene as the ligand for the synthesis of axially chiral compounds via palladium-catalyzed Suzuki-Miyaura coupling reaction.

    PubMed

    Zhang, Shu-Sheng; Wang, Zhi-Qian; Xu, Ming-Hua; Lin, Guo-Qiang

    2010-12-01

    The first palladium-diene-catalyzed asymmetric Suzuki-Miyaura coupling reaction has been achieved. A number of functionalized biaryls were obtained in high yields and in moderate to high enantioselectivities. The existence of an ortho-formyl group greatly improves the catalyst efficiency and permits further synthetic elaborations. PMID:21069984

  13. BF 3·Et 2O catalyzed diastereoselective nucleophilic reactions of 3-silyloxypiperidine N, O-acetal with silyl enol ether and application to the asymmetric synthesis of (+)-febrifugine

    Microsoft Academic Search

    Ru-Cheng Liu; Wei Huang; Jing-Yi Ma; Bang-Guo Wei; Guo-Qiang Lin

    2009-01-01

    The asymmetric BF3·Et2O catalyzed nucleophilic reactions of 3-silyloxypiperidine N,O-acetal 10 with silyl enol ethers derived from ketones are described. (+)-Febrifugine 1, an antimalarial alkaloid, was successfully synthesized based on this nucleophilic substitution. In addition, N,O-acetal 10 was synthesized from l-benzyl glutamate in 11 steps.

  14. A Bifunctional Enzyme (Delta^1Pyrroline5Carboxylate Synthetase) Catalyzes the First Two Steps in Proline Biosynthesis in Plants

    Microsoft Academic Search

    Chien-An A. Hu; Ashton J. Delauney; Desh Pal S. Verma

    1992-01-01

    Many plants synthesize and accumulate proline in response to osmotic stress. Despite the importance of this pathway, however, the exact metabolic route and enzymes involved in the synthesis of proline in plants have not been unequivocally identified. We report here the isolation of a mothbean (Vigna aconitifolia) cDNA clone encoding a bifunctional enzyme, Delta^1-pyrroline-5-carboxylate synthetase (P5CS), with both gamma-glutamyl kinase

  15. Interconversion of ketoprofen recognition in firefly luciferase-catalyzed enantioselective thioesterification reaction using from Pylocoeria miyako (PmL) and Hotaria parvura (HpL) just by mutating two amino acid residues.

    PubMed

    Kato, Dai-ichiro; Hiraishi, Yoshihiro; Maenaka, Mika; Yokoyama, Keisuke; Niwa, Kazuki; Ohmiya, Yoshihiro; Takeo, Masahiro; Negoro, Seiji

    2013-11-01

    We identified the critical amino acid residues for substrate recognition using two firefly luciferases from Pylocoeria miyako (PmL) and Hotaria parvura (HpL), as these two luciferase enzymes exhibit different activities toward ketoprofen. Specifically, PmL can catalyze the apparent enantioselective thioesterification reaction, while HpL cannot. By comparing the amino acid sequences around the active site, we identified two residues (I350 and M397 in PmL and F351 and S398 in HpL) that were different between the two enzymes, and the replacement of these amino acids resulted in changing the ketoprofen recognition pattern. The inactive HpL was converted to the active enzyme toward ketoprofen and vice versa for PmL. These residues also affected the enantioselectivity toward ketoprofen; however, the bioluminescent color was not affected. In addition, using molecular dynamics calculations, the replacement of these two amino acids induced changes in the state of hydrogen bonding between ketoprofen and the S349 side chain through the active site water. As S349 is not considered to influence color tuning, these changes specifically caused the differences in ketoprofen recognition in the enzyme. PMID:23685028

  16. Evolution of Domain Architectures and Catalytic Functions of Enzymes in Metabolic Systems

    E-print Network

    Yeang, Chen-Hsiang

    Evolution of Domain Architectures and Catalytic Functions of Enzymes in Metabolic Systems Summit architectures and catalytic functions of enzymes constitute the centerpieces of a metabolic network. These types. In contrast, prokaryotic enzymes become more versatile by catalyzing multiple reactions with similar chemical

  17. Obtaining enzymes in pure form was an essential prerequisite for understanding the

    E-print Network

    Herschlag, Dan

    Obtaining enzymes in pure form was an essential prerequisite for understanding the underlying and affinity tag- ging2. In addition to the most basic task of identifying distinct enzymes that catalyze dis- tinct reactions (an endeavor that continues in the genomic era), enzymes were shown to exhibit high

  18. A Hands-On Classroom Simulation to Demonstrate Concepts in Enzyme Kinetics

    ERIC Educational Resources Information Center

    Junker, Matthew

    2010-01-01

    A classroom exercise is described to introduce enzyme kinetics in an undergraduate biochemistry or chemistry course. The exercise is a simulation in which a student acts as an enzyme that "catalyzes" the unscrewing of a nut from a bolt. With other students assisting, the student enzyme carries out reactions with bolt-nut substrates under different…

  19. Palladium- and Nickel-Catalyzed Carbon–Carbon Bond Insertion Reactions with Alkylidenesilacyclopropanes

    PubMed Central

    Buchner, Kay M.; Woerpel, K. A.

    2010-01-01

    Palladium and nickel catalysts promoted highly selective carbon–carbon bond insertion reactions with di-tert-butyl-alkylidenesilacyclopropanes. Pd(PPh3)4 was demonstrated to be the optimal catalyst, allowing for a variety of carbon–carbon ?-bond insertion reactions. Depending on the nature of the carbon–carbon ? bond, the insertion reaction proceeded with either direct insertion into the carbon(sp2)–silicon bond or with allylic transposition. Ring-substituted alkylidenesilacyclopropanes required a nickel catalyst to afford insertion products. Using Ni(cod)2 as the carbon–carbon bond insertion catalyst, new double alkyne insertion products and alkene isomerization products were observed. PMID:20419110

  20. Rapid and Efficient Functionalized Ionic Liquid-Catalyzed Aldol Condensation Reactions Associated with Microwave Irradiation

    PubMed Central

    Wang, Chang; Liu, Jing; Leng, Wenguang; Gao, Yanan

    2014-01-01

    Five quaternary ammonium ionic liquid (IL) and two tetrabutylphosphonium ILs were prepared and characterized. An environmentally benign and convenient functionalized ionic liquid catalytic system was thus explored in the aldol condensation reactions of aromatic aldehydes with acetone. The aldol reactions proceeded more efficiently through microwave-assisted heating than through conventional thermal heating. The yield of products obtained under microwave heating for 30 min was approximately 90%, and the ILs can be recovered and reused at least five times without apparent loss of activity. In addition, this catalytic system can be successfully extended to the Henry reactions. PMID:24445262

  1. Heavy atom isotope effects on enzymatic reactions

    NASA Astrophysics Data System (ADS)

    Paneth, Piotr

    1994-05-01

    The theory of isotope effects, which has proved to be extremely useful in providing geometrical details of transition states in a variety of chemical reactions, has recently found an application in studies of enzyme-catalyzed reactions. These reactions are multistep in nature with few steps being partially rate-limiting, thus interpretation of these isotope effects is more complex. The theoretical framework of heavy-atom isotope effects on enzymatic reactions is critically analyzed on the basis of recent results of: carbon kinetic isotope effects on carbonic anhydrase and catalytic antibodies; multiple carbon, deuterium isotope effects on reactions catalyzed by formate decarboxylase; oxygen isotope effects on binding processes in reactions catalyzed by pyruvate kinase; and equilibrium oxygen isotope effect on binding an inhibitor to lactate dehydrogenase. The advantages and disadvantages of reaction complexity in learning details of formal and molecular mechanisms are discussed in the examples of reactions catalyzed by phosphoenolpyruvate carboxylase, orotidine decarboxylase and glutamine synthetase.

  2. Copper(ii)-catalyzed oxidative [3+2] cycloaddition reactions of secondary amines with ?-diazo compounds: a facile and efficient synthesis of 1,2,3-triazoles.

    PubMed

    Li, Yi-Jin; Li, Xue; Zhang, Shao-Xiao; Zhao, Yu-Long; Liu, Qun

    2015-07-25

    A novel copper-catalyzed [3+2] cycloaddition reaction of secondary amines with ?-diazo compounds has been developed via a cross-dehydrogenative coupling process. The reaction involves a sequential aerobic oxidation/[3+2] cycloaddition/oxidative aromatization procedure and provides an efficient method for the construction of 1,2,3-triazoles in a single step in an atom-economic manner from readily available starting materials under very mild conditions. PMID:26076660

  3. Wash Bottle Laboratory Exercises: Iodide-Catalyzed H[subscript 2]O[subscript 2] Decomposition Reaction Kinetics Using the Initial Rate Approach

    ERIC Educational Resources Information Center

    Barlag, Rebecca; Nyasulu, Frazier

    2010-01-01

    A wash bottle water displacement scheme is used to determine the kinetics of the iodide-catalyzed H[subscript 2]O[subscript 2] decomposition reaction. The reagents (total volume 5.00 mL) are added to a test tube that is placed in a wash bottle containing water. The mass of the water displaced in [approximately]60 s is measured. The reaction is…

  4. Nickel-catalyzed Suzuki-Miyaura type cross-coupling reactions of (2,2-difluorovinyl)benzene derivatives with arylboronic acids.

    PubMed

    Xiong, Yang; Huang, Tao; Ji, Xinfei; Wu, Jingjing; Cao, Song

    2015-07-01

    An unprecedented highly stereoselective example of nickel-catalyzed Suzuki-Miyaura type cross-coupling reactions of (2,2-difluorovinyl)benzene derivatives with arylboronic acids was developed. The reaction proceeded efficiently in the presence of 5 mol% NiCl2(PCy3)2 and K3PO4, affording the Z-fluorostyrene derivatives in good to high yields with excellent regioselectivity. PMID:26077810

  5. Metal-Catalyzed Double Migratory Cascade Reactions of Propargylic Esters and Phosphates

    PubMed Central

    Shiroodi, Roohollah Kazem

    2013-01-01

    Propargylic esters and phosphates are easily accessible substrates, which exhibit rich and tunable reactivities in the presence of transition metal catalysts. ?-acidic metals, mostly gold and platinum salts, activate these substrates for an initial 1,2- or 1,3-acyloxy and phosphatyloxy migration processes to form reactive intermediates. These intermediates are able to undergo further cascade reactions leading to a variety of diverse structures. This tutorial review systematically introduces the double migratory reactions of propargylic esters and phosphates as a novel synthetic method, in which further cascade reaction of the reactive intermediate is accompanied by a second migration of a different group, thus offering a rapid route to a wide range of functionalized products. The serendipitous observations, as well as designed approaches involving the double migratory cascade reactions, will be discussed with emphasis placed on the mechanistic aspects and the synthetic utilities of the obtained products. PMID:23443274

  6. Selective, nickel-catalyzed carbon-carbon bond-forming reactions of alkynes

    E-print Network

    Miller, Karen M. (Karen Marie)

    2005-01-01

    Catalytic addition reactions to alkynes are among the most useful and efficient methods for preparing diverse types of substituted olefins. Controlling both regioselectivity and (EIZ)- selectivity in such transformations ...

  7. [Pyrophosphate analogs in the pyrophosphorolysis reaction catalyzed by Escherichia coli RNA polymerase].

    PubMed

    Rozovskaia, T A; Chenchik, A A; Tarusova, N B; Bibilashvili, R Sh; Khomutov, R M

    1981-01-01

    Processive pyrophosphorolysis of RNA from ternary RNA polymerase-nascent RNA-delta D111 T7 DNA complex has been followed in the absence of nucleoside triphosphates. Series of inorganic pyrophosphate analogs were investigated for their ability to sustain the reaction and to compete with inorganic pyrophosphate for the reaction. Methylenediphosphonic, imidodiphosphonic, phosphonacetic acids, inorganic triphosphate, methylenediphosphonic and phosphate were found to be capable of substituting the inorganic pyrophosphate in RNA degradation reaction with tantamount efficiency. They give rise to nucleoside monophosphates for phosphonoacetic acid, nucleoside triphosphates for inorganic pyrophosphate and inorganic triphosphate, nucleoside triphosphates analogs for methylenediphosphonic, imidodiphosphonic acids and methylenediphosphonic acid phosphate as the low molecular weight product of the reaction. The problem of specific interaction of RNA polymerase with nucleoside triphosphates and inorganic pyrophosphate is discussed in the terms of structural requirements for the compounds to be a potent substrate for RNA polymerase. PMID:6275257

  8. Iridium-catalyzed reductive carbon-carbon bond cleavage reaction on a curved pyridylcorannulene skeleton.

    PubMed

    Tashiro, Shohei; Yamada, Mihoko; Shionoya, Mitsuhiko

    2015-04-27

    The cleavage of C?C bonds in ?-conjugated systems is an important method for controlling their shape and coplanarity. An efficient way for the cleavage of an aromatic C?C bond in a typical buckybowl corannulene skeleton is reported. The reaction of 2-pyridylcorannulene with a catalytic amount of IrCl3 ?n?H2 O in ethylene glycol at 250?°C resulted in a structural transformation from the curved corannulene skeleton to a strain-free flat benzo[ghi]fluoranthene skeleton through a site-selective C?C cleavage reaction. This cleavage reaction was found to be driven by both the coordination of the 2-pyridyl substituent to iridium and the relief of strain in the curved corannulene skeleton. This finding should facilitate the design of carbon nanomaterials based on C?C bond cleavage reactions. PMID:25756834

  9. Fluorine modified chromium oxide and its impact on heterogeneously catalyzed fluorination reactions

    Microsoft Academic Search

    B Adamczyk; O Boese; N Weiher; S. L. M Schroeder; E Kemnitz

    2000-01-01

    A series of chromium oxofluorides was prepared by thermal reaction between (NH4)3CrF6 and Cr2O3. No CrF3-phases were detected in the reaction products either by XRD or by XANES. The shift in the peak intensities of the powder diffraction pattern shows that the structure of Cr2O3 (Eskolaite) was modified with increasing fluorine content. Fluorine was found to replace oxygen in the

  10. Investigation at the atomic level of homologous enzymes reveals distinct reaction paths

    NASA Astrophysics Data System (ADS)

    Zoi, Ioanna; Schwartz, Steven D.

    2015-03-01

    Bacterial enzymes Escherichia coli and Vibrio cholerae 5' -Methylthioadenosine nucleosidases (MTANs) have different binding affinities for the same transition state analogue. This was surprising as these enzymes share 60% sequence identity, have almost identical active sites and act under the same mechanism. We performed Transition Path Sampling simulations of both enzymes to reveal the atomic details of the catalytic chemical step, to explain the inhibitor affinity differences. Unlike EcMTAN, VcMTAN has multiple distinct transition states, which is an indication that multiple sets of coordinated protein motions can reach a transition state. We also identified the important residues that participate in each enzyme's reaction coordinate and explained their contribution. Subtle dynamic differences manifest in difference of reaction coordinate and transition state structure and also suggest that MTANs differ from most ribosyl transferases. As experimental approaches report averages regarding reaction coordinate information, this study offers, previously unavailable, detailed knowledge to the explanation of bacterial MTANs catalytic mechanism, and could have a significant impact on pharmaceutical design. We acknowledge the support of the National Institutes of Health through Grant GM068036.

  11. Glutamine-Binding Subunit of Glutamate Synthase and Partial Reactions Catalyzed by this Glutamine Amidotransferase

    Microsoft Academic Search

    Paul P. Trotta; Karen E. B. Platzer; Rudy H. Haschemeyer; Alton Meister

    1974-01-01

    In the course of studies on glutamine-dependent carbamyl phosphate synthetase from Aerobacter aerogenes, we purified another protein which was found to be glutamate synthase (EC 2.6.1.53). The enzyme, obtained in apparently homogeneous form (monomer molecular weight about 227,000; s20,w = 17.6 S), was found to be a typical glutamine amidotransferase in that it exhibits glutaminase activity and can utilize ammonia

  12. Cu/Pd-Catalyzed, Three-Component Click Reaction of Azide, Alkyne, and Aryl Halide: One-Pot Strategy toward Trisubstituted Triazoles.

