Fig 2. MS/MS spectrum for acetylated lysine 238 in F. tularensis rUsp/His₆.

The exact location of the 42.01 Da acetyl adduct is defined by the y1 to y10 ion series and the y11 ion whose structures are shown. The mass of the y11 ion at 1279.71 Da is 42.01 Da higher than the mass of the unmodified y11 ion. Masses of the y1 to y10 ions are consistent with the absence of an adduct on residues NDLIVVGSHR. The MH⁺² parent ion has a mass of m/z 832.9394.