摘要:

AbstractThermodynamic and kinetic calculations were performed in a model of mixed substrate metabolism. The model simulates the catabolic breakdown of a first substrate, glucose (S1), in the presence of a second substrate, formate (S2), which acts as an additional source of free energy. The principal results obtained with different relative rates of uptake ofS2allow to predict and interpret the following experimental observations: (1) the existence of increased ATP yields by mixed substrate utilization with a maximum ATP yield and optimum input (or molar) ratio for both substrates; (2) a greater assimilation ofS1which may be interpreted as a decreasing fraction of energy required for assimilation; (3) a decrease in ATP yields due to increasing energy demand for transport; (4) an increased assimilation of the carbon source (S1) as a function of increasing inputs of the additional energy source; (5) thermodynamic efficiency (η) defined as the ratio between the output power of ATP synthesis and the input catabolic power, increases forS2/S1ratios ranging between 0.08 and 2 while for ratios higher than two a slight decrease of η was noticed; and (6) the observed maximum in ATP yield for optimum molar ratio of the two substrates corresponds to high η predicting that higher biomass yields may be obtained through a variable, high, η by chanelling fluxes through catabolic pathways with different ATP yields. During oscillatory behavior, maxima in fluxes were almost coincident with maxima in forces. Thus, the pattern of dissipation was not so advantageous as in the single substrate model under starvation conditi

ISSN:0006-3592    

DOI:10.1002/bit.260370302

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe oxygen transfer characteristics of a 20‐mm O.D. airlift contactor fitted with an oxygen microelectrode were determined by steady‐state sulfite oxidation measurements. The volumetric mass transfer coefficientkLawas proportional to sparging power input per unit volume raised to a power which varied from 0.41 in water (coalescing bubbles) to 0.76 in NaCl solutions (noncoalescing bubbles). The highest observedkLavalue was 0.012s−1which is sufficient to aerateEscherichia coliin an NMR spectrometer at moderate to high cell densities, depending on the physiological state of the

ISSN:0006-3592    

DOI:10.1002/bit.260370303

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

年代:1991

数据来源: WILEY

摘要:

AbstractAn initial structured unsegregated kinetic model describing monoclonal antibody synthesis by a murine hybridoma cell line (9.2.27) grown in 1 liter batch cultures is described. The model is based on the intracellular balances of the heavy and light chain coding mRNAs, the intracellular balances of heavy and light chains and the description of the kinetics of heavy and light chain assembly. Model parameters were varied with specific growth rate in order to account for changes in the rates of antibody synthesis and secretion with entrance of the cells from the exponential into the stationary phase of growth. The parameters were varied based. on experimental data obtained in our laboratory on the variation of total cellular RNA content and the half‐lives of heavy (H) and light (L) chain mRNAs with specific growth rate, and data from other investigators on immunoglobulin synthesis and secretion. The model successfully predicts the experimentally observed decrease in the intracellular heavy and light chain mRNA levels with entrance of 9.2.27 cells from the exponential into the stationary phase of growth, as well as the extracellular accumulation of antibody (IgG2a) during batch cultur

ISSN:0006-3592    

DOI:10.1002/bit.260370304

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

年代:1991

数据来源: WILEY

摘要:

AbstractAn approach is presented for the stable covalent immobilization of proteins with a high retention of biological activity. First, chemical modification studies were used to establish enzyme structural and functional properties relevant to the covalent immobilization of an enzyme to agarose based supports. Heparinase was used as a model enzyme in this set of studies. Amine modifications result in 75–100% activity loss, but the effect is moderated by a reduction in the degree of derivatization.N‐hydroxysuccinimide, 1,1,1‐trifluoroethanesulfonic acid, and epoxide activated agarose were utilized to determine the effect of amine reactive supports on immobilized enzyme activity retention. Cysteine modifications resulted in 25–50% loss in activity, but free cysteines were inaccessible to either immobilized bromoacetyl orp‐chloromercuribenzoyl groups. Amine reactive coupling chemistries were therefore utilized for the covalent immobilization of heparinase. Second, to ensure maximal stability of the immobile protein–support linkage, the identification and subsequent elimination of the principal sources of protein detachment were systematically investigated. By using high‐performance liquid chromatography (HPLC), electrophoresis, and radiolabeling techniques, the relative contributions of four potential detachment mechanisms—support degradation, proteolytic degradation, desorption of noncovalently bound protein, and bond solvolysis—were quantified. The mechanisms of lysozyme, bovine serum albumin, and heparinase leakage fromN‐hydroxysuccinimide or 1,1,1‐trifluoroethanesulfonic acid activated agarose were elucidated. By use of stringent postimmobilization support wash procedures, noncovalently bound protein loss. An effective postimmobilization washing procedure is presented for the removal of adsorbed protein and the complete elimination of imm

