bluuebunny/crossref_metadata_2025_split huggingface dataset:
Adsorption of Clostridium thermocellum cellulases onto pretreated mixed hardwood, avicel, and lignin
Authors: Bernardez Timothy D. , Lyford Kimberly , Hogsett David A. , Lynd Lee R. 
Published: December 2004

AbstractAdsorption of Avicel‐hydrolyzing activity was examined with respect to: mixed hardwood flour pretreated with 1% sulfuric acid for 9 s at 220°C (PTW220), lignin prepared from PTW220 by either acid or enzymatic hydrolysis, and Avicel. Experiments were conducted at 60°C for all materials, and also at 25°C for PTW220. Based on transient adsorption results and reaction rates, times were selected at which to characterize adsorption at 60°C as follows: PTW220, 1 min; lignin, 30 min; and Avicel, 45 min. Similar results were obtained for adsorption of cellulase activity to PTW220 at 25 and 60°C, and for lignin prepared by enzymatic and acid hydrolysis. For all materials, adsorption was described well by a Langmuir equation, although the reversibility of adsorption was not investigated. Langmuir affinity constants (L/g) were: PTW220, 109; lignin, 17.9; Avicel, 4.3; cellulose from PTW220, ≥187. Langmuir capacity constants were 760 for PTW220 and 42 for Avicel; the cellulase binding capacity of lignin appeared to be very high under the conditions examined, and could not be determined. At low and moderate cellulase loadings at least, the majority of cellulase activity adsorbed to PTW220 is bound to the cellulosic component. The results indicate that PTW220, and its cellulose component in particular, differ radically from Avicel with respect to adsorption. Avicel‐hydrolyzing activity and CMC‐hydrolyzing activities were found to bind to Avicel with a constant ratio of essentially one, consistent with adsorption of a multi‐activity complex. © 1993 John Wiley & Sons, Inc.
Solvent effects on lipase‐catalyzed esterification of glycerol and fatty acids
Authors: Janssen Anja E. M. , Van der Padt Albert , Riet Klaas Van't 
Published: December 2004

AbstractThe lipase‐catalyzed acylglycerol synthesis with fatty acids of different chain length is studied. Measured ester mole fractions at equilibrium are compared with calculated mole fractions. For these calculations the computer program TREP (Two‐phase Reaction Equilibrium Prediction) is used. This program is based on the UNIFAC group contribution method and is developed for nondilute two‐phase reaction systems.With one set of equilibrium constants, namely 1.3, 0.8, and 0.6 for monoester, diester, and triester synthesis, respectively, the equilibrium position of the reaction between glycerol and all saturated fatty acids with a chain length from 6 to 18 and oleic acid (cis‐9‐octadecenoic acid) can be calculated. Deviations, expressed as the ratio between calculated and measured ester mole fractions, usually were between 0.7 and 1.2. In the presence of solvents, the deviations of the monoester mole fractions were higher and rose up to 3. Without addition of a solvent, the ester mole fractions at equilibrium are dependent on the fatty acid chain length. With the short‐chain hexanoic acid, the monoester mole fraction is the highest ester mole fraction, while for the long‐chain oleic acid, the diester mole fraction is the highest one. The ester mole fractions become independent on the chain length of the fatty acid with a solvent added in a sufficient high concentration. Both reactions, with saturated and unsaturated C18 fatty acids, lead to the same equilibrium position. The program TREP is found to make good predictions of the equilibrium amounts of ester and fatty acid. However, systematic deviations arise between measured and calculated amounts of water and glycerol in the organic phase. The calculated water and glycerol amounts are always lower than the measured ones. These deviations seem to be highest in nonpolar media and are probably due to deficiencies in the UNIFAC calculation method. Some preliminary experiments show the effect of the choice of solvent on the reaction rates. In polar solvents, the monoester production rate is enhances by a factor of 1.5 as compared to the reaction rate in a system without solvent. © 1993 John Wiley & Sons, Inc.
Metabolic engineering of Clostridium acetobutylicum ATCC 824 for increased solvent production by enhancement of acetone formation enzyme activities using a synthetic acetone operon
Authors: Mermelstein Lee D. , Papoutsakis Eleftherios T. , Petersen Daniel J. , Bennett George N. 
Published: December 2004

