SwePub - search: L773:1381 1177

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1.	Adlercreutz, Patrick, et al. (author) Enzymatic conversions of polar lipids. Principles, problems and solutions 2001 In: Journal of Molecular Catalysis - B Enzymatic. - 1381-1177. ; 11:4-6, s. 173-178 Research review (peer-reviewed)abstract This text provides a brief overview of the principles of enzymatic lipid conversion and some recent advances in the enzymatic conversion of glycerophospholipids and galactolipids. Lipases and phospholipases are used to exchange fatty acids or the polar group in the lipids. The reactions can be carried out either as hydrolysis-esterification sequences or as one-step transferase reactions. The scope and limitations of the different methods are discussed.
2.	Andersson, Mats, et al. (author) A kinetic study of almond-β-glucosidase catalysed synthesis of hexyl-glycosides in low aqueous media : Influence of glycosyl donor and water activity 2001 In: Journal of Molecular Catalysis - B Enzymatic. - 1381-1177. ; 14:4-6, s. 69-76 Journal article (peer-reviewed)abstract A variety of alkyl and aryl glycosides were investigated as substrates for almond β-glucosidase catalysed synthesis of hexyl-β-D-glycosides in low aqueous hexanol media. The rate-limiting step in the organic media was determined to be the glycosylation of the enzyme. The kinetic constants V max , K m (glycosyl donor) and V max /K m were all influenced by the water activity and they all increased in value with increasing water activity. The increase in V max /K m was mainly determined by the increase in V max and a plot of log(V max /K m ) versus water activity resulted in a straight line with similar slopes for all glycosides but with different absolute values and thus the most reactive substrate p-nitrophenyl glucoside was the best one in the entire water activity range studied (0.53-0.96). The preference for the two competing acceptors, hexanol and water, was not affected by the aglycon part of the glucoside. Surprisingly, the ratio between trans glycosylation and hydrolysis increased with increasing water activity. A decrease in water activity caused an increase in equilibrium yield of hexyl glycoside, as expected, but was not beneficial for the kinetically controlled yield.
3.	Barros, Raúl J., et al. (author) Modeling the performance of immobilized α-chymotrypsin catalyzed peptide synthesis in acetonitrile medium 2001 In: Journal of Molecular Catalysis - B Enzymatic. - 1381-1177. ; 11:4-6, s. 841-850 Journal article (peer-reviewed)abstract A model was developed which describes simultaneous reaction and internal diffusion for kinetically controlled, immobilized α-chymotrypsin-catalyzed, oligopeptide synthesis in acetonitrile medium. The model combines the equations that describe the intrinsic kinetics of four different reactions and the physical characteristics of three different support materials, as determined experimentally, to predict the apparent initial activity and nucleophile selectivity of the immobilized biocatalyst. The model is able to predict reasonably well the experimentally observed initial rate and nucleophile selectivity vs. enzyme loading profiles. The reduction in observed initial rate with enzyme loading when fast reactions are carried out with α-chymotrypsin immobilized on celite, and the larger influence of mass transfer limitations on the initial reaction rates than on nucleophile selectivities are correctly predicted by the numerical calculations. The model is general in terms of its application to other systems - enzymes, reactions, support materials and/or kinetic schemes - as long as the intrinsic kinetics and the characteristics of the enzyme and support material are known.
4.	Costes, David, et al. (author) Cross-linked crystals of hydroxynitrile lyase as catalyst for the synthesis of optically active cyanohydrins 2001 In: Journal of Molecular Catalysis - B Enzymatic. - 1381-1177. ; 11:4-6, s. 607-612 Journal article (peer-reviewed)abstract Purified hydroxynitrile lyase (HNL) from Manihot esculenta was crystallized by the sitting-drop vapour-diffusion method. The bipyramidal crystals formed (10-20 μm) were cross-linked with different amounts of glutaraldehyde and used as biocatalyst for the synthesis of optically active cyanohydrins. The cross-linked crystals were more stable than Celite-immobilized enzymes when incubated in organic solvents, especially in polar solvents. After six consecutive batch reactions in dibutylether, the remaining activity of the cross-linked crystals was more than 70 times higher than for the immobilized enzymes. Nevertheless, the specific activity of the cross-linked crystals (per milligram protein) was reduced compared to the activity of immobilized enzymes. The product enantiopurity was independent of the type of enzyme preparation used.
