| 1. |
- Ademark, Pia, et al.
(författare)
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Multiple alpha-galactosidases from Aspergillus niger: purification, characterization, and substrate specificities
- 2001
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Ingår i: Enzyme and Microbial Technology. - 0141-0229. ; 29:6-7, s. 441-448
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Tidskriftsartikel (refereegranskat)abstract
- Enzymes with α-galactosidase activity are produced by many organisms, often in multiple forms. Here we compare the biochemical and hydrolytic properties of four major α-galactosidase forms (α-gal I-IV) that were purified from the culture filtrate of Aspergillus niger. α-Gal II, III and IV appear to be isoforms of the same enzyme, and N-terminal amino acid sequence data suggest that they are closely related or identical to A. niger AglB in family 27 of the glycosyl hydrolases. α-Gal I is a completely different enzyme that belongs to family 36. α-Gal I had an isoelectric point of 4.15 and appears to be a tetramer composed of four 94-kDa subunits. α-Gal II, III and IV were dimers with monomeric molecular masses of 64 kDa and isoelectric points of 4.5, 4.7 and 4.8, respectively. α-Gal II-IV were stable when incubated for 17 h at 50°C and pH 2–5, whereas α-gal I was most stable at pH 5–6. All enzymes had maximal catalytic activity at pH 4.5 and 60°C, and hydrolyzed melibiose, raffinose and stachyose. α-Gal II-IV also degraded galactomanno-oligosaccharides and released 66% of the galactose side groups from polymeric locust bean gum galactomannan. α-Gal I released galactose from locust bean gum only in combination with A. niger β-mannosidase. Kinetic experiments showed that α-gal I hydrolyzed p-nitrophenyl-α-Image-galactopyranoside and melibiose more efficiently than α-gal II-IV. The distinct hydrolytic and biochemical properties of α-gal I and α-gal II-IV further signifies the difference between α-galactosidases of family 27 and 36.
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| 2. |
- Adlercreutz, Patrick
(författare)
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Novel biocatalyst for the asymmetric reduction of ketones : Permeabilized cells of Gluconobacter oxydans
- 1991
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Ingår i: Enzyme and Microbial Technology. - : Elsevier BV. - 0141-0229. ; 13:1, s. 9-14
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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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| 3. |
- Adlercreutz, Patrick, et al.
(författare)
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Oxygen supply to immobilized cells : 1. Oxygen production by immobilized Chlorella pyrenoidosa
- 1982
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Ingår i: Enzyme and Microbial Technology. - : Elsevier BV. - 0141-0229. ; 4:5, s. 332-336
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen supply at high cell densities of aerobic organisms is a great problem in immobilized cell preparations. To investigate the possibility of in situ oxygen generation the alga Chlorella pyrenoidosa was immobilized on alginate beads. The conditions for optimal oxygen production were investigated and in long term experiments the preparations were successful for at least 30 days.
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| 4. |
- Adlercreutz, Patrick, et al.
(författare)
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Oxygen supply to immobilized cells : 2. Studies on a coimmobilized algae-bacteria preparation with in situ oxygen generation
- 1982
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Ingår i: Enzyme and Microbial Technology. - : Elsevier BV. - 0141-0229. ; 4:6, s. 395-400
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Tidskriftsartikel (refereegranskat)abstract
- A coimmobilized mixed culture of algae, Chlorella pyrenoidosa, and bacteria, Gluconobacter oxydans, has been studied. The conversion of glycerol to dihydroxyacetone(1,3-dihydroxy-2-propanone), catalysed by the bacteria, was used to indicate the oxygen supply in the immobilized preparation. The oxygen produced by the algae in the coimmobilized preparation was used by the bacteria more effectively than when the cells were immobilized separately and mixed within the reactor. A preparation consisting of only bacteria and no algae was much less effective. The coimmobilized preparation was used in the continuous production of dihydroxyacetone for six days without any significant loss of activity.
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| 5. |
- Alkasrawi, Malek, et al.