AbstractThe ability to genetically alter the product‐formation capabilities of Clostridium acetobutylicum is necessary for continued progress toward industrial production of the solvents butanol and acetone by fermentation. Batch fermentations at pH 4.5, 5.5, or 6.5 were conducted using C. acetobutylicum ATCC 824 (pFNK6). Plasmid pFNK6 contains a synthetic operon (the “ace operon”) in which the three homologous acetone‐formation genas (adc, ctfA, and ctfB) are transcribed from the adc promoter. The corresponding enzymes (acetoacetate decarboxylase and CoA‐transferase) were best expressed in pH 4.5 fermentations. However, the highest levels of solvents were attained at pH 5.5. Relative to the plasmid‐free control strain at pH 5.5, ATCC 824 (pFNK6) produced 95%, 37%, and 90% higher final concentrations of acetone, butanol, and ethanol, respectively; a 50% higher yield (g/g) of solvents on glucose; and a 22‐fold lower mass of residual carboxylic acids. At all pH values, the acetone‐formation enzymes were expressed earlier with ATCC 824 (pFNK6) than in control fermentations, leading to earlier induction of acetone formation. Furthermore, strain ATCC 824 (pFNK6) produced butanol significantly earlier in the fermentation and produced significant levels of solvents at pH 6.5. Only trace levels of solvents were produced by strain ATCC 824 at pH 6.5. Compared with ATCC 824, a plasmid‐control strain containing a vector without the ace operon also produced higher levels of solvents [although lower than those of strain ATCC 824 (pFNK6)] and lower levels of acids. Strains containing plasmid‐borne derivatives of the ace operon, in which either the acetoacetate decarboxylase or CoA‐transferase alone were expressed at elevated levels, produced acids and solvents at levels similar to those of the plasmid‐control strain. © 1993 John Wiley & Sons, Inc.
Production of propionic acid from whey permeate by sequential fermentation, ultrafiltration, and cell recycling
Authors: Colomban Agnès , Roger Loïc , Boyaval Patrick 
Published: December 2004

AbstractThis article deals with the production by fermentation of a mycostatic and aromatic food additive based on propionic acid. Membrane bioreactors have been used from laboratory scale up to pilot and industrial production plants. Due to the high cell densities achieved by the sequential recycling mode of operation, a mixed acids solution was rapidly produced from whey permeate. The sterile fermented broth obtained was subsequently concentrated at different levels by evaporation and spray drying according to the projected use. Concentrated Propionibacterium cells (200 g · L−1 DW) were obtained from the process by periodic bleeds and could be used to good effect as cheese starters, silage preservatives, or probiotics. Propionic acid concentrations from 30 to 40 g · L−1 were easily achieved with no residual lactose. The highest volumetric productivity was 1.6 g · L−1 · h−1 for total acid and 1.2 g · L−1 · h−1 for propionic acid with a specific productivity of 0.035 h−1. © 1993 John Wiley & Sons, Inc.
Protein adsorption in polysulfone hollow fiber bioreactors used for serum‐free mammalian cell culture
Authors: Patkar Anant Y. , Bowen Bruce D. , Piret James M. 
Published: December 2004

AbstractThe recovery of serum‐free medium proteins from poly‐sulfone hollow fiber bioreactors (HFBRs) was investigated. More than 99% of the initial transferrin was adsorbed to the hydrophobic hollow fibers within 2 h of HFBR operation. A methodology to minimize transferrin adsorption by pre‐adsorption of bovine serum albumin (BSA) was developed. BSA adsorption on suspended cut fibers was virtually complete within 1 h. BSA‐coated fibers adsorbed only 5% of the transferrin within 10 days, whereas uncoated cut fibers adsorbed more than 99% of the transferrin within 1 h. An improved HFBR startup procedure, using a BSA‐coating step before inoculation, resulted in substantially higher transferrin recovery. Additional factors influenced extracapillary space (ECS) transferrin concentrations. Pronounced downstream polarization of transferrin was observed in the ECS. In addition, the 30‐kDa nominal molecular weight cutoff ultrafiltration membranes rapidly leaked transferrin from the ECS to the lumen. © 1993 John Wiley & Sons, Inc.
Linear constraint relations in biochemical reaction systems: I. Classification of the calculability and the balanceability of conversion rates
Authors: van der Heijden R. T. J. M. , Heijnen J. J. , Hellinga C. , Romein B. , Luyben K. Ch. A. M. 
Published: December 2004