5.	Jönsson, Åsa, et al. (author) Temperature effects on protease catalyzed acyl transfer reactions in organic media 1996 In: Journal of Molecular Catalysis B: Enzymatic. - : Elsevier BV. - 1381-1177. ; 2:1, s. 43-51 Journal article (peer-reviewed)abstract The influence of reaction temperature on synthesis activity, product yield and nucleophile specificity for α-chymotrypsin and subtilisin Carlsberg were studied. The enzymes were immobilized on Celite and used in acetonitrile with a water content of 10%. Acyl-transfer reactions with Ac-PheOEt as acyl donor and 11 different amino acid amides and 3 dipeptides as nucleophiles were studied. The decrease in temperature from 25 to -1°C had a positive effect on the peptide yield in all reactions studied. The most efficient nucleophiles for the two enzymes α-chymotrypsin and subtilisin Carlsberg is arginine amide and glycine amide, respectively. When decreasing the reaction temperature the yield for α-chymotrypsin increased from 86 to 94% with arginine amide as nucleophile and for subtilisin the yield increased from 75 to 84% for glycine amide. The nucleophile specificity was determined as the p value, which describes the competition between nucleophile and water for the acyl enzyme. α-Chymotrypsin showed preference for both small and positively charged amino acid residues and subtilisin preferred small uncharged nucleophiles. The temperature did not affect the specificity order but all nucleophiles became more effective in the competition with water at low temperature. In addition, the results indicate that the temperature effect is more pronounced for the smaller nucleophiles.
6.	Jönsson, Åsa, et al. (author) The influence of water activity on the enantioselectivity in the enzyme- catalyzed reduction of 2-pentanone 1998 In: Journal of Molecular Catalysis - B Enzymatic. - 1381-1177. ; 5:1-4, s. 273-276 Journal article (peer-reviewed)abstract The stereoselective reduction of 2-pentanone by alcohol dehydrogenase from Thermoanaerobium brockii was studied at controlled water activity and at different reaction temperatures. The reaction rate increased when water activity was increased from 0.32 to 0.96 and when raising the temperature from 5°C to 40°C. The enantioselectivity, E, reached a plateau value at high water activities. The enantioselectivity increased with decreasing reaction temperature.
7.	Wehtje, Ernst, et al. (author) Enantioselectivity of lipases : Effects of water activity 1997 In: Journal of Molecular Catalysis - B Enzymatic. - 1381-1177. ; 3:5, s. 221-230 Journal article (peer-reviewed)abstract The enantioselectivity (E) of lipases in esterifications of secondary alcohols with decanoic acid was studied in organic media. The enantioselectivity of 2-octanol differed greatly among the lipases used. Candida antarctica lipase was extremely selective (E= 9 000) while Candida rugosa lipase was much less selective (E= 1.7). Other enzymes (Lipozyme and lipases from Pseudomonas and Rhizopus arrhizus) had intermediate selectivities. In all cases the enantioselectivity for an enzyme was unaffected by changes in water activity. Different methods of determining the enantioselectivity was used: reactions using single enantiomers as well as racemic mixtures. The effect of water activity on enantioselectivity and the enanatioselectivity values themselves were similar irrespective of the method used. The enantioselectivity of other alcohols were also found to be unaffected by the water activity. The enantioselectivity of Pseudomonas lipase was influenced by the organic solvent. The E decreased with increasing hydrophobicity, from 62 in acetonitrile to 40 in toluene and 33 in hexane. In none of these cases was the enantioselectivity affected by the water activity. However, for Lipozyme and Candida rugosa lipase in toluene a trend of increased E with increasing water activity was observed. In summary it can be stated that the water activity does not generally affect the enantioselectivity of the five lipases tested.
