Biomedical subjects

D Riester

Publications and source records attributed to D Riester.

3 recordsLinked to original sources

PubMed2001

Fluorogenic assay for penicillin G acylase activity.

A simple, highly sensitive, and rapid assay for high-throughput screening of penicillin G acylase-producing bacteria is presented. The method is based on the specific release of fluorescent 7-amino-4-methyl-coumarin through cleavage of phenylacetyl-4-methyl-coumaryl-7-amide by penicillin G acylase. The present method is suitable for screening pure enzymes as well as various penicillin G acylases like those from Escherichia coli, Proteus rettgeri, and Kluyvera citrophila in cell extracts. In addition, the new substrate was used for rapid assay of amidase activity in nondenaturing polyacrylamide gels.

Coumarins↗

PubMed1996

Racemization of amino acids in solid-phase peptide synthesis investigated by capillary electrophoresis.

The rate of racemization during solid-phase peptide synthesis was studied using capillary electrophoresis and 18-crown-6 tetracarboxylic acid as chiral selector. For this purpose, the tripeptide D-Tyr-L-Lys-L-Trp as a model compound was synthesized by solid-phase peptide synthesis. A separation method based on capillary electrophoresis was developed which allowed all eight optical isomers of the tripeptide to be separated in a single run. The separation method was validated and was found to be well suited for purity analysis, with a limit of detection of 0.05% of the major compound. The method was revealed to be highly sensitive even to small variations in the buffer pH. Capillary electrophoresis was also employed to prove the enantiomeric purity of the Fmoc-protected amino acids used for peptide synthesis. A separation method based on micellar electrokinetic chromatography and gamma-cyclodextrin was developed for this purpose. The formation of optical isomers during peptide synthesis was investigated in the final product without hydrolyzing the tripeptide. This strategy allowed the rate of racemization to be determined by activation of amino acids in coupling cycles and cleavage of the peptides from the resin and from side-chain protecting groups. The formation of stereoisomers could be verified and was 0.4% or less per synthesis cycle. The experimental data agreed well with theoretical considerations, showing that racemization takes place mainly at the carboxy-activated amino acid during coupling.

Amino Acid Sequence↗

PubMed1995

Evaluation of an optically active crown ether for the chiral separation of di- and tripeptides.

The direct optical resolution of a number of di- and tripeptides was achieved by capillary zone electrophoresis using an enantioselective crown ether as buffer additive. The protonated primary amines form inclusion complexes with the crown ether. Chiral resolution is based on different stability constants of the diastereomeric complexes thereby changing the electrophoretic mobilities of the enantiomers. Enantioselectivity is strongly affected by the distance between the amine functionality and the chiral carbon atom. This effect was studied using di- and tripeptides especially synthesized for this purpose. In general, baseline resolution was obtained for those peptides with the amine group located as far as four bonds from the stereogenic center. Additionally, tripeptides possessing two chiral centers were separated to investigate the potential of the chiral selector for the analysis of complex analytes with related structures. Experimental factors such as crown ether concentration, buffer pH and temperature also show a strong influence on the resolution. These factors can be successfully employed for method optimization.

Amino Acid Sequence↗