| 1. |
- Lyberg, Ann-Marie, et al.
(författare)
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Enzymatic and chemical synthesis of phosphatidylcholine regioisomers containing eicosapentaenoic acid or docosahexaenoic acid
- 2005
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Ingår i: European Journal of Lipid Science and Technology. - : Wiley. - 1438-7697 .- 1438-9312. ; 107:5, s. 279-290
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Tidskriftsartikel (refereegranskat)abstract
- Regioselective incorporation of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) into phosphatidylcholine (PC) was carried out using enzymatic and chemical synthesis. Incorporation at the sn-1 position was successfully achieved by lipase-catalysed esterification of 2-palmitoyl-lysophosphatidylcholine (LPC), although in most cases, the enzymes incorporated EPA and DHA at lower rates than other fatty acids. For the incorporation of DHA, Candida antarctica lipase B was the only useful enzyme, while incorporation of EPA was efficiently carried out using either this enzyme or Rhizopus arrhizus lipase. The highest yields in the lipase-catalysed reactions were obtained at the lowest water activity (close to 0). However, by carrying out the reactions at a higher water activity of 0.22, more EPA and DHA were incorporated. Esterification of 2-palmitoyl-LPC with pure EPA at this water activity converted 66 mol-% of LPC to PC using Rhizopus arrhizus lipase as catalyst. When the fatty acid was DHA and the catalyst Candida antarctica lipase B, 45 mol-% of PC was obtained. For incorporation of EPA and DHA at the sn-2 position, phospholipase A(2) was used, but the reaction was very slow. Chemical coupling of 1 -palmitoyl-LPC and EPA or DHA was more efficient, resulting in complete conversion of LPC.
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| 2. |
- Adlercreutz, Patrick, et al.
(författare)
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Fundamentals of Biocatalysis in Neat Organic Solvents
- 2008
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Ingår i: Organic Synthesis with Enzymes in Non-Aqueous Media. - Weinheim, Germany : Wiley-VCH Verlag GmbH & Co. KGaA. - 9783527318469 - 9783527621729 ; , s. 1-24
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Bokkapitel (refereegranskat)
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| 3. |
- Elovson Grey, Carl, et al.
(författare)
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A mass spectrometric investigation of native and oxidatively inactivated chloroperoxidase
- 2007
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Ingår i: ChemBioChem. - : Wiley. - 1439-4227 .- 1439-7633. ; 8:9, s. 1055-1062
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Tidskriftsartikel (refereegranskat)abstract
- The enzyme chloroperoxidase (CPO) found in Calclariomyces fumago is able to catalyze several stereoselective oxidation reaction by using a dean oxidant, usually hydrogen peroxide (H2O2), without the need for expensive cofactor generation. CPO's lack of operational stability however, is a major limitation for its commercial use. In the present study, a capillary-LC on-line trypsin- digestion system combined with reversed-phase chromatography and mass spectrometric detection was optimized for studying the primary sequence of CPO. Samples containing native CPO, CPO treated with H2O2, and CPO oxidatively inactivated by the use of indole and H2O2 were analyzed and compared. Three oxidized peptides were found in the samples treated with H2O2. Two additional oxidized peptides were found in the CPO samples that were completely inactivated, one of which contained an oxidized cysteine residue, Cys50, which is an essential amio acid due to its function as the axial ligand to the iron in the heme - the prosthetic group in CPO. In addition, the heme group was absent in the inactivated samples but was readily detected in other samples.
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| 4. |
- Grey, Carl, et al.
(författare)
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Evaluation of multiple oxidation products for monitoring effects of antioxidants in Fenton oxidation of 2 '-deoxyguanosine
- 2006
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Ingår i: Journal of Agricultural and Food Chemistry. - : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 54:6, s. 2350-2358
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this study was to investigate the influence of the two antioxidants, ascorbic acid and (+)catechin, on the oxidation of 2'-deoxyguanosine (dG), using an iron-mediated Fenton reaction. The oxidation products 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) and 8,5'-cyclo-2'-deoxyguanosine, together with the secondary oxidation products guanidinohydantoin and dehydroguanidinohydantoin, were identified and quantified through the use of an LC-MS/MS system. The results obtained showed that catechin inhibited the oxidation better than ascorbic acid did, indicating that the chelating ability of catechin rather than the radical scavenging mechanism alone is vital for the observed antioxidative efficiency. The correlation between the different oxidation products was found to be quite low, primarily because of the instability of 8-oxodG, making it prone to further oxidation. This led to apparent anti- and pro-oxidative results being obtained, emphasizing the potential problems in evaluating oxidative stress, by use of a single marker.
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| 5. |
- Grey, Carl, et al.
(författare)
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Improved operational stability of chloroperoxidase through use of antioxidants.
- 2008
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Ingår i: Journal of Biotechnology. - : Elsevier BV. - 1873-4863 .- 0168-1656. ; 135:2, s. 196-201
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Tidskriftsartikel (refereegranskat)abstract
- Chloroperoxidase (CPO) from Caldariomyces fumago is a potentially very useful enzyme due to its ability to catalyze a large variety of stereoselective oxidation reactions, but poor operational stability is a main limitation for commercial use. In the present study, the possibility of increasing the operational stability by use of antioxidants was investigated using the oxidation of indole as model reaction. Caffeic acid was the antioxidant showing the strongest positive effects, reaching a total turnover number (TTN) of 135,000 at pH 4 and 4mM hydrogen peroxide, compared to 28,700 in the absence of antioxidant. Portion-wise addition of hydrogen peroxide in the presence of caffeic acid caused a further increase in TTN to 171,000. An alternative way to reach high TTN was to use tert-butyl hydroperoxide as oxidant instead of hydrogen peroxide: a TTN of 600,000 was achieved although the reaction was quite slow. In this case, antioxidants did not have any positive effect. Possible mechanisms for the observed inactivation of CPO are discussed.