8.	Berglund, Per, et al. (author) Reversed enantiopreference of Candida rugosa lipase supports different modes of binding enantiomers of a chiral acyl donor 1998 In: Journal of Molecular Catalysis - B Enzymatic. - 1381-1177 .- 1873-3158. ; 5:1-4, s. 283-287 Journal article (peer-reviewed)abstract Molecular modelling identifies two different productive modes of binding the enantiomers of a 2-methyldecanoic acid ester to the active site of Candida rugosa lipase (CRL). The fast reacting S-enantiomer occupies the previously identified acyl-binding tunnel of the enzyme, whereas the R- enantiomer leaves the tunnel empty. The modelling suggested that if both enantiomers were forced to bind to the active site leaving the tunnel empty, the enzyme would reverse its enantiopreference to become R-enantioselective. To test this hypothesis, we designed a structural analogue to 2- methyldecanoic acid, 2-methyl-6-(2-thienyl)hexanoic acid, which was expected to be too bulky to fit its acyl moiety into the acyl-binding tunnel. The CRL- catalysed hydrolysis of the ethyl ester of this substrate resulted in the preferential conversion of the R-enantiomer as predicted by molecular modelling. This represents the first kinetic evidence supporting the existence of two different modes of binding the enantiomers of a 2- methyldecanoic acid ester to the active site of CRL. We have shown that a rational 3D based approach in combination with substrate engineering can be used to predict and control the stereochemical outcome of a lipase catalysed reaction.
9.	Hecquet, L, et al. (author) Enzymatic syntheses of ketoses: study and modification of the substrate specificity of the transketolase from Saccharomyces cerevisiae 2001 In: JOURNAL OF MOLECULAR CATALYSIS B-ENZYMATIC. - 1381-1177. ; 11:4-6, s. 771-776 Journal article (other academic/artistic)
10.	Hedenström, Erik, et al. (author) Stereoselective esterification of 2,6-dimethyl-1,7-heptanedioic acid, catalysed by Candida rugosa lipase 2003 In: Journal of Molecular Catalysis B. - 1381-1177 .- 1873-3158. ; 23:1, s. 53-59 Journal article (peer-reviewed)abstract The immobilised Candida rugosa lipase (CRL) displayed S-preference for both stereogenic centres in this sequential esterification of 2,6-dimethyl-1,7-heptanedioic acid (1) (pure meso and meso: (+/-) mixture, 53/47) with n-butanol in cyclohexane at a(w) = 0.8. The reaction was faster when short-chain primary n-alcohols was used and very slow, or even none reactive, when a Ion-chain alcohol was used.
11.	Kalogeris, E, et al. (author) Catalytic properties of the endoxylanase I from Thermoascus aurantiacus 2001 In: Journal of Molecular Catalysis B. - 1381-1177 .- 1873-3158. ; 11:4-6, s. 491-501 Journal article (peer-reviewed)abstract Endo-β-1,4-xylanase I previously purified from Thermoascus aurantiacus solid state culture was further characterized. The enzyme had a molecular weight of 33 kDa by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and 31 kDa by gel filtration. Thin layer chromatography (TLC) analysis showed that endoxylanase liberates aldotetrauronic acid MeGlcAα-1,2-Xylβ-1,4-Xylβ-1,4-Xyl as the shortest acidic fragment from glucuronoxylan and an isomeric xylotriose (Xyl3) of the structure Xylβ1-3Xylβ1-4Xyl from rhodymenan. The enzyme performed ideally on O-acetyl-4-O-methylglucuronoxylan, liberating large amounts of short acetylated and non-acetylated fragments. Also, the enzyme was capable to hydrolyse arabinoxylan to arabinose (Arab), xylose (Xyl) and xylobiose (Xyl2). The enzyme degraded pNPX (4-nitrophenyl β-D-xylopyranoside) by a complex reaction pathway that involved both hydrolysis and glycosyl transfer reactions. The enzyme tolerates the replacement of β-xylopyranosyl units in several artificial substrates by β-glucopyranosyl, α-L-arabinopyranosyl and α-L-arabinofuranosyl units and was active on pNPC (4-nitrophenyl β-D-cellobioside), pNP-Arap (4-nitrophenyl α-L-arabinopyranoside) and pNPAraf (4-nitrophenyl α-L-arabinofuranoside). The enzyme also hydrolysed the 4-methylumbelliferyl glycosides of β-D-xylobiose and β-D-xylotriose at the agluconic linkage. The results suggested that the xylanase I from T. aurantiacus has catalytic properties similar to those belonging to family 10. Copyright © 2001 Elsevier Science B.V.
