UVPD of streptavidin tetramer for precursor charge state 13+ (A, B, and C) and 15+ (D, E, and F). HCD of both 13+ and 15+ resulted in the ejection of highly-charged monomers (A and D). UVPD using 1 mJ pulse energy produced highly-charged monomers (B and E) but after increasing the pulse energy to 3 mJ, the products were more symmetrically charged partitioned (C and F). Reprinted with permission from Morrison, L.J.; Brodbelt, J.S. 193 nm Ultraviolet Photodissociation Mass Spectrometry of Tetrameric Protein Complexes Provides Insight into Quaternary and Secondary Protein Topology. J. Am. Chem. Soc. 2016, 138, 10849–10859. Copyright 2016 American Chemical Society.