| 1. |
- Abou-Hachem, Maher, et al.
(författare)
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The modular organisation and stability of a thermostable family 10 xylanase
- 2003
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Ingår i: Biocatalysis and Biotransformation. - : Informa UK Limited. - 1024-2422 .- 1029-2446. ; 21:5-6, s. 253-260
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Tidskriftsartikel (refereegranskat)abstract
- The thermophilic marine bacterium Rhodothermus marinus produces a modular family 10 xylanase (Xyn10A). It consists of two N-terminal family 4 carbohydrate binding modules (CBMs) followed by a domain of unknown function (D3), and a catalytic module (CM) flanked by a small fifth domain (D5) at its C-terminus. Several truncated mutants of the enzyme have been produced and characterised with respect to biochemical properties and stability. Multiple calcium binding sites are shown to be present in the two N-terminal CBMs and recent evidence suggests that the third domain of the enzyme also has the ability to bind the same metal ligand. The specific binding of Ca2+ was demonstrated to have a pronounced effect on thermostability as shown by differential scanning calorimetry and thermal inactivation studies. Furthermore, deletion mutants of the enzyme were less stable than the full-length enzyme suggesting that module interactions contributed to the stability of the enzyme. Finally, recent evidence indicates that the fifth domain of Xyn10A is a novel type of module mediating cell-attachment.
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| 2. |
- Adlercreutz, Patrick
(författare)
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Cofactor regeneration in biocatalysis in organic media
- 1996
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Ingår i: Biocatalysis and Biotransformation. - : Informa UK Limited. - 1024-2422 .- 1029-2446. ; 14:1, s. 1-30
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Forskningsöversikt (refereegranskat)abstract
- Methods used for the regeneration of cofactors in organic media are reviewed. Substrate-driven regeneration methods include the use of a second substrate of the same enzyme and the use of a second enzyme and its substrate. The use of mediators in oxidoreductions is described and examples of photochemical and electrochemical regeneration methods are presented. General problems and possibilities of cofactor regeneration in organic media are discussed.
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| 3. |
- Anderson, Lars, et al.
(författare)
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Kinetics and stereochemistry of the Cellulomonas fimi beta-mannanase studied using H-1-NMR
- 2008
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Ingår i: Biocatalysis and Biotransformation. - : Informa UK Limited. - 1024-2422 .- 1029-2446. ; 26:1-2, s. 86-95
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Tidskriftsartikel (refereegranskat)abstract
- Endo-1,4-beta-mannanases (beta-mannanases) randomly hydrolyse the mannosidic bonds within the main chain of various mannans and heteromannans. Some of these polysaccharides are hemicelluloses, a major part of the plant cell-wall. The beta-mannanases have been assigned to family 5 and 26 of the glycoside hydrolase clan A. This work presents a detailed kinetic analysis of the family 26 beta-mannanase CfMan26A from the soil-bacterium Cellulomonas fimi. The full-length enzyme consists of five modules: a family 26 catalytic module, an immunoglobulin-like module, a mannan-binding module, a surface layer homology-module and a module of unknown function. A truncated variant consisting of the catalytic module and the immunoglobulin-like module was used in these studies. The degradation of mannotriose, mannotetraose and mannopentaose was studied by H-1-NMR. First, the mutarotation of one of the hydrolysis products (mannose) was determined to be 1.7 10(-5) s(-1) at 5 degrees C and pH 5.0. As expected for a family 26 glycoside hydrolase, the hydrolysis was shown to proceed with overall retention of the anomeric configuration. Many 'retaining' enzymes can perform transglycosylation reactions. However, no transglycosylation could be detected. Kinetic constants were calculated from progress curves using computer simulation. It was revealed that the -3 subsite had a greater impact on the apparent k(cat)/K-m ratio (the catalytic efficiency) than the +2 subsite. The beta-anomer of mannotriose was hydrolysed 1000-times more efficiently than the alpha-anomer indicating selectivity for the beta- over the alpha-anomer in the +1 subsite. With background information from the previous published 3D-structure of the truncated variant of Man26A, a structural explanation for the observations is discussed.
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| 4. |
- Andersson, Mats, et al.
(författare)
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Alcaligenes eutrophus cells containing hydrogenase, a coenzyme regenerating catalyst for NADH-dependent oxidoreductases
- 1997
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Ingår i: Biocatalysis and Biotransformation. - : Informa UK Limited. - 1024-2422 .- 1029-2446. ; 15:4, s. 281-296
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Tidskriftsartikel (refereegranskat)abstract
- Alcaligenes eutrophus cells containing a soluble NAD-dependent hydrogenase was evaluated as a NADH regenerating catalyst. In the presence of hydrogen and permeabilized A. eutrophus cells, NADH regeneration was achieved, and reductions catalyzed by horse liver alcohol dehydrogenase and lactate dehydrogenase proceeded to 90-99% conversion. The operational stability of the hydrogenase was improved by the addition of reducing agents such as dithiothreitol and by immobilization of the cells in calcium alginate.
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| 5. |
- Andersson, Mats, et al.