12.	Ottosson, Jenny, et al. (author) Influence of acyl chain length on the enantioselectivity of Candida antarctica lipase B and its thermodynamic components in kinetic resolution of sec-alcohols 2001 In: Journal of Molecular Catalysis B. - 1381-1177 .- 1873-3158. ; 11:4-6, s. 1025-1028 Journal article (peer-reviewed)abstract The enantioselectivity, E, of Candida antarctica lipase B (CALB) was found to be strongly influenced by the chain length of the achiral acyl donor employed in the transesterification of 3-methyl-2-butanol. Of the four studied acyl donors, the longest, vinyl octanoate, afforded the highest enantioselectivity. This was true over the temperature range studied, 6-70 degreesC. Measurements of the temperature dependence of E allows for separation of the enthalpic and entropic components of enantioselectivity. Changes in E with chain length were mainly caused by changes in the entropic component except for the reaction with vinyl propionate, which differed from the others also in the enthalpic component. Optimisation of acyl donor adds one more possibility to improve the yield of enantiopurity in the production of optically active compounds apart from optimisation of solvent, temperature, water activity, and choice of enzyme.
13.	Stamatis, H., et al. (author) Studies on the synthesis of short-chain geranyl esters catalysed by Fusarium oxysporum esterase in organic solvents 1998 In: Journal of Molecular Catalysis B. - 1381-1177 .- 1873-3158. ; 4:4, s. 229-236 Journal article (peer-reviewed)abstract A novel esterase isolated from Fusarium oxysporum was investigated for the synthesis of short-chain esters of geraniol by alcoholysis and direct esterification reactions in organic solvents. The enzyme was used as a dried powder (i.e., not immobilized). The reaction parameters affecting the enzyme behavior such as the nature of organic solvent and acyl donor, the concentration of substrates and the water activity of the system were studied. High yields (80–90%) were obtained by both approaches (alcoholysis and direct esterification) at low values of water activity (aw=0.11) in n-hexane. The enzyme retain its catalytic activity even after fifth reuse in n-hexane at aw=0.11, demonstrating its stability and efficiency under the conditions of this study.
14.	Alberti, Jean-Christophe, et al. (author) A functional role identified for conserved charged residues at the active site entrance of lipoxygenase with double specificity 2016 In: Journal of Molecular Catalysis B. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 123, s. 167-173 Journal article (peer-reviewed)abstract Plant lipoxygenases (LOXs) are a class of widespread dioxygenases catalyzing the hydroperoxidation of free polyunsaturated fatty acids, producing 9-hydroperoxides or 13-hydroperoxides from linoleic and alpha-linolenic acids, and are called 9-LOX or 13-LOX, respectively. Some LOXs produce both 9- and 13- hydroperoxides. The models proposed to explain the reaction mechanism specificity fail to explain the "double specificity" character of these LOXs. In this study, we used the olive LOX1 with double specificity to investigate the implication of the charged residues R265, R268, and K283 in the orientation of the substrate into the active site. These residues are present in a conserved pattern around the entrance of the active site. Our results show that these residues are involved in the penetration of the substrate into the active site: this positive patch could capture the carboxylate end of the substrate, and then guide it into the active site. Due to its position on alpha 2 helix, the residue K283 could have a more important role, its interaction with the substrate facilitating the motions of residues constituting the "cork of lipoxygenases" or the alpha 2 helix, by disrupting putative hydrogen and ionic bonds.
