N-acetylation of protein variants. Tandem mass spectra of N-acetylated protein variants from Pma1p and Ura2p are displayed. These proteins were found to be N-acetylated on the amino acids N and D as suggested by the 42 Da mass shifts of the b-ion series compared to the same peptides in their non-acetylated forms, which are displayed in the top row. Fragment ions of the y and b series found in the MS/MS spectra are indicated in black in the tables next to the spectra. Missing ions are marked in grey. For each spectrum the start position of the respective peptide is indicated together with the peptide sequence, protein name, accession and MASCOT score.