ARE PEPTIDES WITHOUT BASIC RESIDUES PROTONATED PRIMARILY AT THE AMINO-TERMINUS

The question of site of protonation in peptides that do not contain ba sic residues is addressed. The additional basicity of the peptide conf erred by the amino terminus is removed by N-acetylation. Comparison of the surface-induced dissociation energy requirements for the fragment ation of the peptides with and without the N-terminal amine indicates that the N-terminal amine sequesters the proton. (C) 1998 Elsevier Sci ence B.V.