15.	Bisagni, Serena, et al. (author) Cloning and expression of a Baeyer-Villiger monooxygenase oxidizing linear aliphatic ketones from Dietzia sp. D5 2014 In: Journal of Molecular Catalysis B: Enzymatic. - : Elsevier BV. - 1873-3158 .- 1381-1177. ; 109, s. 161-169 Journal article (peer-reviewed)abstract A Baeyer-Villiger monooxygenase has been identified in the genome sequence of Dietzia sp. D5. Sequence similarity search revealed that the enzyme belongs to a group of BVMOs that are closely related to ethionamide monooxygenase from Mycobacterium tuberculosis (EthA). The BVMO was expressed in E. coli BL21-CodonPlus(DE3)-RP and the best expression was achieved when the E. coli cells were cultivated in terrific broth (TB) at 15 degrees C and induced with 0.1 mM of IPTG. Since the purified enzyme did not show any measurable activity, the substrate scope of the BVMO has been determined using whole-cell and crude cell extract systems. The enzyme was most active towards linear aliphatic substrates. However, it has shown a moderate degree of conversion for cyclobutanone, 2-methylcyclohexanone, bicyclo[3.2.0]hept-2-en-6-one, phenylacetone and thioanisole. There was no detectable conversion of ethionamide, cyclohexanone and acetophenone. (C) 2014 Elsevier B.V. All rights reserved.
16.	Blikstad, Cecilia, et al. (author) Functional characterization of a stereospecific diol dehydrogenase, FucO, from Escherichia coli : substrate specificity, pH dependence, kinetic isotope effects and influence of solvent viscosity 2010 In: Journal of Molecular Catalysis B. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 66:1-2, s. 148-155 Journal article (peer-reviewed)abstract FucO, (S)-1,2-propanediol oxidoreductase, from Escherichia coli is involved in the anaerobic catabolic metabolism of L-fucose and L-rhamnose, catalyzing the interconversion of lactaldehyde to propanediol. The enzyme is specific for the S-enantiomers of the diol and aldehyde suggesting stereospecificity in catalysis. We have studied the enzyme kinetics of FucO with a spectrum of putative alcohol and aldehyde substrates to map the substrate specificity space. Additionally, for a more detailed analysis of the kinetic mechanism, pH dependence of catalysis, stereochemistry in hydride transfer, deuterium kinetic isotope effect of hydride transfer and effect of increasing solvent viscosity were also analyzed. The outcome of this study can be summarized as follows: FucO is highly stereospecific with the highest E-value measured to be 320 for the S-enantiomer of 1,2-propanediol. The enzyme is strictly regiospecific for oxidation of primary alcohols. The enzyme prefers short-chained (2-4 carbons) substrates and does not act on bulkier compounds such as phenyl-substituted alcohols. FucO is an 'A-side' dehydrogenase transferring the pro-R-hydrogen of NADH to the aldehyde substrate. The deuterium KIEs of kcat and kcat/KM were 1.9 and 4.2, respectively, illustrating that hydride transfer is partially rate-limiting but also that other reaction steps contribute to rate limitation of catalysis. Combining the KIE results with the observed effects of increasing medium viscosity proposed a working model for the kinetic mechanism involving slow, rate-limiting, product release and on-pathway conformational changes in the enzyme-nucleotide complexes.
