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. Author manuscript; available in PMC: 2023 Oct 1.
Published in final edited form as: Curr Opin Chem Biol. 2022 Jun 29;70:102180. doi: 10.1016/j.cbpa.2022.102180

Figure 3.

Figure 3

Proton transfer charge reduction (PTCR) reactions may be undertaken on fragment ions produced from top-down MS/MS characterization of proteins. A) UVPD of a protein generates many fragment ions (F) in a variety of charge states. PTCR using a suitable proton-scavenging reagent ion reduce the charge states of fragment ions (charge state z+), thus shifting them to lower m/z values (i.e., retaining the same mass m (aside from loss of a proton) and a lower charge state (z-1)+) and consequently dispersing the fragment ions over a broader m/z range. B) A protein, such as carbonic anhydrase (25+), creates many fragment ions upon UVPD. PTCR reactions undertaken on the groups of fragment ions outlined in the shaded boxes alleviates congestion in the MS/MS spectra and allows confident assignment of a much larger portion of the fragment ions. Adapted from [98].