    PubMed

    Wei, Fang; Li, Haoyu; Song, Chuanling; Ma, Yudao; Zhou, Ling; Tung, Chen-Ho; Xu, Zhenghu

    2015-06-01

    A Cu/Pd-catalyzed, three-component click reaction of azide, alkyne, and aryl halide has been developed. By using this Cu/Pd transmetalation relay catalysis, a variety of 1,4,5-trisubstituted 1,2,3-triazoles were quickly assembled in one step in high yields with complete regioselectivity, just like assembling Lego bricks. Notably, different from the well-established CuAAC click reactions only working on terminal alkynes, this reaction offers an alternative solution for the problem of the click reaction of internal alkynes. PMID:26000564

  13. A surprising observation that oxygen can affect the product enantiopurity of an enzyme-catalysed reaction.

    PubMed

    Fryszkowska, Anna; Toogood, Helen S; Mansell, David; Stephens, Gill; Gardiner, John M; Scrutton, Nigel S

    2012-11-01

    Enzymes are natural catalysts, controlling reactions with typically high stereospecificity and enantiospecificity in substrate selection and/or product formation. This makes them useful in the synthesis of industrially relevant compounds, particularly where highly enantiopure products are required. The flavoprotein pentaerythritol tetranitrate (PETN) reductase is a member of the Old Yellow Enzyme family, and catalyses the asymmetric reduction of ?-alkyl-?-arylnitroalkenes. Under aerobic conditions, it additionally undergoes futile cycles of NAD(P)H reduction of flavin, followed by reoxidation by oxygen, which generates the reactive oxygen species (ROS) hydrogen peroxide and superoxide. Prior studies have shown that not all reactions catalysed by PETN reductase yield enantiopure products, such as the reduction of (E)-2-phenyl-1-nitroprop-1-ene (PNE) to produce (S)-2-phenyl-1-nitropropane (PNA) with variable enantiomeric excess (ee). Recent independent studies of (E)-PNE reduction by PETN reductase showed that the major product formed could be switched to (R)-PNA, depending on the reaction conditions. We investigated this phenomenon, and found that the presence of oxygen and ROS influenced the overall product enantiopurity. Anaerobic reactions produced consistently higher nitroalkane (S)-PNA product yields than aerobic reactions (64% versus 28%). The presence of oxygen dramatically increased the preference for (R)-PNA formation (up to 52% ee). Conversely, the presence of the ROS superoxide and hydrogen peroxide switched the preference to (S)-PNA product formation. Given that oxygen has no role in the natural catalytic cycle, these findings demonstrate a remarkable ability to manipulate product enantiopurity of this enzyme-catalysed reaction by simple manipulation of reaction conditions. Potential mechanisms of this unusual behaviour are discussed. PMID:22978386

  14. Negative resist systems using acid-catalyzed pinacol rearrangement reaction in a phenolic resin matrix

    NASA Astrophysics Data System (ADS)

    Uchino, Shou-ichi; Iwayanagi, Takao; Ueno, Takumi; Hayashi, Nobuaki

    1991-06-01

    Acid-catalyzed dehydration of pinacols known as pinacol rearrangement has been utilized in the design of alkali developable, negative working resist systems. The resist systems are composed of a pinacol compound used as a dissolution inhibitor precursor, diphenyliodonium triflate and a novolak resin. The resist system using hydrobenzoin (HB) shows better lithographic performance than the resist systems using other pinacol compounds such as 1,1,2,2-tetramethylethylene glycol (TMEG), benzopinacole (BP), DL-(alpha) ,(beta) -di-(4-pyridyl) glycol (DPG), and 2,3-di-2-pyridyl-2,3-butanediol (DPB). In the unexposed region, HB acts as a dissolution promoter of novolak resin due to its hydrophilic property. HB reacts with acid to produce hydrophobic materials such as diphenyl-acetaldehyde. Therefore, the solubility of the HB resist film in alkaline developers decrease upon exposure to deep UV radiation and subsequent heating. The resist system has high contrast and high resolution capability. Line-and-space patterns of 0.3 micrometers are obtained using a KrF excimer laser stepper with a 5 mJ/cm2 dose.

  15. Unveiling of a Trinuclear Cyclic Peroxidovanadate: A Potential Oxidant in Vanadium-Catalyzed Reactions.

    PubMed

    Krivosudský, Lukáš; Schwendt, Peter; Gyepes, Róbert

    2015-07-01

    The first peroxidovanadium trimer was prepared in the form of its tetrabutylammonium salt, (NBu4)3[V3O3(O2)6]·2H2O. Its X-ray structure analysis revealed a unique cyclic structure of the [V3O3(O2)6](3-) ion incorporating the yet unobserved ?3-?(2):?(1):?(1) coordination mode of one of its peroxido ligands. While relatively stable in nonaqueous solvents, the [V3O3(O2)6](3-) ion quickly decomposes in diluted aqueous solutions. A higher vanadium concentration or a higher CH3CN content in the mixed CH3CN/H2O solvent facilitates the formation of oligomers [V2O2(O2)4(H2O)](2-) and [V3O3(O2)6](3-). (51)V NMR investigations indicated that the trinuclear species is incorporated in vanadium-catalyzed oxidations in the presence of H2O2. PMID:26067575

  16. Anionic ligand effect on the nature of epoxidizing intermediates in iron porphyrin complex-catalyzed epoxidation reactions.

    PubMed

    Nam, Wonwoo; Jin, Sook Won; Lim, Mi Hee; Ryu, Ju Yeon; Kim, Cheal

    2002-07-15

    We have studied an anionic ligand effect in iron porphyrin complex-catalyzed competitive epoxidations of cis- and trans-stilbenes by various terminal oxidants and found that the ratios of cis- to trans-stilbene oxide products formed in competitive epoxidations were markedly dependent on the ligating nature of the anionic ligands. The ratios of cis- to trans-stilbene oxides obtained in the reactions of Fe(TPP)X (TPP = meso-tetraphenylporphinato dianion and X(-) = anionic ligand) and iodosylbenzene (PhIO) were 14 and 0.9 when the X(-) of Fe(TPP)X was Cl(-) and CF(3)SO(3)(-), respectively. An anionic ligand effect was also observed in the reactions of an electron-deficient iron(III) porphyrin complex containing a number of different anionic ligands, Fe(TPFPP)X [TPFPP = meso-tetrakis(pentafluorophenyl)porphinato dianion and X(-) = anionic ligand], and various terminal oxidants such as PhIO, m-chloroperoxybenzoic acid (m-CPBA), tetrabutylammonium oxone (TBAO), and H(2)O(2). While high ratios of cis- to trans-stilbene oxides were obtained in the reactions of iron porphyrin catalysts containing ligating anionic ligands such as Cl(-) and OAc(-), the ratios of cis- to trans-stilbene oxide were low in the reactions of iron porphyrin complexes containing nonligating or weakly ligating anionic ligands such as SbF(6)(-), CF(3)SO(3)(-), and ClO(4)(-). When the anionic ligand was NO(3)(-), the product ratios were found to depend on terminal oxidants and olefin concentrations. We suggest that the dependence of the product ratios on the anionic ligands of iron(III) porphyrin catalysts is due to the involvement of different reactive species in olefin epoxidation reactions. That is, high-valent iron(IV) oxo porphyrin cation radicals are generated as a reactive species in the reactions of iron porphyrin catalysts containing nonligating or weakly ligating anionic ligands such as SbF(6)(-), CF(3)SO(3)(-), and ClO(4)(-), whereas oxidant-iron(III) porphyrin complexes are the reactive intermediates in the reactions of iron porphyrin catalysts containing ligating anionic ligands such as Cl(-) and OAc(-). PMID:12099867

  17. Factors influencing the mechanism of surfactant catalyzed reaction of vitamin C-ferric chloride hexahydrate system

    NASA Astrophysics Data System (ADS)

    Farrukh, Muhammad Akhyar; Kauser, Robina; Adnan, Rohana

    2013-09-01

    The kinetics of vitamin C by ferric chloride hexahydrate has been investigated in the aqueous ethanol solution of basic surfactant viz. octadecylamine (ODA) under pseudo-first order conditions. The critical micelle concentration (CMC) of surfactant was determined by surface tension measurement. The effect of pH (2.5-4.5) and temperature (15-35°C) in the presence and absence of surfactant were investigated. Activation parameters, ? E a, ? H #, ? S #, ? G ?, for the reaction were calculated by using Arrhenius and Eyring plot. Surface excess concentration (?max), minimum area per surfactant molecule ( A min), average area occupied by each molecule of surfactant ( a), surface pressure at the CMC (?max), Gibb's energy of micellization (? G M°), Gibb's energy of adsorption (? G ad°), were calculated. It was found that the reaction in the presence of surfactant showed faster oxidation rate than the aqueous ethanol solution. Reaction mechanism has been deduced in the presence and absence of surfactant.

  18. Chemoselective Boron-Catalyzed Nucleophilic Activation of Carboxylic Acids for Mannich-Type Reactions.

    PubMed

    Morita, Yuya; Yamamoto, Tomohiro; Nagai, Hideoki; Shimizu, Yohei; Kanai, Motomu

    2015-06-10

    The carboxyl group (COOH) is an omnipresent functional group in organic molecules, and its direct catalytic activation represents an attractive synthetic method. Herein, we describe the first example of a direct catalytic nucleophilic activation of carboxylic acids with BH3·SMe2, after which the acids are able to act as carbon nucleophiles, i.e. enolates, in Mannich-type reactions. This reaction proceeds with a mild organic base (DBU) and exhibits high levels of functional group tolerance. The boron catalyst is highly chemoselective toward the COOH group, even in the presence of other carbonyl moieties, such as amides, esters, or ketones. Furthermore, this catalytic method can be extended to highly enantioselective Mannich-type reactions by using a (R)-3,3'-I2-BINOL-substituted boron catalyst. PMID:26011419

  19. Nickel-catalyzed substitution reactions of propargyl halides with organotitanium reagents.

    PubMed

    Li, Qing-Han; Liao, Jung-Wei; Huang, Yi-Ling; Chiang, Ruei-Tang; Gau, Han-Mou

    2014-10-14

    A simple and mild catalytic coupling reaction of propargyl halides with organotitanium reagents is reported. The reaction of propargyl bromide with organo-titanium reagents mediated by NiCl2 (2 mol%) and PCy3 (4 mol%) in CH2Cl2 afforded coupling product allenes in good to excellent yields (up to 95%) at room temperature. However, NiCl2(PPh3)2 was the best catalyst for substituted propargyl halides to yield allenes or alkynes preferentially. On the basis of the experimental results, a possible catalytic cycle has been proposed. PMID:25143149

  20. Palladium-catalyzed cross coupling reactions of 4-bromo-6H-1,2-oxazines.

    PubMed

    Zimmer, Reinhold; Schmidt, Elmar; Andrä, Michal; Duhs, Marcel-Antoine; Linder, Igor; Reissig, Hans-Ulrich

    2009-01-01

    A number of 4-aryl- and 4-alkynyl-substituted 6H-1,2-oxazines 8 and 9 have been prepared in good yields via cross coupling reactions of halogenated precursors 2, which in turn are easily accessible by bromination of 6H-1,2-oxazines 1. Lewis-acid promoted reaction of 1,2-oxazine 9c with 1-hexyne provided alkynyl-substituted pyridine derivative 12 thus demonstrating the potential of this approach for the synthesis of pyridines. PMID:19936264

  1. Palladium-catalyzed cross coupling reactions of 4-bromo-6H-1,2-oxazines

    PubMed Central

    Schmidt, Elmar; Andrä, Michal; Duhs, Marcel-Antoine; Linder, Igor

    2009-01-01

    Summary A number of 4-aryl- and 4-alkynyl-substituted 6H-1,2-oxazines 8 and 9 have been prepared in good yields via cross coupling reactions of halogenated precursors 2, which in turn are easily accessible by bromination of 6H-1,2-oxazines 1. Lewis-acid promoted reaction of 1,2-oxazine 9c with 1-hexyne provided alkynyl-substituted pyridine derivative 12 thus demonstrating the potential of this approach for the synthesis of pyridines. PMID:19936264

  2. A kinetic and thermodynamic study of the reaction catalyzed by argininosuccinate synthetase 

    E-print Network

    Ghose, Chandralekha

    1984-01-01

    N MATERIALS AND METHODS rv v11 Enzyme Assays HPLC Assays Sta. tic Quench Assay s 10 Dynamic Quench Assays 10 Alpha Methyl Aspartate Experiments 12 Purification of Arginosuccinate synthetase From Bovine Liver RESULTS 13 16 Purification... mM MgClq, 1 mM ATI', 1 mM AMP, 0. 16 mM NADH, 0. 2 mM PEP, 5 units of lactate dehydrogenase, arid 5 units of pyruvate kinase. HPLC Assavs The concentration of AMP was determmed by monitoring i, he ab- 10 sorbance at 260 nm on a Gilson HPLC system...

  3. One-pot synthesis of keto thioethers by palladium/gold-catalyzed click and pinacol reactions.

    PubMed

    Cadu, Alban; Watile, Rahul A; Biswas, Srijit; Orthaber, Andreas; Sjöberg, Per J R; Samec, Joseph S M

    2014-11-01

    An atom-efficient synthesis of keto thioethers was devised via tandem gold/palladium catalysis. The reaction proceeds through a regioselective thiol attack at the ?-position of the alcohol, followed by an alkyl, aryl, or benzyl 1,2-shift. Both acyclic and cyclic systems were studied, in the latter case leading to the ring expansion of cyclic substrates. PMID:25325145

  4. A novel rhodium-catalyzed domino-hydroformylation-reaction for the synthesis of sulphonamides.

    PubMed

    Dong, Kaiwu; Fang, Xianjie; Jackstell, Ralf; Beller, Matthias

    2015-03-25

    An efficient and highly selective method for the synthesis of sulphonamides by a domino hydroformylation-reductive sulphonamidation reaction has been developed. Various olefins and sulphonamides are converted into the desired products in good yields and with excellent selectivities in the presence of a rhodium/Naphos catalyst. PMID:25712242

  5. Intramolecular C-H activation through gold(I)-catalyzed reaction of iodoalkynes.

    PubMed

    Morán-Poladura, Pablo; Rubio, Eduardo; González, José M

    2015-03-01

    The cycloisomerization reaction of 1-(iodoethynyl)-2-(1-methoxyalkyl)arenes and related 2-alkyl-substituted derivatives gives the corresponding 3-iodo-1-substituted-1H-indene under the catalytic influence of IPrAuNTf2 [IPr=1,3-bis(2,6-diisopropyl)phenylimidazol-2-ylidene; NTf2=bis(trifluoromethanesulfonyl)imidate]. The reaction takes place in 1,2-dichloroethane at 80?°C, and the addition of ttbp (2,4,6-tri-tert-butylpyrimidine) is beneficial to accomplish this new transformation in high yield. The overall reaction implies initial assembly of an intermediate gold vinylidene upon alkyne activation by gold(I) and a 1,2-iodine-shift. Deuterium labeling and crossover experiments, the magnitude of the recorded kinetic primary isotopic effect, and the results obtained from the reaction of selected stereochemical probes strongly provide support for concerted insertion of the benzylic C-H bond into gold vinylidene as the step responsible for the formation of the new carbon-carbon bond. PMID:25604107

  6. Red Seaweed Enzyme-Catalyzed Bromination of Bromophenol Red: An Inquiry-Based Kinetics Laboratory Experiment for Undergraduates

    ERIC Educational Resources Information Center

    Jittam, Piyachat; Boonsiri, Patcharee; Promptmas, Chamras; Sriwattanarothai, Namkang; Archavarungson, Nattinee; Ruenwongsa, Pintip; Panijpan, Bhinyo

    2009-01-01

    Haloperoxidase enzymes are of interest for basic and applied bioscientists because of their increasing importance in pharmaceutical industry and environmental cleanups. In a guided inquiry-based laboratory experiment for life-science, agricultural science, and health science undergraduates, the bromoperoxidase from a red seaweed was used to…

  7. Malic enzyme (ME) catalyzes the oxidative decarboxylation of L-malate to pyruvate with the concomitant reduction of the

    E-print Network

    Tong, Liang

    , with fumarate as an activator and ATP as an inhibitor9, which is unique among malic enzymes. The amino acid in most living organisms, from bacteria to humans, and their amino acid sequences are highly conserved acid sequence homology to other proteins, such as the dehydro- genases and the decarboxylases. We

  8. Effect of polyvinylpyrrolidone on mesoporous silica morphology and esterification of lauric acid with 1-butanol catalyzed by immobilized enzyme

    SciTech Connect

    Zhang, Jinyu; Zhou, Guowei, E-mail: guoweizhou@hotmail.com; Jiang, Bin; Zhao, Minnan; Zhang, Yan

    2014-05-01

    Mesoporous silica materials with a range of morphology evolution, i.e., from curved rod-shaped mesoporous silica to straight rod-shaped mesoporous silica, were successfully prepared using polyvinylpyrrolidone (PVP) and triblock copolymer as dual template. The effects of PVP molecular weight and concentration on mesoporous silica structure parameters were studied. Results showed that surface area and pore volume continuously decreased with increased PVP molecular weight. Mesoporous silica prepared with PVP K30 also possessed larger pore diameter, interplanar spacing (d{sub 100}), and cell parameter (a{sub 0}) than that prepared with PVP K15 and PVP K90. In addition, with increased PVP concentration, d{sub 100} and a{sub 0} continuously decreased. The mechanism of morphology evolution caused by the change in PVP concentration was investigated. The conversion rate of lauric acid with 1-butanol catalyzed by immobilized Porcine pancreatic lipase (PPL) was also evaluated. Results showed that PPL immobilized on amino-functionalized straight rod-shaped mesoporous silica maintained 50% of its esterification conversion rate even after five cycles of use with a maximum conversion rate was about 90.15%. - Graphical abstract: Curved rod-shaped mesoporous silica can be obtained at low and the highest PVP concentration, while straight rod-shaped mesoporous silica can be obtained at higher PVP concentration. - Highlights: • Mesoporous silica with morphology evolution from CRMS to SRMS were prepared. • Effects of PVP molecular weight and concentration on silica morphology were studied. • A possible mechanism for the formation of morphology evolution SiO{sub 2} was proposed. • Esterification of lauric acid with 1-butanol catalyzed by immobilized PPL.

  9. Two herbivore-induced cytochrome P450 enzymes CYP79D6 and CYP79D7 catalyze the formation of volatile aldoximes involved in poplar defense.