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| 6. |
- Grey, Carl, et al.
(författare)
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Time and concentration dependence of Fenton-induced oxidation of dG
- 2006
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Ingår i: Nucleosides, Nucleotides & Nucleic Acids. - : Informa UK Limited. - 1525-7770 .- 1532-2335. ; 25:3, s. 259-278
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Tidskriftsartikel (refereegranskat)abstract
- The influence of incubation time and Fenton reagent concentrations was investigated on the oxidation of 2'-deoxyguanosine. The compounds identified and quantified, through use of an LC-MS/MS system, were 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) and 8,5'- cyclo-2'-deoxyguanosine (8,5'cyclodG) and the secondary oxidation products guanidinohydantoin and dehydro-guanidinohydantoin. 8-oxodG and 8,5'cyclodG formed very quickly, reaching a maximum rapidly, but with 8-oxodC a rapid decline occurred thereafter due to its further oxidation into the secondary products, which formed more slowly. Due to the better stability, 8,5'cyclodG correlated better with the general level of oxidation than 8-oxodG. The results emphasize the advantages of measuring other oxidation adducts than 8-oxodG atone.
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| 7. |
- Hagström, Anna, et al.
(författare)
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A water activity control system for enzymatic reactions in organic media
- 2007
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 1097-0290 .- 0006-3592. ; 97:2, s. 235-241
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Tidskriftsartikel (refereegranskat)abstract
- A water activity control system for enzymatic synthesis in organic media, for litre-scale reactors has been constructed. Water activity, a(w), is a key factor when using enzymes in non-conventional media and the optimum value varies for different enzymes. The control system consists of a water activity sensor in the headspace of a jacketed glass reactor (equipped with narrow steel tubes to introduce air), gas-washing bottles containing blue silica gel (a(w) = 0) and water (a(w) = 1), a PC to monitor water activity and a programmable logic controller (PLC) to control the water activity. The system was evaluted by adjusting water activity in the medium, with a defviation from the set point less than +/- 0.05. Synthesis of cetyl palmitate, under controlled water activity and catalysed by two different lipase preparations, namely, Novozym (R) 435 (immobilised Candida anarctica lipase B) and immobilised Candida rugosa lipase, were also performed. Novozym (R) 435 catalyses reactions very well at extremely low water activity while C. rugosa lipase shows low activity for a(w) < 0.05.
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| 8. |
- Hagström, Anna, et al.
(författare)
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Biocatalytic polyester acrylation-process optimization and enzyme stability.
- 2009
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 1097-0290 .- 0006-3592. ; 102, s. 693-699
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Tidskriftsartikel (refereegranskat)abstract
- An OH-functional polyester has been acrylated via transesterification of ethyl acrylate, catalyzed by Candida antarctica lipase B (CalB) in two different preparations: Novozym(R) 435 and immobilized on Accurel(R) MP1000. The batch process resulted in incomplete acrylation as well as severe degradation of the polyester. A high degree of acrylation was achieved by optimization through the application of low pressure (15 kPa), continuous inflow of ethyl acrylate and continuous distillation to evaporate the by-product, ethanol. The enzyme preparations displayed good stability with half-lives of 180 and 324 h for Novozym(R) 435 and CalB/MP1000, respectively. This translates into product yields of 3600 and 6200 times the weight of the catalyst, indicating that the enzyme will have a marginal impact on the total process cost. Biotechnol. Bioeng. 2008. (c) 2008 Wiley Periodicals, Inc.
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| 9. |
- Hagström, Anna, et al.
(författare)
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Wax esters produced by solvent-free energy-efficient enzymatic synthesis and their applicability as wood coatings
- 2005
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Ingår i: Green Chemistry. - : Royal Society of Chemistry (RSC). - 1463-9270 .- 1463-9262. ; 7:12, s. 837-843
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Tidskriftsartikel (refereegranskat)abstract
- The study aimed at developing a process for making a wood coating wax based on the principles of green chemistry. The research was conducted within the Swedish interdisciplinary research programme Greenchem. Wax esters are attractive since they are non-hazardous, biodegradable and can be produced in an atom-efficient process from building blocks obtained from renewable resources. Four wax esters were prepared in a solvent-free process using an immobilised lipase as catalyst. When the water was removed during the process from what was initially an equimolar mixture of the starting materials carboxylic acid and alcohol by a stream of dry air passed through the reactor, there was a 95-99% conversion to the ester. The enzymatic process consumed 34% less energy and generated less waste than chemical esterification using a strong acid as catalyst. Two of the esters worked well in the industrial wood coating equipment employed and produced surfaces resistant to water and somewhat less to fat stains.
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| 10. |
- Leak, David J., et al.
(författare)
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Biocatalysts for selective introduction of oxygen
- 2009
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Ingår i: Biocatalysis and Biotransformation. - : Informa UK Limited. - 1024-2422 .- 1029-2446. ; 27:1, s. 1-26
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Forskningsöversikt (refereegranskat)abstract
- Three types of oxygenase biocatalysts are treated in detail in this review: the non-haem iron alkene mono-oxygenases, the haem and vanadium haloperoxidases, and flavin-based Baeyer-Villiger mono-oxygenases. Other oxygenases are briefly included for comparison. Characteristics of the biocatalysts are presented, and the scope and limitations concerning their applicability for the selective introduction of oxygen are discussed. Key issues include catalytic activity, productivity, cloning and expression, as well as process engineering aspects. Various bottlenecks are identified for the different biocatalysts and measures to increase the number of oxygenase reactions in practical use are discussed.
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