| 1. |
- ADLERCREUTZ, PATRICK, et al.
(författare)
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Enzymatic Peptide Synthesis in Organic Media
- 1990
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Ingår i: Annals of the New York Academy of Sciences. - : Wiley. - 0077-8923 .- 1749-6632. ; 613:1, s. 517-520
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Bloomer, Scott, et al.
(författare)
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Triglyceride interesterification by lipases. 1. Cocoa butter equivalents from a fraction of palm oil
- 1990
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Ingår i: Journal of the American Oil Chemists' Society. - 0003-021X. ; 67:8, s. 519-524
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Tidskriftsartikel (refereegranskat)abstract
- Twelve commercially available triacylglycerol lipase preparations were screened for their suitability as catalysts in the interesterification of palm oil mid fraction and ethyl stearate to form a cocoa butter equivalent. Five fungal lipase preparations were found to be suitable. The hydrolytic activity of the commercial lipase preparations was tested with sunflower seed oil and was independent of their interesterification activity. The operational stability of three of the preparations most suited for production of cocoa butter equivalents was examined. The amount of a commercial lipase preparation loaded onto a support was surveyed for optimum short-term catalytic activity. The influence of solvent concentration on the reaction rate and the purity of the product was examined at two temperatures. The optimum solvent concentration at 40°C was 1-1.5 grams of solvent/gram of substrate; at 60°C, the rate of interesterification diminished and the purity of the product decreased with increasing amounts of solvent. Four of the commercial lipase preparations found to be suitable interesterification catalysts were immobilized on five supports and their ability to catalyze the interesterification of a triglyceride and palmitic acid or ethyl palmitate was measured. The choice of support and substrate form (esterified or free fatty acid) greatly affected the catalytic activity. Some preparations were more affected by the choice of support, others by the form of the substrate. No preparation yielded maximum activity on all supports, and no support was found which produced an immobilized enzyme preparation of high activity with every commercial lipase preparation. Caution is advised in transferring observations about the suitability of a support from tests on one commerical enzyme preparation to others; individual testing is required.
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| 3. |
- Clapés, Pere, et al.
(författare)
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Enzymatic peptide synthesis in organic media : a comparative study of water-miscible and water-immiscible solvent systems
- 1990
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Ingår i: Journal of Biotechnology. - 0168-1656. ; 15:4, s. 323-338
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Tidskriftsartikel (refereegranskat)abstract
- Peptide synthesis was carried out in a variety of organic solvents with low contents of water. The enzyme was deposited on the support material, celite, from an aqueous buffer solution. After evaporation of the water the biocatalyst was suspended in the reaction mixtures. The chymotrypsin-catalyzed reaction between Z-Phe-OMe and Leu-NH2 was used as a model reaction. Under the conditions used ([Z-Phe-OMe]0 ≤ 40 mM, [ Leu-NH2]0 ([Z-Phe-OMe]0 = 1.5) the reaction was first order with respect to Z-Phe-OMe. Tris buffer, pH 7.8, was the best buffer to use in the preparation of the biocatalyst. In water-miscible solvents the reaction rate increased with increasing water content, but the final yield of peptide decreased due to the competing hydrolysis of Z-Phe-OMe. Among the water-miscible solvents, acetonitrile was the most suitable, giving 91% yield with 4% (by vol.) water. In water-immiscible solvents the reaction rate and the product distribution were little affected by water additions in the range between 0% and 2% (vol. %) in excess of water saturation. The reaction rates correlated well with the log P values of the solvent. The highest yield (93%) was obtained in ethyl acetate; in this solvent the reaction was also fast. Under most reaction conditions used the reaction product was stable; secondary hydrolysis of the peptide formed was normally negligible. The method presented is a combination of kinetically controlled peptide synthesis (giving high reaction rates) and thermodynamically controlled peptide synthesis (giving stable reaction products).
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| 4. |
- Larsson, Karin M., et al.
(författare)
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Enzymatic catalysis in microemulsions : Enzyme reuse and product recovery
- 1990
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 0006-3592 .- 1097-0290. ; 36:2, s. 135-141
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Tidskriftsartikel (refereegranskat)abstract
- A technique for enzyme reuse and product recovery from enzymatic catalysis in microemulsions is demonstrated. The enzymatic reaction is performed in a homogeneous isotropic microemulsion; AOT (sodium bis‐(2‐ethyl‐ hexyl)sulfosuccinate)/isooctane/buffer or C12E5(penta ethylene glycol dodecyl ether)/heptane/buffer. By small temperature changes the systems are shifted to two phase regions, where an oil‐rich phase, containing the product, coexists with a water‐rich phase containing surfactant and enzyme. The oil‐rich phase may be replaced by an oil solution containing new substrate. Thus, the reaction may be continued and the enzyme reused. This procedure was repeated nine times in the present study. Data on phase behavior in presence and in absence of protein, partitioning of the components and a radioactive‐labelled protein between the phases, and the repeated use of horse liver alcohol dehydrogenase (HLADH) in the microemulsions are presented.