    PubMed

    Irmisch, Sandra; McCormick, Andrea Clavijo; Boeckler, G Andreas; Schmidt, Axel; Reichelt, Michael; Schneider, Bernd; Block, Katja; Schnitzler, Jörg-Peter; Gershenzon, Jonathan; Unsicker, Sybille B; Köllner, Tobias G

    2013-11-01

    Aldoximes are known as floral and vegetative plant volatiles but also as biosynthetic intermediates for other plant defense compounds. While the cytochrome P450 monooxygenases (CYP) from the CYP79 family forming aldoximes as biosynthetic intermediates have been intensively studied, little is known about the enzymology of volatile aldoxime formation. We characterized two P450 enzymes, CYP79D6v3 and CYP79D7v2, which are involved in herbivore-induced aldoxime formation in western balsam poplar (Populus trichocarpa). Heterologous expression in Saccharomyces cerevisiae revealed that both enzymes produce a mixture of different aldoximes. Knockdown lines of CYP79D6/7 in gray poplar (Populus × canescens) exhibited a decreased emission of aldoximes, nitriles, and alcohols, emphasizing that the CYP79s catalyze the first step in the formation of a complex volatile blend. Aldoxime emission was found to be restricted to herbivore-damaged leaves and is closely correlated with CYP79D6 and CYP79D7 gene expression. The semi-volatile phenylacetaldoxime decreased survival and weight gain of gypsy moth (Lymantria dispar) caterpillars, suggesting that aldoximes may be involved in direct defense. The wide distribution of volatile aldoximes throughout the plant kingdom and the presence of CYP79 genes in all sequenced genomes of angiosperms suggest that volatile formation mediated by CYP79s is a general phenomenon in the plant kingdom. PMID:24220631

  10. One- and two-dimensional chemical exchange nuclear magnetic resonance studies of the creatine kinase catalyzed reaction

    SciTech Connect

    Gober, J.R.

    1988-01-01

    The equilibrium chemical exchange dynamics of the creatine kinase enzyme system were studied by one- and two-dimensional {sup 31}P NMR techniques. Pseudo-first-order reaction rate constants were measured by the saturation transfer method under an array of experimental conditions of pH and temperature. Quantitative one-dimensional spectra were collected under the same conditions in order to calculate the forward and reverse reaction rates, the K{sub eq}, the hydrogen ion stoichiometry, and the standard thermodynamic functions. The pure absorption mode in four quadrant two-dimensional chemical exchange experiment was employed so that the complete kinetic matrix showing all of the chemical exchange process could be realized.

  11. Photoexcited chemical wave in the ruthenium-catalyzed Belousov-Zhabotinsky reaction.

    PubMed

    Nakata, Satoshi; Matsushita, Mariko; Sato, Taisuke; Suematsu, Nobuhiko J; Kitahata, Hiroyuki; Amemiya, Takashi; Mori, Yoshihito

    2011-07-01

    The excitation of the photosensitive Belousov-Zhabotinsky (BZ) reaction induced by light stimulation was systematically investigated. A stepwise increase in the light intensity induced the excitation, whereas a stepwise decrease did not induce the excitation. The threshold values for the excitation were found to be a function of the initial and final light intensities, time variation in light intensity, and the concentration of NaBrO(3). The experimental results were qualitatively reproduced by a theoretical calculation based on a three-variable Oregonator model modified for the photosensitive BZ reaction. These results suggest that although the steady light irradiation is known to inhibit oscillation and chemical waves in the BZ system under almost all conditions, the stepwise increase in the light irradiation leads to the rapid production of an activator, resulting in the photoexcitation. PMID:21563834

  12. Production of propylene glycol fatty acid monoesters by lipase-catalyzed reactions in organic solvents

    Microsoft Academic Search

    Jei-Fu Shaw; Shian Lo

    1994-01-01

    Fatty acid monoesters of propylene glycol (1,2-propanediol) are good water-in-oil emulsifiers. These esters were synthesized\\u000a enzymatically to overcome the problems associated with chemical processes. APseudomonas lipase was added to reaction mixtures containing propylene glycol and various acyl donors (fatty acids, fatty acid ethyl\\u000a esters, fatty acid anhydrides and triglycerides) in organic solvents, and the mixtures were shaken at 30C. The

  13. Enantioselective Synthesis of Chromanones via a Peptidic Phosphane Catalyzed Rauhut-Currier Reaction.

    PubMed

    Scanes, Robert J H; Grossmann, Oleg; Grossmann, André; Spring, David R

    2015-05-15

    The enantioselective intramolecular Rauhut-Currier reaction has been developed using a bifunctional dipeptidic phosphane catalyst, providing a direct access to biologically active ?-methylene-?-valerolactones in high yields and enantiomeric excesses. The novel catalyst is accessible in only four steps from commercial sources and exhibits unusual binding selectivities for a small molecule, suggesting the possibility for long-range interactions between the catalyst and the substrate. PMID:25915565

  14. Ag nanoparticle-catalyzed chemiluminescent reaction between luminol and hydrogen peroxide

    Microsoft Academic Search

    Ji-Zhao Guo; Hua Cui; Wei Zhou; Wei Wang

    2008-01-01

    Ag colloid was found to enhance intensely the chemiluminescence (CL) from the reaction between luminol and hydrogen peroxide. Ag nanoparticles exhibited the better CL catalysis activity than gold and platinum nanoparticles. The superoxide anion scavenger nitro blue tetrazolium and superoxide dismutase was added to the hydrogen peroxide–Ag colloid and the luminol–hydrogen peroxide–Ag colloid systems, respectively, showing that the decomposition of

  15. H(3)PW(12)O(40)-catalyzed multicomponent reaction for efficient synthesis of highly substituted piperidines.

    PubMed

    Khaksar, Samad; Baghbanian, Seyed Meysam; Barsan, Nastaran

    2014-01-01

    A simple, diastereoselective, inexpensive, and efficient route for the synthesis of highly functionalized piperidines by the condensation of ?-keto-esters, aromatic aldehydes and anilines using H3PW12O40 as a catalyst is described. The catalyst could be easily recovered after completion of the reaction and reused without a considerable change in its activity. Furthermore, in most cases the piperidine precipitates out of solution. PMID:24372051

  16. Electroreductive dehalogenation of chlorinated aromatic ethers. Unexpected electrogenerated base catalyzed reactions

    Microsoft Academic Search

    Makoto Kimura; Hiroyoshi Miyahara; Noriyuki Moritani; Yasuhiko Sawaki

    1990-01-01

    The electroreductive dehalogenation of several mono- and polychlorinated aromatic ethers that serve as models of dioxins has been studied. The dechlorination was achieved by a simple constant-current electrolysis using a lead cathode in dimethylformamide. It was shown that 2,4,6-trichloroanisole undergoes successive dechlorination and the chlorine in the 2-position is selectively eliminated. Competitive reactions and cyclic voltammetric measurements suggested the increasing

  17. Low temperature iron- and nickel-catalyzed reactions leading to coalbed gas formation

    Microsoft Academic Search

    Juan Carlos Medina; Steven J. Butala; Calvin H. Bartholomew; Milton L. Lee

    2000-01-01

    Hydrocarbon hydrogenolysis and CO 2 hydrogenation in the presence of Fe\\/SiO 2 and Ni\\/SiO 2 catalysts were evaluated as potential mechanisms contributing to natural gas formation in coalbeds. The hydrocarbons used as reactants in hydrogenolysis included butane, octane, 1-octene, and 1-dodecene. The reactions carried out in a laboratory batch reactor produced gas that contained methane concentrations greater than 90%, which

  18. Low temperature iron- and nickel-catalyzed reactions leading to coalbed gas formation

    Microsoft Academic Search

    Juan Carlos Medina; Steven J Butala; Calvin H Bartholomew; Milton L Lee

    2000-01-01

    Hydrocarbon hydrogenolysis and CO2 hydrogenation in the presence of Fe\\/SiO2 and Ni\\/SiO2 catalysts were evaluated as potential mechanisms contributing to natural gas formation in coalbeds. The hydrocarbons used as reactants in hydrogenolysis included butane, octane, 1-octene, and 1-dodecene. The reactions carried out in a laboratory batch reactor produced gas that contained methane concentrations greater than 90%, which resembles the composition

  19. Palladium-catalyzed cross-coupling reactions of organogold(I) phosphanes with allylic electrophiles.

    PubMed

    Peña-López, Miguel; Ayán-Varela, Miguel; Sarandeses, Luis A; Pérez Sestelo, José

    2012-02-28

    Aryl and alkenylgold(I) phosphanes react regioselectively with allylic electrophiles such as cinnamyl and geranyl halides (bromide, chloride and acetates) under palladium catalysis in THF at 80 °C to afford the ?-substitution product with moderate to high yields. When the reaction is performed with a chiral enantiopure secondary acetate, the ?-substituted cross-coupling product is obtained with complete inversion of the stereochemistry. PMID:22266785

  20. Selective N-chelation-directed C-H activation reactions catalyzed by Pd(II) nanoparticles supported on multiwalled carbon nanotubes.

    PubMed

    Korwar, Sudha; Brinkley, Kendra; Siamaki, Ali R; Gupton, B Frank; Ellis, Keith C

    2015-04-01

    N-Chelation-directed C-H activation reactions that utilize the Pd(II)/Pd(IV) catalytic cycle have been previously reported. To date, these reactions employ only homogeneous palladium catalysts. The first use of a solid-supported Pd(II) catalyst [Pd(II) nanoparticles on multiwalled carbon nanotubes, Pd(II)/MWCNT] to carry out N-chelation-directed C-H to C-O, C-Cl, and C-Br transformations is reported. The results presented demonstrate that the solid-supported Pd(II)/MWCNT catalyst can effectively catalyze C-H activation reactions using the Pd(II)/Pd(IV) catalytic cycle. PMID:25789562

  1. Hydrogen-bond-assisted activation of allylic alcohols for palladium-catalyzed coupling reactions.

    PubMed

    Gumrukcu, Yasemin; de Bruin, Bas; Reek, Joost N H

    2014-03-01

    We report direct activation of allylic alcohols using a hydrogen-bond-assisted palladium catalyst and use this for alkylation and amination reactions. The novel catalyst comprises a palladium complex based on a functionalized monodentate phosphoramidite ligand in combination with urea additives and affords linear alkylated and aminated allylic products selectively. Detailed kinetic analysis show that oxidative addition of the allyl alcohol is the rate-determining step, which is facilitated by hydrogen bonds between the alcohol, the ligand functional group, and the additional urea additive. PMID:24436302

  2. Iodoarene-Catalyzed Stereospecific Intramolecular sp(3) C-H Amination: Reaction Development and Mechanistic Insights.

    PubMed

    Zhu, Chendan; Liang, Yong; Hong, Xin; Sun, Heqing; Sun, Wei-Yin; Houk, K N; Shi, Zhuangzhi

    2015-06-24

    A new strategy is reported for intramolecular sp(3) C-H amination under mild reaction conditions using iodoarene as catalyst and m-CPBA as oxidant. This C-H functionalization involving iodine(III) reagents generated in situ occurs readily at sterically hindered tertiary C-H bonds. DFT (M06-2X) calculations show that the preferred pathway involves an iodonium cation intermediate and proceeds via an energetically concerted transition state, through hydride transfer followed by the spontaneous C-N bond formation. This leads to the experimentally observed amination at a chiral center without loss of stereochemical information. PMID:26035639

  3. Rhenium-catalyzed anti-Markovnikov addition reaction of methanetricarboxylates to unactivated terminal acetylenes.

    PubMed

    Hori, Shunsuke; Murai, Masahito; Takai, Kazuhiko

    2015-02-01

    A novel anti-Markovnikov addition reaction of methanetricarboxylates with terminal acetylenes under neutral conditions was achieved using a rhenium complex. This transformation represents a rare example of intermolecular anti-Markovnikov addition of carbon nucleophiles to unactivated terminal acetylenes. 1,3-Diesters having bulky substituents at the active methylene carbon are also applicable as substrates to provide anti-Markovnikov adducts as single regio- and stereoisomers. Preliminary mechanistic studies imply that the rhenium vinylidene species is the key intermediate in the current catalytic cycle. PMID:25563809

  4. The Roles of Acids and Bases in Enzyme Catalysis

    ERIC Educational Resources Information Center

    Weiss, Hilton M.

    2007-01-01

    Many organic reactions are catalyzed by strong acids or bases that protonate or deprotonate neutral reactants leading to reactive cations or anions that proceed to products. In enzyme reactions, only weak acids and bases are available to hydrogen bond to reactants and to transfer protons in response to developing charges. Understanding this…

  5. Shared traits on the reaction coordinates of ribonuclease and an RNA enzyme

    PubMed Central

    Torelli, Andrew T.; Spitale, Robert C.; Krucinska, Jolanta; Wedekind, Joseph E.

    2008-01-01

    Reaction-intermediate analogs have been used to understand how phosphoryl-transfer enzymes promote catalysis. Herein we report the first structure of a small ribozyme crystallized with a 3?-OH, 2?,5?-linkage in lieu of the normal phosphodiester substrate. The new structure shares features of the reaction coordinate exhibited in prior ribozyme structures including a vanadate complex that mimicked the oxyphosphorane transition state. As such, the structure exhibits reaction-intermediate traits that allow direct comparison of stabilizing interactions to the 3?-OH, 2?,5?-linkage contributed by the RNA enzyme and its protein counterpart, ribonuclease. Clear similarities are observed between the respective structures including hydrogen bonds to the non-bridging oxygens of the scissile-phosphate. Other commonalities include carefully poised water molecules that may alleviate charge build-up in the transition state and placement of a positive charge near the leaving group. The advantages of 2?,5?-linkages to investigate phosphoryl-transfer reactions are discussed, and argue for their expanded use in structural studies. PMID:18423397

  6. Chemically directed assembly of photoactive metal oxide nanoparticle heterojunctions via the copper-catalyzed azide-alkyne cycloaddition "click" reaction.

    PubMed

    Cardiel, Allison C; Benson, Michelle C; Bishop, Lee M; Louis, Kacie M; Yeager, Joseph C; Tan, Yizheng; Hamers, Robert J

    2012-01-24

    Metal oxides play a key role in many emerging applications in renewable energy, such as dye-sensitized solar cells and photocatalysts. Because the separation of charge can often be facilitated at junctions between different materials, there is great interest in the formation of heterojunctions between metal oxides. Here, we demonstrate use of the copper-catalyzed azide-alkyne cycloaddition reaction, widely referred to as "click" chemistry, to chemically assemble photoactive heterojunctions between metal oxide nanoparticles, using WO(3) and TiO(2) as a model system. X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy verify the nature and selectivity of the chemical linkages, while scanning electron microscopy reveals that the TiO(2) nanoparticles form a high-density, conformal coating on the larger WO(3) nanoparticles. Time-resolved surface photoresponse measurements show that the resulting dyadic structures support photoactivated charge transfer, while measurements of the photocatalytic degradation of methylene blue show that chemical grafting of TiO(2) nanoparticles to WO(3) increases the photocatalytic activity compared with the bare WO(3) film. PMID:22196212

  7. Origin of Fast Catalysis in Allylic Amination Reactions Catalyzed by Pd-Ti Heterobimetallic Complexes.

    PubMed

    Walker, Whitney K; Kay, Benjamin M; Michaelis, Scott A; Anderson, Diana L; Smith, Stacey J; Ess, Daniel H; Michaelis, David J

    2015-06-17

    Experiments and density functional calculations were used to quantify the impact of the Pd-Ti interaction in the cationic heterobimetallic Cl2Ti(N(t)BuPPh2)2Pd(?(3)-methallyl) catalyst 1 used for allylic aminations. The catalytic significance of the Pd-Ti interaction was evaluated computationally by examining the catalytic cycle for catalyst 1 with a conformation where the Pd-Ti interaction is intact versus one where the Pd-Ti interaction is severed. Studies were also performed on the relative reactivity of the cationic monometallic (CH2)2(N(t)BuPPh2)2Pd(?(3)-methallyl) catalyst 2 where the Ti from catalyst 1 was replaced by an ethylene group. These computational and experimental studies revealed that the Pd-Ti interaction lowers the activation barrier for turnover-limiting amine reductive addition and accelerates catalysis up to 10(5). The Pd-Ti distance in 1 is the result of the N(t)Bu groups enforcing a boat conformation that brings the two metals into close proximity, especially in the transition state. The turnover frequency of classic Pd ? allyl complexes was compared to that of 1 to determine the impact of P-Pd-P coordination angle and ligand electronic properties on catalysis. These experiments identified that cationic (PPh3)2Pd(?(3)-CH2C(CH3)CH2) catalyst 3 performs similarly to 1 for allylic aminations with diethylamine. However, computations and experiment reveal that the apparent similarity in reactivity is due to very fast reaction kinetics. The higher reactivity of 1 versus 3 was confirmed in the reaction of methallyl chloride and 2,2,6,6-tetramethylpiperidine (TMP). Overall, experiments and calculations demonstrate that the Pd-Ti interaction induces and is responsible for significantly lower barriers and faster catalysis for allylic aminations. PMID:25946518

  8. Aspartate aminotransferase catalyzed oxygen exchange with solvent from oxygen-18-enriched alpha-ketoglutarate: Evidence for slow exchange of enzyme-bound water

    SciTech Connect

    McLeish, M.J.; Julin, D.A.; Kirsch, J.F. (Univ. of California, Berkeley (USA))

    1989-05-02

    Partitioning of the ketimine (or ketimine + quinonoid) intermediate(s) in the mitochondrial aspartate aminotransferase reactions was investigated by following the rates of loss of {sup 18}O from carbonyl-{sup 18}O-enriched alpha-ketoglutarate together with the rate of L-glutamate formation. The ratio of these rate constants was found to equal 1 at 10{degree}C, implying that the above intermediate(s) face(s) equal barriers with respect to the forward and reverse reactions. This partition ratio of 1 together with that measured from the alpha-amino acid side of the reaction suggests that the rate constant for exchange of alpha-ketoglutarate-derived H{sub 2}(18)O from the ketimine (or ketimine + quinonoid) form(s) of the enzyme with solvent is comparable with that for kcat.

