| 1. |
- Bramble, J L, et al.
(författare)
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Calcium and Phosphate Effects on Growth and Alkaloid Production in Coffea arabica: Experimental Results and Mathematical Model.
- 1991
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 0006-3592 .- 1097-0290. ; 37:9, s. 859-868
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Tidskriftsartikel (refereegranskat)abstract
- Plant, mammalian, and microbial cells are commonly immobilized in calcium alginate gels for the production of valuable secondary metabolites. However, calcium ions are known to inhibit growth in various type of cells, and calcium is an integral part of such gels. Therefore, an investigation was conducted to evaluate the effect of calcium on the growth and alkaloid production of a model cell-line, Coffea arabica, in suspension culture before attempting to immobilize such cells in alginate. A kinetic model was then developed from the results to describe cell growth and alkaloid production and the mechanism by which calcium influences these variables. In addition, it was observed that there was a characteristic relationship between the concentration of calcium in the external medium and the concentration of extracellular and intracellular phosphate. The intracellular phosphate level was, in turn, related to the production of alkaloids. Using these results, a dynamic mathematical model of cell growth and alkaloid production was developed based on the proposed roles of calcium and phosphate. The model showed satisfactory agreement with three sets of experiments at different calcium concentrations. A possible linkage between the calcium and phosphate results is postulated based on the limited solubility of calcium phosphate.
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| 2. |
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| 3. |
- Larsson, Karin M., et al.
(författare)
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Enzymatic catalysis in microemulsions : Enzyme reuse and product recovery
- 1990
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 0006-3592 .- 1097-0290. ; 36:2, s. 135-141
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Tidskriftsartikel (refereegranskat)abstract
- A technique for enzyme reuse and product recovery from enzymatic catalysis in microemulsions is demonstrated. The enzymatic reaction is performed in a homogeneous isotropic microemulsion; AOT (sodium bis‐(2‐ethyl‐ hexyl)sulfosuccinate)/isooctane/buffer or C12E5(penta ethylene glycol dodecyl ether)/heptane/buffer. By small temperature changes the systems are shifted to two phase regions, where an oil‐rich phase, containing the product, coexists with a water‐rich phase containing surfactant and enzyme. The oil‐rich phase may be replaced by an oil solution containing new substrate. Thus, the reaction may be continued and the enzyme reused. This procedure was repeated nine times in the present study. Data on phase behavior in presence and in absence of protein, partitioning of the components and a radioactive‐labelled protein between the phases, and the repeated use of horse liver alcohol dehydrogenase (HLADH) in the microemulsions are presented.
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| 4. |
- Otamiri, Marina, et al.
(författare)
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A differential scanning calorimetric study of chymotrypsin in the presence of added polymers
- 1994
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 0006-3592 .- 1097-0290. ; 44:1, s. 73-78
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Tidskriftsartikel (refereegranskat)abstract
- Scanning calorimetry measurements of different amounts of chymotrypsin in water alone gave a temperature of denaturation (Td) value of 54°C. However, when high‐molecular‐weight poly(ethylene glycol) was added to aqueous solutions of chymotrypsin, the thermostability of the enzyme was enhanced. For example, the addition of 20% (w/w) of poly(ethylene glycol) of molecular weight of 100,000 increased the Td/ value to 66°C. In toluene containing various amounts of added water, ethyl cellulose was used to improve the thermostability of chymotrypsin. For this system, a Td value of 82°C was obtained with a 20% (w/w/) concentration of ethyl cellulose and 2% (v/v) of added water. Polymers in these solvents interact with water, which could otherwise denature the enzyme; polymers also from complexes with enzyme molecules to produce a more stable structure. © 1994 John Wiley & Sons, Inc.
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| 5. |
- Otamiri, Marina, et al.
(författare)
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Polymer–polymer organic solvent two‐phase system : A new type of reaction medium for bioorganic synthesis
- 1994
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 0006-3592 .- 1097-0290. ; 43:10, s. 987-994
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Tidskriftsartikel (refereegranskat)abstract
- Mixing solutions of polymers dissolved in chloroform resulted in turbid solutions that parted into two separate phases upon standing. Each phase consisted primarily of one of the two polymers and contained only small amounts of the other. An enzyme (α‐chymotrypsin) added to the two‐phase system partitioned preferentially to one of the phases; this was observed with native enzyme and with enzyme associated with one of the polymers through non‐convalent interactions. Under the conditions studied, α‐chymotrypsin was active and expressed even higher activity and stability than native enzyme added to the organic solvent without polymer. An emulsion was easily formed on mixing with small droplets of one of the phases suspended in the other phase. By operating with the enzyme in the emulsion, a very attractive system for carrying out enzyme‐catalyzed conversions was created. Short diffusion distances and minimized steric hindrance are two characteristics of such systems. At the conclusion of the reaction, stirring/mixing was ceased and, after phase separation, it was possible to recover the enzyme as well as the product, under ideal conditins, from different phases. The enzyme was then reused. © 1994 John Wiley & Sons, Inc.
