Figure 4.

MS/MS and MS spectra of the peptide ¹⁰KSTGGKAPR¹⁸ from histone H3 identified in the three cell lines under study with several PTMs in three of the residues. Lys¹⁰ was mono-, di-, and trimethylated and acetylated; Ser¹¹ was phosphorylated; and Lys¹⁵ was acetylated. Representative MS/MS spectra of the peptide with mono-, di-, and trimethylated Lys¹⁰ are illustrated in A, C, and E, respectively. B, D, and F correspond to survey scans showing the isotopic distribution of the peptide mono-, di-, and trimethylated in Lys¹⁰ in the three cell lines. The reported values correspond to the degree of endogenous acetylation in the Lys¹⁵ residue, confirmed by MS/MS of the signals 501.794, 486.287, and 493.294 Th, respectively. G, representative MS/MS spectrum of the double-charge signal 494.785 Th corresponding to the peptide with Lys¹⁵ residue endogenously acetylated. H, survey scans showing the isotopic distribution of the peptide fully acetylated in the three cell lines. The reported values correspond to the degree of endogenous acetylation in one and both lysine residues. I, representative MS/MS spectrum of the double-charge signal 534.769 Th corresponding to the peptide with the Ser¹¹ residue phosphorylated and the Lys¹⁵ residue endogenously acetylated. J, survey scans showing the isotopic distribution of the acetylated peptide with phosphorylated Ser¹¹ in the three cell lines. The reported values correspond to the degree of endogenous acetylation in the Lys¹⁵ residue.