CAPILLARY ZONE ELECTROPHORESIS OF DEGRADATIVE AND CYCLIC LACTAM DERIVATIVES OF THE GROWTH HORMONE-RELEASING FACTOR PEPTIDE

Capillary zone electrophoresis (CZE) was used to monitor deamidation of the Asn8 residue in the human growth hormone-releasing factor peptide, GRF(1-44)-NH2. The deamidation proceeds via cyclic imide formation yielding isomeric Asp8 and beta-Asp8 containing products. It is demonstrated that GRF peptides differing only by isomerization at a single aspartic acid residue can be separated by CZE at pH 2.5-4.5 as a result of the greater acidity of the beta-Asp side-chain carboxylic acid versus that of the normal Asp isomer. The dependence of electrophoretic mobility on the size and charge of GRF peptide fragments was studied by CZE for proteolysis of GRF(1-29)-NH2 by trypsin and endoproteinase Glu-C. CZE was also used to separate cyclic lactam analogs of GRF that all bear approximately the same net charge and differ only by the ring size or orientation of the lactam bridge.