摘要:

AbstractThe effects of temperature, speed of agitation, enzyme concentration, etc., on butyl laurate synthessis usingMucor mieheilipase (Lipozyme™) have been studied. Although the soluble enzyme was quite thermcstable in aqeous solution, it deactivated rapidly at and above 40°C in the presence of butanol. This enzyme immobilized on an anion‐exchange resin (Lipozyme™) showed enhanced stability (as compared to the soluble form) to denaturation by butanol under the same conditions. The denaturation ofM. mieheilipase was found to be a function of the butanol concentration in the aqueous phase, and rapid denaturation takes place at the concentration corresponding to its saturation at that temperature. © 1995 John Wiley&So

ISSN:0006-3592    

DOI:10.1002/bit.260460102

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe combination of an improved bacterial desorption method, scanning electron microscopy (SEM), diffuse reflectance and transmission infrared Fourier transform spectroscopy, and a desorption‐leaching device like high‐pressure liquid chromatography (HPLC) was used to analyze bacterial populations (adhering and free bacteria) and surface‐oxidized phases (ferric arsenates and elemental sulfur) during the arsenopyrite biooxidation byThiobacillus ferrooxidans. The bacterial distribution, the physicochemical composition of the leachate, the evolution of corrosion patterns, and the nature and amount of the surface‐oxidized chemical species characterized different behavior for each step of arsenopyrite bioleaching. The first step is characterized by a slow but strong adhesion of bacteria to mineral surfaces, the appearance of a surface phase of elemental sulfur, the weak solubilization of Fe(II), As(III), and As(V), and the presence of the first corrosion patterns, which follow the fragility zones and the crystallographic orientation of mineral grains. After this short step, growth of the unattached bacteria begins, while ferrous ions in solution are oxidized by them. Ferric ions produced by the bacteria can oxidize the sulfide directly and are regenerated by Fe(II) bacterial oxidation. At this time, a bioleaching cycle takes place and a coarse surface phase of ferric arsenate (FeAsO4·xH2O wherex≈ 2) and deep ovoid pores appear. At the end of the bioleaching cycle, the high concentration of Fe(III) and As(V) in solution promotes the precipitation of a second phase of amorphous ferric arsenate (FeAsO4·xH2O wherex≈ 4) in the leachate. Then the biooxidation process ceases: The bacteria adhering to the mineral sufaces are coated by the ferric arsenates and the concentration of Fe(III) on the leachate is found to have decreased greatly. Both oxidation mechanisms (direct and indirect oxidation) have been stopped. © 1995 John W

ISSN:0006-3592    

DOI:10.1002/bit.260460103

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe secretion rate of activated protein C (APC) by BHK cells was increased 35‐fold by increasing the cDNA copy number per cell from 50 to 240. In this range, the relation between APC secretion and cDNA copy number was not linear and the rate of APC secretion per cDNA copy increased sevenfold. This apparent cooperative effect of multiple cDNA copies could be related to their integration in tandem. For cDNA copy numbers higher than 240, the APC secreation rate per cDNA and per cell decreased dramatically. The γ‐carboxylation of glutamic acid residues, a posttranslational modification required for APC biological activity, was also investigated. The proportion of APC that was fully γ‐carboxylated decreased as the secretion rate of APC increased. © 1995 John Wiley&S

ISSN:0006-3592    

DOI:10.1002/bit.260460104

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe transmission and rate of filtration of the enzyme yeast alcohol dehydrogenase (YADH) has been studied at capillary pore microfiltration membranes. Photon correlation spectroscopy (PCS) with nanometer resolution showed that the enzyme existed as discreate molecules only for a narrow range of pH and ionic strength. Under such conditions, the transmission of the enzyme was high. However, the rate of filtration still decreased continuously with time. Analyssis of the time dependence of the rate of filtration indicated that this decrease was due to in‐pore enzyme deposition at low concentration (“standard blocking model”) and suface depositon at high concentration (“cake filtration model”). Use of atomic force microscopy (AFM) gave unequivocal and quantitative confirmation of these inferences. The work shows the great advantage of using advanced physical characterization techniques, both for the identification of the optimum conditions for filtration (PCS) and for the elucidation of mechanisms giving rise to inefficiencies in the filtration process (AFM). © 1995 John Wiley

