M.-R. Kula

Some New Developments in Reductive Amtnation with Cofactor Regeneration

The substrate specificity of LeuDH from Bacillus stearothermophilus and of PheDH from Rhodococcus sp. was investigated and found to be complementary. LeuDH from different organisms have remarkably similar substrate specificity. During optimization of the synthesis of L-tert-leucine, two byproducts (N-α-pivaloyl-tert-leucine amide (I) and 2,4-di-tert-butyl-5-hydroxyimidazol (II)) were found and identified which originate from chemical reactions of keto acid and ammonia.

Continuous (R)-mandelic acid production in an enzyme membrane reactor

SummaryThe continuous conversion of phenylglyoxylic acid to (R)-mandelic acid was performed in an enzyme membrane reactor with simultaneous coenzyme regeneration employing mandelate dehydrogenase and formate dehydrogenase. A mathematical model of the coupled enzyme reactions was formulated and applied to determine optimal conditions for (R)-mandelic acid production. The experiments and calculations showed that the optimal operational points depend strongly on enzyme kinetics. The individual kinetic parameters determined were appropriate for the description of (R)-mandelic acid production in the simultaneous two-enzyme process. Space time yields of 700 g/(l·day) were obtained at low enzyme consumption.

Confocal laser scanning microscopy as an analytical tool in chromatographic research

In recent years, confocal laser scanning microscopy has been developed into a non-invasive tool to probe intra-particle profiles of protein in chromatographic adsorbents. A necessary prerequisite when using this technique lies in the labeling of proteins with fluorescent probes. The quality of the obtained results is thus strongly dependent on the probes used, its sensitivity on experimental parameters and the change of protein characteristics upon binding. In this review, the fundamental issues when using fluorescent probes are described, before giving a critical evaluation on published literature in the field of confocal laser scanning microscopy for the analysis of chromatographic principles.

Cost structure and estimation for the recycling of salt in a protein extraction process

The costs for the recycling of salt from the primary bottom phase are estimated in a protein extraction process. The extraction of 1 kg potassium phosphate in a phase system formed in the presence of ethanol costs approximately 6 to 7 DM. This is within the same order as for the cost resulting from the purchase price of 3 DM/kgsalt and the additional costs for deposition of the primary bottom phase. A mathematical description of the cost structure is developed and allows to estimate cost for various conditions.

Purification and characterization of a newly screened microbial peptide amidase

A microbial peptide amidase was found in a limited screening and purified about 500-fold from Stenotrophomonas maltophilia. The native enzyme has a molecular mass of 38 kDa (gel filtration). The sequence of the first 16 amino acids was determined by Edman degradation. The isoelectric point was found to be around 5.8. The peptide amidase exhibited a pH optimum of 6.0 and a temperature optimum of about 39–45°C. The enzyme is stable in 50 mM TRIS/HCl, pH 7.5, at 30°C, and the residual activity was found to be above 90% after 1 week of incubation. The biocatalyst is not inhibited by potential inhibitors like Hg2+, EDTA, d-cycloserine or dithiothreitol and only weakly influenced by inhibitors of serine proteases. The peptide amidase deamidates selectively C-terminal amide groups in peptide amides without hydrolysing internal peptide bonds or amide functions in the side-chain of glutamine or asparagine. Unprotected amino acid amides are not hydrolysed. The enzyme is stereoselective with regard to l-enantiomers in the C-terminal position.

Staphylococcus carnosus aldolase as catalyst for enzymatic aldol reactions

Abstract The substrate specificity of S.carnosus aldolase is reported. 5,6-Dideoxyhexulose was synthesized in preperative scale from dihydroxyacetone phosphate and propionaldehyde. The product was isolated and characterized by NMR.

