摘要:

AbstractAn anion exchange method for lactic acid recovered from lactic acid–glucose solution in an ion‐exchange membrane‐based extractive fermentation system was examined. The exchange isotherms of anion exchange resins for lactic acid recovered were measured batchwise, and the exchange–desorption kinetics of lactic acid passing through the exchange column was investigated. The determined typical breakthrough and elution curves were measured and simulated by conventional mode. The mass transfer coefficients were identified by numberical method. The effects of the velocity of the fluid on the dynamics were studied. Aqueous NaOH solution was found to be the best solvent for elution. An experiment on anioun exchange from clarified lactic acid fermentation broth was carried out to obtain knowledge of the performance of the ion exchange system from a borth. The ion‐exchange mass‐transfer coefficient and efficiency from the fermentation broth is found to be lower when compared with aqueous solutions of pure lactic acid. The results show that the separation method with anion exchange resins may be used in the production of lactic acid by fermentation.© 1995 John Wil

ISSN:0006-3592    

DOI:10.1002/bit.260470102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractEscherichia coliproduces lactate and acetate in significant amounts during both aerobic and anaerobic glycolysis. A model describing the mechanism of protein mediated lactate transport has previously bee proposed. A simple theoretical analysis here indicates that the proposed model would be drain cellular energy resources by catalytically dissipating the proton‐motive force. An experimental analysis of lactate and acetate transport employ nuclear magnetic resonance (NMR) spectroscopy to measure the relative concentration of these end products on the two sides of the cytoplasmic membrane of anaerobically glycolyzing cells. Comparison of measured concentration rations to those expected at equilibrium for various transport modes indicates that acetate is a classical uncoupling agent, permeating the membrane oat comparable rates in the dissociated and undissociated forms. The lactate concentration ratio changes market markedly after an initial period of sustained glycolysis. This change is most readily explained as resulting from a lactate transport system that responds to an indicator of glycolytic activity. The data further indicates that lactate permeates the membrane in both dissociated and undissociated forms. Both acids, then are capable of catalytically dissipating the proton‐motives force. © 1995 John Wiley&Sons,

ISSN:0006-3592    

DOI:10.1002/bit.260470103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractA polymerized liposome (PLS) was prepared using a synthesized phospholipid with a diacetylene moiety in the hydrophobic chain and an amino group in the hydrophilic head. The PLS was used as a novel ligand carrier for affinity precipitation of proteins because it showed a reversibly precipitable property on salt addition and removal. Soybean trypsin inhibitor (STI) was easily immobilized on the PLS by a one‐step carbodiimide reaction. The PLS showed no nonspecific adsoprtion of proteins. It had a large ligand coupling capacity, and then a large adsorption capacity for trypsin after STI immobilization. The PLS with immpbilized STI was recycled three times for the purification of trypsin from a crude pancreatic extract. Although the degree of purification was compromised by the impurity of the STI employed, in each run the purification factor reached about 6 and more than 80% of trypsin activity was recovered. The results indicated that the PLS was a potential ligand carrier for affinity precipitation of proteins. © 1995 John Wiley&Sons, I

ISSN:0006-3592    

DOI:10.1002/bit.260470104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractFundamental kinetic studies on the reduction of nitrate, nitrite, and their mixtures were performed with a strain ofPseudomonas denitrificans(ATCC 13867). Methanol served as the carbon source and was supplied in excess (2:1 mole ratio relative to nitrate and/or nitrite). Nitrate and nitrite served as terminal electron acceptors as well as sources of nitrogen for biomass synthesis. The results were explained under the assumption that respiration is a growth‐associated process. It was found that the sequence of complete reduction of nitrate to nitrogen gas is via nitrite and nitrous oxide.It was found that the specific growth rate of the biomass on either nitrate or nitrite follows Andrews inhibitory kinetics and nitrite is more inhibitory than nitrate. It was also found that the culture has severe maintenance requirements which can be described by Herbert's model, i.e., by self‐oxidation of portions of the biomass. The specific maintenance rates at 30°C and pH 7.1 were found to be equal to about 28% of the maximum specific growth rate on nitrate and 23% of the maximum specific growth rate on nitrite. Nitrate and nitrite were found to be involved in a cross‐inhibitory noncompetitive kinetic interaction. The extent of this interaction is negligible when the presence of nitrite is low but is considerable when nitrite is present at levels above 15 mg/L.Studies on the effect of temperature have shown that the culture cannot grow at temperatures above 40°C. The optimal temperature for nitrate or nitrite reduction was found to be about 38°C. Using an Arrhenius expression to describe the effect of temperature on the specific growth rates, it was found that the activation energy for the use of nitrate by the culture is 8.6 kcal/mol and 7.21 kcal/mol for nitrite. Arrhenius‐type expressions were also used in describing the effect of temperature on each of the parameters appearing in the specific growth rate expressions. Studies on the effect of pH at 30°C have shown that the culture reduces nitrate optimally at a pH between 7.4 and 7.6, and nitrite at a pH between 7.2 and 7.3. © 1995 John Wil

ISSN:0006-3592    

DOI:10.1002/bit.260470105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractWith glucose‐limited continuous cultures ofPetunia hybridasix steady states were obtained at specific growth rates varying from 0.0035 to 0.012 h−1(corresponding with culture residence times varying from 285 to 85 h). The macromolecular and the elemental biomass composition which were determined in four steady states showed no major differences over the range of growth rates examined. During all six steady states specific subtrate and oxygen consumption as well as biomass and extracellular product formation rates were monitored. Moreover the specific activities of the mitochondrial cytochrome and alternative pathway were determined and used to estimate specific adenosine triphosphate (ATP) production rates. Data thus obtained were used in the determination of maintenance and true growth yield parameters. For the maintenance on glucose and ATP values of 0.0070 C‐mol/C‐mol/h and 0.034 mol/C‐mol/h were obtained, respectively. True yields of biomass on glucose and ATP were 0.50 C‐mol/C‐mol and 0.28 C‐mol/mol, respectively. © 1995 John

