摘要:

AbstractA stochastic model is proposed to simulate the growth of anchorage dependent cells on a flat surface. The model, based on representing the cell shapes on the surface as external irregular polygons with the nuclei distributed as a set of Poisson points (producing a modified Voronoi tessellation of 2 space) and incorporating a distribution function to describe cell division of the perimeter cells of the colony, provides data not only on population dynamics but also on the patterns produced by clusters of cells in the colony. These patterns produced by the model are qualitatively similar to observations reported for some cell cultures. The periods of induction, rapid growth, and decreasing growth asymptoting to zero as confluence is reached are predicted by the model. Quantitative comparison with published experimental data for this is good. The specific growth rate computed for the period of rapid growth predicted by the model is dependent on the distribution function describing the cell division time. As the standard deviation of this increases, the specific growth rate decreases as with a consequent increase in time to achieve confluence. The removal of cells from the colony by shear forces or death is considered in the model. As the probability for removal increases, the cell density at confluence and specific growth rate decrease. The clusters of cells, patterns, in the colony are very sensitive to cell removal. By analyzing these patterns in experiments, an estimate of cell removal can be made. The areas covered by cells on a substrate are fractal patterns. The fractal dimension is always greater than 1 and is a function of the removal probability.

ISSN:0006-3592    

DOI:10.1002/bit.260360602

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

年代:1990

数据来源: WILEY

摘要:

AbstractA model flow field representative of Kolmogorov eddies in turbulence is proposed, and its two parameters are expressed in terms of the known bioreactor variables ε, the rate of turbulent power dissipation, and ν, the fluid kinematic viscosity. The trajectory through this flow field of a small sphere representing a cell is determined, and from that the time‐varying local shear rate can be found. This allows calculation of the shear stress at any point on the sphere's surface as it rotates in and moves through the model eddy. The maximum shear stress imposed on the cell by the surrounding turbulence has a range of 0.5–5 dyn/cm2, and can be estimated by 5.33ρ(εν)1/2. The shear stress has two major frequency components with ranges of 1–4 and 20–80 s−1; the higher frequency component is estimated by 0.678(ε/ν)1/2. The rotation of the direction of the shear stress vector at each point on the cell's surface is also discussed. Two ways in which external stresses might affect cell gro

ISSN:0006-3592    

DOI:10.1002/bit.260360603

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

年代:1990

数据来源: WILEY

摘要:

AbstractA protein separation scheme combining affinity or ion exchange sorption with hollow fiber cross‐flow filtration is described. Sorptive gel particles were loaded into the shell side of a hollow fiber membrane module. In the adsorption step, crude protein mixtures were passed through the lumen and permeating proteins passed through the membrane to bind on the gel particles in the shell. During elution, a buffer of adequate ionic strength to desorb the bound proteins was passed through the lumen and permeated through the shell. The eluant was then collected at the outlet to the shell of the hollow fiber module. The concept is illustrated by two examples: the purification of butyrylcholinesterase (EC 3.1.1.7) from raw horse serum using the affinity gel procainamide–Sepharose as the packing and the separation of carboxylesterase (EC 3.1.1.1) from beef liver homogenate using DEAE–Sephadex as the packing. The technique has the advantage of high volumetric throughputs typical of hollow fiber membrane modules as well as the high capacity characteristic of chromatographic packings. In addition, cross‐flow filtration of particulates, agglomerates, and debris in passing protein from lumen to shell side can help eliminate the need for extensive pretr

ISSN:0006-3592    

DOI:10.1002/bit.260360604

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

年代:1990

数据来源: WILEY

摘要:

AbstractA structured, segregated model is presented for an asynchronously growing population of genetically modifiedEscherichia colicells. A finite representation method was modified so that 272 cells could be used to represent a microbial population. The concept of a “limbo” compartment was introduced to allow random plasmid distribution to daughter cells upon cell division while restricting the number of computer cells included in the calculation. This scheme enabled us to predict plasmid instability and distribution of plasmid‐originated properties in a population without a priori determination of growth rates or probability of forming plasmid‐free cells from plasmid‐containing cells. Predictions of population behavior using a single‐cell model requires no adjustable parameters. The results comparing different induction strategies suggest that in continuous culture, there exists an optimum efficiency of partial induction that maximizes the long‐term productivity of the gene product due to plasmid stability. With the optimum efficiency of partial induction, constant induction appears to prove more stable than cycl

ISSN:0006-3592    

DOI:10.1002/bit.260360605

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

年代:1990

数据来源: WILEY

摘要:

AbstractA lipoprotein lipase (LPL) was made water insoluble by immobilizing onto the surface of polyacrolein (PAA) microspheres with and without oligoglycines as spacer. The activity of the immobilized LPL was found to remain high toward a small ester substrate,p‐nitrophenyl laurate (pNPL). The relative activity of the immobilized LPL without spacer decreased gradually with the decreasing surface concentration of the immobilized LPL on the PAA microsphere. On the contrary, the immobilized LPL with oligoglycine spacers gave an almost constant activity for the substrate hydrolysis within the surface concentration region studied and gave a much higher relative activity than that without any spacer. The Michaelis constantKmand the maximum reaction velocityVmwere estimated for the free and the immobilized LPL. The apparentKmwas larger for the immobilized LPL than for the free one, whileVmwas smaller for the immobilized LPL. The pH, thermal, and storage stabilities of the immobilized LPL were higher than those of the free one. The initial enzymatic activity of the immobilized LPL maintained almost unchanged without any leakage and inactivation of LPL when the batch enzyme reaction was performed repeatedly, indicating the excellent durability of the immobilized LP

ISSN:0006-3592    

DOI:10.1002/bit.260360606

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

年代:1990

数据来源: WILEY

摘要:

