Well-resolved ion signals of intact large protein
assemblies, with molecular masses extending above one million
Dalton, have been detected and mass analyzed using electrospray
ionization mass spectrometry, with an uncertainty in mass
of <0.2%. The mass spectral data seem to reflect known
solution-phase behavior of the studied protein assembly
and have therefore been directly used to probe the protein
assembly topology and stability as a function of ionic
strength and pH.