ISSN:0006-3592    

DOI:10.1002/bit.260460105

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

年代:1995

数据来源: WILEY

摘要:

AbstractEnzymatic depolymerization of polysaccharides with α‐amylase has been studied in mixed aqueous dimethylsulfoxide (DMSO)/water solvents. Polysaccharide substrate chemical compositions, configurational structures, and bonding pattersn are known to affect observed enzymatic reaction kinetics. The branching structures of polysaccharides and their effects on the kinetic mechanisms of depolymerization reactions via endo‐acting hydrolyzing enzyme was studied via size exclusion chromatography coupled to low angle laser light scattering (SEC/LALLS). The glycogen branching structure is a heterogeneously distributed “cluster” structure rather than a homogeneously distributed “treelike” structure. The action pattern of α‐amylase on glycogen, which is composed of highly branched clusters, as end‐products, has a “pseudo‐exo‐attack” in contrast to an expected “endoattack” as seen in the hydrolysis of amylose or amylopectin substrates. These effects of branched substrates for mixed amylose/glycogen α‐amylolysis have been predicted and demonstrated by both experimental and theoretical analysis using the kinetic model presented in this report. The “lumped” kinetic model employed, assumes that the enzyme simultaneously attacks both linear and branched substrates. In general, excellent agreement between the model predictions and the experimental observations, both qualitatively and quantitatively, was o

ISSN:0006-3592    

DOI:10.1002/bit.260460106

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

年代:1995

数据来源: WILEY

摘要:

AbstractA detailed model acetate‐utilizing methanogenic biofilms accounting for the diffusion of neutral and ionic species, chemical equilibrium, electroneutrality, gas production within the biofilm, pH‐dependent Monod kinetics, and the presence of a concentration boundary layer is presented. The model qualitatively fits the pH profiles that are reported for acetate‐utilizing methanogenic aggregates. A sensitivity analysis on the biological parameters showed that the flux of acetate is sensitive to the maximum utilization rate, half‐saturation constant, and biofilm density for the bulk conditions investigated. Criteria when traditional biofilm models can be used to predict the flux of acetate into the biofilm are established. If the maximum pH change predicted using a hypothetical system is within ±0.05, the traditional model predicts the flux to within ±5% of the value calculated with the model developed in this study. © 1995 John Wiley

ISSN:0006-3592    

DOI:10.1002/bit.260460107

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

年代:1995

数据来源: WILEY

摘要:

AbstractA rigorous steady‐state model of anaerobic biofilm reactors taking into account acid–base and gas–phase equilibria in the reactor in conjunction with detailed chemical equilibria and mass transfer in acetate‐utilizing methanogenic biofilms is presented. The performances of ideal completely stirred tank reactors (CSTRs) and plug‐flow reactors, as well as reactors with nonideal hydraulic conditions, are simulated. Decreasing the surface loading rate increases the acetate removal efficiency, while decreasing the influent pH and increasing the buffering capacity improves the removal efficiency only if the bulk pH of the reactor shifts toward more optimal values between 6.8 to 7.0. The reactor can have negative or positive removal efficiencies depending on the start‐up conditions. The respiration coefficient plays a critical role in determining the minimum influent pH required for reactor recovery after failure. Having multiple CSTRs‐in‐series generally increases the overall removal efficiency for the influent conditions investigated. Monitoring of the influent feed quality is critical for plug‐flow reactors, becasue failure of the initial sections of the reactor may cause a cascading effect that may lead to a rapid reactor failure. © 1995 Jo

ISSN:0006-3592    

DOI:10.1002/bit.260460108

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

年代:1995

数据来源: WILEY

摘要:

