摘要:

AbstractThe production of ethanol from carob pod extract by free and immobilizedSaccharomyces cerevisiaecells in batch and fed‐batch culture was investigated. Fed‐batch culture proved to be a better fermentation system for the production of ethanol than batch culture. In fed‐batch culture, both free and immobilizedS. cerevisiaecells gave the same maximum concentration (62 g/L) of final ethanol at an initial sugar concentration of 300 g/L andF= 167 mL/h. The maximum ethanol productivity (4.4 g/L h) was obtained with both free and immobilized cells at a substrate concentration of 300 g/L andF= 334 mL/h. In repeated fed‐batch culture, immobilizedS. cerevisiaecells gave a higher overall ethanol concentration compared with the free cells. The immobilizedS. cerevisiaecells in Ca‐alginate beads retained their ability to produce ethanol for 10 days. © 1994 John Wiley

ISSN:0006-3592    

DOI:10.1002/bit.260430302

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

年代:1994

数据来源: WILEY

摘要:

AbstractA new scale‐up concept based upon mixing models for bioreactors equipped with Rushton turbines using the tanks‐in‐series concept is presented. The physical mixing model includes four adjustable parameters, i.e., radial and axial circulation time, number of ideally mixed elements in one cascade, and the volume of the ideally mixed turbine region. The values of the model parameters were adjusted with the application of a modified Monte‐Carlo optimization method, which fitted the simulated response function to the experimental curve. The number of cascade elements turned out to be constant (N= 4). The model parameter radial circulation time is in good agreement with the one obtained by the pumping capacity. In case of remaining parameters a first or second order formal equation was developed, including four operational parameters (stirring and aeration intensity, scale, viscosity). This concept can be extended to several other types of bioreactors as well, and it seems to be a suitable tool to compare the bioprocess performance of different types of bioreactors. © 1994 John Wiley&S

ISSN:0006-3592    

DOI:10.1002/bit.260430303

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

年代:1994

数据来源: WILEY

摘要:

AbstractA new composite membrane was designed and studied for permselectivity of various molecular weight proteins. The membrane is composed of a porous substrate membrane [Durapore; poly(vinylidene fluoride)] coated with a thin dense layer of regenerated cellulose. This composite membrane was fabricated by spin coating a cellulose acetate solution onto the membrane, followed by alkaline hydrolysis of the cellulose acetate coating to regenerate cellulose. The coated layer was physically characterized by scanning electron microscopy (SEM) and infrared (IR) spectroscopy. In addition, the water uptake into and permeation properties of macromolecules across the coated and uncoated membranes were studied. A typical composite membrane coating was 0.8 ± 0.2 μm thick, resulting in a molecular weight cutoff of approximately 40,000 daltons. This composite membrane also demonstrated negligible diffusional lag time for permeants, due to the diffusional barrier. © 1994 John Wiley&Sons, I

ISSN:0006-3592    

DOI:10.1002/bit.260430304

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

年代:1994

数据来源: WILEY

摘要:

AbstractElectron paramagnetic resonance spectroscopy is used to characterize the active site dynamics of α‐chymotrypsin solubilized in reversed micelles. Of particular interest is the behavior of the enzyme when the micellar system is subjected to enhanced gas pressures and low temperatures. At specific thermodynamic conditions, clathrate hydrates from from the intramicellar water, reducing the micelle size and water content. Also, beyond a critical pressure, micellar instbility results. The EPR spectra under these conditions indicate that the rotational correlation times increase appreciably only when the water‐to‐surfactant molar ratio,W0, is reduced to values lower than 10. The EPR characterization also reveals a remarkable resilience of the enzyme when subjected to pressure‐induced changes; when returned to ambient conditions, activity and active site dynamics are fully restored. © 1994 John Wiley&

ISSN:0006-3592    

DOI:10.1002/bit.260430305

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

年代:1994

数据来源: WILEY

摘要:

AbstractAn extracellular proteinase fromThermusstrain Rt41A was immobilized to controlled pore glass (CPG) beads. The properties of the free and CPG‐immobilized enzymes were compared using both a large (azocasein) and a small (peptidase) substrate. The specific activity of the immobilized proteinase was 5284 azoU/mg with azocasein and 144 sucU/mg for SucAAPFpNA. The percentage recovery of enzyme activity was unaffected by pore size when it was immobilized at a fixed level of activity/g of beads, whereas it increased with increasing pore size when added at a fixed level/m2of support. Saturation of the CPG beads was observed at 540 azoU/m2of 105‐nm beads. Lower levels (50 azoU/m2of 50‐nm beads) were used in characterization experiments. The pH optimum of the immobilized Rt41A proteinase was 8.0 for azocasein and 9.5 for SucAAPFpNA, compared with the free proteinase which was 10.5 for both substrates. The immobilized enzyme retained 65% of its maximum activity against azocasein at pH 12, whereas the free proteinase retained less than 10% under the same conditions. Stability at 80°C increased on immobilization at all pH values between 5 and 11, the greatest increase in half‐life being approximately 12‐fold at pH 7.0. Temperature–activity profiles for both the free and immobilized enzymes were similar for both substrates. The stability of the immobilized proteinase, however, was higher than that of the free enzyme in the absence and presence of CaCl2. Overall, the results show that low levels of calcium (10 μM) protect against thermal denaturation, but that high calcium or immobilization are required to protect against autolysis. © 1994 John W

