SEPARATION OF CIS TRANS ISOMERS OF A PROLYL PEPTIDE-BOND BY CAPILLARYZONE 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 p eaks of the thioxo compound coincided gradually when the temperature w as increased to 60 degrees C. Peak fusion was reverted by cooling down the heated sample. This behavior could be attributed to the electroph oresis-mediated separation of the cis/trans prolyl bond isomers of the thioxo peptide, allowing data of this conformational equilibrium to b e determined. Derived from computational data about molecular volume a nd the hydration energy of low-energy cis and trans isomeric structure s, the more rapid migration of the cis form in comparison to trans may be explained by structural parameters.