摘要:

AbstractActivation energies of suspended and immobilized nitrifying bacteria were determined and compared to determine if diffusion limitation results in decreased sensitivity for temperature. The activation energy for the respiration activity of suspendedNitrosomonas europaeaandNitrobacter agiliswas found to be 86.4 and 58.4 kJ mol−1, respectively. The activation energy for oxygen diffusion in the support material, κ‐carrageenan, determined from the effect of temperature on the effective diffusion coefficient (D), was 17.2 kJ mol−1. Consequently, the apparent actvation energy of diffusion limited cells should be lower. It was indeed shown that due to the effect of diffusion limitation and to temperature effects on the Monod constantKs, the immobilized‐cell activity was less sensitive to temperature. The apparent activation energy for immobilizedNs. europaeawas between 28.6 and 94.2 kJ mol−1and for immobilizedNb. agilisbetween 1.4 and 72.9 kJ mol−1, depending on the oxygen concentration and temperature. © 1995 John Wi

ISSN:0006-3592    

DOI:10.1002/bit.260450102

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

年代:1995

数据来源: WILEY

摘要:

AbstractSubtilisin has been modified with polyethylene glycol (PEG) monomethacrylate (MW 8000) by reductive alkylation, and incorporated into polymethyl methacrylate durring free‐radical initiated polymerization. The activity and stability of the PEG‐modified enzymes have been determined in aqueous buffer and organic solvents. TheKmandVmaxvalues for unmodified, singly and doubly modified subtilisin were compared in these environments, and the half‐lives of both modified enzymes were remarkably high (up to 2 months). The protein‐containing polymer was analyzed for activity and polymer properties, and our results indicate that active subtilisin can be incorporated into polymethyl methacrylate during polymerization in organic solvents while retaining its activity and stability. © 1995 John Wiley&S

ISSN:0006-3592    

DOI:10.1002/bit.260450103

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

年代:1995

数据来源: WILEY

摘要:

AbstractIn the present study, the steady‐state cell density (X) of chemostat cultures of murine hybridoma was varied by the concentration of glucose and glutamine in culture medium and the dissolved oxygen partial pressure. Except at low glutamine and low oxygen levels, the specific death rate (kd) of the cultures was found to decrease with increasing dilution rate (D). However, the plot ofkdvs.X/Dyielded linear relation, which suggests that cell death was due to a non‐growth‐linked inhibitory product of the cells. Thekdvalue measured at low glutamine and low oxygen levels remained practically unchanged over a wide range ofDbetween 0.020 and 0.029 h−1. Thekdfor low oxygen cultures was always lower than the values obtained in low glucose and low glutamine cultures. A low‐molecular‐weight component of possibly less than 3000 MW was detected to be cell‐death‐inducing in the supernatant of exponentially growing cultures. It was neither lactate nor ammonium. The autoinhibitor was not cell‐line specific. © 1995 Jo

ISSN:0006-3592    

DOI:10.1002/bit.260450104

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

年代:1995

数据来源: WILEY

摘要:

AbstractSeveral surfactant‐coated enzymes have been prepared by coating lipases of various origins with a nonionic surfactant, glutamic acid dioleylester ribitol (2C18Δ9GE). Enzymatic interesterification of tripalmitin with oleic acid using the surfactant‐coated lipase was carried out in organic media. The surfactant‐coated lipases could effectively catalyze the interesterification of glycerides better than did the powder lipases. A suitable organic solvent was an aliphatic hydrocarbon such as isooctane. The enzymatic activity for the interesterification strongly depended on the origin of the lipase. The surfactant‐coated lipase prepared byMucor javanicusshowed the highest enzymatic activity for the interesterification of glycerides, although its powder lipase did not show enzymatic activity. Selective interesterification of glycerides could be performed by adjusting the concentration ratio of oleic acid to tripalmitin in isooctane. Di‐substituted glyceride could be selectively produced when the concentration ratio of carboxylic acid to glycerides was 7. © 1995 John Wile

ISSN:0006-3592    

DOI:10.1002/bit.260450105

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe activity of purifiedPseudomonas cepacialipase has been investigated in esterification reactions of various aliphatic alcohols with natural fatty acids. The reactions were carried out in microemulsions formed in isooctane by bis‐(2‐ethylhexyl)sulfosuccinate sodium salt (AOT). Kinetic studies showed that the reaction follows a ping‐pong bi–bi mechanism with inhibition by both substrates. The apparent kinetic parameters of the reaction were found to beKmoctanol= 310 mM,Kmlauric acid= 78 mM, andVmax= 250 μmol min−1mg−1. The same system was used for the synthesis of mono‐ and diglycerides from glycerol and lauric acid, which was successful at very lowwovalues. The catalytic behavior ofP. cepacialipase was also studied in esterification reactions performed in a nonionic microemulsion system formulated by tetraethyleneglycoldodecylether (C12E4). The optimum activity was found at aboutwo= 8. The apparent values ofVmax appandKm appfor octanol were calculated and found to be 100 μmol min−1mg−1and 76 mM, respectively. © 1995

ISSN:0006-3592    

DOI:10.1002/bit.260450106

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

年代:1995

数据来源: WILEY

摘要:

