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Holger Pfruender

Publications and source records attributed to Holger Pfruender.

4 recordsLinked to original sources
PubMed2006

Water immiscible ionic liquids as solvents for whole cell biocatalysis.

Whole cell biocatalysis can effectively be used for the production of enantiomerically pure compounds, but efficiency is often low. Toxicity and poor solubility of substrates and products are the main obstacles. In this study, water immiscible ionic liquids are shown to have no damaging effects on the cell membranes of Escherichia coli and Saccharomyces cerevisiae. Thus, they can be used as biocompatible solvents for microbial biotransformations exemplified by an increase in yield of chiral alcohol synthesis. As key point to the success of these processes, the distribution ratio of the reactants between the ionic liquid and the aqueous phase was identified. The use of ionic liquids as substrate reservoir and in situ extracting agent for the asymmetric reduction of various ketones resulted in an increase of chemical yield from <50% to 80-90% in simple batch processes. (R)-1-(4-chlorophenyl)ethanol was produced at a higher initial reaction rate in the biphasic system (>50 microM s(-1) L(-1)) compared to the aqueous system. This result demonstrates that good mass transfer rates can be obtained despite the relatively high viscosity of ionic liquids.

Biocompatible Materials↗
PubMed2004

Production of Lactobacillus kefir cells for asymmetric synthesis of a 3,5-dihydroxycarboxylate.

An efficient fedbatch process for the production of Lactobacillus kefir DSM 20587 cells was developed. An improvement in space time yield of 270% (3.7 g(DCW) l(-1)-day(-1)) and in final enzyme activity of 440% (9.1 U/ml) was achieved on a 150 l scale by controlling the oxygen transfer rate to 7--9 mmol l(-1) h(-1). The cells exhibited good and highly stereoselective reducing activities against tert-butyl 6-chloro-3,5-dioxohexanoate. tert-Butyl (3R,5S)-6-chloro-dihydroxyhexanoate, a chiral building block for HMG-CoA reductase inhibitor synthesis, was produced with 47.5% yield and >99% ee at C(3)3 and C(5)5 in a simple batch biotransformation process.

Biomass↗
PubMed2003

Alphavirus cDNA-based expression vectors: effects of RNA transcription and nuclear export.

The construction of layered DNA-RNA replicons has facilitated and expanded the use of alphavirus vectors to vaccine development, construction of packaging cell lines and long-term heterologous gene expression. In these vector systems, the alphavirus replicon is under the control of a strong RNA polymerase II promoter and replicon RNA is transcribed from DNA before transport to the cytoplasm. Efficient RNA amplification catalyzed by the viral replicase results in high levels of mRNA and the recombinant protein. Recently, we developed a temperature-regulated Sindbis replicon-based DNA expression system characterized by a linear increase of expression upon decrease of the temperature from 37 degrees C to 29 degrees C. Modifications known to affect transcription and nuclear export of RNA led to a 5-fold increase in expression in BHK cells and up to over 80-fold increase in CHO cells and BF fibroblasts in transient transfection experiments. Furthermore, reducing cell proliferation resulted in a further 2- to 3-fold higher expression. While increased expression per cell was responsible for some of the enhanced production, it was primarily the number of expressing cells that made the difference in most cell lines. Further experiments indicated that a threshold amount of replicon RNA had to reach the cytoplasm in order for replication to occur. Thus, alterations that improve transcription, nuclear export and stability of the RNA had a significant impact on protein production in the pCytTS expression system and probably in other layered DNA-based viral vectors. Furthermore the results indicate that RNA replication is differentially regulated in DNA layered RNA replicons versus viral infection.

Active Transport, Cell Nucleus↗