Purification and characterization of a class I fructose 1,6-bisphosphate aldolase from Staphylococcus carnosus

SummaryA fructose 1,6-bisphosphate aldolase (E.C.4.1.2.13) from Staphylococcus carnosus DSM 20501 was purified for the first time. The enzymatic activity was insensitive to high levels of EDTA indicating that the enzyme is a class I aldolase. This enzyme exhibits good stability at high temperatures and extreme stability over a wide pH range. The Km for fructose 1,6-bisphosphate as substrate was 0.022 mm. The S. carnosus aldolase is a monomeric enzyme with a molecular mass of about 33 kDa. It exhibits a relatively broad pH optimum between pH 6.5 and 9.0. Furthermore, the aldolase accepts other aldehydes in place of its natural substrate, glyceraldehyde 3-phosphate, allowing the synthesis of various sugar phosphates.

Fed-batch production of recombinant human calcitonin precursor fusion protein using Staphylococcus carnosus as an expression-secretion system.

Abstract A pH-auxostatic fed-batch process was developed for the secretory production of a fusion protein consisting of the pro-part of Staphylococcus hyicus lipase and two synthetic human calcitonin (hCT) precursor repeats under the control of a xylose-inducible promotor from Staphylococcus xylosus. Using glycerol as the energy source and pH-controlled addition of yeast extract resulted in the production of 2000 mg l−1 of the fusion protein (420 mg l−1 of the recombinant hCT precursor) within 14 h, reaching 45 g l−1 cell dry mass with Staphylococcus carnosus in a stirred-tank reactor. Product titer and space-time yield (30 mg calcitonin precursor l−1 h−1) were thus improved by a factor of 2, and 4.5, respectively, compared to Escherichia coli expression-secretion systems for the production of calcitonin precursors. Two hundred grams of the fusion protein was secreted by the recombinant S. carnosus on a 150-l scale (scale-up factor of 50) with a minimum use of technical-grade yeast extract (40 mg fusion protein g−1 yeast extract).

An approach to integrated antibody production: Coupling of fluidized bed cultivation and fluidized bed adsorption

Continuous culture may be an efficient way of producing proteins which are susceptible to secondary processing in the course of a fermentation process. Short residence times in these systems support the production of correctly assembled proteins by avoiding substrate limitations and product inhibitions and also minimize the contact of sensitive bioproducts with degrading enzymes. Thus products of increased stability and integrity are obtained from continuous processes. The downstream process following continuous culture has to be adapted to the specific conditions of continuous fermentations, e.g. large liquid volumes and diluted process solutions. In this paper an approach is shown how a fluidized bed adsorption as first recovery operation may be coupled directly to a continuous production. Immobilized hybridoma cells are cultivated in porous glass microcarriers in a continuous fluidized bed process, the cell containing harvest is purified by fluidized bed adsorption using an agarose based cation exchange matrix. By this coupled mode of operation the large biomass containing harvest volume resulting from the continuous cultivation may be applied directly to a fluidized chromatographic matrix without prior clarification, leading to a particle free and initially purified product solution of reduced volume. In an experimental setup a bench-scale fluidized bed bioreactor of 25 ml carrier volume was coupled to a fluidized bed adsorption column operated with 300 ml of adsorbent. This configuration yielded up to 20 mg of monoclonal antibody per day in a cell free solution at fourfold concentration and fivefold purification. The process was run for more than three weeks with consistent product output.

Investigating expression systems for the stable large-scale production of recombinant L-leucine-dehydrogenase from Bacillus cereus in Escherichia coli.

Abstract The established Escherichia coli expression vectors ptrc99a, pKK223-3, pPLλ, pAsk75, pRA95, and pRA96, which differ in copy number, mode of induction, selection marker, and use of par sequences for stabilization, were investigated for the stable expression of recombinant L-leucine dehydrogenase from Bacillus cereus with a view to large-scale production. Best results were achieved with pIET98, a runaway-replication system derived from pRA96. Expression of L-leucine dehydrogenase was controlled by its constitutive B. cereus promoter and depended on host strain, cultivation temperature, induction time, and media composition. After cell cultivation at 30 °C and shifting to 41 °C to induce plasmid replication, E. coli BL21[pIET98] yielded 200 U LeuDH/mg protein, which corresponds to >50% of the soluble cell protein. Continuous cultivation in a semisynthetic high-cell-density medium verified structural and segregational stability over 100 generations in the absence of a selection pressure.