ISSN:0006-3592    

DOI:10.1002/bit.260430306

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

年代:1994

数据来源: WILEY

摘要:

AbstractLipases fromCandida cyclindracea(L‐1754) and wheat germ (L‐3001) have been used to hydrolyze esters to their corresponding alcohols and acids in reverse micelles. Alcohol dehydrogenase from baker's yeast (YADH) was subsequently used to reduce the alcohol products to aldehydes. Cofactor recycling in the redox reaction was achieved using a sacrificial cosubstrate, as described previously. Four surfactants (sodium dioctylsulfosuccinate, Nonidet P‐40 with Triton X‐35, polyoxyethylene, 10‐cetyl‐ether, polyoxyethylene sorbitan trioleate) were employed to determine the effect of amphiphile on ester hydrolysis and redox reaction rates separately. The effect of type of organic solvent,W0[(water]/[surfactant)], and substrate concentration on separte enzyme activity were also investigated. A brief investigation of a single phase, two‐step reaction catalyzed by the combination of lipase and YADH in reverse micelles is also reported. The activities of the enzymes are significantly different when used together instead of independently. © 1994 John W

ISSN:0006-3592    

DOI:10.1002/bit.260430307

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

年代:1994

数据来源: WILEY

摘要:

AbstractA theoretical method for comparing the performance of rival models of bacterial genetic regulation is presented. The particukar difficulties involved in describing the regulated synthesis of proteins that strongly influence cell growth are identiied, and the method is specifically designed to treat such cases. The method employs a mathematical description of intrinsic perturbations occurring during exponential growth to test the performance of regulatory models. Specific models of transcriptional and translational regulation are inserted into a general gene‐expression framework in order to determine their control responses. Applying thhis approach to examine the regulation of RNA polymerase synthesis inEschericia coliprovides support for the hypothesis that rpoB translation is regulated by cooperative binding of multiple RNA polymerase molecules to the mRNA. The framework is of a sufficiently general form that the method can be used to study mechanisms involved in controlling synthesis of any bacterial protein. © 1994 John Wiley&Sons, I

ISSN:0006-3592    

DOI:10.1002/bit.260430308

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

年代:1994

数据来源: WILEY

摘要:

AbstractMethanococcus jannaschii, an extremely thermophilic methanogen isolated from a deep‐sea hydrothermal vent, was grown at 80°C in continuous culture on a mineral salts medium gassed with H2and CO2at three different flow rates. The maximum specific growth rate was 0.56 h−1, and the maximum specific methane productivity was 0.32 (mol g−1h−1). Uncoupling of growth and methane production was evidenced by an increase in teh non‐growth‐associated rate of methane formation, β, with increasing gaseous input. The specific hydrogenase activity exhibited growth‐assiciated behaviour at low growth rates, but showed no dependence on growth at higher growth rates. The growth dependence of hydrogenase activity is consistent with the pressure dependence of hydrogenase activity measured in previous experiments. In contrast, the specific protease activity was independent of the growth rate over the entire range of dilution rates studied. © 1994 John

ISSN:0006-3592    

DOI:10.1002/bit.260430309

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

年代:1994

数据来源: WILEY

摘要:

AbstractA potentially implantable glucose biosensor for continuous monitoring of glucose levels in diabetic patients has been developed. The glucose biosensor is based on an amperometric oxygen electrode and glucose oxidase immobilized on carbon powder held in a form of a liquid suspension. The enzyme material can be replaced (the sensor recharged) without sensor disassembly. Recharging of the biosensor is achieved by injecting fresh immobilized enzyme into the sensor using a septum. Diffusion membranes made of silastic latex‐rubber coatings over a microporous polycarbonate membrane are used. Calibration curves of the amperometric signal show linearity over a wide range of glucose concentrations—up to 500 mg/dL (28 mM), covering hypoglycemic, normoglycemic, and hyperglycemic conditions. Preliminary in vitro studies of the biosensor show stable performance during several recharge cycles (of 14 days each) over a period of 4 months. © 1994 John Wiley&Sons,

ISSN:0006-3592    

DOI:10.1002/bit.260430310

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

年代:1994

数据来源: WILEY

ISSN:0006-3592    

DOI:10.1002/bit.260430301

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

年代:1994

数据来源: WILEY