(författare)
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The effect of Tween-20 on simultaneous saccharification and fermentation of softwood to ethanol
- 2003
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Ingår i: Enzyme and Microbial Technology. - 0141-0229. ; 33:1, s. 71-78
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Tidskriftsartikel (refereegranskat)abstract
- Simultaneous sacchatification and fermentation (SSF) of steam-pretreated wood constitutes an attractive process configuration for ethanol production from biomass. However, the high enzyme addition in SSF contributes to a high process cost. In this study we explore the effect of the non-ionic surfactant Tween-20 as an additive in SSE Tween-20 addition at 2.5 g/l had several positive effects on SSF: (i) the ethanol yield was increased by 8%; (ii) the amount of enzyme loading could be reduced by 50%, while maintaining a constant yield; (iii) the enzyme activity increased in the liquid fraction at the end of SSF, probably by preventing unproductive binding of the cellulases to lignin, which could facilitate enzyme recovery; (iv) the time required to attain maximum ethanol concentration was reduced. Surfactants as an additive in SSF can significantly lower the operational cost of the process. However, less expensive surfactants must be investigated. (C) 2003 Elsevier Science Inc. All rights reserved.
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| 6. |
- Andersson, Mats, et al.
(författare)
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Evaluation of electron mediators for the electromicrobial reduction of chloropyruvate by Proteus vulgaris cells
- 1997
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Ingår i: Enzyme and Microbial Technology. - 0141-0229. ; 20:2, s. 150-156
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Tidskriftsartikel (refereegranskat)abstract
- Different electron mediators were evaluated for the electromicrobial reduction of chloropyruvate to chlorolactate. The reaction was catalyzed by a mediatol-dependent D-lactate dehydrogenase in whole cells of Proteus vulgaris and yielded D-(S)-chlorolactate with high optical purity (> 97% e.e.). The ideal mediatol should favor a high rate in the enzymatic reaction and a low rate in the nonenzymatic dehalogenation of the substrate. The latter reaction causes the formation of pyruvate and subsequently lactate. Viologens as mediators provided better yields than cobalt sepulchrate, safranine O, and an anthraquinone derivative. The best results were obtained with 1,1'-carbamoylmethylviologen as mediator.
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| 7. |
- Andersson, Mats, et al.
(författare)
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Microbial production of D-(S)-chlorolactic acid by Proteus vulgaris cells
- 1998
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Ingår i: Enzyme and Microbial Technology. - 0141-0229. ; 22:3, s. 170-178
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Tidskriftsartikel (refereegranskat)abstract
- Hydroxy carboxylate viologen oxidoreductase (HVOR) contained in Proteus vulgaris cells was used in the reduction of chloropyruvic acid to D-(S)-chlorolactic acid. A synthetic electron mediator 1,1'-carbamoylmethylviologen (CAV) was used to transfer electrons to HVOR. Three different methods for regenerating the mediator were evaluated: (1) electrochemically driven reduction; (2) reduction driven by formate using formate dehydrogenase; and (3) reduction driven by hydrogen gas using hydrogenase. On a small scale, all three methods provided yields of D-(S)-chlorolactic acid of around 80%. For gram-scale conversions, the method using formate dehydrogenase and formate appeared best. It was found beneficial to add the chloropyruvic acid continuously during the reaction so as to avoid side reactions. Using 2.8 mg ml -1 of P. vulgaris cells, 4.4 mM CAV and a reaction time of 14 h, a preparative yield of 81% (6.6 mmol) of D-(S)-chlorolactic acid (ee > 97%) was obtained.
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| 8. |
- Bakhtiar, Shahrzad, et al.
(författare)
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Stability characteristics of a calcium-independent alkaline protease from Nesterenkonia sp.
