CAPILLARY ELECTROSEPARATIONS OF ENKEPHALIN-RELATED PEPTIDES AND PROTEIN-KINASE-A PEPTIDE-SUBSTRATES

The separations of enkephalin-related peptides and protein kinase A pe ptide substrates, with the common structural feature -Arg-Arg-X-Ser-Va l-, were studied in micellar electrokinetic chromatography (MEKC) syst ems and compared with the capillary zone electrophoresis (CZE) mode. T he influence of the magnitude and the direction of the electroosmotic flow on the selectivity was studied. Reversed electroosmosis was obtai ned by adding a hydrophobic amine, dimethyldodecylamine, to the backgr ound electrolyte; the amine forms cationic micelles with a low critica l micelle concentration (0.3 mM). The neutral micellar agent, Brij 35, competes with the amine for adsorption sites on the capillary surface decreasing the reversed electroosmosis, In such a system, mixed catio nic micelles are formed to which the peptides were not distributed at low pH, but an improved resolution was obtained due to the effects on electroosmosis. In systems containing the less hydrophobic amine dimet hyloctylamine, in which probably no mixed micelles are formed, an impr oved separation of protein kinase A peptide substrates was obtained du e to distribution to Brij 35 micelles. In separations of enkephalins, a high pH gave very low efficiencies due to surface-analyte interactio ns? and the best CZE separations were obtained at low pH. Changes in m igration order were observed in the pH range 2-3, possibly due to diff erences in peptide pk:, values or conformation changes of the peptides . The enkephalins were only to a small extent distributed to the Brij 35 micelles, but this improved the separation at pH 2 compared to the CZE mode.