| 1. |
- 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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| 2. |
- Adlercreutz, Patrick, et al.
(författare)
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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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| 3. |
- Adlercreutz, Patrick
(författare)
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Oxidation of trans- and cis-1,2-cyclohexanediol by Gluconobacter oxydans - Preparation of (R)- and (S)-2-hydroxycyclohexanone
- 1989
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Ingår i: Applied Microbiology and Biotechnology. - 0175-7598. ; 30:3, s. 257-263
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Tidskriftsartikel (refereegranskat)abstract
- The enzymatic oxidation of 1,2-cyclohexanediol and related substrates by Gluconobacter oxydans (ATCC 621) was investigated. At low pH, membrane-bound enzymes were active and at high pH, NAD-dependent, soluble enzymes showed activity. Whole bacterial cells were used to catalyze some bioconversions. Racemic trans-1,2-cyclohexanediol was oxidized at pH 3.5 to give (R)-2-hydroxycyclohexanone (96% e.e.) and at pH 8.0 the same substrate was oxidized to (S)-2-hydroxycyclohexanone (97% e.e.). The latter conversion was severely inhibited by the reaction product while the former was not significantly product inhibited. (S)-2-hydroxycyclohexanone (97% e.e.) was also prepared from cis-1,2-cyclohexanediol by oxidation with G. oxydans cells at pH 3.5 in a reaction which continued to 100% conversion.
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| 4. |
- Adlercreutz, Patrick
(författare)
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Oxygen supply to immobilized cells : 5. Theoretical calculations and experimental data for the oxidation of glycerol by immobilized Gluconobacter oxydans cells with oxygen or p‐benzoquinone as electron acceptor
- 1986
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 0006-3592 .- 1097-0290. ; 28:2, s. 223-232
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical calculations of reaction kinetics were done for one‐step reactions catalyzed by cells immobilized in spherical beads. The reactions catalyzed by free cells were assumed to obey Michaelis–Menten kinetics for a one‐substrate reaction. Both external (outside the beads) and internal (inside the beads) mass transfer of the substrate were considered for the immobilized preparations. The theoretical calculations were compared with experimental data for the oxidation of glycerol to dihydroxyacetone by Gluconobacter oxydans cells immobilized in calcium alginate gel. Glycerol was present in excess so that the reaction rate was limited by oxygen. The correlation between experimental data and theoretical calculations was quite good. The calculations showed how the overall effectiveness factor was influenced by, for example, the particle size and the cell density in the beads. In most cases the reaction rate was mainly limited by internal mass transfer of the substrate (oxygen). As shown previously, p‐benzoquinone can replace oxygen as the electron acceptor in this reaction. The same equations for reaction kinetics and mass transfer were used with p‐benzoquinone as the rate‐limiting substrate. Parameters such as diffusivity, maximal reaction rate, and K were, of course, different. In this case also, the correlation between the model and the experimental results was quite good. Much higher production rates were obtained with p‐benzoquinone as the electron acceptor compared to when oxygen was used. The reasons for this fact were that p‐benzoquinone gave a higher maximal reaction rate for free cells and the solubility of p‐benzoquinone was higher than for oxygen. Different methods of increasing the rate of microbial oxidation reactions are discussed.
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| 5. |
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| 6. |
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| 7. |
- Adlercreutz, Patrick
(författare)
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Use of artificial electron acceptors in oxidation reactions catalyzed by acetic acid bacteria
- 1987
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Ingår i: Biotechnology Techniques. - 0951-208X. ; 1:2, s. 103-108
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Tidskriftsartikel (refereegranskat)abstract
- The ability of several electron acceptors to promote the Gluconobacter oxydans catalyzed oxidation of glycerol was investigated. p-Benzoquinone was the most effective electron acceptor. The reaction rate obtained with p-benzoquinone was higher than the maximal rate with the natural electron acceptor, oxygen, in all the oxidation reactions tested.
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| 8. |
- Kaul, Rajni, et al.
(författare)
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Coimmobilization of substrate and biocatalyst : A method for bioconversion of poorly soluble substances in water milieu
- 1986
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 0006-3592 .- 1097-0290. ; 28:9, s. 1432-1437
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Tidskriftsartikel (refereegranskat)abstract
- Coimmobilization of biocatalyst and substrate was studied as a method to increase the conversion rate in systems with substrates of extremely low solubility in water. The system studied was the conversion of hydrocortisone to prednisolone by Arthrobacter simplex. As a matrix for coimmobilization, alginate turned out to be superior to agar and agarose. After the reaction was complete, the beads were solubilized, andthe cells recovered for reuse, by centrifugation, whereas the prednisolone was extracted from the supernatant.
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| 9. |
- Larsson, Karin M., et al.
(författare)
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Activity and stability of horse‐liver alcohol dehydrogenase in sodium dioctylsulfosuccinate/cyclohexane reverse micelles
- 1987
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Ingår i: European Journal of Biochemistry. - : Wiley. - 0014-2956 .- 1432-1033. ; 166:1, s. 157-161
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Tidskriftsartikel (refereegranskat)abstract
- Horse liver alcohol dehydrogenase (EC 1.1.1.1) solubilized in sodium dioctylsulfosuccinate (AOT)/cyclohexane reverse micelles was used for the oxidation of ethanol and reduction of cyclohexanone in a coupled substrate/coenzyme recycling system. The activity of the enzyme was studied as a function of pH and water content. The enzyme was optimally active in microemulsions prepared with buffer of pH around 8. An increase in enzymatic activity was observed as a function of increasing water content. The Km values for the substrates were calculated based on the total reaction volume. The apparent Km for ethanol in reverse micelles was about eight times lower as compared to that in buffer solution, whereas the Km for cyclohexanone was almost unaltered. Storage and operational stability were investigated. It was found that the specific activity of the alcohol dehydrogenase operating in reverse micellar solution was good for at least two weeks. The steroid eticholan‐3ß‐ol‐17‐one was also used as a substrate. In this case the reaction rate was approximately five times higher in a reverse micellar solution than in buffer.
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| 10. |
- Mattiasson, Bo, et al.
(författare)
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Perfluorochemicals in biotechnology
- 1987
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Ingår i: Trends in Biotechnology. - : Elsevier BV. - 0167-7799. ; 5:9, s. 250-254
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Forskningsöversikt (refereegranskat)abstract
- Gas transport often is a limiting factor in biotechnology. Perfluorochemicals provide a new vehicle for the transport of gases.
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