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S Meyer

Publications and source records attributed to S Meyer.

At least 325 records · Page 18Linked to original sources
PubMedDate not supplied

Separation of cis/trans isomers of a prolyl peptide bond by capillary zone electrophoresis.

On capillary electrophoresis of the chemically pure thioxo peptide Ala-Phe-psi[CS-N]-Pro-Phe-4-nitroanilide a peak splitting was observed at a capillary temperature of 25 degrees C. By contrast, the oxo peptide analogue exhibits a single, sharp peak under these conditions. Both peaks of the thioxo compound coincided gradually when the temperature was increased to 60 degrees C. Peak fusion was reverted by cooling down the heated sample. This behavior could be attributed to the electrophoresis-mediated separation of the cis/trans prolyl bond isomers of the thioxo peptide, allowing data of this conformational equilibrium to be determined. Derived from computational data about molecular volume and the hydration energy of low-energy cis and trans isomeric structures, the more rapid migration of the cis form in comparison to trans may be explained by structural parameters.

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PubMedDate not supplied

Growth rate related concentration changes of the starvation response regulators sigmaS and ppGpp in glucose-limited fed-batch and continuous cultures of Escherichia coli.

The entry of Escherichia coli into glucose starvation is connected to the induction of both the stringent response and the general stress response. The concentration of the corresponding response regulators ppGpp and sigmaS (RpoS, KatF) was investigated during glucose-limited growth at different growth rates and with different cultivation strategies, including fed-batch fermentation, chemostat, and a continuous-cultivation technique with computer-controlled decrease of the feeding rate (A-stat). This study confirms the model of the in vivo effect of ppGpp on sigmaS by the direct measurement of ppGpp and sigmaS levels. The response of both regulators was clearly shown in situations where a nutrient shift occurs. A correlation in the concentration of both regulators was also shown under steady-state conditions. However, during transients with slow continuous changes of the nutrient availability, this concerted reaction of ppGpp and sigmaS is less apparent, indicating the specific importance of these regulators for the adaptation of the cells to fast changes of environmental parameters.

Bacterial Proteins↗