  9. Conserved enzymes mediate the early reactions of carotenoid biosynthesis in nonphotosynthetic and photosynthetic prokaryotes

    SciTech Connect

    Armstrong, G.A.; Hearst, J.E. (Univ. of California, Berkeley (United States) Lawrence Berkeley Lab., CA (United States)); Alberti, M. (Lawrence Berkeley Lab., CA (United States))

    1990-12-01

    Carotenoids comprise one of the most widespread classes of pigments found in nature. The first reactions of C{sub 40} carotenoid biosynthesis proceed through common intermediates in all organisms, suggesting the evolutionary conservation of early enzymes from this pathway. The authors report here the nucleotide sequence of three genes from the carotenoid biosynthesis gene cluster of Erwinia herbicola, a nonphotosynthetic epiphytic bacterium, which encode homologs of the CrtB, CrtE, and CrtI proteins of Rhodobacter capsulatus, a purple nonsulfur photosynthetic bacterium. CrtB (prephytoene pyrophosphate synthase), CrtE (phytoene synthase), and CrtI (phytoene dehydrogenase) are required for the first three reactions specific to the carotenoid branch of general isoprenoid metabolism. All three dehydrogenases possess a hydrophobic N-terminal domain containing a putative ADP-binding {beta}{alpha}{beta} fold characteristic of enzymes known to bind FAD or NAD(P) cofactors. These data indicate the structural conservation of early carotenoid biosynthesis enzymes in evolutionary diverse organisms.

  10. Using metal-catalyzed oxidation reactions and mass spectrometry to identify amino acid residues within 10 Å of the metal in Cu-binding proteins

    Microsoft Academic Search

    Juma D. Bridgewater; Jihyeon Lim; Richard W. Vachet

    2006-01-01

    Metal-catalyzed oxidation (MCO) reactions and mass spectrometry (MS) can be used together to determine the amino acids bound\\u000a to Cu in a metalloprotein. Selective oxidation of only amino acids bound to Cu during the MCO\\/MS approach relies on proper\\u000a choice of the types and concentrations of the reducing and oxidizing agents. We show here that if these MCO reagent concentrations

  11. BIOCHEMISTRY: De Novo Design of an Enzyme

    NSDL National Science Digital Library

    Reinhard Sterner (Universität Regensburg, Institut für Biophysik und Physikalische Biochemie; )

    2004-06-25

    Access to the article is free, however registration and sign-in are required. Enzymes catalyze biological reactions with amazing efficiency, and years of biochemical research have been directed at understanding how they work. In their Perspective, Sterner and Schmid describe recent work (Dwyer et al.) that brings us closer to the ultimate goal of designing enzymes with tailored activities by using computer design to build catalytic activity onto an inert protein scaffold.

  12. N-hydroxymethyl acrylamide polymer brush and its application in catalyzing coupling reaction.

    PubMed

    Fu, Zhihua; Zhang, Na; Liu, Jie; Li, Tiesheng; Xu, Wenjian; Wang, Fei; Wang, Tao; Zhai, Zhen; Liu, Linlin; Mao, Luyan; Wu, Yangjie

    2013-03-15

    Poly (N-hydroxy methyl acrylamide)-grafted silicon, glass, and quartz surfaces were successfully prepared by surface-initiated atom transfer radical polymerization (SI-ATRP) with methyl alcohol/water mixtures as solvents and CuCl/2,2-dipyridyl as a catalyst. The modified surfaces were characterized by water contact angle, atomic force microscope (AFM), Fluorescence spectrophotometer, Low-angle X-ray diffraction (LAXRD), and X-ray Photoelectron Spectroscopy (XPS). The results showed that the homogeneous and well hydrophilic N-hydroxymethyl acrylamide polymer brushes (NHAM-brushes), which had high hydrophilic properties and the added advantage of providing 3-D coatings with higher binding capacities, were obtained successfully. Cyclopalladated arylimine functionalized polymer brushes were also obtained by reacting HAM-brushes with N,N'-Carbonyldiimidazole (CDI) and cyclopalladated arylimine. The catalyst functionalized PHAM-brushes had good catalytic activity in heterogeneous compared to homogeneous catalyst and exhibited much improved stability and recyclability over time in Suzuki cross-coupling reaction. PMID:23375806

  13. Study of fluorescence quenching mechanism between quercetin and tyrosine-H 2O 2-enzyme catalyzed product

    NASA Astrophysics Data System (ADS)

    Zhang, Miao; Lv, Qingluan; Yue, Ningning; Wang, Huaiyou

    2009-04-01

    Because of catalysis of horseradish peroxidase, the tyrosine reacted with H 2O 2 to form the product S which was a strong fluorescence substance. To the product S, the quercetin was acted as a quencher. The fluorescence quenching mechanism was studied by the measurement of fluorescence lifetime and based on the Stern-Volmer plot. The reaction mechanism, which was the static quenching process between quercetin and product S, was studied. The binding constant, K = 4.03 × 10 5 L mol -1 and the number of binding sites n = 1.09, were obtained against this reaction. The thermodynamic parameters were estimated. The data, ? H = -75.68 kJ mol -1, ? S = -147.9 J K -1 mol -1 and ? G = -29.17 kJ mol -1 showed that the reaction was spontaneous and exothermic. What is more, both ? H and ? S were negative values indicated that van der Waals interaction and hydrogen bonding were the predominant intermolecular forces between quercetin and product S.

  14. Isolation of the heme-thiolate enzyme cytochrome P-450TYR, which catalyzes the committed step in the biosynthesis of the cyanogenic glucoside dhurrin in Sorghum bicolor (L.) Moench.

    PubMed Central

    Sibbesen, O; Koch, B; Halkier, B A; Møller, B L

    1994-01-01

    The cytochrome P-450 enzyme (hemethiolate enzyme) that catalyzes the N-hydroxylation of L-tyrosine to N-hydroxytyrosine, the committed step in the biosynthesis of the cyanogenic glucoside dhurrin, has been isolated from microsomes prepared from etiolated seedlings of Sorghum bicolor (L.) Moench. The cytochrome P-450 enzyme was solubilized with the detergents Renex 690, reduced Triton X-100, and 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate and isolated by ion-exchange (DEAE-Sepharose) and dye (Cibacron blue and reactive red 120) column chromatography. To prevent irreversible aggregation of the cytochrome P-450 enzyme, the isolation procedure was designed without any concentration step--i.e., with dilution of the ion-exchange gel with gel filtration material. The isolated enzyme, which we designate the cytochrome P-450TYR enzyme, gives rise to the specific formation of a type I substrate binding spectrum in the presence of L-tyrosine. The microsomal preparation contains 0.2 nmol of total cytochrome P-450/mg of protein. The cytochrome P-450TYR enzyme is estimated to constitute approximately 20% of the total cytochrome P-450 content of the microsomal membranes and about 0.2% of their total protein content. The apparent molecular mass of the cytochrome P-450TYR enzyme is 57 kDa, and the N-terminal amino acid sequence is ATMEVEAAAATVLAAP. A polyclonal antibody raised against the isolated cytochrome P-450TYR enzyme is specific as monitored by Western blot analysis and inhibits the in vitro conversion of L-tyrosine to p-hydroxymandelonitrile catalyzed by the microsomal system. The cytochrome P-450TYR enzyme exhibits high substrate specificity and acts as an N-hydroxylase on a single endogenous substrate. The reported isolation procedure based on dye columns constitutes a gentle isolation method for cytochrome P-450 enzymes and is of general use as indicated by its ability to separate cytochrome P-450TYR from the cytochrome P-450 enzyme catalyzing the C-hydroxylation of p-hydroxyphenylacetonitrile and from cinnamic acid 4-hydroxylase. Images PMID:7937883

  15. Enzymatic synthesis of dimaltosyl-beta-cyclodextrin via a transglycosylation reaction using TreX, a Sulfolobus solfataricus P2 debranching enzyme.

    PubMed

    Kang, Hee-Kwon; Cha, Hyunju; Yang, Tae-Joo; Park, Jong-Tae; Lee, Seungjae; Kim, Young-Wan; Auh, Joong-Hyuck; Okada, Yasuyo; Kim, Jung-Wan; Cha, Jaeho; Kim, Chung Ho; Park, Kwan-Hwa

    2008-02-01

    Di-O-alpha-maltosyl-beta-cyclodextrin ((G2)(2)-beta-CD) was synthesized from 6-O-alpha-maltosyl-beta-cyclodextrin (G2-beta-CD) via a transglycosylation reaction catalyzed by TreX, a debranching enzyme from Sulfolobus solfataricus P2. TreX showed no activity toward glucosyl-beta-CD, but a transfer product (1) was detected when the enzyme was incubated with maltosyl-beta-CD, indicating specificity for a branched glucosyl chain bigger than DP2. Analysis of the structure of the transfer product (1) using MALDI-TOF/MS and isoamylase or glucoamylase treatment revealed it to be dimaltosyl-beta-CD, suggesting that TreX transferred the maltosyl residue of a G2-beta-CD to another molecule of G2-beta-CD by forming an alpha-1,6-glucosidic linkage. When [(14)C]-maltose and maltosyl-beta-CD were reacted with the enzyme, the radiogram showed no labeled dimaltosyl-beta-CD; no condensation product between the two substrates was detected, indicating that the synthesis of dimaltosyl-beta-CD occurred exclusively via transglycosylation of an alpha-1,6-glucosidic linkage. Based on the HPLC elution profile, the transfer product (1) was identified to be isomers of 6(1),6(3)- and 6(1),6(4)-dimaltosyl-beta-CD. Inhibition studies with beta-CD on the transglycosylation activity revealed that beta-CD was a mixed-type inhibitor, with a K(i) value of 55.6 micromol/mL. Thus, dimaltosyl-beta-CD can be more efficiently synthesized by a transglycosylation reaction with TreX in the absence of beta-CD. Our findings suggest that the high yield of (G2)(2)-beta-CD from G2-beta-CD was based on both the transglycosylation action mode and elimination of the inhibitory effect of beta-CD. PMID:18060856

  16. Enantioselective Synthesis of 5,7-Bicyclic Ring Systems from Axially Chiral Allenes Using a Rh(I)-Catalyzed Cyclocarbonylation Reaction

    PubMed Central

    Grillet, Francois; Brummond, Kay M.

    2013-01-01

    A transfer of chirality in an intramolecular Rh(I)-catalyzed allenic Pauson-Khand reaction (APKR) to access tetrahydroazulenones, tetrahydrocyclopenta[c]azepinones and dihydrocyclopenta[c]oxepinones enantioselectively (22 – 99% ee) is described. The substitution pattern of the allene affected the transfer of chiral information. Complete transfer of chirality was obtained for all trisubstituted allenes, but loss of chiral information was observed for disubstituted allenes. This work constitutes the first demonstration of a transfer of chiral information from an allene to the 5-position of a cyclopentenone using a cyclocarbonylation reaction. The absolute configuration of the corresponding cyclocarbonylation product was also established, something that is rarely done. PMID:23485149

  17. Studies in asymmetric ?-lactone synthesis: extensions of the chiral nucleophile catalyzed aldol-lactonization (NCAL) reaction and new transformations of chlorinated ?-lactones

    E-print Network

    Tennyson, Reginald L.

    2001-01-01

    . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . 45 3. 5. 4. Organotin Addition 46 3. 5. 5. Hydride Addition. . . . . 47 Sg2' . . 48 3. 6. 1. Cuprate Addition. . . 48 3. 7. Dyotropic Rearrangements. 3. 7. 1. 7-Lactone Synthesis 49 49 Miscellaneous 4. 1. Decarboxylation 4. 1. 1, Thermal... condensation reaction between lithium ynolates, aldehydes and ketones. For example, they showed that the reaction of ynolate 6 with 5-keto ester 8 gives the bicyclic P-lactone 10, which underwent acid-catalyzed decarboxylation to give cyclohexene 11 in 74...

  18. Glycyl radical activating enzymes: Structure, mechanism, and substrate interactions?

    PubMed Central

    Shisler, Krista A.; Broderick, Joan B.

    2014-01-01

    The glycyl radical enzyme activating enzymes (GRE–AEs) are a group of enzymes that belong to the radical S-adenosylmethionine (SAM) superfamily and utilize a [4Fe–4S] cluster and SAM to catalyze H-atom abstraction from their substrate proteins. GRE–AEs activate homodimeric proteins known as glycyl radical enzymes (GREs) through the production of a glycyl radical. After activation, these GREs catalyze diverse reactions through the production of their own substrate radicals. The GRE–AE pyruvate formate lyase activating enzyme (PFL-AE) is extensively characterized and has provided insights into the active site structure of radical SAM enzymes including GRE–AEs, illustrating the nature of the interactions with their corresponding substrate GREs and external electron donors. This review will highlight research on PFL-AE and will also discuss a few GREs and their respective activating enzymes. PMID:24486374

  19. Structural and functional studies of a trans-acyltransferase polyketide assembly line enzyme that catalyzes stereoselective ?- and ?-ketoreduction.

    PubMed

    Piasecki, Shawn K; Zheng, Jianting; Axelrod, Abram J; Detelich, Madeline E; Keatinge-Clay, Adrian T

    2014-09-01

    While the cis-acyltransferase modular polyketide synthase assembly lines have largely been structurally dissected, enzymes from within the recently discovered trans-acyltransferase polyketide synthase assembly lines are just starting to be observed crystallographically. Here we examine the ketoreductase (KR) from the first polyketide synthase module of the bacillaene nonribosomal peptide synthetase/polyketide synthase at 2.35-Å resolution. This KR naturally reduces both ?- and ?-keto groups and is the only KR known to do so during the biosynthesis of a polyketide. The isolated KR not only reduced an N-acetylcysteamine-bound ?-keto substrate to a D-?-hydroxy product, but also an N-acetylcysteamine-bound ?-keto substrate to an L-?-hydroxy product. That the substrates must enter the active site from opposite directions to generate these stereochemistries suggests that the acyl-phosphopantetheine moiety is capable of accessing very different conformations despite being anchored to a serine residue of a docked acyl carrier protein. The features enabling stereocontrolled ?-ketoreduction may not be extensive since a KR that naturally reduces a ?-keto group within a cis-acyltransferase polyketide synthase was identified that performs a completely stereoselective reduction of the same ?-keto substrate to generate the D-?-hydroxy product. A sequence analysis of trans-acyltransferase KRs reveals that a single residue, rather than a three-residue motif found in cis-acyltransferase KRs, is predictive of the orientation of the resulting ?-hydroxyl group. PMID:24634061

  20. Expanding the substrate scope in palladium-catalyzed C-N and C-C bond-forming reactions

    E-print Network

    Anderson, Kevin William

    2006-01-01

    Chapter 1. The first detailed study of the palladium-catalyzed amination of aryl nonaflates is reported. Use of bulky electron-rich monophosphinobiaryl ligands or BINAP allow for the catalytic amination of electron-rich ...