AbstractTo monitor gas reaction rates in animal cell culture at constant dissolved oxygen concentration (DO) and constant pH it was necessary to develop improved control methods. Decoupling of both controllrs was obtained by manipulation of molar fractions of oxygen and carbon dioxide in the gas phase. Two pairs of DO and pH controllers were designed and tested both in simulation and exprimental runs. The first controller pair was developed for headspace aeration only, whereas the second controller pair was designed for bubble aeration using a microsparger and flushing the headspace with helium. pH was controlled by a conventional discrete PID controller in its velocity form. For DO control two linear state space feedback controllers with parameter adaptation were established. In these controllers the oxygen uptake rate (OUR) was considered as a disturbance and was not included in the mathematical model. The feedback gain adaptation was based on the difference between the actual molar fraction of oxygen at time stepnand the initial molar fraction. This difference is related to OUR and was used to increase or decrease the state feedback controller gain (kandk1, respectively) in a slow manner. With these controllers it was possible to get an excellent online estimate of OUR. In the case of bubble aeration a simple gas phase mass balance was sufficient, whereas during the headspace aeration a liquid phase balance was required. It has been shown that determination of OUR using gas balance requires a significantly better controller performance compared to just keeping DO and pH within reasonable limits. © 1995 John Wiley&Sons, Inc

ISSN:0006-3592    

DOI:10.1002/bit.260450107

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

年代:1995

数据来源: WILEY

摘要:

AbstractDifferent methods for oxygen uptake rate (OUR) determinations in animal cell cultivation were investigated using a high quality mass spectrometer.Dynamic measurementshave considerable disadvantages because of disturbances of the growing cells by the necessary variations of dissolved oxygen concentration. Only infrequent discrete measurements are possible using this method.Stationary liquid phase balanceyielded better results with much higher frequency. Gas phase balancing has the advantage of not requiring dissolved oxygen measurement and knowledge ofKLa, both of them are easily biased. It was found that simple gas phase balancing is either very inaccurate (error larger than expected signal) or very slow, with gas phase residence times of several hours. Therefore, anew method of aerationwas designed. Oxygen and CO2transfer are mainly achieved via sparging. The gas released to the headspace is diluted with a roughly 100‐fold stream of an inert gas (helium). Through this dilution, gas ratios are not changed for O2, CO2, Ar, and N2. The measurement of lower concentrations (parts per million and below) is easy using mass spectrometry with a secondary electron multiplier. With this new method an excellent accuracy and sufficient speed of analysis were obtained. All these on‐line methods for OUR measurement were tested during the cultivation of animal cells. The new method allowed better study of the kinetics of animal cell cultures as was shown with a hybridoma cell line (HFN 7.1, ATCC CRL 1606) producing monoclonal antibodies against human fibronectin. With the aid of these methods it was possible to find a correlation between a rapid decrease in oxygen uptake rate (OUR) and glutamine concentration. The sudden decrease in OUR can be attributed to glutamine depletion. This provided a basis for the controlled addition of glutamine to reduce the formation of ammonia produced by hydrolysis. This control method based on OUR measurement resulted in increased cell concentration and threefold higher product concentration. © 1995 John Wiley&Sons,

ISSN:0006-3592    

DOI:10.1002/bit.260450108

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe concentration of diatomic hydrogen in the liquid phase of an anaerobic digester was used to determine the onset of digester failure induced by substrate overloading. The construction of an inexpensive probe to measure dissolved hydrogen, having a partial pressure detection limit of 30 Pa, is described. An increase in the partial pressure of dissolved hydrogen, from less than 30 Pa to 400 Pa, was observed when theD‐glucose concentration in a laboratory‐scaled digester was increased rapidly to 10 mM. However, when the digester was gradually overloaded, an increase in the dissolved‐hydrogen partial pressure was not observed until after the digester failed. The accumulation of volatile fatty acids and digester failure were observed at dissolved‐hydrogen partial pressures below 30 Pa. © 1995 John Wiley&S

ISSN:0006-3592    

DOI:10.1002/bit.260450109

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

年代:1995

数据来源: WILEY

摘要:

AbstractStoichiometrically based flux balance models provide a method to quantify the metabolic pathway fluxes within a living cell. Predictions of flux balance models are expected to have applications in pathway engineering as well as in bioprocess design and control. These models utilize optimality principles applied to metabolic pathway stoichiometry along with the metabolic requirements for growth to determine the flux distribution in a metabolic network. A flux balance model has been developed forEscherichia coliW3110 using five experimentally determined strain‐specific parameters. In this report, we determine the sensitivity of the predictions of the flux balance model to these five strain‐specific parameters. Model predictions are shown to be sensitive to the two parameters describing metabolic capacity, while they are relatively insensitive to the three parameters that describe the metabolic requirements for growth. Thus, when stoichiometrically based models are formulated for additional strains one needs to measure the metabolic capacity (maximum rates of nutrient and oxygen utilization) accurately. Determination of metabolic capacity from batch experiments is relatively easy to perform. On the other hand, the harder to determine maintenance parameters need not be as accurately determined. © 1995 John Wiley&Sons,

ISSN:0006-3592    

DOI:10.1002/bit.260450110

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe broth rheologies and morphologies of three actinomycetes (Saccharopolyspora erythraea, Actinomadura roseorufa, andStreptomyces rimosus) in submerged culture have been examined. The rheology of all the broths became pseudoplastic as soon as significant growth occurred with the power law index,n, falling to 0.20 to 0.25. The consistency index,K, rose with biomass concentration although in some instances it fell later in the fermentation. The mean main hyphal lengths of all cultures were in the range, 15 to 25 μm, and did not alter greatly even when large changes inKwere occurring. © 1995 John Wiley&Sons, In

ISSN:0006-3592    

DOI:10.1002/bit.260450111

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

年代:1995

数据来源: WILEY