Table I Truncated H2B proteoforms observed in IIPT/parallel ion parking MS/MS spectrum

Observed m/z and theoretical precursor m/z values are shown. The masses reported are those of the most abundant isotopologue in the charge state envelope. UniProt sequences from isoforms of H2B with residues matching those contained in the truncated H2B are given. Note these are not confirmed by MS/MS, and identification is based on accurate mass and MS/MS spectra of other truncated H2Bs seen in LC-MS analyses performed without parallel ion parking. Observed mass accuracies are reported in ppm and were calculated from the most abundant isotopologue.

PeakObserved m/zPrecursor m/zPossible H2B isoformResiduesObserved mass accuracy (ppm)
A2134.4929 (+3)801.0661 (+8)P6280768–125−2.16
B2167.1735 (+3)813.3221 (+8)O6081467–125−3.09
C2172.5071 (+3)815.3215 (+8)P6280767–125−2.16
D2200.1957 (+3)825.7057 (+8)O6081466–125−3.32
E2205.5313 (+3)827.7050 (+8)P6280766–125−1.50