  1. Study on the synthesis of sucrose-6-acetate catalyzed by fructosyltransferase from Aspergillus oryzae.

    PubMed

    Han, Yawei; Liu, Guoming; Huang, Dongye; Qiao, Baojian; Chen, Liping; Guan, Lihong; Mao, Duobin

    2011-01-31

    The study had mainly investigated the synthesis of sucrose-6-acetate (s-6-a) in fructosyltransferase action. The synthesis reaction of s-6-a was performed between sucrose and glucose-6-acetate (g-6-a), and identified by high performance liquid chromatography (HPLC). According to the reaction of s-6-a catalyzed by fructosyltransferase from Aspergillus oryzae, the effect factors of reaction, such as the ratio of g-6-a to sucrose, temperature, time, pH, substrate and enzyme concentration in the reaction, were investigated. All results indicated that the fructosyltransferase could catalyze the s-6-a synthesis, and the optimal conditions of fructosyltransferase in reaction were 50°C, pH 6.2, 48h reaction time, 60% sucrose, 1:3 ratio of g-6-a to sucrose and 4.0mg/L concentration of enzyme. This study plays the important role in sucralose synthesis, because it is very cumbersome in the reported methods. PMID:20643232

  2. Synthesis of 1,5-benzothiazepine dipeptide mimetics via two CuI-catalyzed cross coupling reactions.

    PubMed

    Gan, Jiangang; Ma, Dawei

    2009-07-01

    CuI-catalyzed coupling of 4-methylphenyl bromide with amino acids gives N-aryl amino acids, which are converted into linear dipeptides via iodination and condensation with L-cysteine derived acyl chloride. Cyclization is achieved via a CuI/N,N-dimethylglycine catalyzed intramolecular coupling of aryl iodides with the liberated thiol to afford 1,5-benzothiazepine dipeptide mimetics. PMID:19480438

  3. Atomic-Resolution Structures of Discrete Stages on the Reaction Coordinate of the [Fe4S4] Enzyme IspG (GcpE).

    PubMed

    Quitterer, Felix; Frank, Annika; Wang, Ke; Rao, Guodong; O'Dowd, Bing; Li, Jikun; Guerra, Francisco; Abdel-Azeim, Safwat; Bacher, Adelbert; Eppinger, Jörg; Oldfield, Eric; Groll, Michael

    2015-06-19

    IspG is the penultimate enzyme in non-mevalonate biosynthesis of the universal terpene building blocks isopentenyl diphosphate and dimethylallyl diphosphate. Its mechanism of action has been the subject of numerous studies but remained unresolved due to difficulties in identifying distinct reaction intermediates. Using a moderate reducing agent and an epoxide substrate analogue, we were now able to trap and crystallographically characterize various stages in the IspG-catalyzed conversion of 2-C-methyl-d-erythritol-2,4-cyclo-diphosphate into (E)-1-hydroxy-2-methylbut-2-enyl-4-diphosphate. In addition, the enzyme's structure was determined in complex with several inhibitors. These results, combined with recent electron paramagnetic resonance data, allowed us to deduce a detailed and complete IspG catalytic mechanism, which describes all stages from initial ring opening to formation of (E)-1-hydroxy-2-methylbut-2-enyl-4-diphosphate via discrete radical and carbanion intermediates. The data presented in this article provide a guide for the design of selective drugs against many prokaryotic and eukaryotic pathogens to which the non-mevalonate pathway is essential for survival and virulence. PMID:25868383

  4. The Reaction Kinetics of 3-Hydroxybenzoate 6-Hydroxylase from Rhodococcus jostii RHA1 Provide an Understanding of the para-Hydroxylation Enzyme Catalytic Cycle*

    PubMed Central

    Sucharitakul, Jeerus; Tongsook, Chanakan; Pakotiprapha, Danaya; van Berkel, Willem J. H.; Chaiyen, Pimchai

    2013-01-01

    3-Hydroxybenzoate 6-hydroxylase (3HB6H) from Rhodococcus jostii RHA1 is an NADH-specific flavoprotein monooxygenase that catalyzes the para-hydroxylation of 3-hydroxybenzoate (3HB) to form 2,5-dihydroxybenzoate (2,5-DHB). Based on results from stopped-flow spectrophotometry, the reduced enzyme-3HB complex reacts with oxygen to form a C4a-peroxy flavin with a rate constant of 1.13 ± 0.01 × 106 m?1 s?1 (pH 8.0, 4 °C). This intermediate is subsequently protonated to form a C4a-hydroperoxyflavin with a rate constant of 96 ± 3 s?1. This step shows a solvent kinetic isotope effect of 1.7. Based on rapid-quench measurements, the hydroxylation occurs with a rate constant of 36 ± 2 s?1. 3HB6H does not exhibit substrate inhibition on the flavin oxidation step, a common characteristic found in most ortho-hydroxylation enzymes. The apparent kcat at saturating concentrations of 3HB, NADH, and oxygen is 6.49 ± 0.02 s?1. Pre-steady state and steady-state kinetic data were used to construct the catalytic cycle of the reaction. The data indicate that the steps of product release (11.7 s?1) and hydroxylation (36 ± 2 s?1) partially control the overall turnover. PMID:24129570

  5. Tight gas sands research program: Field operations and analysis. Degradation of hydroxypropyl guar fracturing fluids by enzyme, oxidative, and catalyzed oxidative breakers. Part 1. Linear hydroxypropyl guar solutions. Topical report, February 1991-December 1991

    SciTech Connect

    Craig, D.; Holditch, S.A.

    1993-12-01

    The research was designed to accomplish the following objectives: Determine the effects of pH, temperature, and polymer concentration on HPG solution degradation by enzyme, oxidative (ammonium persulfate), and catalyzed oxidative breakers (ammonium persulfate with triethanolamine); Identify the appropriate breaker system for HPG solutions in the temperature range of 120 deg F - 140 deg F; and Determine the temperature range for HPG solutions where chemical breakers are not necessary to degrade the fluid.

  6. Palladium-catalyzed asymmetric synthesis of axially chiral (allenylmethyl)silanes and chirality transfer to stereogenic carbon centers in S(E)' reactions.

    PubMed

    Ogasawara, Masamichi; Ueyama, Kazuhito; Nagano, Takashi; Mizuhata, Yoshiyuki; Hayashi, Tamio

    2003-01-23

    [reaction: see text] Novel stereoselective reactions of 4-substituted-1-trimethylsilyl-2,3-butadienes ((allenylmethyl)silanes) were developed. The axially chiral (allenylmethyl)silanes were prepared from (3-bromopenta-2,4-dienyl)trimethylsilane by a Pd-catalyzed asymmetric reaction with soft nucleophiles with up to 88% enantioselectivity. The (allenylmethyl)silanes reacted with acetals in the presence of a TiCl(4) promoter to give 1,3-diene derivatives via an S(E)' pathway. The 1,3-dienyl products have (E)-geometry exclusively and up to 88%( )()chirality transfer from the axially chiral allenes to the centrally chiral 1,3-dienes was observed in the S(E)' reaction. PMID:12529144

  7. An investigation of the relationships between rate and driving force in simple uncatalysed and enzyme-catalysed reactions with applications of the findings to chemiosmotic reactions.

    PubMed Central

    Stoner, C D

    1992-01-01

    Both the rate and the driving force of a reaction can be expressed in terms of the concentrations of the reactants and products. Consequently, rate and driving force can be expressed as a function of each other. This has been done for a single-reactant, single-product, uncatalysed reaction and its enzyme-catalysed equivalent using the van't Hoff reaction isotherm and Haldane's generalized Michaelis-Menten rate equation, the primary objective being explanation of the exponential and sigmoidal relationships between reaction rate and delta mu H+ commonly observed in studies on chemiosmotic reactions. Acquisition of a purely thermodynamic rate vs. driving-force relationship requires recognition of the intensive and extensive variables and maintenance of the extensive variables constant. This relationship is identical for the two reactions and is hyperbolic or sigmoidal, depending on whether the equilibrium constant is smaller or larger than unity. In the case of the catalysed reaction, acquisition of the purely thermodynamic relationship requires the assumption that the enzyme be equally effective in catalysing the forward and backward reactions. If this condition is not met, the relationship is modified by the enzyme in a manner which can be determined from the ratio of the Michaelis constants of the reactant and product. Under conditions of enzyme saturation in respect to reactant+product, the rate vs. driving-force relationship is determined exclusively by the thermodynamics of the reaction and a single kinetic parameter, the magnitude of which is determined by the relative effectiveness of the enzyme in catalysing the forward and backward reactions. In view of this finding, it is pointed out that, since the catalytic components of chemiosmotic reactions appear to be saturated with respect to the reactant-product pair that is varied in experimental rate vs. delta mu H+ determinations, and that, since many complex enzymic reactions conform to the simple Michaelis-Menten equation with respect to a single reactant-product pair when the concentrations of all other reactants and products are maintained constant, one might expect to be capable of simulating the experimental relationships simply from knowledge of the thermodynamics of the reaction and the relative effectiveness of the catalytic component in catalysing the forward and backward reactions using the simple Michaelis-Menten equation. That this expectation appears to be largely correct is demonstrated with model reactions.(ABSTRACT TRUNCATED AT 400 WORDS) PMID:1533514

  8. Rhenium-Catalyzed Aromatic Propargylation

    E-print Network

    Toste, Dean

    Rhenium-Catalyzed Aromatic Propargylation Joshua J. Kennedy-Smith, Lauren A. Young, and F. Dean propargylation reaction, employing an air- and moisture-tolerant rhenium-oxo complex ((dppm)ReOCl3) as a catalyst. The potential of this rhenium(V)-catalyzed reaction is exemplified by application of the propargylation

  9. Determination of berberine and the study of fluorescence quenching mechanism between berberine and enzyme-catalyzed product

    NASA Astrophysics Data System (ADS)

    Wang, Huaiyou; Zhang, Miao; Lv, Qingluan; Yue, Ningning; Gong, Bin

    2009-08-01

    A new method for determining berberine has been established based on the principle of fluorescence quenching. The calibration curve was found to be linear between F0/ F and the concentration of berberine with the range of 3.00-20.0 ?g mL -1. The detection limit was 0.51 ?g mL -1 and the relative standard derivative was 0.18%. Effects of pH, foreign ions and the optimization of variables on the determination of berberine have been examined. The mechanism of the fluorescence quenching has been discussed. The binding constant and the number of binding sites were 1.70 × 10 6 L mol -1 and 1.14, respectively. The data, ? H = 42.71 kJ mol -1, ? S = 264.3 J K -1 mol -1 and the mean value ? G = -39.65 kJ mol -1 were estimated which showed that the reaction was spontaneous and endothermic. The main binding force was hydrophobic force because both ? H and ? S were positive.

  10. Enzyme sequence similarity improves the reaction alignment method for cross-species pathway comparison

    SciTech Connect

    Ovacik, Meric A. [Chemical and Biochemical Engineering Department, Rutgers University, Piscataway, NJ 08854 (United States); Androulakis, Ioannis P., E-mail: yannis@rci.rutgers.edu [Chemical and Biochemical Engineering Department, Rutgers University, Piscataway, NJ 08854 (United States); Biomedical Engineering Department, Rutgers University, Piscataway, NJ 08854 (United States)

    2013-09-15

    Pathway-based information has become an important source of information for both establishing evolutionary relationships and understanding the mode of action of a chemical or pharmaceutical among species. Cross-species comparison of pathways can address two broad questions: comparison in order to inform evolutionary relationships and to extrapolate species differences used in a number of different applications including drug and toxicity testing. Cross-species comparison of metabolic pathways is complex as there are multiple features of a pathway that can be modeled and compared. Among the various methods that have been proposed, reaction alignment has emerged as the most successful at predicting phylogenetic relationships based on NCBI taxonomy. We propose an improvement of the reaction alignment method by accounting for sequence similarity in addition to reaction alignment method. Using nine species, including human and some model organisms and test species, we evaluate the standard and improved comparison methods by analyzing glycolysis and citrate cycle pathways conservation. In addition, we demonstrate how organism comparison can be conducted by accounting for the cumulative information retrieved from nine pathways in central metabolism as well as a more complete study involving 36 pathways common in all nine species. Our results indicate that reaction alignment with enzyme sequence similarity results in a more accurate representation of pathway specific cross-species similarities and differences based on NCBI taxonomy.

  11. Green polymer chemistry: enzyme catalysis for polymer functionalization.

    PubMed

    Sen, Sanghamitra; Puskas, Judit E

    2015-01-01

    Enzyme catalyzed reactions are green alternative approaches to functionalize polymers compared to conventional methods. This technique is especially advantageous due to the high selectivity, high efficiency, milder reaction conditions, and recyclability of enzymes. Selected reactions can be conducted under solventless conditions without the application of metal catalysts. Hence this process is becoming more recognized in the arena of biomedical applications, as the toxicity created by solvents and metal catalyst residues can be completely avoided. In this review we will discuss fundamental aspects of chemical reactions biocatalyzed by Candida antarctica lipase B, and their application to create new functionalized polymers, including the regio- and chemoselectivity of the reactions. PMID:26007188

  12. Facile synthesis and palladium-catalyzed cross-coupling reactions of 2,3-bis(pinacolatoboryl)-1,3-butadiene.

    PubMed

    Shimizu, Masaki; Kurahashi, Takuya; Shimono, Katsuhiro; Tanaka, Kei; Nagao, Ikuhiro; Kiyomoto, Shin-ichi; Hiyama, Tamejiro

    2007-11-01

    Treatment of 1,1-bis(pinacolatoboryl)ethene with an excess of 1-bromo-1-lithioethene gave 2,3-bis(pinacolatoboryl)-1,3-butadiene in high yield. Palladium-catalyzed cross-coupling of the resulting diborylbutadiene with aryl iodides took place smoothly in the presence of a catalytic amount of Pd(OAc)2/PPh3 and aqueous KOH to give 2,3-diaryl-1,3-butadienes in good yields. The coupling reaction with commercially available 4-acetoxyphenylmethyl chloride under the same conditions followed by hydrolysis of the acetyl groups gave anolignan B in a one-pot manner. A variety of [3]- to [6]dendralenes were synthesized by palladium-catalyzed coupling of the diene or 1,1-bis(pinacolato)borylethene with alkenyl or dienyl halides, respectively, in good yields. PMID:17828718

  13. Kinetic analysis of chemical reactions coupled to an enzymic step. Application to acid phosphatase assay with Fast Red.

    PubMed Central

    Escribano, J; García-Carmona, F; García-Cánovas, F; Iborra, J L; Lozano, J A

    1984-01-01

    Acid phosphatase assay with alpha-naphthyl phosphate as substrate and the use of diazonium salt (Fast Red TR) for chromophore formation was kinetically analysed as a system of two chemical reactions coupled to an enzymic reaction. This system follows a mechanism defined as enzymic-chemical-chemical (EzCC). The accumulation of chromophore with reaction time presented a marked lag period, which was only dependent on the rate constants of the chemical reactions and was independent of the enzymic step. The specific rate constants of each chemical step were determined in 3.8-5.0 pH and 10-35 degrees C temperature ranges. Thermodynamic parameters of the chemical steps were also obtained. Measurement of acid phosphatase activity can be carried out in the pH range 3.8-5.0 (4.8 was optimal pH) without the need to eliminate the lag period. PMID:6508735

  14. Suicide Inactivation of Peroxidases and the Challenge of Engineering More Robust Enzymes

    Microsoft Academic Search

    Brenda Valderrama; Marcela Ayala; Rafael Vazquez-Duhalt

    2002-01-01

    As the number of industrial applications for proteins continues to expand, the exploitation of protein engineering becomes critical. It is predicted that protein engineering can generate enzymes with new catalytic properties and create desirable, high-value, products at lower production costs. Peroxidases are ubiquitous enzymes that catalyze a variety of oxygen-transfer reactions and are thus potentially useful for industrial and biomedical

  15. 3-Hydroxy-3-methylglutaryl-CoA synthase: participation of invariant acidic residues in formation of the acetyl-S-enzyme reaction intermediate.

    PubMed

    Chun, K Y; Vinarov, D A; Miziorko, H M

    2000-11-28

    Inactivation of HMG-CoA synthase by a carboxyl-directed reagent, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), in a concentration-dependent and substrate-protectable manner suggested that the active site contains reactive acidic amino acids. This observation prompted functional evaluation of 11 invariant acidic amino acids by site-directed mutagenesis. Characterization of the isolated synthase variants' ability to catalyze overall and partial reactions identified three mutant synthases (D99A, D159A, and D203A) that exhibit significant diminution of k(cat) for the overall reaction (10(2)-, 10(3)-, and 10(4)-fold decreases, respectively). D99A, D159A, and D203A form the acetyl-S-enzyme intermediate very slowly (0.0025, 0.0026, 0.0015 U/mg, respectively, measured at pH 7. 0 and 22 degrees C) as compared to the wild-type synthase (1.59 U/mg), where intermediate formation approaches rate-limiting status. Differences in substrate saturation do not account for impaired activities or rates of intermediate formation. The structural integrity of the purified mutants' active sites is demonstrated by their abilities to bind a spin-labeled acyl-CoA analogue (R.CoA) with affinities and stoichiometries comparable to values measured for wild-type synthase. The impact of three distinct amino acids on reaction intermediate formation supports a mechanism of acetyl-S-enzyme formation that probably requires formation and directed collapse of a tetrahedral adduct. (18)O-induced shift of the (13)C NMR signal of (13)C acetyl-S-enzyme demonstrates that an analogous tetrahedral species is produced upon solvent exchange with the acetyl-S-enzyme. Partial discrimination between the functions of D99, D159, and D203 becomes possible based on the observation that D159A and D203A synthases exhibit retarded kinetics of solvent (18)O exchange while D99A fails to support (18)O exchange. PMID:11087424

  16. P1 Trisaccharide (Gal?1,4Gal?1,4GlcNAc) Synthesis by Enzyme Glycosylation Reactions Using Recombinant Escherichia coli

    PubMed Central

    Liu, Ziye; Lu, Yuquan; Zhang, Jianbo; Pardee, Keith; Wang, Peng George

    2003-01-01

    The frequency of Escherichia coli infection has lead to concerns over pathogenic bacteria in our food supply and a demand for therapeutics. Glycolipids on gut cells serve as receptors for the Shiga-like toxin produced by E. coli. Oligosaccharide moiety analogues of these glycolipids can compete with receptors for the toxin, thus acting as antibacterials. An enzymatic synthesis of the P1 trisaccharide (Gal?1,4Gal?1,4GlcNAc), one of the oligosaccharide analogues, was assessed in this study. In the proposed synthetic pathway, UDP-glucose was generated from sucrose with an Anabaena sp. sucrose synthase and then converted with an E. coli UDP-glucose 4-epimerase to UDP-galactose. Two molecules of galactose were linked to N-acetylglucosamine subsequently with a Helicobacter pylori ?-l,4-galactosyltransferase and a Neisseria meningitidis ?-1,4-galactosyltransferase to produce one molecule of P1 trisaccharide. The four enzymes were coexpressed in a single genetically engineered E. coli strain that was then permeabilized and used to catalyze the enzymatic reaction. P1 trisaccharide was accumulated up to 50 mM (5.4 g in a 200-ml reaction volume), with a 67% yield based on the consumption of N-acetylglucosamine. This study provides an efficient approach for the preparative-scale synthesis of P1 trisaccharide with recombinant bacteria. PMID:12676690

  17. Transition-metal-catalyzed C-N bond forming reactions using organic azides as the nitrogen source: a journey for the mild and versatile C-h amination.

