Tandem mass spectrometric analysis of C-13-containing ions from a mixture of homologous peptides differing by one mass unit at a residue

Tandem mass spectrometry of a mixture of two peptides that differ from each other by a single mass unit due to mutation is presented. The mutant beta- globin of hemoglobin Hoshida is present along with the normal counterpart, and the amino acid substitution of glutamine for glutamic acid is located w ithin tryptic peptide T5 of M-r 2057.9. The mass of the mutated peptide is 1 u lower. In the isotopic cluster for the doubly charged ion of the peptid e T5, the resolved ion with mass of 1030.0 represents the normal peptide wi th 93 C-12 atoms and the mutated one with 92 C-12 and one C-13 atoms. Colli sion-induced dissociation (CID) of this composite ion identified the mutati on by presenting a key fragment derived from the C-12-only mutant peptide, as reported in a previous study. Similarly, when an ion containing multiple C-13 atoms was selected as a precursor for CID, the mutation could be iden tified, even in large fragments, by a marked change in the shape of the iso topic cluster for the consecutive product ions. This study demonstrates the merit of selecting a resolved ion rather than the whole isotopic cluster a s a precursor in the CID measurements of large peptides or proteins for cha racterizing heterozygous mutations. Copyright (C) 2000 John Wiley & Sons, L td.