Fig. 5.

Sample tandem mass spectra of the doubly charged, histone H3 peptide (aa 73–83), EIAQDFK₇₉TDLR. (A) Mass spectrum of the control sample of histone incubated with only Hst2 shows this peptide with acetylated K79. (B) Mass spectrum of the histone H3 peptide biotinylated at K79. The sample was treated with Hst2 in the presence of NAD⁺, resulting in the replacement of the acetyl group on K79 with a biotin tag. There is therefore a 92 Da mass increase of the precursor ion and a 184 Da increase in mass between the y₄ and y₅ ions.