(författare)
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Prediction of the remaining activity of horse liver alcohol dehydrogenase after exposure to various organic solvents
- 1998
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Ingår i: Biocatalysis and Biotransformation. - : Informa UK Limited. - 1024-2422 .- 1029-2446. ; 16:4, s. 259-273
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Tidskriftsartikel (refereegranskat)abstract
- Twenty solvents were selected from a principal component (PC) analysis of 103 organic solvents. The solvents were selected so as to obtain a set of test items that spanned a large range of molecular properties of the selected solvents. The activity of free and Celite-immobilized horse liver alcohol dehydrogenase (HLADH) obtained after 20 h exposure to these solvents were used to create a PLS model based on 14 solvent descriptors. A correlation coefficient of 0.997 between the predicted and the observed remaining activity was obtained. A slightly worse PLS model was obtained using only three solvent descriptors (log P, dielectric constant and melting point). A correlation coefficient of 0.957 between the predicted and the observed remaining activity was obtained. The latter model was used to predict the remaining activity of HLADH after its exposure to 93 organic solvents.
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| 6. |
- Andersson, Mats, et al.
(författare)
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Stabilisation of chloroperoxidase towards peroxide dependent inactivation
- 2000
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Ingår i: Biocatalysis and Biotransformation. - : Informa UK Limited. - 1024-2422 .- 1029-2446. ; 18:6, s. 457-469
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Tidskriftsartikel (refereegranskat)abstract
- The addition of polyethyleneimine with a molecular weight of 2000 to chloroperoxidase from Caldariomyces fumago dramatically improved the stability of the enzyme towards peroxide dependent inactivation. The rate constant for the H 2 O 2 -dependent inactivation of chloroperoxidase decreased from 0.0016s -1 to 1.1 * 10 -5 s -1 in the presence of 1% polyethyleneimine. The stabilising effect towards tert-butyl hydroperoxide was even more impressive. The half-life of the chloroperoxidase when exposed to a solution of 40 mM tert-butyl hydroperoxide increased from 3.2 minutes to ≥ 70 hours in presence of 0.1% polyethyleneimine.
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| 7. |
- Andersson, Mats, et al.
(författare)
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Use of celite-immobilised chloroperoxidase in predominantly organic media
- 1999
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Ingår i: Biocatalysis and Biotransformation. - : Informa UK Limited. - 1024-2422 .- 1029-2446. ; 17:4, s. 293-303
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Tidskriftsartikel (refereegranskat)abstract
- It is possible to use the chloroperoxidase from Caldariomyces fumago to catalyse the oxidation of benzyl alcohol to benzaldehyde in predominantly organic media, even at water activities below 1.0, if the oxidant is tert-butyl hydroperoxide. The enzyme activity increased with increasing water activity and no enzyme activity was observed at water activities below 0.6. Hydrophobic solvents such as cyclohexane showed the highest initial activities. It was beneficial in terms of obtainable yield to use high concentrations of the peroxide due to the kinetics of the system. The apparent K(m) for benzyl alcohol in cyclohexane was estimated to be 13 mM while the initial reaction rate increased almost linearly up to 250 mM tert-butyl hydroperoxide.
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| 8. |
- Barros, Raúl J., et al.
(författare)
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Physical characterization of porous materials and correlation with the activity of immobilized enzyme in organic medium
- 1998
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Ingår i: Biocatalysis and Biotransformation. - : Informa UK Limited. - 1024-2422 .- 1029-2446. ; 16:1, s. 67-85
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Tidskriftsartikel (refereegranskat)abstract
- A series of commonly used porous supports was characterized by determination of particle size distribution, porosity, surface area (total and distributions with pore diameters) and skeletal density. The performance of immobilized α-chymotrypsin catalyzed dipeptide synthesis in an acetonitrile medium was correlated with these physical properties.At high enzyme loading, when internal mass transfer limitations are expected to occur, the activity can be correlated with the support characteristic parameter. This is a combination of physical properties such as particle size, porosity, and volumetric porosity, which influence the substrate diffusion rate. At low enzyme loading the important parameter is the accessible surface area, which will determine how the enzyme is distributed in the pores of the support. When assessing the effect of the support material on enzymatic activity, the geometric considerations studied here should always be contemplated before making any assumptions about direct effects of support material on enzymatic catalytic properties.
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| 9. |
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| 10. |
- Björup, Peter, et al.
(författare)
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Effects of acetonitrile-water mixtures on α-chymotrypsin catalyzed dipeptide synthesis
- 1996
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Ingår i: Biocatalysis and Biotransformation. - : Informa UK Limited. - 1024-2422 .- 1029-2446. ; 13:3, s. 189-200
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Tidskriftsartikel (refereegranskat)abstract
- α-Chymotrpysin (EC 3.4 21.1) was immobilized by deposition on celite and subsequent cross-linking with glutaraldehyde. The effects of different mixtures of aqueous buffer and acetonitrile on the immobilized preparation were evaluated using a dipeptide synthesis as model reaction. The initial reaction rate at 6-95% of water increased with increasing water content. The maximum yield of peptide had two maxima; the first one at 6% of water (92%) and the second one at 80% of water (39%). The presence of two maxima was due to severe enzyme inactivation at intermediate water contents (50-60%). The immobilisation procedure slowed the inactivation of α-chymotrypsin. Cross-linked enzyme was inactivated to a lesser extent than both free enzyme and enzyme that had been deposited on celite. The increased resistance to inactivation was, however, not sufficient to make peptide synthesis attractive at intermediate water contents (50-60%). In order to obtain good peptide yields, low water contents (below 10%) should be used.
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