| 101. |
- Adlercreutz, Patrick, et al.
(författare)
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Aspects of biocatalyst stability in organic solvents
- 1987
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Ingår i: Biocatalysis and Biotransformation. - : Informa UK Limited. - 1024-2422. ; 1:2, s. 99-108
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Forskningsöversikt (refereegranskat)abstract
- The stability of biocatalysis in systems containing organic solvents is reviewed. Among the examples presented are homogeneous mixtures of water and water-miscible organic solvents, aqueous/organic two-phase systems, solid biocatalysts suspended in organic solvents, enzymes in reverse micelles and modified enzymes soluble in water immiscible solvents. The stability of biocatalysts in organic solvents depends very much on the conditions. The hydrophobicity or the polarity of the solvent is clearly of great importance. More hydrophobic solvents (higher log P values) are less harmful to enzymes than less hydrophobic solvents. The water content of the system is a very important parameter. Some water is essential for enzymatic activity; however, the stability of enzymes decreases with increasing water content. Mechanisms of enzyme inactivation are discussed.
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| 102. |
- Adlercreutz, Patrick
(författare)
-
Asymmetric reduction of ketones with enzymes from acetic acid bacteria
- 1991
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Ingår i: Biotechnology Letters. - 0141-5492. ; 13:4, s. 229-234
-
Tidskriftsartikel (refereegranskat)abstract
- Six strains of acetic acid bacteria were evaluated with respect to their capability to catalyze the stereoselective reduction of ketones. The cells were permeabilized before the bioconversions. The best strains were Gluconobacter oxydans DSM 50049 and Acetobacter aceti DSM 2002. Using either of these two strains it was possible to reduce all 12 ketones to (S)-alcohols with an enantiomeric excess of ≥94 %. The highest level of enzymatic activity was found in Acetobacter aceti DSM 2002.
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| 103. |
- Adlercreutz, P., et al.
(författare)
-
Catalytic properties of α-chymotrypsin in organic media
- 1991
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Ingår i: Biomedica Biochimica Acta. - 0232-766X. ; 50:10-11, s. 55-60
-
Tidskriftsartikel (refereegranskat)abstract
- α-Chymotrypsin was deposited on Celite and the resulting immobilized preparations were used to carry out peptide synthesis reactions in organic media with only small amounts of water present. The influence of different parts of the donor ester and acceptor nucleophile substrate molecules on the kinetics of the enzymatic reactions was studied. The specificity of α-chymotrypsin in organic media was a combination of its substrate specificity in aqueous media and solvent effects. The kinetics of peptide synthesis can thus be modulated by using suitable solvents and protecting groups.
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| 104. |
- Adlercreutz, Patrick, et al.
(författare)
-
Characterization of Gluconobacter oxydans immobilized in calcium alginate
- 1985
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Ingår i: Applied Microbiology and Biotechnology. - 0175-7598. ; 22:1, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- Gluconobacter oxydans cells were immobilized in calcium alginate and the preparation was used for the oxidation of glycerol to dihydroxyacetone. The characterization was done according to the guidelines given by the Working Party on Immobilized Biocatalysts of the European Federation of Biotechnology. The pH optimum of the preparation was found to be 5.0 and the temperature optimum was 40°C. However, the operational stability was better at 30°C. The glycerol concentration required to obtain half the maximal reaction rate was about 5 mM for both immobilized and free cells. At low concentrations of glycerol and high concentrations of dihydroxyacetone a slight inhibition was noted. No loss of activity of the immobilized preparation was observed after storage for 68 days at +4°C. Investigation of the operational stability revealed a half-life of 5 days. Studies of the influence of particle size and cell densities as well as that of oxygen concentration revealed that the oxygen supply was the rate limiting step.
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| 105. |
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| 106. |
- ADLERCREUTZ, PATRICK, et al.