AbstractThis report continues or examination of the effect of genetically engineered charge modifications on the partitioning behavior of proteins in aqueous two‐phase extration. The genetic modifications consisted of the fusion of charged peptide tails to β‐galactosidase and charge‐change point mutations to T4 lysozyme. Our previous article examined the influence of these charge modifications on partitioning as a function of interfacial potential difference. In this study, we examined charge directed partitioning behavior in PEG/dextran systems containing small amounts of the charged polymers diethylaminoethyl‐dextran (DEAE‐dextran) or dextran sulfate. The best results were obtained when attractive forces between the protein and polymer were present. Nearly 100% of the β‐galactosidase, which carries a net negative charge, partitioned to the DEAE‐dextran‐rich phase regardless of whether the phase was dextran or PEG. In these cases, cloudiness of the protein‐rich phases suggest that strong charge interactions resulted in protein/polymer aggregation, which may have contributed to the extreme partitioning. Unlike the potentialdriven partitioning reported previously, consistent partitioning trends were observed as a result of the fusion tails, with observed shifts in partition coefficient (Kp) of up to 37‐fold. However, these changes could not be solely attributed to charge‐based interactions. Similarly, T4 lysozyme, carrying a net positive charge, partitioned to the dextran sulfate‐containing phase, and displayed four‐ to sevenfold shifts inKpas a result of the point mutations. These shifts were two to four times stronger than those observed for potential driven partitioning. Little effect on partitioning was observed when the protein and polymer had the same charge, with the exception of β‐galactosidase with polyarginine tails. The high positive charge density of these tails provided for a localized interaction with the dextran sulfate, and resulted in 2‐ to 15‐fold shifts

ISSN:0006-3592    

DOI:10.1002/bit.260460109

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe esterification of lauric acid with geraniol catalyzed by the commercially immobilized lipase preparation fromMucor miehei, Lipozyme®, was studied in well‐stirred flasks. The enzyme support was characterized in terms of its internal and external surface area, protein location, and protein content. It was found that the enzyme was mainly located on the external surface of the support, therefore, internal diffusional limitations were not important. It was also shown that the protein content of the support depends on the size of the particle, with smaller particles containing higher amounts of protein per unit weight. Under the conditions studied, the reaction was not under external mass transfer limitations, and the initial reaction rate depended on the size of the support particles. This was mainly due to the different protein contents on the support as a function of particle size and not to internal or external mass transfer limitations. Also, it was found that the inhibition exerted by water was predominantly a physical effect due to its accumulation around the enzyme. It was also found that the reaction was substrate inhibited by lauric acid, but not by geraniol. © 1995 John Wiley&Sons,

ISSN:0006-3592    

DOI:10.1002/bit.260460110

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

年代:1995

数据来源: WILEY

摘要:

AbstractQuinolie degradation byComamonas acidovoranswas studied in a continuously operated three‐phase airlift reactor. Porous glass beads were applied as support matrix for cell imobilization by colonization. Under steady‐state conditions (S∼ 0), cell attachment was poor at low dilution rates but imporved considerably with increasing dilution rate. Conversion of quinoline was investigated below and above the washout for suspended culture (Dcrit= μmax= 0.42 h−1). With immobilized cells the reactor could be operated atD>μmax, and complete conversion of quinoline was achieved as long as the specific quinoline feed rateD*S0/Xdid not exceed the maximum specific degradation rate (rS, max). The biofilm thickness was about 100 μm, and its efficiency was about 54% compared to suspended organisms. If quinoline overloads were supplied to the reactor, quinoline, as overloads were supplied to the reactor, quinoline, as well as its pathway intermediates, appeared in the reactor and conversion was low. Hence, the immobilized microorganisms remained viable and active. They could survive quinoline overloads. If the quinoline feed rate was reduced agains, complete conversion was reestablished. © 1995 John Wile

ISSN:0006-3592    

DOI:10.1002/bit.260460111

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

年代:1995

数据来源: WILEY