STUDY OF THE CHARGE-REMOTE FRAGMENTATION OF BRADYKININ USING CF-252 PLASMA DESORPTION MASS-SPECTROMETRY

The Cf-252-plasma desorption mass spectra of the peptide bradykinin and several chemical derivatives of bradykinin were studied with emphasis on the fragmentation of the peptide and the effect of the derivatization on the fragmentation. Through these studies, we have determined that charge-remote fragmentation is the primary process for peptide fragmentation in plasma desorption mass spectrometry (PDMS) for peptides containing basic amino acids. The relative intensities of the charge-remote fragment ions containing a basic amino acid follow the same progression as the gas-phase basicities of the basic amino acid: arg > his > lys. Through the observation of C-terminal fragment ions from an N-terminal triphenylphosphonium bradykinin derivative, evidence for fragment ion formation from a doubly charged molecular ion was obtained. For two bradykinin derivatives which did not contain strong basic sites, fragmentation was still observed in PDMS. The observed fragmentation of these non-basic bradykinin derivatives suggest involvement of the proline residues, where fragmentation is charge induced, resulting from protonation of the proline amide bond. These non-basic bradykinin derivatives exhibited M+. molecular ions rather than the typical (M + H)+ "quasi-molecular" ion, and strong (M + Na)+ and (M + K)+ ions even though only trace amounts of sodium and potassium were present.