- 2003
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Ingår i: Enzyme and Microbial Technology. - 0141-0229. ; 32:5, s. 525-531
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Tidskriftsartikel (refereegranskat)abstract
- Thermodynamic stability of an alkaline protease from a new alkaliphilic Nesterenkonia sp. AL-20, was investigated and compared with that of Subtilisin Carlsberg. The amount of calcium bound to the AL-20 protease was determined to be only about 0.14 mol/mol of protease. Differential scanning calorimetry scan of the enzyme at increasing temperature showed the denaturation of the enzyme to be a two-state process with melting temperature, Tm of about 74 °C at pH 10.0, which was unaltered upon addition of calcium as well as after treatment with chelating agents. The thermodynamic parameters were nearly the same over a pH range of 7.0–10.0. Tm was reduced to 69.7 °C at pH 6.0 and 72 °C at pH 11.0. The secondary structure of the protease was unaffected during storage at 50 °C, even in the presence of 1% SDS as observed by circular dichroism. The protease activity was extremely stable in the presence of hydrogen peroxide and various sequestering agents used in detergents.
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| 9. |
- Barros, Raúl J., et al.
(författare)
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Enhancement of immobilized protease catalyzed dipeptide synthesis by the presence of insoluble protonated nucleophile
- 1999
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Ingår i: Enzyme and Microbial Technology. - 0141-0229. ; 24:8-9, s. 480-488
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Tidskriftsartikel (refereegranskat)abstract
- α-Chymotrypsin immobilized on celite catalyzing a kinetically controlled dipeptide synthesis reaction in acetonitrile medium showed an odd behavior in response to additions of triethylamine to the reaction mixture. This base is used to deprotonate the nucleophilic reagent, l-alaninamide hydrochloride, in order to increase its nucleophilicity and solubility. However, the enzyme performance is apparently enhanced by additions of triethylamine below one equivalent (in the range 15-20 mm) while the used concentration of nucleophilic reagent is 30 mm. Under these conditions, the initial rate is up to 2.5 times higher and the nucleophile specificity is approximately 30% better than when one equivalent is added. The activating effect on initial rates of dipeptide synthesis was not observed when polyamide was used as support. Unlike polyamide, celite is a material with quite low porosity. Improvement of nucleophile specificity was observed using both supports. It is shown that this activation arises due to the presence of a separate dense liquid phase of insoluble l-alaninamide hydrochloride that intimately contacts with the enzyme preparation, and does not depend on the addition of triethylamine itself. Additions of l-alaninamide hydrochloride improved initial rates of synthesis more than 2.5-fold, and nucleophile specificity more than threefold. The initial rate activation was also observed when using non-porous glass beads to immobilize the enzyme at a loading of 5 mg enzyme g-1 glass but not at 1 mg enzyme g-1 glass when no mass transfer limitations in the immobilized enzyme layer are expected to occur. The results suggest that the presence of the separate phase helps to relieve mass transfer limitations on the system caused by overloading at the supports. One possible mechanism for the initial rate activation might be that the enzyme is partially desorbed from the support particles into the separate phase of nucleophile, and the better nucleophile specificity observed is due to increased local concentrations of the nucleophile within this phase. Copyright (C) 1999 Elsevier Science Inc. All rights reserved.
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| 10. |
- Bloomer, Scott, et al.
(författare)
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Facile synthesis of fatty acid esters in high yields
- 1992
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Ingår i: Enzyme and Microbial Technology. - : Elsevier BV. - 0141-0229. ; 14:7, s. 546-552
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Tidskriftsartikel (refereegranskat)abstract
- The facile synthesis of esters by lipase-catalysed esterification of fatty acids and ethanol is demonstrated. Evaporation of the water generated in the reaction allowed the rapid production of esters of >99% yield in refluxing pentane or hexane. Water was trapped by condensing the refluxing vapor phase and passing it over activated molecular sieves in a reflux trap. High yields were rapidly obtained in synthesis of ethyl esters of oleic, linoleic, α-linolenic, and arachidonic acids without peroxidation of double bonds. The wax ester oleyl oleate was also synthesized rapidly with little peroxidation. A molar excess of 1.25 to 1.5 of ethanol allowed the most rapid ester synthesis. Synthesis of ethyl stearate was carried out on a preparative scale (50 g). Greater than 99% conversion was obtained in 50 min.
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