Protein structural effects in gas phase ion/molecule reactions with diethylamine

The relationship between gas‐phase protein structure and ion/molecule reactivity is explored in comparisons between native and disulfide‐reduced aprotinin, lysozyme, and albumin. Reactions are performed in the reactions with equal concentrations of diethylamine, multiply protonated molecules generated by electrospray ionization (ESI) of ‘native’ proteins shifted to lower charge states than did multiply protonated molecules from ESI of the disulfide‐reduced counterparts, suggesting that the disulfide‐reduced protein ions are less reactive than native protein ions of the same charge state. Differences in reactivity may arise from protonation of different amino acid residues and/or differences in the proximites of charge sites in two molecules. These results suggest that the reactivity of multiply charged proteins can be significantly affected by their gas‐phase structure.