ISSN:0006-3592    

DOI:10.1002/bit.260370305

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe insect cell (Sf9)‐baculovirus (AcNPV) expression system was employed for the synthesis of β‐galactosidase, a model heterologous protein. In the recombinant virus studied, thelacZgene is fused to a portion of the polyhedrin structural gene and is under the control of the polyhedrin promoter. The effect of the multiplicity of infection (MOI) on product titer was determined by infecting cells with MOI values ranging from 0 to 100 and monitoring the production of β‐galactosidase with time. The relationship between final product titer and MOI was dependent on the growth phase of the cells prior to infection. The final product titer from cells infected in the early exponential phase was relatively independent of MOI. For cells infected in late‐exponential phase there was a logarithmic relationship between the final β‐galactosidase titer and the MOI used, with the highest MOI studied resulting in greatest protein synthesis. The synthesis and degradation rates of β‐galactosidase were investigated by a pulse‐chase technique usingL‐[35S]‐methionine. At 24 h postinfection, the degradation rate is of the same order of magnitude as the synthesis rate. However, the synthesis rate of β‐galactosidase increases dramatically at 96 h postinfection. During this later period, the degradation rate is negligible. Although degradation of recombinant protein occurs in this system, degradation activity declines as infection proceeds and is insignificant late in intention when recombinant prote

ISSN:0006-3592    

DOI:10.1002/bit.260370306

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

年代:1991

数据来源: WILEY

摘要:

AbstractDebarking wastewaters of the forest industry contain high concentrations of tannins that are inhibitory to methane bacteria. The tannins can be polymerized to nontoxic colored compounds by the applications of an autoxidation pretreatment, enabling the anaerobic treatment of easily biodegradable components in the wastewater. The continuous anaerobic treatment of untreated and autoxidized pine bark extract was studied in laboratory‐scale columns packed with a granular sludge bed. The autoxidation doubled the conversion efficiency of bark extract COD to methane (from 19 to 40%). After 5 months of operation, anaerobic treatment of the autoxidized extracts was feasible at high influent concentrations (14 g COD/L) and loading rates (26 g biodegradable COD/L · d) with 98% elimination of the biodegradable fraction. The detoxification pretreatment polymerized the toxic tannins to poorly biodegradable high molecular weight tannins and humic compounds which were not eliminated during anaerobic treatment. Although the original tannins of the untreated extract were eliminated by 60%, they were not biodegraded to volatile fatty acids and methane but instead were transformed to phenolic degradation intermediates (phenol,p‐cresol, 3‐phenyl‐propionate, and carboxycyclohexane). Therefore, the autoxidation pretreatment did not decrease the content of readily biodegradable substrates which accounted for 53% of the extract COD. The recalcitrant COD expected in the effluents of reactors treating autoxidized debarking waste‐water can be effectively separated by calcium precipitation prior to anaerobic

ISSN:0006-3592    

DOI:10.1002/bit.260370307

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

年代:1991

数据来源: WILEY

摘要:

AbstractProcess improvement of the production of cyclosporin A (Cy A), a powerful immunosuppressive fungal metabolite, has been undertaken by analyzing suspended and immobilized cell cultures in parallel. Conidiospores of the producer microorganism,Tolypocladium inflatum, were entrapped into porous celite particles. Easier germination of the entrapped spores and more active growth of the immobilized cells were manifested when compared with free cell cultures initiated with spores or with mycelial inocula. Significant differences in precursor flow between the immobilized and free cell systems were evident when the effects ofL‐valine (a constituent amino acid of the Cy A molecule) on Cy A biosynthesis were compared in the two systems. For the freely suspended cells,L‐valine supplemented early in the fermentation served as a possible precursor or stimulator of Cy A biosynthesis. A significant increase in specific production and Cy A yield on carbon source was observed in this system relative to suspended cultures supplemented withL‐valine during or after exponential growth. In contrast to the free cell cultures, the addition ofL‐valine during the initial stage of immobilized cell growth had a negative effect on Cy A production but resulted in somewhat increased cell growth. This suggests an incompatibility between primary and secondary metabolic networks involved in Cy A biosynthesis in the immobilized state upon external addition of the ami