17.	Bohlin, Christina, et al. (author) Differences in stereo-preference in the oxidative degradation of diastereomers of the lignin model compound 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol with enzymic and non-enzymic oxidants 2007 In: Journal of Molecular Catalysis - B Enzymatic. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 45:1-2, s. 21-26 Journal article (peer-reviewed)abstract Mixtures of equal amounts of the erythro and the threo forms of the β-O-4 lignin model compound 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol were oxidized with different ligninolytic enzymes and non-enzymic oxidants. The oxidants included cerium(IV)ammonium nitrate (CAN), Fenton’s reagent, lead(IV) tetraacetate (LTA), laccase, laccase–mediator systems (based on the mediators ABTS, HBT,TEMPO, and VLA), and lignin peroxidase. The stereo-preference of the different oxidants was compared based on analyses of remaining substrateusing HPLC and UV-diode array detector or 1H NMR spectroscopy. Fenton’s reagent was the only oxidant tested that did not show preferentialdegradation of either the erythro or the threo form. CAN, LTA and lignin peroxidase preferentially oxidized the threo form. The stereo-preferenceof the laccase–mediator systems depended on the mediator. Oxidation mediated by HBT, TEMPO or VLA resulted in a preferential degradationof the threo form. Laccase/ABTS was the only system tested that showed preferential oxidation of the erythro form. The stereo-preference of theoxidants is discussed based on their redox potentials and their classification as outer-sphere and inner-sphere oxidants.
18.	Bohlin, Christina, et al. (author) Product profiles in enzymic and non-enzymic oxidations of the lignin model compound erythro-1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol 2005 In: Journal of Molecular Catalysis - B Enzymatic. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 35:4-6, s. 100-107 Journal article (peer-reviewed)abstract The erythro form of the lignin model compound 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol (1) was oxidized with laccase/ABTS, lead(IV) tetraacetate (LTA), lignin peroxidase/H2O2, cerium(IV) ammonium nitrate (CAN) and Fenton's reagent. The product profiles obtained with the different oxidants were compared after separation, identification and quantification of the products using HPLC, UV-diode array detector and electrospray ionization mass spectrometry in positive ionization mode. The oxidants generated different product profiles that reflected their different properties. Oxidation with laccase/ABTS resulted almost exclusively in formation of 1-(3,4-dimethoxyphenyl)-3-hydroxy-2-(2-methoxyphenoxy)-1-propanone (2). Oxidation with LTA resulted in more 3,4-dimethoxybenzaldehyde (3) than ketone 2. Lignin peroxidase and CAN gave similar product profiles and aldehyde 3 was the predominant product (only small amounts of ketone 2 were formed). Oxidation with Fenton's reagent resulted in the formation of more aldehyde 3 than ketone 2 but the yields were very low. CAN served as an excellent model for the lignin peroxidase-catalyzed oxidation, while the laccase-mediator system, LTA and Fenton's reagent provided distinctly different product profiles. Erythro-1-(3,4-dimethoxyphenyl)-1,2,3-propanetriol was present among the products obtained on oxidation with LTA, lignin peroxidase, CAN and Fenton's reagent. The differences in redox potential between the oxidants afford an explanation of the diverse product patterns but other factors may also be of importance. The reactions leading to cleavage of the β-ether bond with formation of 1-(3,4-dimethoxyphenyl)-1,2,3-propanetriol (veratrylglycerol) were found to proceed without affecting the configuration at the β-carbon atom.
19.	Branneby, Cecilia, et al. (author) Aldol Additions with Mutant Lipase : Analysis by Experiments and Theoretical Calculations 2004 In: Journal of Molecular Catalysis B. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 31:4-6, s. 123-128 Journal article (peer-reviewed)abstract A Ser105Ala mutant of Candida antarctica lipase B has previously been shown to catalyze aldol additions. Quantum chemical calculations predicted a reaction rate similar to that of natural enzymes, whereas experiments showed a much lower reaction rate. Molecular dynamics simulations, presented here, show that the low reaction rate is a consequence of the low frequencies of near attack complexes in the enzyme. Equilibrium was also considered as a reason for the slow product formation, but could be excluded by performing a sequential reaction to push the reaction towards product formation. In this paper, further experimental results are also presented, highlighting the importance of the entire active site for catalysis.
