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| 2. |
- Cheeseman, J. D., et al.
(författare)
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Structure of an aryl esterase from Pseudomonas fluorescens
- 2004
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Ingår i: Acta Crystallographica Section D. - 0907-4449 .- 1399-0047. ; 60:7, s. 1237-1243
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Tidskriftsartikel (refereegranskat)abstract
- The structure of PFE, an aryl esterase from Pseudomonas fluorescens, has been solved to a resolution of 1.8 Å by X-ray diffraction and shows a characteristic α/β-hydrolase fold. In addition to catalyzing the hydrolysis of esters in vitro, PFE also shows low bromoperoxidase activity. PFE shows highest structural similarity, including the active-site environment, to a family of non-heme bacterial haloperoxidases, with an r.m.s. deviation in 271 Cα atoms between PFE and its five closest structural neighbors averaging 0.8 Å. PFE has far less similarity (r.m.s. deviation in 218 Cα atoms of 5.0 Å) to P. fluorescens carboxyl esterase. PFE favors activated esters with small acyl groups, such as phenyl acetate. The X-ray structure of PFE reveals a significantly occluded active site. In addition, several residues, including Trp28 and Met95, limit the size of the acyl-binding pocket, explaining its preference for small acyl groups.
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| 3. |
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| 4. |
- Jordi, C, et al.
(författare)
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The design and performance of the Gaia photometric system
- 2006
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 367:1, s. 290-314
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Tidskriftsartikel (refereegranskat)abstract
- The European Gaia astrometry mission is due for launch in 2011. Gaia will rely on the proven principles of the ESA Hipparcos mission to create an all-sky survey of about one billion stars throughout our Galaxy and beyond, by observing all objects down to 20 mag. Through its massive measurement of stellar distances, motions and multicolour photometry, it will provide fundamental data necessary for unravelling the structure, formation and evolution of the Galaxy. This paper presents the design and performance of the broad- and medium-band set of photometric filters adopted as the baseline for Gaia. The 19 selected passbands (extending from the UV to the far-red), the criteria and the methodology on which this choice has been based are discussed in detail. We analyse the photometric capabilities for characterizing the luminosity, temperature, gravity and chemical composition of stars. We also discuss the automatic determination of these physical parameters for the large number of observations involved, for objects located throughout the entire Hertzsprung-Russell diagram. Finally, the capability of the photometric system (PS) to deal with the main Gaia science case is outlined.
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| 5. |
- Bernhardt, Peter, et al.
(författare)
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Molecular basis of perhydrolase activity in serine hydrolases
- 2005
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Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 44:18, s. 2742-2746
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Tidskriftsartikel (refereegranskat)abstract
- (Chemical Equation Presented) Changing substrates: A mutation that forms a cis-proline-peptide bond in a loop structure close to the active site of an aryl esterase from Pseudomonas fluorescens converts the enzyme into a perhydrolase (see picture). The switch in activity is explained by a new hydrogen bond formed between a backbone carbonyl oxygen atom and the peroxy deacylation intermediate.
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| 6. |
- Park, S., et al.
(författare)
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Focusing mutations into the P. fluorescens esterase binding site increases enantioselectivity more effectively than distant mutations
- 2005
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Ingår i: Chemistry and Biology. - : Elsevier BV. - 1074-5521 .- 1879-1301. ; 12:1, s. 45-54
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Tidskriftsartikel (refereegranskat)abstract
- Rational design of enzymes with improved properties, such as enantioselectivity, usually focuses mutations within the substrate binding site. On the other hand, directed evolution of enzymes usually targets the entire protein and discovers beneficial mutations far from the substrate binding site. In this paper, we propose an explanation for this discrepancy and show that a combined approach-random mutagenesis within the substrate binding site-is better. To increase the enantioselectivity (E) of a Pseudomonas fluorescens esterase (PFE) toward methyl 3-bromo-2-methylpropionate, we focused mutagenesis into the substrate binding site at Trp28, Val121, Phe198, and Val225. Five of the catalytically active mutants (13%) showed better enantioselectivity than wild-type PFE. The increases in enantioselectivity were higher (up to 5-fold, reaching E = 61) than with mutants identified by random mutagenesis of the entire enzyme.
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| 7. |
- Park, S., et al.
(författare)
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Vacuum-driven lipase-catalysed direct condensation of L-ascorbic acid and fatty acids in ionic liquids : synthesis of a natural surface active antioxidant
- 2003
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Ingår i: Green Chemistry. - : Royal Society of Chemistry (RSC). - 1463-9262 .- 1463-9270. ; 5:6, s. 715-719
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Tidskriftsartikel (refereegranskat)abstract
- L- Ascorbic acid ( vitamin C) is a useful natural antioxidant, but is highly polar and does not dissolve in fats and oils. One solution is the synthesis of 6- O- L- ascorbyl fatty acid esters, which are surface- active and protect fats and oils from oxidation. Previous syntheses of 6- O- L- ascorbyl fatty acid esters by Candida antarctica lipase B ( CAL- B)- catalysed esterification were inefficient due to either the poor solubility of L- ascorbic acid in nonpolar organic solvents or poor lipase activity in polar organic solvents. We report that replacing organic solvents with ionic liquids such as 1- alkyl- 3- methylimidazolium tetrafluoroborates makes this synthesis more efficient and greener for three reasons. First, like polar organic solvents, ionic liquids dissolve polar substrates such as ascorbic acid ( e. g., similar to 130 mg mL(-1) in sBMIM . BF4 at 60degreesC), but unlike polar organic solvents, ionic liquids do not inactivate CAL- B. For this reason, using an ionic liquid as the solvent gave a faster reaction and a higher yield of product. Second, it eliminates toxic organic solvents that easily evaporate. Third, since ionic liquids are not volatile, we could use vacuum to drive the equilibrium toward product formation. This ability eliminated the need to use an excess of acyl donor or an activated acyl donor. One problem we encountered was product inhibition due to its precipitation on the immobilized lipase particles. To avoid this inhibition, we added a hydrophobic phase such as hexane or polypropylene beads. A CAL- B- catalysed direct esterification of stoichiometric amounts of ascorbic acid and oleic acid gave a high conversion ( 83%). The product 6- O- L- ascorbyl oleate was isolated as a mixture with oleic acid using only water and ethanol or methanol in 61% yield.
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