ISSN:0006-3592    

DOI:10.1002/bit.260370308

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe recovery of copper from synthetic aqueous media circulating in a loop fluidized bed reactor operated batchwise was investigated by using the following biopolymer systems: (1) a viscous solution of sodium alginate (from kelp) dispensed directly into the reactor fluid containing dissolved copper (sulfate salt) at initial concentrations of 60–200 ppm, (2) partially coagulated calcium alginate spheres for absorbing dissolved copper at initial concentrations of 10–40 ppm, and (3) a mixture of green algaeMicrocystisand sodium alginate dispensed directly into the reactor fluid. The recovery of copper and cobalt, a strategic metal, from cobalt ore leachate was achieved by a two‐step approach: direct dispensing of sodium alginate to absorb the bulk of metals followed by the addition of partially coagulated calcium alginate spheres to “polish” the leachate. Metal binding capacity and conditional stability constant of each biopolymer system as well as the effective diffusivity of cupric ion in the matrix of biopolymer gels are

ISSN:0006-3592    

DOI:10.1002/bit.260370309

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

年代:1991

数据来源: WILEY

摘要:

AbstractWhen purified xylanases fromTrichoderma harzianumE58 or from a clone ofBacillus circulanswere incubated with various low‐yield wood pulps, little of the original enzyme activity could be detected in the filtrate at the end of the reaction. Partial bleaching of the pulps prior to enzymatic treatment generally resulted in an increased recovery of the xylanase activity. It appears that both nonspecific adsorption and soluble inhibitors may be responsible for the loss of much of the xylanase activity. However, xylanases fromAureobasidium pullulansandSchizophyllum communewere not as inhibited by the pulps, and the activity of the latter enzyme actually increased after incubation with several high‐yield pulps. Although a lignin preparation from spent sulfite liquor at a concentration of 0.06 mg/mL could inhibit the xylanase activity ofT. harzianumandB. circulansby 65% and 50%, respectively, xylanases fromThermoascus aurantiacus,S. commune, andA. pullulanswere activated at similar lignin concentrations. At higher concentrations these latter xylanases were also inhibited. Water‐soluble lignins extracted from a variety of pulps and used at a lignin concentration of 2.5 μg/mL resulted in inhibition of more than 65% of the original activity of the xylanase fromT. harzianum.Kinetic studies showed that lignin from spent sulfite liquor resulted in noncompetitive inhibition of this

ISSN:0006-3592    

DOI:10.1002/bit.260370310

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe capability of binding enzymes adsorptively to unmodified and silanized silica and glass as well as modified polystyrene carriers was studied for α‐amylase, β‐amylase, and α‐chymotrypsin. In most cases a high percentage of protein was bound very firmly under considerable loss of activity. The leakage of protein from the carriers was studied by measuring the intrinsic protein fluorescence on β‐amylase adsorptively bound to aminopropyl silica, aminomethyl, and hexadecylaminomethyl polystyrene. It was compared with the leakage of β‐amylase covalently bound to the same carriers via glutaraldehyde, trichloro‐triazine, or benzoquinone. In the absence and in the presence of substrate, at 25 and at 60°C, the leakage rates of the adsorptively bound enzymes were not higher than in the covalently bound systems. The poorest binding stability was found in benzoquinone‐coupled β‐amylase derivatives. It is even reduced at higher temperatures, whereas the temperature did not show any remarkable influence on the leakage of the other derivatives. In adsorptively as well as in all the covalently bound systems, the presence of substrate did not promo

ISSN:0006-3592    

DOI:10.1002/bit.260370311

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

年代:1991

数据来源: WILEY