20.	Carlquist, Magnus, et al. (author) Kinetic resolution of racemic 5,6-epoxy-bicyclo[2.2.1]heptane-2-one using genetically engineered Saccharomyces cerevisiae 2009 In: Journal of Molecular Catalysis B: Enzymatic. - : Elsevier BV. - 1873-3158 .- 1381-1177. ; 58:2, s. 98-102 Journal article (peer-reviewed)abstract (+)-5,6-Epoxy-bicyclo[2.2.1]heptane-2-one, (+)-1, and endo-(−)-5,6-epoxy-bicyclo[2.2.1]heptane-2-ol, endo-(−)-2, were obtained by kinetic resolution of rac-1 by asymmetric bioreduction catalyzed by whole cells of a genetically engineered Saccharomyces cerevisiae yeast strain. The strain, TMB4100, had 1% phosphoglucose isomerase (PGI) activity and overexpressed a specific short-chain dehydrogenase, encoded by the gene YMR226c. The whole cell biocatalystwas demonstrated to be significantly inactivated within 24 h, thus restricting the reaction to lowconcentration. Despite this, the resolution method could be used to produce optically pure (+)-1 and endo-(−)-2 from the racemic mixture at 5 g/L substrate. At optimal conditions, 1 g of rac-1 was kinetically resolved to give (+)-1 in 95% ee and 28% yield and endo-(−)-2 in 74% ee, 80% de and 45% yield.
21.	Chávez, Georgina, et al. (author) Baeyer-Villiger oxidation with peracid generated in situ by CaLB-CLEA catalyzed perhydrolysis 2013 In: Journal of Molecular Catalysis B: Enzymatic. - : Elsevier BV. - 1873-3158 .- 1381-1177. ; 89, s. 67-72 Journal article (peer-reviewed)abstract Candida antarctica lipase B, immobilized as cross linked enzyme aggregates (CLEAs) was used to mediate the Baeyer-Villiger oxidation of cyclohexanone to epsilon-caprolactone, and the reaction was compared with the one using Novozym (R) 435 as catalyst. The conversion was dependent on the initial concentration of cyclohexanone, and was about 90% after 48 h at concentrations of up to 0.25 M but was decreased at higher concentrations. Caprolactone concentrations up to 0.6 M had no effect on the reaction efficiency. Among the cyclic ketones tested, the highest degree of conversion was achieved for cyclopentanone (88%) and the lowest for cyclooctanone (about 2%). The effect of methyl substitution and position of substitution on the cycloketone was studied using methylcyclohexanone and it has shown to influence the conversion efficiency. Both hydrogen peroxide and the reaction by-product acetic acid had a deleterious effect on the stability of the biocatalyst. (C) 2012 Elsevier B.V. All rights reserved.
22.	Chen, Shan, et al. (author) Stabilization of an amine transaminase for biocatalysis 2016 In: Journal of Molecular Catalysis B. - : Elsevier. - 1381-1177 .- 1873-3158. ; 124, s. 20-28 Journal article (peer-reviewed)abstract The amine transaminase from Chromobacterium violaceum (Cv-ATA) is a well-known enzyme to achievechiral amines of high enantiomeric excess in laboratory scales. However, the low operational stabilityof Cv-ATA limits the enzyme applicability on larger scales. In order to improve the operational stabilityof Cv-ATA, and thereby extending its applicability, factors (additives, co-solvents, organic solvents anddifferent temperatures) targeting enzyme stability and activity were explored in order to find out how tostore and apply the enzyme. The present investigation shows that the melting point of Cv-ATA is improvedby adding sucrose or glycerol, separately. Further, by storing the enzyme at higher concentrations and inco-solvents, such as; 50% glycerol, 20% methanol or 10% DMSO, the active dimeric structure of Cv-ATAis retained. Enzyme stored in 50% glycerol at −20◦C was e.g., still fully active after 6 months. Finally,the enzyme performance was improved 5-fold by a co-lyophilization with surfactants prior to usage inisooctane.
