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Biomedical subjects

C Wandrey

Publications and source records attributed to C Wandrey.

51 records · Page 3Linked to original sources
PubMed1990

Optimization of enzyme-mediated peptide bond formation.

Enzyme-catalyzed peptide bond formation requires thorough examination and optimization of each coupling step. In order to identify factors influencing the selectivity between aminolysis and hydrolysis, a systematic study was carried out for the kinetically controlled peptide synthesis. The reaction temperature, the type of C-terminal protecting group, and different organic cosolvents showed little influence on the selectivity. The enzyme, excess nucleophile, pH, N-terminal protecting group, and ionic strength of the solution were identified as major factors controlling the selectivity and, therefore, the yield of the dipeptide synthesis. Under optimized conditions, the selectivity of the chymotrypsin-catalyzed synthesis of PheSer could be increased from 35 to 100%.

Carboxypeptidases↗
PubMed1988

Preparation of cellodextrins and isolation of oligomeric side components and their characterization.

Cellodextrin (beta-1,4-glucose oligomer) mixtures are prepared by precipitation of oligomers with 1-propanol and ethanol after partial hydrolysis of cellulose with hydrochloric acid or by acetolysis of cellulose. Cellooligomers (DP3-DP8) can be isolated by high-resolution size-exclusion chromatography on Bio-Gel P 4 using water as eluent. Recycle operation of the columns allows the separation of oligomers up to a degree of polymerization of 12. However, ion-exchange chromatography of their borate complexes demonstrates the heterogeneity of cellodextrins, homogeneous according to size-exclusion chromatography. At least four secondary oligomeric components are observed in the different samples. By preparative affinity chromatography on phenyl-boronate-agarose two of these components could be purified and subsequently characterized. In one series of oligosaccharides the glucose unit at the reducing end of the beta-1,4-glucose oligomers is derivatized to fructose. This enolization reaction occurs during size-exclusion chromatography. The precipitation step with alkanols during preparation of oligomer mixtures generates oligomeric glycosides. Additionally, the formation of amines from respective beta-1,4-glucose oligomers is observed with the ammonium carbonate eluent used in affinity chromatography. Analysis methods combined to assess for the homogeneity of cellodextrins include enzyme- and acid-catalyzed (partial) hydrolysis of the different oligomers and subsequent analysis of degradation products by sugar borate chromatography; 13C and 1H NMR spectroscopy; and fast atom bombardment mass spectroscopy.

Cellulose↗
PubMed1987

Investigation of the action mechanism of a cellodextrin glucohydrolase using soluble cellodextrins as substrates.

A mathematical model was developed that can satisfactorily describe the system of parallel and series reactions during the degradation of cellodextrins by a glucohydrolase in batch experiments. The enzyme sequentially splits off glucose units from the oligomer chains. Using a thin-channel membrane reactor, the model was then shown to be able to predict the conversion of cellohexaose in continuous experiments. This has, to the best of our knowledge, been the first time that such an oligosaccharide conversion has been experimentally followed and modeled for a continuous stirred tank reactor.

Biotechnology↗
PubMed1986

An automated method for the quasi-continuous analysis of degradation and transfer products during the enzymatic hydrolysis of oligosaccharides.

A method is presented which allows for the automated quasi-continuous analysis of the degradation and transfer products developing during the enzymatic hydrolysis of oligosaccharides. A liquid chromatographic system is integrated into the bypass of a small batch reactor which makes it possible to take oligomer spectra without any manual sample processing being necessary. The time intervals between analyses are substantially reduced by making use of an overlapping analysis technique. Postcolumn derivatization with an orcinol sulfuric acid reagent gives a high sensitivity for carbohydrates. The great potential of this method is demonstrated for the characterization of a beta-glucosidase (pI 8.4) from Trichoderma reesei QM 9414 and an alpha 1,4-glucan glucohydrolase from Aspergillus niger with cellotetraose and maltohexaose as examplary substrates.

Aspergillus niger↗
PubMed1980

Influence of substrate or product inhibition on the performance of enzyme reactors.