    PubMed

    Shin, Kwangmin; Kim, Hyunwoo; Chang, Sukbok

    2015-04-21

    Owing to the prevalence of nitrogen-containing compounds in functional materials, natural products and important pharmaceutical agents, chemists have actively searched for the development of efficient and selective methodologies allowing for the facile construction of carbon-nitrogen bonds. While metal-catalyzed C-N cross-coupling reactions have been established as one of the most general protocols for C-N bond formation, these methods require starting materials equipped with functional groups such as (hetero)aryl halides or their equivalents, thus generating stoichiometric amounts of halide salts as byproducts. To address this aspect, a transition-metal-catalyzed direct C-H amination approach has emerged as a step- and atom-economical alternative to the conventional C-N cross-coupling reactions. However, despite the significant recent advances in metal-mediated direct C-H amination reactions, most available procedures need harsh conditions requiring stoichiometric external oxidants. In this context, we were curious to see whether a transition-metal-catalyzed mild C-H amination protocol could be achieved using organic azides as the amino source. We envisaged that a dual role of organic azides as an environmentally benign amino source and also as an internal oxidant via N-N2 bond cleavage would be key to develop efficient C-H amination reactions employing azides. An additional advantage of this approach was anticipated: that a sole byproduct is molecular nitrogen (N2) under the perspective catalytic conditions. This Account mainly describes our research efforts on the development of rhodium- and iridium-catalyzed direct C-H amination reactions with organic azides. Under our initially optimized Rh(III)-catalyzed amination conditions, not only sulfonyl azides but also aryl- and alkyl azides could be utilized as facile amino sources in reaction with various types of C(sp(2))-H bonds bearing such directing groups as pyridine, amide, or ketoxime. More recently, a new catalyst system using Ir(III) species was developed for the direct C-H amidation of arenes and alkenes with acyl azides under exceptionally mild conditions. As a natural extension, amidation of primary C(sp(3))-H bonds could also be realized on the basis of the superior activity of the Cp*Ir(III) catalyst. Mechanistic investigations revealed that a catalytic cycle is operated mainly in three stages: (i) chelation-assisted metallacycle formation via C-H bond cleavage; (ii) C-N bond formation through the in situ generation of a metal-nitrenoid intermediate followed by the insertion of an imido moiety to the metal carbon bond; (iii) product release via protodemetalation with the concomitant catalyst regeneration. In addition, this Account also summarizes the recent advances in the ruthenium- and cobalt-catalyzed amination reactions using organic azides, developed by our own and other groups. Comparative studies on the relative performance of those catalytic systems are briefly described. PMID:25821998

  18. Synthesis of oxazines and N-arylpyrroles by reaction of unfunctionalized dienes with nitroarenes and carbon monoxide, catalyzed by palladium-phenanthroline complexes.

    PubMed

    Ragaini, Fabio; Cenini, Sergio; Brignoli, Daniela; Gasperini, Michela; Gallo, Emma

    2003-01-24

    The reaction between an unfunctionalized conjugated diene and a nitroarene under CO pressure and at 100 degrees C, catalyzed by [Pd(Phen)2][BF4]2 (Phen = 1,10-phenanthroline), affords the corresponding hetero-Diels-Alder adduct (oxazine) in up to 91% yields in one pot. If the reaction mixture is then heated to 200 degrees C, the oxazines are converted into the corresponding N-arylpyrroles in good yields. Pressures as low as 5 bar can be employed, and 0.08% catalyst is sufficient to effect the transformation. The reaction can be equally run by employing the nitroarene or the diene as limiting agent and works well for nitroarenes bearing either electron-withdrawing or mildly electron-donating substituents. A moderate steric hindrance on the nitroarene (o-methyl) is well tolerated, but 1,4-disubstituted-1,3-dienes are not suitable substrates. PMID:12530872

  19. Enzyme, medium, and reaction engineering to design a low-cost, selective production method for mono- and dioleoylglycerols

    Microsoft Academic Search

    J. A. Arcos; C. Otero

    1996-01-01

    The selective enzymic production of mono- and diolein (MO, DO) was optimized at high yields. A comparative study of the following\\u000a distinct enzymic reactions was conducted: ethyl oleate glycerolysis, triolein (TO) glycerolysis, and direct esterification\\u000a Solvent-free systems were compared with media that contained different solvents. Native, modified (with polyethylene glycol),\\u000a and immobilized lipases were used. Mechanical resistance, the support effect

  20. Enzyme-linked immunosorbent assay and latex agglutination inhibition reaction test for cocaine and benzoylecgonine in urine

    Microsoft Academic Search

    Kimiko Aoki; Yasuko Shikama; Takemi Yoshida; Yukio Kuroiwa

    1996-01-01

    An enzyme-linked immunosorbent assay (ELISA) and a latex agglutination inhibition reaction test (LAIRT) for cocaine and benzoylecgonine have been established. In ELISA with polystyrene microtiter wells coated with anti-benzoylecgonine antibody and alkaline phosphatase (ALP)-labeled benzoylecgonine, the activity of antibody-bound ALP was measured with the enzyme cycling method. The range of benzoylecgonine measurable by ELISA was 12 pg-25 ng\\/well; the analysis

  1. Lanthanide (III)-catalyzed enantioselective Diels-Alder reactions. Stereoselective synthesis of both enantiomers by using a single chiral source and a choice of achiral ligands

    SciTech Connect

    Kobayashi, Shu; Ishitani, Haruro (Science Univ. of Tokyo (Japan))

    1994-05-04

    In this paper, we disclose a conceptually different approach to obtaining both enantiomers; choice of enatiofacial selectivity by use of the enatiomerically same chiral source and different achiral ligands. Both enantiomers of the Diels-Alder adducts between e-acyl-1,3-oxazolidin-2-ones and cyclopentadiene were prepared by chiral lanthanides(III)-catalyzed reactions using the same chiral source, (R)-(+)-binaphthol. It is noted that the chiral catalysts with reverse enantiofacial selectivities could be prepared by using the same chiral source and a choice of achiral ligands. 14 refs., 3 tabs.

  2. Palladium catalyzed C-C coupling reactions of 3,5-dichloro-4H-1,2,6-thiadiazin-4-one.

    PubMed

    Ioannidou, Heraklidia A; Kizas, Christos; Koutentis, Panayiotis A

    2011-07-01

    Palladium catalyzed Suzuki-Miyaura, Stille, and Sonogashira coupling reactions are reported for the electron-deficient heterocyclic scaffold 3,5-dichloro-4H-1,2,6-thiadiazin-4-one (1). Furthermore, 3,5-di(thien-2-yl)-4H-1,2,6-thiadiazin-4-one (7m) is further elaborated to afford the tetrathienyl 3,5-bis[(2,2'-bithien)-5-yl]-4H-1,2,6-thiadiazin-4-one (9). All compounds are fully characterized. PMID:21648403

  3. Extending synthetic routes for oligosaccharides by enzyme, substrate and reaction engineering.

    PubMed

    Seibel, Jürgen; Jördening, Hans-Joachim; Buchholz, Klaus

    2010-01-01

    The integration of all relevant tools for bioreaction engineering has been a recent challenge. This approach should notably favor the production of oligo- and polysaccharides, which is highly complex due to the requirements of regio- and stereoselectivity. Oligosaccharides (OS) and polysaccharides (PS) have found many interests in the fields of food, pharmaceuticals, and cosmetics due to different specific properties. Food, sweeteners, and food ingredients represent important sectors where OS are used in major amounts. Increasing attention has been devoted to the sophisticated roles of OS and glycosylated compounds, at cell or membrane surfaces, and their function, e.g., in infection and cancer proliferation. The challenge for synthesis is obvious, and convenient approaches using cheap and readily available substrates and enzymes will be discussed. We report on new routes for the synthesis of oligosaccharides (OS), with emphasis on enzymatic reactions, since they offer unique properties, proceeding highly regio- and stereoselective in water solution, and providing for high yields in general. PMID:20182930

  4. Nested arithmetic progressions of oscillatory phases in Olsen's enzyme reaction model.

    PubMed

    Gallas, Marcia R; Gallas, Jason A C

    2015-06-01

    We report some regular organizations of stability phases discovered among self-sustained oscillations of a biochemical oscillator. The signature of such organizations is a nested arithmetic progression in the number of spikes of consecutive windows of periodic oscillations. In one of them, there is a main progression of windows whose consecutive number of spikes differs by one unit. Such windows are separated by a secondary progression of smaller windows whose number of spikes differs by two units. Another more complex progression involves a fan-like nested alternation of stability phases whose number of spikes seems to grow indefinitely and to accumulate methodically in cycles. Arithmetic progressions exist abundantly in several control parameter planes and can be observed by tuning just one among several possible rate constants governing the enzyme reaction. PMID:26117128

  5. Nested arithmetic progressions of oscillatory phases in Olsen's enzyme reaction model

    NASA Astrophysics Data System (ADS)

    Gallas, Marcia R.; Gallas, Jason A. C.

    2015-06-01

    We report some regular organizations of stability phases discovered among self-sustained oscillations of a biochemical oscillator. The signature of such organizations is a nested arithmetic progression in the number of spikes of consecutive windows of periodic oscillations. In one of them, there is a main progression of windows whose consecutive number of spikes differs by one unit. Such windows are separated by a secondary progression of smaller windows whose number of spikes differs by two units. Another more complex progression involves a fan-like nested alternation of stability phases whose number of spikes seems to grow indefinitely and to accumulate methodically in cycles. Arithmetic progressions exist abundantly in several control parameter planes and can be observed by tuning just one among several possible rate constants governing the enzyme reaction.

  6. Extending Synthetic Routes for Oligosaccharides by Enzyme, Substrate and Reaction Engineering

    NASA Astrophysics Data System (ADS)

    Seibel, Jürgen; Jördening, Hans-Joachim; Buchholz, Klaus

    The integration of all relevant tools for bioreaction engineering has been a recent challenge. This approach should notably favor the production of oligo- and polysaccharides, which is highly complex due to the requirements of regio- and stereoselectivity. Oligosaccharides (OS) and polysaccharides (PS) have found many interests in the fields of food, pharmaceuticals, and cosmetics due to different specific properties. Food, sweeteners, and food ingredients represent important sectors where OS are used in major amounts. Increasing attention has been devoted to the sophisticated roles of OS and glycosylated compounds, at cell or membrane surfaces, and their function, e.g., in infection and cancer proliferation. The challenge for synthesis is obvious, and convenient approaches using cheap and readily available substrates and enzymes will be discussed. We report on new routes for the synthesis of oligosaccharides (OS), with emphasis on enzymatic reactions, since they offer unique properties, proceeding highly regio- and stereoselective in water solution, and providing for high yields in general.

  7. Reaction of Mycobacterium tuberculosis cytochrome P450 enzymes with nitric oxide.

    PubMed

    Ouellet, Hugues; Lang, Jérôme; Couture, Manon; Ortiz de Montellano, Paul R

    2009-02-10

    During the initial growth infection stage of Mycobacterium tuberculosis (Mtb), (*)NO produced by host macrophages inhibits heme-containing terminal cytochrome oxidases, inactivates iron/sulfur proteins, and promotes entry into latency. Here we evaluate the potential of (*)NO as an inhibitor of Mtb cytochrome P450 enzymes, as represented by CYP130, CYP51, and the two previously uncharacterized enzymes CYP125 and CYP142. Using UV-visible absorption, resonance Raman, and stopped-flow spectroscopy, we investigated the reactions of (*)NO with these heme proteins in their ferric resting form. (*)NO coordinates tightly to CYP125 and CYP142 (submicromolar) and with a lower affinity (micromolar) to CYP130 and CYP51. Anaerobic reduction of the ferric-NO species with sodium dithionite led to the formation of two spectrally distinct classes of five-coordinate ferrous-NO complexes. Exposure of these species to O(2) revealed that the ferrous-NO forms of CYP125 and CYP142 are labile and convert back to the ferric state within a few minutes, whereas ferrous CYP130 and CYP51 bind (*)NO almost irreversibly. This work clearly indicates that, at physiological concentrations (approximately 1 microM), (*)NO would impair the activity of CYP130 and CYP51, whereas CYP125 and CYP142 are more resistant. Selective P450 inhibition may contribute to the inhibitory effects of (*)NO on Mtb growth. PMID:19146393

  8. High-throughput polymerase chain reaction chemiluminescent enzyme immunoassay for typing and quantifying human papillomavirus DNAs.

    PubMed

    Ambretti, Simone; Mirasoli, Mara; Venturoli, Simona; Zerbini, Marialuisa; Baraldini, Mario; Musiani, Monica; Roda, Aldo

    2004-09-15

    A miniaturized polymerase chain reaction (PCR) chemiluminescent enzyme immunoassay (CLEIA) based on a 384-well microtiter plate for detection and typing of oncogenic high- and low-risk human papillomavirus (HPV) in genital lesions is described. The assay relies on PCR consensus amplification, hybridization of the digoxigenin-labeled product by means of type-specific biotin-labeled oligoprobes immobilized on the streptavidin-coated wells of a 384-well microtiter plate, and quantification by means of a horseradish peroxidase-labeled antidigoxigenin antibody and chemiluminescence detection. The method provides semiquantitative information on the viral load, with a limit of detection of 10-50 DNA copies for HPV 6, 11, 16, 18, 31, 33, 35, 39, 45, 51, 52, 53, 54, 58, and 59 and high reproducibility (intraassay CV 7.5%, interassay CV 9.5%). Results obtained on 60 clinical samples were concordant with those obtained with a conventional PCR-enzyme-linked immunosorbent assay colorimetric assay. The 384 PCR-CLEIA method, which is amenable to automation, represents a fast and high-throughput method for detecting and typing HPV DNAs in screening programs and evaluating the viral load. PMID:15325304

  9. Palladium-complex-catalyzed regioselective Markovnikov addition reaction and dehydrogenative double phosphinylation to terminal alkynes with diphenylphosphine oxide

    Microsoft Academic Search

    Naotomo Dobashi; Kouichiro Fuse; Takako Hoshino; Jun Kanada; Taigo Kashiwabara; Chihiro Kobata; Satish Kumar Nune; Masato Tanaka

    2007-01-01

    Palladium-1,2-bis(diphenylphosphino)ethane complex catalyzes regioselective Markovnikov addition of diphenylphosphine oxide to terminal alkynes in propionitrile, while the use of triarylphopshines, di(o-tolyl)phenylphosphine in particular, as the ligand leads to dehydrogenative double addition forming 1,2-diphenylphosphinyl-1-alkenes as major products.

  10. Fat content for nutritional labeling by supercritical fluid extraction and an on-line lipase catalyzed reaction

    Microsoft Academic Search

    Janet M. Snyder; Jerry W. King; Michael A. Jackson

    1996-01-01

    A method using sequential supercritical fluid extraction (SFE) and enzymatic transesterification has been developed for the rapid determination of total nutritional fat content in meat samples. SFE conditions of 12.16 MPa and 50°C were utilized to extract lipid species from the sample matrix. The enzymatic transesterification of the lipids by methanol was catalyzed by an immobilized lipase isolated from Candida

  11. Detection of Covalent and Noncovalent Intermediates in the Polymerization Reaction Catalyzed by a C149S Class III Polyhydroxybutyrate Synthase

    E-print Network

    Li, Ping

    Polyhydroxybutyrate (PHB) synthases catalyze the conversion of 3-hydroxybutyryl coenzyme A (HBCoA) to PHB with a molecular mass of 1.5 MDa. The class III synthase from Allochromatium vinosum is a tetramer of PhaEPhaC (each ...

  12. Water plays a different role on activation thermodynamic parameters of alcoholysis reaction catalyzed by Lipase in gaseous and organic media

    E-print Network

    Boyer, Edmond

    catalyzed by Lipase in gaseous and organic media Marianne Graber, Marie-Pierre Bousquet-Dubouch, Nadine, fax: (33) 5 46 45 82 65, Email: mgraber@univ-lr.fr KEY WORDS Lipase B from Candida antarctica by immobilized Candida antarctica lipase B (CALB) has been compared in a continuous solid/gas reactor

  13. Direct Synthesis of 5-Aryl Barbituric Acids by Rhodium(II)-Catalyzed Reactions of Arenes with Diazo Compounds**

    PubMed Central

    Best, Daniel; Burns, David J; Lam, Hon Wai

    2015-01-01

    A commercially available rhodium(II) complex catalyzes the direct arylation of 5-diazobarbituric acids with arenes, allowing straightforward access to 5-aryl barbituric acids. Free N—H groups are tolerated on the barbituric acid, with no complications arising from N—H insertion processes. This method was applied to the concise synthesis of a potent matrix metalloproteinase (MMP) inhibitor. PMID:25959544

  14. Following solid-acid-catalyzed reactions by MAS NMR spectroscopy in liquid phase--zeolite-catalyzed conversion of cyclohexanol in water.

