What causes multiple closely spaced peaks in ESI-MS of pure protein?
In electrospray ionization of a single purified protein, multiple protonation states coexist because different numbers of basic residues can be protonated during droplet evaporation process. Each charge state appears as distinct peak with its own m/z value, creating an envelope of closely spaced signals rather than one peak. Mathematical deconvolution transforms this envelope to zero-charge molecular weight. Aggregation, oxidation, or denaturation would produce additional heterogeneity or broaden peaks, but characteristic ladder of peaks for pure protein arises specifically from multiple charg
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.