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| 6. |
- Svensson, Ingemar, et al.
(författare)
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Effects of water activity on reaction rates and equilibrium positions in enzymatic esterifications
- 1994
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 0006-3592 .- 1097-0290. ; 44:5, s. 549-556
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Tidskriftsartikel (refereegranskat)abstract
- A technique of continuous water activity control was used to examine the effects of water activity on enzyme catalysis in organic media. Esterification catalyzed by Rhizopus arrhizus lipase was preferably carried out at a water activity of 0.33, which resulted in both maximal initial reaction rate and a high yield. When Pseudomonas lipase was used as catalyst it was beneficial to start the reaction at high water activity (giving the optimal reaction rate with this enzyme) and then shift to a lower water activity toward the end of the reaction to obtain a high yield. The apparent equilibrium constant of the reaction was influenced by the water activity of the organic solvent. © 1994 John Wiley & Sons, Inc.
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| 7. |
- Wehtje, Ernst, et al.
(författare)
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Formation of C—C bonds by mandelonitrile lyase in organic solvents
- 1990
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 0006-3592 .- 1097-0290. ; 36:1, s. 39-46
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Tidskriftsartikel (refereegranskat)abstract
- Mandelonitrile lyase (EC 4.1.2.10) catalyzes the formation of D‐mandelonitrile from HCN and benzaldehyde. Mandelonitrile lyase was immobilized by adsorption to support materials, for example, Celite. The enzyme preparations were used in diisopropyl ether for production of D‐mandelonitrile. In order to obtain optically pure D‐mandelonitrile it was necessary to use reaction conditions which favor the enzymatic reaction and suppress the competing spontaneous reaction, which yields a racemic mixture of D, L‐mandelonitrile. The effects of substrate concentrations, water content, and support materials on both the spontaneous and enzymatic reactions were studied. The enzymatic reaction was carried out under conditions where the importance of the spontaneous reaction was negligible and high enantiomeric purity of D‐mandelonitrile was achieved (at least 98% enantiomeric excess). The operational stability of the enzyme preparations was studied in batch as well as in continuous systems. It was vital to control the water content in the system to maintain an active preparation. In a packed bed reactor the enzyme preparations were shown to be active and stable. The reactors were run for 50 h with only a small decrease in product yield.
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| 8. |
- Wehtje, Ernst, et al.
(författare)
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Improved activity retention of enzymes deposited on solid supports
- 1993
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 0006-3592 .- 1097-0290. ; 41:2, s. 171-178
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Tidskriftsartikel (refereegranskat)abstract
- Enzymes deposited on solid support usually show good stability when operated in organic solvents. Decreased stability of the enzyme preparations was noticed when low enzyme loadings were used (e.g., with Celite as support; less than 1 mg enzyme/g). It was possible to avoid the activity loss by the addition of an additive which protects the enzyme during the immobilization. Proteins (such as albumin, gelatin, and casein) and poly(ethylene glycol) were effective additives whereas amino acids, monomeric carbohydrates, and polysaccharides had no effect. The amount of additive needed for stabilization was shown to depend on the structure of the support, more additive being required for a support with high porosity. The stabilizing effect was investigated in a series of glyceryl‐controlled‐pore glass (CPG) with varying specific surface areas (9.5–180 m2/g). The minimum addition of albumin, giving full stabilization, on the different supports correlated to a monolayer coverage of the surface, approximately 2–3 mg protein/m2. The effect of the additive was less pronounced when increasing amounts of enzyme were immobilized (5–40 mg enzyme/g Celite). The effect of the additives was studied using mandelonitrile lyase, but α‐chymotrypsin and lipase P were also shown to be stabilized. © 1993 John Wiley & Sons, Inc.
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| 9. |
- Westrin, BA, et al.
(författare)
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Diffusion in gels containing immobilized cells - A critical review
- 1991
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 1097-0290 .- 0006-3592. ; 38:5, s. 439-446
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Tidskriftsartikel (refereegranskat)abstract
- Eleven experimental investigations of diffusion in gels containing immobilized cells are reviewed. The experimental data, which quantitatively express the diffusion coefficient as a function of the cell concentration, are compared with a number of well-known equations developed for mass transfer in heterogeneous media. Based on this comparison, a procedure for the theoretical prediction of effective diffusion coefficients in cell-containing gels is recommended.
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