Peptide studies using a fast atom bombardment high field mass spectrometer and data system. 2—characteristics of positive ionization spectra of peptides,m/z 858 tom/z 5729

Abstract

Sixteen peptides ranging in molecular weights from 858 to 5729 were examined under positive ionization fast atom bombardment conditions employing a high field magnet mass spectrometer and data system. The contributions of the polyisotopic elements to the molecular protonated ion envelope become important in the interpretation of the data at higher mass. For masses less than 2000 u, the most abundant ion within this envelope is the monoisotopic molecular protonated ion. Above 2000 u, the most abundant ion in the envelope is a polyisotopic molecular protonated ion. Characterization of the peptide requires identification of both the molecular protonated ion envelope and significant fragment ions. Partial spectra displaying both the molecular ion and significant fragment ions are presented for mastoparan (mol. wt = 1478), somatostatin (mol. wt = 1637), bovine parathyroid hormone (1–34) (mol. wt = 4106), and bovine insulin (mol. wt = 5729). A partial spectrum for bovine ribonuclease A (mol. wt = 13673) displayed significant fragment ions that identified the protein. The types of fragment ions included those that indicated the amino acid sequence and the location of disulfide bonds. The abundance of these ions appears to be influenced by the characteristics of the noble gas fast atom beam and the sample matrix.