    PubMed

    Vjunov, Aleksei; Hu, Mary Y; Feng, Ju; Camaioni, Donald M; Mei, Donghai; Hu, Jian Z; Zhao, Chen; Lercher, Johannes A

    2014-01-01

    A microautoclave magic angle spinning NMR rotor is developed enabling in?situ monitoring of solid-liquid-gas reactions at high temperatures and pressures. It is used in a kinetic and mechanistic study of the reactions of cyclohexanol on zeolite HBEA in 130?°C water. The (13) C?spectra show that dehydration of 1-(13) C-cyclohexanol occurs with significant migration of the hydroxy group in cyclohexanol and the double bond in cyclohexene with respect to the (13) C label. A simplified kinetic model shows the E1-type elimination fully accounts for the initial rates of 1-(13) C-cyclohexanol disappearance and the appearance of the differently labeled products, thus suggesting that the cyclohexyl cation undergoes a 1,2-hydride shift competitive with rehydration and deprotonation. Concurrent with the dehydration, trace amounts of dicyclohexyl ether are observed, and in approaching equilibrium, a secondary product, cyclohexyl-1-cyclohexene is formed. Compared to phosphoric acid, HBEA is shown to be a more active catalyst exhibiting a dehydration rate that is 100-fold faster per proton. PMID:24282024

  15. Enzymic synthesis of indole-3-acetyl-1-O-beta-d-glucose. I. Partial purification and characterization of the enzyme from Zea mays

    NASA Technical Reports Server (NTRS)

    Leznicki, A. J.; Bandurski, R. S.

    1988-01-01

    The first enzyme-catalyzed reaction leading from indole-3-acetic acid (IAA) to the myo-inositol esters of IAA is the synthesis of indole-3-acetyl-1-O-beta-D-glucose from uridine-5'-diphosphoglucose (UDPG) and IAA. The reaction is catalyzed by the enzyme, UDPG-indol-3-ylacetyl glucosyl transferase (IAA-glucose-synthase). This work reports methods for the assay of the enzyme and for the extraction and partial purification of the enzyme from kernels of Zea mays sweet corn. The enzyme has an apparent molecular weight of 46,500 an isoelectric point of 5.5, and its pH optimum lies between 7.3 and 7.6. The enzyme is stable to storage at zero degrees but loses activity during column chromatographic procedures which can be restored only fractionally by addition of column eluates. The data suggest either multiple unknown cofactors or conformational changes leading to activity loss.

  16. Nickel-Catalyzed Cross-Coupling Reactions of o-Carboranyl with Aryl Iodides: Facile Synthesis of 1-Aryl-o-Carboranes and 1,2-Diaryl-o-Carboranes.

    PubMed

    Tang, Cen; Xie, Zuowei

    2015-06-22

    A nickel-catalyzed arylation at the carbon center of o-carborane cages has been developed, thus leading to the preparation of a series of 1-aryl-o-carboranes and 1,2-diaryl-o-carboranes in high yields upon isolation. This method represents the first example of transition metal catalyzed C,C'-diarylation by cross-coupling reactions of o-carboranyl with aryl iodides. PMID:25959849

  17. Complete Proteomic-Based Enzyme Reaction and Inhibition Kinetics Reveal How Monolignol Biosynthetic Enzyme Families Affect Metabolic Flux and Lignin in Populus trichocarpa[W

    PubMed Central

    Wang, Jack P.; Naik, Punith P.; Chen, Hsi-Chuan; Shi, Rui; Lin, Chien-Yuan; Liu, Jie; Shuford, Christopher M.; Li, Quanzi; Sun, Ying-Hsuan; Tunlaya-Anukit, Sermsawat; Williams, Cranos M.; Muddiman, David C.; Ducoste, Joel J.; Sederoff, Ronald R.; Chiang, Vincent L.

    2014-01-01

    We established a predictive kinetic metabolic-flux model for the 21 enzymes and 24 metabolites of the monolignol biosynthetic pathway using Populus trichocarpa secondary differentiating xylem. To establish this model, a comprehensive study was performed to obtain the reaction and inhibition kinetic parameters of all 21 enzymes based on functional recombinant proteins. A total of 104 Michaelis-Menten kinetic parameters and 85 inhibition kinetic parameters were derived from these enzymes. Through mass spectrometry, we obtained the absolute quantities of all 21 pathway enzymes in the secondary differentiating xylem. This extensive experimental data set, generated from a single tissue specialized in wood formation, was used to construct the predictive kinetic metabolic-flux model to provide a comprehensive mathematical description of the monolignol biosynthetic pathway. The model was validated using experimental data from transgenic P. trichocarpa plants. The model predicts how pathway enzymes affect lignin content and composition, explains a long-standing paradox regarding the regulation of monolignol subunit ratios in lignin, and reveals novel mechanisms involved in the regulation of lignin biosynthesis. This model provides an explanation of the effects of genetic and transgenic perturbations of the monolignol biosynthetic pathway in flowering plants. PMID:24619611

  18. Steroid promiscuity: Diversity of enzyme action.

    PubMed

    Lathe, Richard; Kotelevtsev, Yuri; Mason, J Ian

    2015-07-01

    This Special Issue on the topic of Steroid and Sterol Signaling: Promiscuity and Diversity, dwells on the growing realization that the 'one ligand, one binding site' and 'one enzyme, one reaction' concepts are out of date. Focusing on cytochromes P450 (CYP), hydroxysteroid dehydrogenases (HSDs), and related enzymes, the Special Issue highlights that a single enzyme can bind to diverse substrates, and in different conformations, and can catalyze multiple different conversions (and in different directions), thereby, generating an unexpectedly wide spectrum of ligands that can have subtly different biological actions. This article is part of a Special Issue entitled 'Steroid/Sterol Signaling' . PMID:25596328

  19. Physiology and Bioenergetics of [NiFe]-Hydrogenase 2-Catalyzed H2-Consuming and H2-Producing Reactions in Escherichia coli

    PubMed Central

    Pinske, Constanze; Jaroschinsky, Monique; Linek, Sabine; Kelly, Ciarán L.

    2014-01-01

    Escherichia coli uptake hydrogenase 2 (Hyd-2) catalyzes the reversible oxidation of H2 to protons and electrons. Hyd-2 synthesis is strongly upregulated during growth on glycerol or on glycerol-fumarate. Membrane-associated Hyd-2 is an unusual heterotetrameric [NiFe]-hydrogenase that lacks a typical cytochrome b membrane anchor subunit, which transfers electrons to the quinone pool. Instead, Hyd-2 has an additional electron transfer subunit, termed HybA, with four predicted iron-sulfur clusters. Here, we examined the physiological role of the HybA subunit. During respiratory growth with glycerol and fumarate, Hyd-2 used menaquinone/demethylmenaquinone (MQ/DMQ) to couple hydrogen oxidation to fumarate reduction. HybA was essential for electron transfer from Hyd-2 to MQ/DMQ. H2 evolution catalyzed by Hyd-2 during fermentation of glycerol in the presence of Casamino Acids or in a fumarate reductase-negative strain growing with glycerol-fumarate was also shown to be dependent on both HybA and MQ/DMQ. The uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP) inhibited Hyd-2-dependent H2 evolution from glycerol, indicating the requirement for a proton gradient. In contrast, CCCP failed to inhibit H2-coupled fumarate reduction. Although a Hyd-2 enzyme lacking HybA could not catalyze Hyd-2-dependent H2 oxidation or H2 evolution in whole cells, reversible H2-dependent reduction of viologen dyes still occurred. Finally, hydrogen-dependent dye reduction by Hyd-2 was reversibly inhibited in extracts derived from cells grown in H2 evolution mode. Our findings suggest that Hyd-2 switches between H2-consuming and H2-producing modes in response to the redox status of the quinone pool. Hyd-2-dependent H2 evolution from glycerol requires reverse electron transport. PMID:25368299

  20. Propensity approach to nonequilibrium thermodynamics of a chemical reaction network: Controlling single E-coli ?-galactosidase enzyme catalysis through the elementary reaction stepsa)

    NASA Astrophysics Data System (ADS)

    Das, Biswajit; Banerjee, Kinshuk; Gangopadhyay, Gautam

    2013-12-01

    In this work, we develop an approach to nonequilibrium thermodynamics of an open chemical reaction network in terms of the elementary reaction propensities. The method is akin to the microscopic formulation of the dissipation function in terms of the Kullback-Leibler distance of phase space trajectories in Hamiltonian system. The formalism is applied to a single oligomeric enzyme kinetics at chemiostatic condition that leads the reaction system to a nonequilibrium steady state, characterized by a positive total entropy production rate. Analytical expressions are derived, relating the individual reaction contributions towards the total entropy production rate with experimentally measurable reaction velocity. Taking a real case of Escherichia coli ?-galactosidase enzyme obeying Michaelis-Menten kinetics, we thoroughly analyze the temporal as well as the steady state behavior of various thermodynamic quantities for each elementary reaction. This gives a useful insight in the relative magnitudes of various energy terms and the dissipated heat to sustain a steady state of the reaction system operating far-from-equilibrium. It is also observed that, the reaction is entropy-driven at low substrate concentration and becomes energy-driven as the substrate concentration rises.

  1. Palladium-Catalyzed One-Pot Reaction of Hydrazones, Dihaloarenes, and Organoboron Reagents: Synthesis and Cytotoxic Activity of 1,1-Diarylethylene Derivatives.

    PubMed

    Roche, Maxime; Salim, Salim Mmadi; Bignon, Jérôme; Levaique, Hélène; Brion, Jean-Daniel; Alami, Mouad; Hamze, Abdallah

    2015-07-01

    A new three-component assembly reaction between N-tosylhydrazones, dihalogenated arenes, and boronic acids or boronate esters was developed, producing highly substituted 1,1-diarylethylenes in good yields. The two C-C bonds formed through this coupling have been catalyzed by a single Pd-catalyst in a one-pot fashion. It is noted that the one-pot pinacol boronate cross-coupling reaction generally provides products in high yields, offers an expansive substrate scope, and can address a broad range of aryl, styrene, vinyl, and heterocyclic olefinic targets. The scope of this one-pot coupling has been also extended to the synthesis of the 1,1-diarylethylene skeleton of the natural product ratanhine. The new compounds were evaluated for their cytotoxic activity, and this allowed the identification of compound 4ab that exhibits excellent antiproliferative activity in the nanomolar concentration range against HCT116 cancer cell lines. PMID:26036279

  2. Synthesis of novel 1,2,3-triazolyl derivatives of pregnane, androstane and D-homoandrostane. Tandem "click" reaction/Cu-catalyzed D-homo rearrangement.

    PubMed

    Kotovshchikov, Yury N; Latyshev, Gennadij V; Lukashev, Nikolay V; Beletskaya, Irina P

    2014-06-14

    Copper-catalyzed 1,3-dipolar cycloaddition has been employed in the reaction of steroidal azides with various terminal alkynes. A number of novel 1,2,3-triazolyl derivatives of pregnane, androstane and D-homoandrostane were obtained in high yield (70-98%). The developed synthetic protocols allowed us to attach the triazolyl moiety to both the side chain and the steroidal backbone directly, despite the steric hindrance exerted by the polycyclic system. The presence of Cu(II) was shown to evoke d-homo rearrangement under mild conditions. A rational choice of the copper precatalyst permitted us to carry out the "click" reaction either along with tandem d-homo rearrangement or in the absence of this process. The tendency of 16-heterosubstituted steroids to undergo D-homo rearrangement under Cu(II) catalysis was studied. PMID:24781658

  3. Reaction of CO2 with propylene oxide and styrene oxide catalyzed by a chromium(III) amine-bis(phenolate) complex.

    PubMed

    Dean, Rebecca K; Devaine-Pressing, Katalin; Dawe, Louise N; Kozak, Christopher M

    2013-07-01

    A diamine-bis(phenolate) chromium(III) complex, {CrCl[O2NN'](BuBu)}2 catalyzes the copolymerization of propylene oxide with carbon dioxide. The synthesis of this metal complex is straightforward and it can be obtained in high yields. This catalyst incorporates a tripodal amine-bis(phenolate) ligand, which differs from the salen or salan ligands typically used with Cr and Co complexes that have been employed as catalysts for the synthesis of such polycarbonates. The catalyst reported herein yields low molecular weight polymers with narrow polydispersities when the reaction is performed at room temperature. Performing the reaction at elevated temperatures causes the selective synthesis of propylene carbonate. The copolymerization activity for propylene oxide and carbon dioxide, as well as the coupling of carbon dioxide and styrene oxide to give styrene carbonate are presented. PMID:23192332

  4. Oxidation of 2,4-dichlorophenol catalyzed by horseradish peroxidase: characterization of the reaction mechanism by UV-visible spectroscopy and mass spectrometry.

    PubMed

    Laurenti, Enzo; Ghibaudi, Elena; Ardissone, Silvia; Ferrari, Rosa Pia

    2003-06-01

    The hydrogen peroxide-oxidation of 2,4-dichlorophenol catalyzed by horseradish peroxidase has been studied by means of UV-visible spectroscopy and mass spectrometry in order to clarify the reaction mechanism. The dimerization of 2,4-dichlorophenol to 2,4-dichloro-6-(2,4-dichlorophenoxy)-phenol and its subsequent oxidation to 2-chloro-6-(2,4-dichlorophenoxy)-1,4-benzoquinone together with chloride release were observed. The reaction rate was found to be pH-dependent and to be influenced by the pK(a) value of 2,4-dichlorophenol. The dissociation constants of the 2,4-dichlorophenol/horseradish peroxidase (HRP) adduct at pH 5.5 and 8.5 were also determined: their values indicate the unusual stability of the adduct at pH 5.5 with respect to several adducts of HRP with substituted phenols. PMID:12763662

  5. Pd-Catalyzed Wacker Cyclizations Palladium-Catalyzed Oxidative Wacker

    E-print Network

    Stoltz, Brian M.

    Pd-Catalyzed Wacker Cyclizations Palladium-Catalyzed Oxidative Wacker Cyclizations in Nonpolar. Trend, Yeeman K. Ramtohul, Eric M. Ferreira, and Brian M. Stoltz* Catalytic asymmetric oxidation-electron oxidations that do not involve heteroatom transfer. Some potentially valuable reactions of this type include

  6. A DNA enzyme with N-glycosylase activity

    NASA Technical Reports Server (NTRS)

    Sheppard, T. L.; Ordoukhanian, P.; Joyce, G. F.

    2000-01-01

    In vitro evolution was used to develop a DNA enzyme that catalyzes the site-specific depurination of DNA with a catalytic rate enhancement of about 10(6)-fold. The reaction involves hydrolysis of the N-glycosidic bond of a particular deoxyguanosine residue, leading to DNA strand scission at the apurinic site. The DNA enzyme contains 93 nucleotides and is structurally complex. It has an absolute requirement for a divalent metal cation and exhibits optimal activity at about pH 5. The mechanism of the reaction was confirmed by analysis of the cleavage products by using HPLC and mass spectrometry. The isolation and characterization of an N-glycosylase DNA enzyme demonstrates that single-stranded DNA, like RNA and proteins, can form a complex tertiary structure and catalyze a difficult biochemical transformation. This DNA enzyme provides a new approach for the site-specific cleavage of DNA molecules.

  7. Evolutionarily conserved linkage between enzyme fold, flexibility, and catalysis

    SciTech Connect

    Ramanathan, Arvind [ORNL; Agarwal, Pratul K [ORNL

    2011-01-01

    Proteins are intrinsically flexible molecules. The role of internal motions in a protein's designated function is widely debated. The role of protein structure in enzyme catalysis is well established, and conservation of structural features provides vital clues to their role in function. Recently, it has been proposed that the protein function may involve multiple conformations: the observed deviations are not random thermodynamic fluctuations; rather, flexibility may be closely linked to protein function, including enzyme catalysis. We hypothesize that the argument of conservation of important structural features can also be extended to identification of protein flexibility in interconnection with enzyme function. Three classes of enzymes (prolyl-peptidyl isomerase, oxidoreductase, and nuclease) that catalyze diverse chemical reactions have been examined using detailed computational modeling. For each class, the identification and characterization of the internal protein motions coupled to the chemical step in enzyme mechanisms in multiple species show identical enzyme conformational fluctuations. In addition to the active-site residues, motions of protein surface loop regions (>10 away) are observed to be identical across species, and networks of conserved interactions/residues connect these highly flexible surface regions to the active-site residues that make direct contact with substrates. More interestingly, examination of reaction-coupled motions in non-homologous enzyme systems (with no structural or sequence similarity) that catalyze the same biochemical reaction shows motions that induce remarkably similar changes in the enzyme substrate interactions during catalysis. The results indicate that the reaction-coupled flexibility is a conserved aspect of the enzyme molecular architecture. Protein motions in distal areas of homologous and non-homologous enzyme systems mediate similar changes in the active-site enzyme substrate interactions, thereby impacting the mechanism of catalyzed chemistry. These results have implications for understanding the mechanism of allostery, and for protein engineering and drug design.

  8. Extracellular Enzymes Lab Biochemistry

    E-print Network

    Vallino, Joseph J.

