FAST-ATOM-BOMBARDMENT AND (CF-252) PLASMA DESORPTION MASS-SPECTROMETRY OF SYNTHETIC PEPTIDES FOR EPITOPE MAPPING

Systematic epitope screening of proteins is currently carried out usin g a panel of synthetic peptides. We have synthesized by solid phase si xteen octapeptides, four octadecapeptides and purified one tricosapept ide encompassing the whole sequence of the a-neurotoxin molecule, a 61 amino acid protein isolated from the cobra Naja nigricollis venom. Th e purity and the correctness of the chemical sequence of each peptide were estimated respectively by HPLC and automatic Edman degradation. T he peptide was then characterized by the observation of the protonated molecule (MH+) in FAB mass spectrometry and PDMS. The observed m/z va lues fit in with the corresponding calculated values. Accordingly, the peptides were considered as sufficiently homogenous before the epitop e mapping experiments. Fragmentation of the T-cell stimulating peptide (32-41) in FAB-MS was observed. An addition reaction occurred between thioglycerol from the matrix and the maleoyl group of the (29-36) der ivatized peptide in FAB-MS. Finally, peptides which are constitutive e lements of the T-cell epitope were identified as fragments (32-41) and (24-41).