AbstractTrypsin either modified with polyethylene glycol or as a suspended powder was used to catalyze digestion of protein substrates in benzene in order to get insight into protein–protein interactions in water‐immiscible organic media. Depending on whether suspended or soluble trypsin was used, catalysis was found to proceed differently. In the first case, the amount of water in the reaction mixture (up to 1% v/v) appeared to be critical, and adsorption of water from the reaction medium by the protein substrate allowed it to behave as a hydrophilic support material comparable to that involved in immobilized enzymes. In the latter case, the presence of an additional nucleophile was a prerequisite for catalysis to proceed, and thus both water and nucleophile concentrations had some influence on trypsin activity. Phe–NH2was the most potent nucleophile for proteolysis catalyzed by polyethylene glycol‐modified trypsin in organic media containing 1–2% water (v/v). The organic solvent‐soluble enzyme was found to bind reversibly to the protein substrate as a function of both extent of hydration of the reaction medium and time of incubation. The overall results strongly suggested that modified trypsin catalyzed peptide bond hydrolysis at the protein substrate‐organic solvent interface. Peptide mapping of bovine insulin digest by reversed‐phase high‐performance liquid chromatography definitely showed that enzyme‐catalyzed proteolysis did occur in organic solvents with a concomitant and significant transp

ISSN:0006-3592    

DOI:10.1002/bit.260360607

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

年代:1990

数据来源: WILEY

摘要:

AbstractA previously developed immobilization technique involving latex coatings on solid particulate supports was investigated further for penicillin G production byPenicillium chrysogenum.Several modifications were found to decrease the germination lag time, including a higher spore concentration, a thinner latex layer, an increased latex porosity, and a decreased drying time. This approach enabled the development of immobilized mycelial pellets within 2–3 days from the onset of biocatalyst preparation and incubation.A continuous immobilized‐cell airlift bioreactor produced penicillin G in a series of runs in which the production phase lasted up to 30 days. The productivity of this system was 3–6 times greater than the productivity of the corresponding free‐cell shake flask ferme

ISSN:0006-3592    

DOI:10.1002/bit.260360608

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

年代:1990

数据来源: WILEY

摘要:

AbstractLipase fromPseudomonas fluorescensbiotype I was immobilized by adsorption of anion exchange resin using glutaraldehyde to enhance the adsorption. The activity yield of the immobilized lipase was very low (below 1%) when lipase activity was measured using emulsion substrate. The activity yield was 10–70% when lipase activity was measured using non‐emulsion substrate. Countercurrent reactors for hydrolysis of oil using non‐emulsion substrate were studied. A fluidized bed reactor was found to be superior to a fixed bed one since in a fixed bed reactor the separation rate of the two layers was slow and the flow rate of the reactor had to be slower than the separation rate. A fluidized bed reactor system equipped with settling compartments and stirring compartments was devised. Continuous lipolysis at 60 °C and continuous separation of oily product and water soluble product were performed. After continuous operation for more than 3 months, 70% of the initial activity of the immobilized lipase was observed at the end of the re

ISSN:0006-3592    

DOI:10.1002/bit.260360609

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe production of prourokinase (PUK) by a human kidney tumor cell line is studied in long term cultures. Cells are grown on microcarriers which are retained inside the reactor by sedimentation or with a spin filter. Two modes of operation are compared: feed harvest at an average medium exchange rate of 0.3 d−1and continuous perfusion at a higher dilution rate of 1.5 d−1. In the two systems a stable production of PUK has been maintained for more than 400 h. Kinetics of cellular growth, nutrient consumption, and metabolite and PUK excretion are similar. After an initial rapid growth period, one observes a 10‐fold reduction in all the cellular metabolic activities during the stationary phase. Continuous perfusion yields a higher cell density (7 × 106cells·mL−1) than feed harvest (3 × 106cells·mL−1), which results in a twofold increase in the reactor productivity. But higher final enzyme activities, about 250 ru·mL−1, are obtained in the feed harvest recovered medium than in the perfusion medium, 100–150 ru·mL−1. The cumulative medium consumption per mass of product is the same in the repeated batch and in the cont

ISSN:0006-3592    

DOI:10.1002/bit.260360610

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe effects of cell density as well as the concentration levels of glucose and glutamine on the specific respiration rate of a hybridoma cell line were investigated. The experimental oxygen consumption rate was found to be constant over a wide range of dissolved oxygen levels if the suspension medium contained glutamine. In glutamine‐free medium, however, the rate of oxygen consumption decreased slowly with time.In a stationary flask batch culture, the specific respiration rate decreased from about 7 to 2.9 μmol/min per 109cells as the cell density increased exponentially from 1 × 105to 1.2 × 106/mL. To isolate the effect of cell density, cells were re suspended in fresh culture medium so that nutrient concentrations were the same for all experiments. The specific respiration rate decreased with increasing cell density in the same manner as in the stationary flask culture, falling from 8 to 4 μmol/min per 109cells as the cell density increased from 105to 106cells/mL, then declining to 2 μmol/min per 109cells when the cell density reached 107cells/mL.Cells suspended in Hanks balanced sale solution (HBSS) were used to elucidate the effect of glucose and glutamine levels on respiration. The addition of glucose in concentrations of 0.25, 0.50, and 0.75 g/L had no observable effect on the specific oxygen uptake rate; however, a glucose concentration of 1 g/L reduced the uptake rate by 22%. Glutamine in a concentration of 0.30 g/L increased the specific respiration rate in HBSS containing 0 and 1 g/L glucose by approximate

ISSN:0006-3592    

DOI:10.1002/bit.260360611

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

年代:1990

数据来源: WILEY