    Extracellular Enzymes Lab Biochemistry · All organisms convert small organic compounds, of which there are more than 1000, are catalyzed by enzymes. Glucose (C6) Pentose (C5) Triose (C3) Pyruvate Complete Metabolic Network TOP #12;#12;Enzymes · Enzymes are large proteins that all organisms synthesize

  9. Porphyrin-catalyzed oxidation of trichlorophenol

    SciTech Connect

    Hasan, S.; Sublette, K.L. [Univ. of Tulsa, OK (United States)

    1997-12-31

    Porphyrin-metal complexes are potentially useful to catalyze redox reactions, which convert toxic and biologically recalcitrant compounds to compounds that are less toxic and more amenable to biotreatment. Porphyrins, in the absence of proteins as in ligninases, peroxidases, and oxidases, are potentially more robust than enzymes and microbial cultures in the treatment of inhibitory substances. 2,4,6-Trichlorophenol was used as a model compound for chlorinated phenols and as a substrate for various porphyrin-metal complexes acting as oxidation catalysts. t-Butyl hydroperoxide was the oxidizing agent. TCP was shown to be at least partially dechlorinated and the aromatic ring broken in reaction products. All porphyrins exhibited saturation kinetics with regard to the initial TCP concentration in reaction mixtures. Electron-withdrawing substituents on the porphyrins were observed to increase stability of the catalysts to inactivating ring-centered oxidation. 16 refs., 3 figs., 2 tabs.

  10. Palladium-catalyzed cross-coupling reactions of organosilanols and their salts: practical alternatives to boron- and tin-based methods.

    PubMed

    Denmark, Scott E; Regens, Christopher S

    2008-11-18

    In the panoply of modern synthetic methods for forming carbon-carbon and carbon-heteroatom bonds, the transition metal-catalyzed cross-coupling of organometallic nucleophiles with organic electrophiles enjoys a preeminent status. The preparative utility of these reactions is, in large measure, a consequence of the wide variety of organometallic donors that have been conscripted into service. The most common of these reagents are organic derivatives of tin, boron, and zinc, which each possess unique advantages and shortcomings. Because of their low cost, low toxicity, and high chemical stability, organosilanes have emerged as viable alternatives to the conventional reagents in recent years. However, unlike the tin- and zinc-based reactions, which require no activation, or the boron-based reactions, which require only heating with mild bases, silicon-based cross-coupling reactions often require heating in the presence of a fluoride source; this has significantly hampered the widespread acceptance of organosilanes. To address the "fluoride problem", we have introduced a new paradigm for palladium-catalyzed, silicon-based cross-coupling reactions that employs organosilanols, a previously underutilized class of silicon reagents. The use of organosilanols either in the presence of Brønsted bases or as their silanolate salts represents a simple and mild alternative to the classic fluoride-based activation method. Organosilanols are easily available by many well-established methods for introducing carbon-silicon bonds onto alkenes, alkynes, and arenes and heteroarenes. Moreover, we have developed four different protocols for the generation of alkali metal salts of vinyl-, alkenyl-, alkynyl-, aryl-, and heteroarylsilanolates: (1) reversible deprotonation with weak Brønsted bases, (2) irreversible deprotonation with strong Brønsted bases, (3) isolation of the salts from irreversible deprotonation, and (4) silanolate exchange with disiloxanes. We have demonstrated the advantages of each of these methods for a number of different coupling classes. The defining feature of this new process is the formation of a covalently linked palladium silanolate species that facilitates the critical transmetalation step. We have verified the intermediacy of a critical species that contains the key Si-O-Pd linkage by its identification as the resting state in reaction mixtures, by X-ray analysis, and by demonstrating its competence in thermal cross-coupling with no additives. Our conclusions contradict the long-standing dogma that silicon-based cross-coupling reactions require the generation of a pentacoordinate siliconate prior to transmetalation. This revelation has opened a new vista for discovery of reactions that involve this critical process. PMID:18681465

  11. Elucidation of acyl migration during lipase-catalyzed production of structured phospholipids

    Microsoft Academic Search

    Anders F. Vikbjerg; Huiling Mu; Xuebing Xu

    2006-01-01

    Elucidation of acyl migration was carried out in the Lipozyme RM IM (Rhizomucor miehei)-catalyzed transesterification between soybean phosphatidylcholine (PC) and caprylic acid in solvent-free media. A five-factor\\u000a response surface design was used to evaluate the influence of five major factors and their relationships. The five factors—enzyme\\u000a dosage, reaction temperature, water addition, reaction time, and substrate ratio—were varied on three levels

  12. Enzymatic synthesis of dimaltosyl-{beta}-cyclodextrin via a transglycosylation reaction using TreX, a Sulfolobus solfataricus P2 debranching enzyme

    SciTech Connect

    Kang, Hee-Kwon; Cha, Hyunju; Yang, Tae-Joo; Park, Jong-Tae; Lee, Seungjae [Center for Agricultural Biomaterials, Department of Food Science and Biotechnology, College of Agriculture and Life Sciences, Seoul National University, San 56-1, Shillim-dong, Kwanak-gu, Seoul 151-921 (Korea, Republic of); Kim, Young-Wan [Department of Food and Biotechnology, Korea University, Jochiwon, Chungnam 339-700 (Korea, Republic of); Auh, Joong-Hyuck [Department of Food Science and Technology, Chungang University, Anseong 456-756 (Korea, Republic of); Okada, Yasuyo [School of Pharmaceutical Sciences, Mukogawa Women's University, Nishinomiya 663-8179 (Japan); Kim, Jung-Wan [Department of Biology, University of Incheon, Incheon 402-749 (Korea, Republic of); Cha, Jaeho [Department of Biological Science, Pusan National University, Busan 609-735 (Korea, Republic of); Kim, Chung Ho [Department of Food and Nutrition, Seowon University, Cheongju 361-742 (Korea, Republic of); Park, Kwan-Hwa [Center for Agricultural Biomaterials, Department of Food Science and Biotechnology, College of Agriculture and Life Sciences, Seoul National University, San 56-1, Shillim-dong, Kwanak-gu, Seoul 151-921 (Korea, Republic of)], E-mail: parkkh@plaza.snu.ac.kr

    2008-02-01

    Di-O-{alpha}-maltosyl-{beta}-cyclodextrin ((G2){sub 2}-{beta}-CD) was synthesized from 6-O-{alpha}-maltosyl-{beta}-cyclodextrin (G2-{beta}-CD) via a transglycosylation reaction catalyzed by TreX, a debranching enzyme from Sulfolobus solfataricus P2. TreX showed no activity toward glucosyl-{beta}-CD, but a transfer product (1) was detected when the enzyme was incubated with maltosyl-{beta}-CD, indicating specificity for a branched glucosyl chain bigger than DP2. Analysis of the structure of the transfer product (1) using MALDI-TOF/MS and isoamylase or glucoamylase treatment revealed it to be dimaltosyl-{beta}-CD, suggesting that TreX transferred the maltosyl residue of a G2-{beta}-CD to another molecule of G2-{beta}-CD by forming an {alpha}-1,6-glucosidic linkage. When [{sup 14}C]-maltose and maltosyl-{beta}-CD were reacted with the enzyme, the radiogram showed no labeled dimaltosyl-{beta}-CD; no condensation product between the two substrates was detected, indicating that the synthesis of dimaltosyl-{beta}-CD occurred exclusively via transglycosylation of an {alpha}-1,6-glucosidic linkage. Based on the HPLC elution profile, the transfer product (1) was identified to be isomers of 6{sup 1},6{sup 3}- and 6{sup 1},6{sup 4}-dimaltosyl-{beta}-CD. Inhibition studies with {beta}-CD on the transglycosylation activity revealed that {beta}-CD was a mixed-type inhibitor, with a K{sub i} value of 55.6 {mu}mol/mL. Thus, dimaltosyl-{beta}-CD can be more efficiently synthesized by a transglycosylation reaction with TreX in the absence of {beta}-CD. Our findings suggest that the high yield of (G2){sub 2}-{beta}-CD from G2-{beta}-CD was based on both the transglycosylation action mode and elimination of the inhibitory effect of {beta}-CD.

  13. Two enzymes catalyze vitamin K 2,3-epoxide reductase activity in mouse: VKORC1 is highly expressed in exocrine tissues while VKORC1L1 is highly expressed in brain.

    PubMed

    Caspers, Michael; Czogalla, Katrin J; Liphardt, Kerstin; Müller, Jens; Westhofen, Philipp; Watzka, Matthias; Oldenburg, Johannes

    2015-05-01

    VKORC1 and VKORC1L1 are enzymes that both catalyze the reduction of vitamin K2,3-epoxide via vitamin K quinone to vitamin K hydroquinone. VKORC1 is the key enzyme of the classical vitamin K cycle by which vitamin K-dependent (VKD) proteins are ?-carboxylated by the hepatic ?-glutamyl carboxylase (GGCX). In contrast, the VKORC1 paralog enzyme, VKORC1L1, is chiefly responsible for antioxidative function by reduction of vitamin K to prevent damage by intracellular reactive oxygen species. To investigate tissue-specific vitamin K 2,3-epoxide reductase (VKOR) function of both enzymes, we quantified mRNA levels for VKORC1, VKORC1L1, GGCX, and NQO1 and measured VKOR enzymatic activities in 29 different mouse tissues. VKORC1 and GGCX are highly expressed in liver, lung and exocrine tissues including mammary gland, salivary gland and prostate suggesting important extrahepatic roles for the vitamin K cycle. Interestingly, VKORC1L1 showed highest transcription levels in brain. Due to the absence of detectable NQO1 transcription in liver, we assume this enzyme has no bypass function with respect to activation of VKD coagulation proteins. Our data strongly suggest diverse functions for the vitamin K cycle in extrahepatic biological pathways. PMID:25747820

  14. Mechanistic studies of an unprecedented enzyme-catalysed 1,2-phosphono-migration reaction

    E-print Network

    Chang, Wei-chen

    (S)-2-hydroxypropylphosphonate ((S)-2-HPP) epoxidase (HppE) is a mononuclear non-haem-iron-dependent enzyme1, 2, 3 responsible for the final step in the biosynthesis of the clinically useful antibiotic fosfomycin4. Enzymes ...

  15. FREE ENERGIES OF CHEMICAL REACTIONS IN SOLUTION AND IN ENZYMES WITH AB INITIO QM/MM METHODS

    PubMed Central

    Hu, Hao; Yang, Weitao

    2013-01-01

    Combined QM/MM methods provide an accurate and efficient energetic description of complex chemical and biological systems, leading to significant advances in the understanding of chemical reactions in solution and in enzymes. Progress in QM/MM methodology and application will be reviewed, with a focus on ab initio QM based approaches. Ab initio QM/MM methods capitalize on the accuracy and reliability of the associated quantum mechanical approaches, however at a much higher computational cost compared with semiempirical quantum mechanical approaches. Thus reaction path and activation free energy calculations based on ab initio QM/MM methods encounter unique challenges in simulation timescales and phase space sampling. Recent developments overcoming these challenges and enabling accurate free energy determination for reaction processes in solution and enzymes will be featured in this review, along with applications. PMID:18393679

  16. Mechanistic diversity in the RuBisCO superfamily: RuBisCO from Rhodospirillum rubrum is not promiscuous for reactions catalyzed by RuBisCO-like proteins.

    PubMed

    Warlick, Benjamin P E; Imker, Heidi J; Sriram, Jaya; Tabita, F Robert; Gerlt, John A

    2012-11-27

    d-Ribulose 1,5-bisphosphate carboxylase/oxygenases (RuBisCOs) are promiscuous, catalyzing not only carboxylation and oxygenation of d-ribulose 1,5-bisphosphate but also other promiscuous, presumably nonphysiological, reactions initiated by abstraction of the 3-proton of d-ribulose 1,5-bisphosphate. Also, RuBisCO has homologues that do not catalyze carboxylation; these are designated RuBisCO-like proteins or RLPs. Members of the two families of RLPs catalyze reactions in the recycling of 5'-methylthioadenosine (MTA) generated by polyamine synthesis: (1) the 2,3-diketo-5-methylthiopentane 1-phosphate (DK-MTP 1-P) "enolase" reaction in the well-known "methionine salvage" pathway in Bacillus sp. and (2) the 5-methylthio-d-ribulose 1-phosphate (MTRu 1-P) 1,3-isomerase reaction in the recently discovered "MTA-isoprenoid shunt" that generates 1-deoxy-d-xylulose 5-phosphate for nonmevalonate isoprene synthesis in Rhodospirillum rubrum. We first studied the structure and reactivity of DK-MTP 1-P that was reported to decompose rapidly [Ashida, H., Saito, Y., Kojima, C., and Yokota, A. (2008) Biosci., Biotechnol., Biochem. 72, 959-967]. The 2-carbonyl group of DK-MTP 1-P is rapidly hydrated and can undergo enolization both nonenzymatically and enzymatically via the small amount of unhydrated material that is present. We then examined the ability of RuBisCO from R. rubrum to catalyze both of the RLP-catalyzed reactions. Contrary to a previous report [Ashida, H., Saito, Y., Kojima, C., Kobayashi, K., Ogasawara, N., and Yokota, A. (2003) Science 302, 286-290], we were unable to confirm that this RuBisCO catalyzes the DK-MTP 1-P "enolase" reaction either in vitro or in vivo. We also determined that this RuBisCO does not catalyze the MTRu 1-P 1,3-isomerase reaction in vitro. Thus, although RuBisCOs can be functionally promiscuous, RuBisCO from R. rubrum is not promiscuous for either of the known RLP-catalyzed reactions. PMID:23110715

  17. Mechanistic Diversity in the RuBisCO Superfamily: RuBisCO from Rhodospirillum rubrum is Not Promiscuous for Reactions Catalyzed by RuBisCO-Like Proteins (RLPs)†

    PubMed Central

    Warlick, Benjamin P. E.; Imker, Heidi J.; Sriram, Jaya; Tabita, F. Robert; Gerlt, John A.

    2012-01-01

    D-Ribulose 1,5-bisphosphate carboxylase/oxygenases (RuBisCOs) are promiscuous, catalyzing not only carboxylation and oxygenation of D-ribulose 1,5-bisphosphate but also other promiscuous, presumably nonphysiological, reactions initiated by abstraction of the 3-proton of D-ribulose 1,5-bisphosphate. Also, RuBisCO has homologues that do not catalyze carboxylation; these are designated RuBisCO-like proteins or RLPs. Members of the two families of RLPs catalyze reactions in the recycling of 5?-methylthioadenosine (MTA) generated by polyamine synthesis: 1) the 2,3-diketo-5-methylthiopentane 1-phosphate (DK-MTP 1-P) “enolase” reaction in the well-known “methionine salvage” pathway in species of Bacilli; and 2) the 5-methylthio-D-ribulose 1-phosphate (MTRu 1-P) 1,3-isomerase reaction in the recently discovered “MTA-isoprenoid shunt” that generates 1-deoxy-D-xylulose 5-phosphate (DXP) for nonmevalonate isoprene synthesis in Rhodospirillum rubrum. We first studied the structure and reactivity of DK-MTP 1-P which was reported to decompose rapidly [Ashida, H., Saito, Y., Kojima, C., and Yokota, A. (2008) Biosci Biotechnol Biochem 72, 959–67]. The 2-carbonyl group of DK-MTP 1-P is rapidly hydrated in solution and can undergo enolization both nonenzymatically and enzymatically via the small amount of unhydrated material that is present. We then examined the ability of RuBisCO from R. rubrum to catalyze both of the RLP-catalyzed reactions. Contrary to a previous report [Ashida, H., Saito, Y., Kojima, C., Kobayashi, K., Ogasawara, N., and Yokota, A. (2003) Science 302, 286–290], we were unable to confirm that this RuBisCO catalyzes the DK-MTP 1-P “enolase” reaction either in vitro or in vivo. We also determined that this RuBisCO does not catalyze the MTRu 1-P 1,3-isomerase reaction in vitro. Thus, although RuBisCOs can be functionally promiscuous, RuBisCO from R. rubrum is not promiscuous for either of the known RLP-catalyzed reactions. PMID:23110715

  18. Use of Dissolved H2 Concentrations To Determine Distribution of Microbially Catalyzed Redox Reactions in Anoxic Groundwater

    E-print Network

    Lovley, Derek

    chemistryof nonequi- librium aroundwaters. Introduction Anoxic reduction-oxidation (redox) reactions greatly. A major goal in hydrogeology is to deduce the redox reactions taking place in subsurfaceenvironments based production of these compounds. This com- plicates attempts to localize the redox reactions taking place

  19. Production of extremophilic bacterial cellulase enzymes in aspergillus niger.

    SciTech Connect

    Gladden, John Michael

    2013-09-01

    Enzymes can be used to catalyze a myriad of chemical reactions and are a cornerstone in the biotechnology industry. Enzymes have a wide range of uses, ranging from medicine with the production of pharmaceuticals to energy were they are applied to biofuel production. However, it is difficult to produce large quantities of enzymes, especially if they are non-native to the production host. Fortunately, filamentous fungi, such as Aspergillus niger, are broadly used in industry and show great potential for use a heterologous enzyme production hosts. Here, we present work outlining an effort to engineer A. niger to produce thermophilic bacterial cellulases relevant to lignocellulosic biofuel production.

  20. The o-Phenylenediamine-Horseradish Peroxidase System: Enzyme Kinetics in the General Chemistry Laboratory

    Microsoft Academic Search

    T. M. Hamilton; A. A. Dobie-Galuska; S. M. Wietstock

    1999-01-01

    We have developed an enzyme kinetics laboratory experiment that can easily be incorporated into an undergraduate chemistry program. The purpose of the experiment is to measure the kinetic parameters in the oxidative coupling reaction of o-phenylenediamine (OPD) to 2,3-diaminophenazine (DAP), a reaction catalyzed by the enzyme horseradish peroxidase (HRP). Horseradish peroxidase is a protein with a mass of 34 kDa