23.	Gaber, Yasser, et al. (author) Rational mutagenesis of pig liver esterase (PLE-1) to resolve racemic clopidogrel 2015 In: Journal of Molecular Catalysis B: Enzymatic. - : Elsevier BV. - 1873-3158 .- 1381-1177. ; 122, s. 156-162 Journal article (peer-reviewed)abstract Clopidogrel is an important and widely used antiplatelet drug; only the (S)-isomer is the active biological enantiomer. The industrial production of the active enantiomer involves resolution of the racemic compound using stoichiometric amounts of L-camphor sulphonic acid and crystallization in a process using large amounts of solvent. In the present study, the possibility of enzyme catalysed kinetic resolution was investigated. Screening of a number of hydrolytic enzymes showed the crude pig liver esterase (PLE) to exhibit modest enantioselectivity in the hydrolysis of racemic clopidogrel. Molecular modeling simulations were applied on the homology model of PLE-1, the major isoenzyme in the crude PLE, and distinct sites of mutations were proposed and 'produced in the laboratory. The PLE-1 variants with one mutation i.e. PLE-1-F407L and PLE-1-F407I resolved the racemic substrate yielding the (R)-isomer with E value >100. Contrarily, the isoenzyme PLE-3 resolved the racemic substrate yielding (S)-clopidogrel with E value of 10. (C) 2015 Elsevier B.V. All rights reserved.
24.	Gaffney, Darragh, et al. (author) Preparation and characterisation of a Ni2+/Co2+-cyclam modified mesoporous cellular foam for the specific immobilisation of His(6)-alanine racemase 2014 In: Journal of Molecular Catalysis B. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 109, s. 154-160 Journal article (peer-reviewed)abstract Nickel and cobalt cyclam modified mesocellular foam (MCF) materials were prepared and characterised. The metal cyclam modified materials displayed reduced surface areas and pore diameters in comparison to MCF. The modified materials were used to specifically anchor a histidine tagged form of the enzyme, alanine racemase (HT-AlaR). Non-specific adsorption was predominantly hydrophobic//hydrophilic in nature and could be significantly reduced in the presence of 2% polyethylene glycol. The activity of HT-AlaR immobilised on Ni and Co-MCF was essentially the same as that of the free enzyme, demonstrating that enzymes can be specifically immobilised within the pores of mesoporous materials in a stable and catalytically active manner.
25.	Hamnevik, Emil, et al. (author) Kinetic characterization of Rhodococcus ruber DSM 44541 alcohol dehydrogenase A 2014 In: Journal of Molecular Catalysis B. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 99, s. 68-78 Journal article (peer-reviewed)abstract An increasing interest in biocatalysis and the use of stereoselective alcohol dehydrogenases in synthetic asymmetric catalysis motivates detailed studies of potentially useful enzymes such as alcohol dehydrogenase A (ADH-A) from Rhodococcus ruber. This enzyme is capable of catalyzing enantio-, and regioselective production of phenyl-substituted α-hydroxy ketones (acyloins) which are precursors for the synthesis of a range of biologically active compounds. In this study, we have determined the enzyme activity for a selection of phenyl-substituted vicinal diols and other aryl- or alkyl-substituted alcohols and ketones. In addition, the kinetic mechanism for the oxidation of (R)- and (S)-1-phenylethanol and the reduction of acetophenone has been identified as an Iso Theorell-Chance (hit and run) mechanism with conformational changes of the enzyme-coenzyme binary complexes as rate-determining for the oxidation of (S)-1-phenylethanol and the reduction of acetophenone. The underlying cause of the 270-fold enantiopreference for the (S)-enantiomer of 1-phenylethanol has been attributed to non-productive binding of the R-enantiomer. We have also shown that it is possible to tune the direction of the redox chemistry by adjusting pH with the oxidative reaction being favored at pH values above 7.

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