AbstractMeasurements provide the basis for process monitoring and control as well as for model development and validation. Systematic approaches to increase the accuracy and credibility of the empirical data set are therefore of great value. In (bio)chemical conversions, linear conservation relations such as the balance equations for charge, enthalpy, and/or chemical elements, can be employed to relate conversion rates. In a pactical situation, some of these rates will be measured (in effect, be calculated directly from primary measurements of, e.g., concentrations and flow rates), as others can or cannot be calculated from the measured ones. When certain measured rates can also be calculated from other measured rates, the set of equations, the accuracy and credibility of the measured rates can indeed be improved by, respectively, balancing and gross error diagnosis. The balanced conversion rates are more accurate, and form a consistent set of data, which is more suitable for further application (e.g., to calculate nonmeasured rates) than the raw measurements. Such an approach has drawn attention in previous studies. The current study deals mainly with the problem of mathematically classifying the conversion rates into balanceable and calculable rates, given the subset of measured rates. The significance of this problem is illustrated with some examples. It is shown that a simple matrix equation can be derived that contains the vector of measured conversion rates and the redundancy matrix R. Matrix R plays a predominant role in the classification problem. In supplementary articles, significance of the redundancy matrix R for an improved gross error diagnosis approach will be shown. In addition, efficient equations have been derived to calculate the balanceable and/or calculable rates. The method is completely based on matrix algebra (principally different from the graph‐theoretical approach), and it is easily implemented into a computer program. © 1994 John Wiley & Sons, Inc.
Linear constraint relations in biochemical reaction systems: II. Diagnosis and estimation of gross errors
Authors: van der Heijden R. T. J. M. , Romein B. , Heijnen J. J. , Hellinga C. , Luyben K. Ch. A. M. 
Published: December 2004

AbstractConservation equations derived from elemental balances, heat balances, and metabolic stoichiometry, can be used to constrain the values of conversion rates of relevant components. In the present work, their use will be discussed for detection and localization of significant errors of the following types:

At least one of the primary measurements has a significant error (gross measurement error).
The system definition is incorrect: a component

is not included in the system description.
has a composition different from that specified.

The specified variances are too small, resulting in a too‐sensitive test.
The error diagnosis technique presented here, is based on the following: given the conservation equations, for each set of measured rates, a vector of residuals of these equations can be constructed, of which the direction is related to the error source, as its length is a measure of the error size. The similarity of the directions of such a residual vector and certain compare vectors, each corresponding to a specific error source, is considered in a statistical test. If two compare vectors that result from different error sources have (almost) the same direction, errors of these types cannot be distinguished from each other. For each possible error in the primary measurements of flows and concentrations, the compare vector can be constructed a priori, thus allowing analysis beforehand, which errors can be observed. Therefore, the detectability of certain errors likely to occur can be insured by selecting a proper measurement set. The possibility of performing this analysis before experiments are carried out is an important advantage, providing a profound understanding of the detectability of errors. The characteristics of the method with respect to diagnosis of simultaneous errors and error size estimation are discussed and compared to those of the serial elimination method and the serial compensation strategy, published elsewhere. © 1994 John Wiley & Sons, Inc.
Protein fractionation using fast flow immobilized metal chelate affinity membranes
Authors: Serafica Gonzalo C. , Belfort Georges , Pimbley Joseph 
Published: December 2004

AbstractA new group‐specific affinity membrane using metal chelates as ligands and inorganic glass hollow fiber microfiltration membranes as support matrices is developed and tested. The study focused on developing the optimum activation and coupling procedures to bind the chelating agent (iminodiacetic acid, IDA) to the surface of the microporous glass hollow fiber membrane and testing the resultant affinity membrane. Starting with three different glass surfaces, five modification reactions were evaluated. All the modified “active surfaces” were first tested for their protein adsorptive properties in batch mode with suspended microporous glass grains using model proteins with known binding characteristics with Cu–IDA systems. The metal loading capacities of the surfaces exhibiting favorable fractionation were then measured by atomic absorption spectroscopy.The results were compared with the results obtained with a commercial material used in immobilized metal affinity column chromatography. The protein binding characteristics of the hollow fiber affinity membranes were also evaluated under conditions of convective flow. This was performed by flowing single solute protein solutions through the microporous membrane at different flow rates. These results were then used to estimate the optimum loading and elution times for the process. A mathematical model incorporating radial diffusion was solved using a finite difference discretization method. Comparison between model predictions and experimental results was performed for four different proteins at one flow rate. These results suggested that the kinetics of adsorption was concentration dependent. Finally, the hollow fiber affinity membranes were challenged with two component mixtures to test their ability to fractionate mixed protein solutions. Efficient separation and good purity were obtained.The results presented here represent the development of a new fast flow affinity membrane process–immobilized metal affinity membranes (IMAM). © 1994 John Wiley & Sons, Inc.
Mini‐review: Osteoblasts: An in vitro model of bone‐implant interactions
Authors: Bizios Rena 
Published: December 2004

AbstractWell‐characterized osteoblasts provide a successful in vitro model to study bone‐biomaterial interactions. Knowledge of the events occurring at this tissue‐biomaterial interface could lead to the design of improved orthopedic/dental biomaterials which elicit specific and desirable responses from surrounding cells/tissues, optimize function of osteoblasts (the boneforming cells), and enhance long‐term bone‐implant bonding. © 1994 John Wiley & Sons, Inc.
Homogenization theory and digital imaging: A basis for studying the mechanics and design principles of bone tissue
Authors: Hollister S. J. , Kikuchi N. 
Published: December 2004

AbstractBone tissue is a complex multilevel composite which has the ability to sense ad respond to its mechanical environment. It is believed that bone cells called osteocytes within the bone matrix sense the mechanical environment and determine whether structural alterations are needed. At present it is not known, however, how loads are transferred from the whole bone level to cells. A computational procedure combining representative volume element (RVE) based homogenization theory with digital imaging is proposed to estimate strains at various levels of bone structure. Bone tissue structural organization and RVE based analysis are briefly reviewed. The digital image based computational procedure was applied to estimate strains in individual trabeculae (first‐level microstructure). Homogenization analysis of an idealized model was used to estimate strains at one level of bone structure around osteocyte lacunae (second‐level trabecular microstructure). The results showed that strain at one level of bone structure is amplified to a broad range at the next microstructural level. In one case, a zeor‐level tensile principal strain of 495 μE engendered strains ranging between ‐1000 and 7000 μE in individual trabeculae (first‐level microstructure). Subsequently, a first‐level tensile principal strains of 1325 μE within an inidividual trabecula engendered strains ranging between 782 and 2530 μE around osteocyte lacunae. Lacunar orientation was found to influence strains around osteocyte lacunae much more than lacunar ellipticity. In conclusion, the computational procedure combining homogenization theory with digital imaging can proveide estimates of cell level strains within whole bones. Such results may be used to bridge experimental studies of bone adaptation at the whole bone and cell culture level. © 1994 John Wiley & Sons, Inc.
Fed‐batch operation of recombinant Escherichia coli containing trp promoter with controlled specific growth rate
Authors: Yoon Sung Kwan , Kang Whan Koo , Park Tai Hyun 
Published: December 2004

AbstractA feb‐batch operation for the production of bovine somatotropin (bST) under the control of tryptophan promoter in Escherichia coli was investigated. The plasmid used contains a two‐cistron system and altered codon usage for higher expression of bST. Specific growth rate is an important parameter in the fermentation, because it affects the production of growth‐inhibitory organic acids and the expression of recombinant protein. The feeding rate was adjusted to keep the specific growth rate constant in this study. The variable growth yield expressed as a function of time was used for the calculation of the feeding rate. The growth yield decreases during the fermentation as product expression is induced. The specific growth rate was well controlled; however, intracellular bST concentration decreased at high cell concentrations. This is considered to be due to degradation by proteases. The decrease was prevented by an exponential feeding of the yeast extract as an organic nitrogen source. © 1994 John Wiley & Sons, Inc.
Characterization of tryptic casein phosphopeptides prepared under industrially relevant conditions
Authors: Adamson Nicholas J. , Reynolds Eric C. 
Published: December 2004

AbstractAnticariogenic casein phosphopeptides (ACPP) contain the cluster sequence ‐Ser(P)–Ser(P)–Ser(P)–Glu–Glu‐ and have commercial potential as toothpaste, mouthwash, and food additives for the prevention of dental caries. In an approach to develop a commercial‐scale process for the production of ACPP we have comprehensively characterized casein phosphopeptides (CPP) produced under industrially relevant conditions. Sodium caseinate (10% w/v) was hydrolyzed by Novo trypsin (commercial grade) at 50°C for 2 h and CPP were purified from the acid clarified hydrolysate by a single‐step selective precipitation procedure involving Ca2+ (20 mol/mol casein) and ethanol (50% v/v) at pH 4.6 or 8.0. The individual peptides of the CPP preparations were purified by reversed‐phase high‐performance liquid chromatography (HPLC) and then identified by amino acid composition and sequence analyses. The yield of the pH 8.0 precipitate (13.85 ± 0.48 wt % of the caseinate) was slightly higher than that of the pH 4.6 precipitate (11.04 ± 0.30 wt % of the caseinate). However, the pH 4.6 precipitate contained predominantly (86.4 mol %) ACPP cluster peptides with small amounts of the diphosphorylated peptides (13.6 mol %), αs1(43–58) and αs2(126–136). In the pH 8.0 precipitate the cluster peptides represented a smaller proportion of the total peptides (61.9 mol %) due to increased recoveries of the diphosphorylated peptides (24.4 mol %) as well as the additional recovery of the monophosphorylated peptide β(33–48) (13.7 mol %) indicating increased cross‐linking by Ca2+ at the higher pH. The recovery of the ACPP from the original caseinate was similar for both the pH 4.6 and 8.0 precipitates. Slight chymotryptic activity was detected in the industrial‐grade enzyme, resulting in minor truncation of some peptides. Also some deamidation and methionine oxidation of one peptide, αs1(59–79), were detected. In conclusion, ACPP can be produced under industrially relevant conditions with only minor modifications such as slight truncation, deamidation, and methionine oxidation. However, in order to prepare casein phosphopeptides predominantly containing the cluster sequence ‐Ser(P)–Ser(P)–Ser(P)–Glu–Glu‐, the single‐step selective precipitation with Ca2+/ethanol should be performed at pH 4.6 rather than pH 8.0. © 1995 John Wiley & Sons, Inc.
Batch cultivation of Methylosinus trichosporium OB3B: IV. Production of hydrogen‐driven soluble or particulate methane monooxygenase activity
Authors: Shah Nilesh N. , Hanna M. Leslie , Jackson Kenneth J. , Taylor Robert T. 
Published: December 2004

AbstractBatch culture conditions were established for the formation of H2‐driven whole‐cell soluble or particulate methane monooxygenase (sMMO or pMMO) activity in the obligate methanotroph, Methylosinus trichosporum Ob3b, to expand its potential uses in groundwater bioremediation and the production of specific chemicals. Addition of either Ni and H2 to a nitrate‐containing minimal salts growth medium or Ni and Mo to a nitrate‐lacking growth medium (induces a nitrogenase that generates intracellular H2) markedly enhanced both the hydrogenase and the accompanying washed‐cell H2‐driven MMO activities of shake‐flask cultured cells. For sMMO containing cells, H2 provided in vitro reducing power for the oxidation of chlorinated solvents such as chloroform and trichloroethylene. Cell cultivations under N2‐fixing conditions in a 5‐L bioreactor, however, required an initial nitrate concentration of at least 1 to 2 mM to achieve high biomass yields (5 to 7 g of dry cell wt/L) for cells producing H2‐driven sMMO or pMMO activity. Elevation of the initial medium nitrate concentration to 20 mM shortened the culture time for pMMO producing cells by 40%, yet still generated an equivalent growth yield. High nitrate also shortened the culture time for sMMO containing cells by ∼25%, but it lowered their biomass yield by 26%. Upon storage for 5 weeks at room temperature, washed resting‐state cells retained 90% and 70% of their H2‐driven sMMO and pMMO activity, respectively. This makes their practical use quite feasible. © 1995 John Wiley & Sons, Inc.