For the design of an enzyme reactor a detailed knowledge of the kinetic parameters of the catalyst under operational conditions is essential. For technical applications high initial substrate concentrations and high degrees of conversions are desirable, in order to save reactor volume and energy in recovery processes. Most of the kinetic data available in the literature have been derived from dilute solutions under initial rate conditions. These data cannot be extrapolated with confidence for technically interesting concentrations because substrate as well as product-inhibition may occur, which would not be observed in dilute solutions and by initial rate measurements. Because of this difficulty effective and fast methods to obtain significant data for technical applications have been developed based on-line rate determinations. Such extensive treatment has proved necessary for the following enzymes: alanine dehydrogenase, formate dehydrogenase and alpha-glucosidase, indicating that we are dealing with a general phenomenon.

Alanine Dehydrogenase↗
PubMed1977

Application of immobilized chymotrypsin in a multistage fluidized-bed reactor.

The stereospecific hydrolysis of D,L-phenylalanine methylester with immobilized alpha-chymotrypsin was carried out as a model reaction for the racemate resolution of aromatic amino acids in a five staged fluidized-bed reactor (FBR). Owing to ester hydrolysis, a pH shift occurred along the reactor. Because of the pH-dependent enzyme activity a particular longitudinal pH profile had to be enforced by a proper entrance pH in order to gain an optimum conversion. In the FBR with optimum pH profile, higher conversions were achieved than in a continuous stirred tank reactor (CSTR) at the pH optimum and at the same contact time. By the application of a proton balance and the results of kinetic measurements a model was developed for the prediction of the optimum longitudinal pH profile with regard to the maximum conversion.

Chymotrypsin↗
PubMedDate not supplied

Human chymotrypsinogen B production with Pichia pastoris by integrated development of fermentation and downstream processing. Part 1. Fermentation.

Based on an integrated approach of genetic engineering, fermentation process development, and downstream processing, a fermentative chymotrypsinogen B production process using recombinant Pichia pastoris is presented. Making use of the P. pastoris AOX1-promotor, the demand for methanol as the single carbon source as well as an inducer of protein secretion enforced the use of an optimized feeding strategy by help of on-line analysis and an advanced controller algorithm. By using an experimental system of six parallel sparged column bioreactors, proteolytic product degradation could be minimized while also optimizing starting conditions for the following downstream processing. This optimization of process conditions resulted in the production of authentic chymotrypsinogen at a final concentration level of 480 mg.L(-)(1) in the whole broth and a biomass concentration of 150 g.L(-)(1) cell dry weight, thus comprising a space-time yield of 5.2 mg.L(-)(1).h(-)(1). Alternatively to the high cell density fermentation approach, a continuous fermentation process was developed to study the effects of reduced cell density toward oxygen demand, cooling energy, and biomass separation. This development led to a process with a highly increased space-time yield of 25 mg.L(-)(1).h(-)(1) while reducing the cell dry weight concentration from 150 g.L(-)(1) in fed-batch to 65 g.L(-)(1) in continuous cultivation.

Chymotrypsinogen↗
PubMedDate not supplied

Influence of alginate characteristics on the properties of multi-component microcapsules.

A variety of sodium alginates, differing in molar mass and structural composition, have been evaluated in the preparation of multi-component microbeads and microcapsules. Bead formation occurred by gelation with calcium chloride. Capsules were produced by reacting the pre-formed beads with the oligocation poly(methylene-co-guanidine). Despite the equiponderous (1:1) mixing with a second polyanion, sodium cellulose sulphate, the influence of the alginate properties remains evident. Specifically, the effect of the chemical composition was found to be more significant than that of the molar mass for both the mechanical and transport properties. Furthermore, for alginates of 73% alpha-l-guluronic acid content less shrinking was observed compared to the 38% guluronic materials. This results in the case of the same encapsulator settings in larger microsphere diameters and thicker membranes accompanied by enhanced mechanical resistance though, also, in a higher permeability for the high-G capsules. However, subsequent coating with lower molar mass alginate allows one to adjust the permeability over a broad range, suitable for cell encapsulation and immunoprotection, without compromising the durability.

Alginates↗