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| 5. |
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| 6. |
- Larsson, Karin M., et al.
(författare)
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Three systems used for biocatalysis in organic solvents a comparative study
- 1990
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Ingår i: Biocatalysis and Biotransformation. - : Informa UK Limited. - 1024-2422. ; 4:2-3, s. 163-175
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Tidskriftsartikel (refereegranskat)abstract
- The activity and operational stability of horse liver alcohol dehydrogenase (HLADH) and αchymotrypsin were investigated in three systems commonly used for biocatalysis in organic solvents: 1. enzyme adsorbed on a solid support (celite) and added to the organic solvent (isooctane) 2. enzyme powder directly added to the organic solvent (isooctane). 3. enzyme dissolved in a microemulsion (AOT/isooctane). The activity and the operational stability in all systems were strongly dependent on the water content. The initial reaction rate was high in both the microemulsion and the celite system, but was much lower when adding the enzymes directly to the organic solvent. HLADH was observed to be more stable when added directly to the organic solvent or dissolved in the microemulsion than when adsorbed on celite, whereas for αchymotrypsin stability was higher when adsorbed on celite or added directly to the organic solvent. For a hydrolytic reaction, a microemulsion was preferred due to the high water content. When adding the enzymes directly to the organic solvent both HLADH and chymotrypsin were adsorbed strongly to the glass walls of the reaction vessel. None of the systems were superior in all respects for the two enzymes studied.
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| 7. |
- Pietikäinen, Pekka, et al.
(författare)
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Influence of the reaction medium on the product distribution of peroxidase-catalysed oxidation of p-cresol
- 1990
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Ingår i: Applied Microbiology and Biotechnology. - 0175-7598. ; 33:4, s. 455-458
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Tidskriftsartikel (refereegranskat)abstract
- p-Cresol was oxidized by hydrogen peroxide in a reaction catalysed by horseradish peroxidase and the low molecular weight products were investigated. In aqueous media Pummerer's ketone (I) was the dominating product but in organic media the product distribution was quite different; 2,2'-dihydroxy-5,5'-dimethyldiphenyl (II) was the main low molecular weight product. Similar product distributions were obtained with peroxidase adsorbed on a solid support and suspended in toluene and with peroxidase solubilized in a microemulsion containing the same solvent. The best selectivity for the formation of (II) was obtained when the enzyme was adsorbed on Celite and suspended in water-saturated chloroform with 0.5% (v/v) extra water added. The yield of low molecular weight products in this case was 28%; of this fraction, 95% was (II).
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| 8. |
- Svensson, Ingemar, et al.
(författare)
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Interesterification of phosphatidylcholine with lipases in organic media
- 1990
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Ingår i: Applied Microbiology and Biotechnology. - 0175-7598. ; 33:3, s. 255-258
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Tidskriftsartikel (refereegranskat)abstract
- Lipases were investigated with respect to their ability to catalyse the incorporation of fatty acids into phosphatidylcholine (PC) by interesterification reactions. The enzymes were dried onto solid support materials and the conversions were carried out in water-saturated toluene. Three lipases (two fungal and one plant enzyme) had the desired activity; immobilized lipase from Mucor miehei (Lipozyme) was the most active enzyme. The Lipozyme-catalysed interesterification was selective for the sn-1 position of PC and during 48 h of reaction around 50% of the fatty acids in this position were replaced with heptadecanoic acid, a fatty acid which was practically absent in the original phospholipid. Due to adsorption on the support material and the competing hydrolysis reaction the total amount of PC in the reaction solution decreased to about 40% of the original amount. Higher interesterification rates were obtained with free fatty acids as acyl donors than with fatty acid esters.
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| 9. |
- Wehtje, Ernst, et al.
(författare)
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Formation of C—C bonds by mandelonitrile lyase in organic solvents
- 1990
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 0006-3592 .- 1097-0290. ; 36:1, s. 39-46
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Tidskriftsartikel (refereegranskat)abstract
- Mandelonitrile lyase (EC 4.1.2.10) catalyzes the formation of D‐mandelonitrile from HCN and benzaldehyde. Mandelonitrile lyase was immobilized by adsorption to support materials, for example, Celite. The enzyme preparations were used in diisopropyl ether for production of D‐mandelonitrile. In order to obtain optically pure D‐mandelonitrile it was necessary to use reaction conditions which favor the enzymatic reaction and suppress the competing spontaneous reaction, which yields a racemic mixture of D, L‐mandelonitrile. The effects of substrate concentrations, water content, and support materials on both the spontaneous and enzymatic reactions were studied. The enzymatic reaction was carried out under conditions where the importance of the spontaneous reaction was negligible and high enantiomeric purity of D‐mandelonitrile was achieved (at least 98% enantiomeric excess). The operational stability of the enzyme preparations was studied in batch as well as in continuous systems. It was vital to control the water content in the system to maintain an active preparation. In a packed bed reactor the enzyme preparations were shown to be active and stable. The reactors were run for 50 h with only a small decrease in product yield.
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