ISSN:0006-3592    

DOI:10.1002/bit.260470106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractThe link between the growth stage and the production stage in a two‐stage batch process was investigated using (filtered) inocula from different periods of the stationary phase of the growth cycle. In the production stage, ajmalicine production byCatharanthusroseus in a 3‐L stirred tank reactor was induced with a high glucose concentration (80 g/L). Ajmalicine production in cultures started with cells from the late stationary phase was five times higher than in cultures started with cells from the early stationary phase. After transfer to the production stage, cells from the early stationary phase showed a transient increase in respiration and enzyme induction, followed by culture browning. In contrast, cells in the late stationary phase showed a typical induction pattern: constant respiration, and permanent enzyme induction. A striking similarity between the geraniol‐10‐hydroxylase (G10H) activity and the ajmalicine accumulation profile could be observed in all cultures, suggesting that G 10H regulated ajmalicine production in this investigation. The intracellular nitrate concentration was significantly higher in the inoculum showing a high ajmalicine production than in the inoculum with a low production. Consequently, nitrate may act as a marker for the start of the production stage: as soon as the nitrate is depleted in the growth medium secondary metabolism can be induced. © 1995 John Wiley&S

ISSN:0006-3592    

DOI:10.1002/bit.260470107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractThe performance of lipases fromCandida rugosaand wheat germ have been investigated in three reaction media using three acetate hydrolyses as model reactions (ethyl acetate, allyl acetate, and prenyl acetate). The effect of substrate properties and water content were studied for each system (organic solvent, biphasic system, and reverse micelles). Not unexpectedly, the effect of water content is distinct for each system, and the optimal water content for enzyme activity is not always the same as that for productivity. A theoretical model has been used to simulate and predict enzyme performance in reverse micelles, and a proposed partitioning model for biphasic systems agrees well with experimental results. While the highest activities observed were in the micellar system, productivity in microemulsions is limited by low enzyme concentrations. Biphasic systems, however, support relatively good activity and productivity. The addition of water to dry organic solvents, combined with the dispersion of lyophilized enzyme powders in the solvent, resulted in significant enzyme aggregation, which not surprisingly limits the applicability of the “anhydrous” enzyme suspension approach. © 1995 John Wiley&Sons,

ISSN:0006-3592    

DOI:10.1002/bit.260470108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractWhen it is assumed that organic solvents do not interfere with the binding process nor with the catalytic mechanism, the contribution of substrate‐solvent interactions to enzyme kinetics can be accounted for by just replacing substrate concentrations in the equations by thermodynamic activities. It appears from the transformation that only the affinity parameters (Km,Ksp) are affected by this. Thus, in theory, the values of these corrected, intrinsic parameters (K mint,k spint) and the maximal rate (V1) should be equal for all media. This was tested for hydrolysis, transesterification, and esterification reactions catalyzed by pig pancreas lipase andPseudomonas cepacialipase in various organic solvents. Correction was carried out via experimentally determined activity coefficients for the substrates in these solvents or, if not feasible, from values in data bases. However, although the kinetic performances of each enzyme in the solvents became much more similar after correction, differences still remained. Analysis of the enzyme suspensions revealed massive particles, which explains the low activity of enzymes in organic solvents. However, no correlation was found between estimates of the amount of catalytically available enzyme (present at the surface of suspended particles or immobilized on beads) and the maximal rates observed. Moreover, the solvents had similar effects on the intrinsic parameters of suspended and immobilized enzyme. The possible causes for the effects of the solvents on the catalytic performance of the enzymes, remaining after correction for solvent‐substrate interactions and the amount of participating enzyme, are discussed with respect to the premises on which the correction method is based. © 1995 John Wiley&S

ISSN:0006-3592    

DOI:10.1002/bit.260470109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractThis article reports a novel nondisruptive technique for measuring the thicknesses of membrane‐attached biofilms in situ, using a single tube extractive membrane bioreactor (STEMB). The biodegradation of a toxic volatile organic compound (VOC) (1,2‐dichloroethane [DCE]) byXanthobacter autotrophicusGJ10 has been used as a model system to develop the technique. The results give information on the biomass‐silicone rubber attachment phenomena, and on the development over time of biofilms growing on the silicone membrane, without disrupting operation. Experimental results are presented showing the evolution over time of biofilm thickness, and also the density of biofilms for four experimental runs. The hydrodynamic conditions on the biomedium side of the membrane were found to influence the initial attachment phenomena and subsequent biofilm growth. © 1995 John Wiley&Son

ISSN:0006-3592    

DOI:10.1002/bit.260470110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractThis article reports a study of the performance of membrane‐attached biofilms grown in a single tube extractive membrane bioreactor (STEMS) used for the treatment of a synthetic wastewater containing a toxic VOC (1,2‐dichloroethane [DCE]). Mass balances show that complete mineralization of DCE was achieved, and that the biofilms were effective in reducing air stripping to negligible levels. Experimental results are presented showing the evolution over time of biofilm thickness and its influence on the flux of DCE across the membrane. It has been found that a trade‐off exists between the positive influence of biofilms in reducing air‐stripping of DCE, and the negative influence of biofilms in reducing DCE flux across the membrane. These considerations lead to an optimal biofilm thickness in the region of 200 to 400 μm being recommended for this system. © 1995 John Wiley&

ISSN:0006-3592    

DOI:10.1002/bit.260470111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY