Figure 7.

EThcD tandem mass spectrum of doubly protonated pSGXGK (A) and pSGR(Me)GK (B) histone peptides. The undetected charge-reduced precursor is only signed as M. Hydrogen atom loss is depicted as ’. Neutral losses of ammonia (*), water (deg), the citrulline-selective carbamoyl radical (currency sign), or isocyanic acid (@) as well as the N^G-methylarginine-selective methylamine (÷) and N-methylcarbodiimide losses (§) are also shown. Note that all b_i related fragments may represent c_i* ones, and all z_i related fragments may represent y_i* as well.