(författare)
-
Enzymatic Peptide Synthesis in Organic Media
- 1990
-
Ingår i: Annals of the New York Academy of Sciences. - : Wiley. - 0077-8923 .- 1749-6632. ; 613:1, s. 517-520
-
Tidskriftsartikel (refereegranskat)
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| 107. |
- Adlercreutz, Patrick
(författare)
-
Enzyme-catalysed lipid modification
- 1994
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Ingår i: Biotechnology and Genetic Engineering Reviews. - : Informa UK Limited. - 0264-8725 .- 2046-5556. ; 12:1, s. 231-254
-
Forskningsöversikt (refereegranskat)
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| 108. |
- Adlercreutz, Patrick
(författare)
-
Novel biocatalyst for the asymmetric reduction of ketones : Permeabilized cells of Gluconobacter oxydans
- 1991
-
Ingår i: Enzyme and Microbial Technology. - : Elsevier BV. - 0141-0229. ; 13:1, s. 9-14
-
Tidskriftsartikel (refereegranskat)abstract
- Gluconobacter oxydans (ATCC 621) were permeabilized with toluene and then lyophilized. This crude enzyme preparation was used to reduce eleven ketones to (S)-alcohols with high enantiomeric excess (for most alcohols 93%-99% e.e.). The coenzyme NADH was regenerated either by adding a second enzyme, formate dehydrogenase, and its substrate, formate, or with 2-butanol as a second substrate for the G. oxydans enzyme(s). With the first of these methods, almost complete conversion was achieved. Permeabilized cells immobilized in calcium alginate gel were used for 18 days without any significant loss of catalytic activity.
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| 109. |
- ADLERCREUTZ, Patrick
(författare)
-
On the importance of the support material for enzymatic synthesis in organic media : Support effects at controlled water activity
- 1991
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Ingår i: European Journal of Biochemistry. - : Wiley. - 0014-2956 .- 1432-1033. ; 199:3, s. 609-614
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Tidskriftsartikel (refereegranskat)abstract
- Enzymes were deposited on different porous support materials and these preparations were used to catalyze reactions in organic media. Reactions were carried out at specific water activities, achieved by equilibrating both the enzyme preparation and the substrate solution at the desired water activity before mixing them and thereby starting the reactions. The reaction rates obtained at the same water activity with different supports differed greatly, indicating a direct influence of the support on the enzyme. For horse liver alcohol dehydrogenase, Celite was the best support, and the reaction rate increased with increasing water activity. In the α‐chymotrypsin‐catalyzed alcoholysis of N‐acetyl‐l‐phenylalanine ethyl ester with 1‐butanol, high rates were again obtained with Celite, but with this support only about one third of the ethyl ester was converted to butyl ester, the rest was hydrolyzed. With the polyamide support, Accurel PA6, alcoholysis was the dominating reaction, and by using a low water activity (0.33), hydrolysis was completely suppressed while still maintaining a high alcoholysis activity. Controlled pore glass (CPG), derivatized with either hexyl or glucosyl groups, had quite different properties as enzyme supports. For horse liver alcohol dehydrogenase, glucose‐CPG was a much better support than hexyl‐CPG, and in the α‐chymotrypsin‐catalyzed reactions, glucose‐CPG favored hydrolysis, and hexyl‐CPG alcoholysis, at water activities exceeding 0.8. The results are discussed considering the absorption of water on the enzymes, on the supports and the solubility of water in the reaction media; all these parameters were measured separately.
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| 110. |
- Adlercreutz, Patrick
(författare)
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On the Importance of the Support Material for Enzymatic Synthesis in Organic Media. Support Effects at Controlled Water Activity
- 1992. - C
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Ingår i: Progress in Biotechnology. - 0921-0423. ; 8:C, s. 55-61
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Bokkapitel (refereegranskat)abstract
- Enzymes adsorbed or deposited on porous support materials have been succesfully used as catalysts in organic media. However, the support must be chosen with great care. The support can affect the partitioning of substrates, products and water in the reaction mixture and thereby indirectly influence the catalytic properties of the enzyme. Furthermore, the support can influence both the enzyme kinetics and the number of catalytically active enzyme molecules. The effects of the support on water partitioning in the system can be interpreted by measurements of the aquaphilicity (water attracting capacity) of the supports. Normally, high reaction rates are obtained with supports having low aquaphilicity. Even in experiments carried out at fixed enzyme hydration (fixed water activity) the support influences both the total activity of the enzyme and the relative rates of different reactions catalyzed by the same enzyme.
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