| 1. |
- 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
- 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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| 2. |
- GOLOLOBOV, Mikhail Y., et al.
(författare)
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The second nucleophile molecule binds to the acyl‐enzyme–nucleophile complex in α‐chymotrypsin catalysis : Kinetic evidence for the interaction
- 1993
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Ingår i: European Journal of Biochemistry. - : Wiley. - 0014-2956 .- 1432-1033. ; 217:3, s. 955-963
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Tidskriftsartikel (refereegranskat)abstract
- α‐Chymotrypsin‐catalyzed acyl tranfer was studied using three acyl‐group donors (Mal‐l‐Ala‐l‐Ala‐l‐PheOMe, Bz‐l‐TyrOEt and Ac‐l‐TrpOEt; Mal, maleyl; Bz, benzoyl; OMe, methyl ester; OEt, ethyl ester) and a series of amino‐acid amides. Most of the reactions studied can be described by the simplest kinetic model without the nucleophile binding to the acyl‐enzyme. The α‐chymotrypsin‐catalyzed transfer of the Mal‐l‐Ala‐l‐Ala‐l‐Phe group to the amides of L‐Phe and L‐Tyr showed a linear dependence of the partition constant, p, on the nucleophile concentration which can be interpreted by the hydrolysis of the acyl‐enzyme–nucleophile complex. The α‐chymotrypsin‐catalyzed transfer of the Bz‐l‐Tyr and Ac‐l‐Trp groups to several amino‐acid amides showed unusual behavior which can be interpreted by the kinetic model involving formation of a complex of the acyl‐enzyme with two nucleophile molecules. These observations can explain the conflicting conclusions concerning the kinetics of α‐chymotrypsin‐catalyzed acyl transfer evident in previous studies.
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| 3. |
- 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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| 4. |
- RESLOW, Mats, et al.
(författare)
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On the importance of the support material for bioorganic synthesis : Influence of water partition between solvent, enzyme and solid support in water‐poor reaction media
- 1988
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Ingår i: European Journal of Biochemistry. - : Wiley. - 0014-2956 .- 1432-1033. ; 172:3, s. 573-578
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Tidskriftsartikel (refereegranskat)abstract
- α‐Chymotrypsin was adsorbed on solid support materials and the catalytic activity of the preparations in organic solvents was studied. The activity was highly dependent on the nature of the support material and on the amount of water present in the reaction mixture. There appears to be competition for the water in the system between the enzyme, the support material and the solvent. The support materials were characterized by measuring their ability to absorb water from water‐saturated diisopropyl ether. For the quotient: (amount of water on the support)/(amount of water in the solvent) in the model system the term aquaphilicity was proposed. The activity of adsorbed chymotrypsin in diisopropyl ether decreased with increasing aquaphilicity of the support material. The same trend was observed when the activity of horse liver alcohol dehydrogenase adsorbed on different supports was measured in diisopropyl ether.
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| 5. |
- Reslow, Mats, et al.
(författare)
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The influence of water on protease‐catalyzed peptide synthesis in acetonitrile/water mixtures
- 1988
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Ingår i: European Journal of Biochemistry. - : Wiley. - 0014-2956. ; 177:2, s. 313-318
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Tidskriftsartikel (refereegranskat)abstract
- Protease‐catalyzed peptide synthesis in acetonitrile water mixtures, containing 0–90% water, was investigated. α‐Chymotrypsin, as well as thermolysin, were deposited on solid supports, prior to exposure to the reaction media. Peptide syntheses were performed using both a kinetically controlled process (chymotrypsin) and an equilibrium‐controlled synthesis (thermolysin). The activity of chymotrypsin decreased at low water contents. However, at low water contents (1–10%) hydrolytic side reactions were suppressed and high yields of dipeptides were obtained. Optimal water content for the thermolysin‐catalyzed reaction was 4–8%. The dipeptides produced were fully soluble in the reaction mixtures. High operational stability for α‐chymotrypsin was obtained during 216 h of reaction.
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