Segmental charge distributions of Cytochrome c on transfer into the gas phase

Segmental charge distributions of Cytochrome c ions in the transition from solution to gas phase are studied by native electron capture dissociation (NECD). The data suggest that the solution charge distribution of native Cytochrome c is partially preserved during the electrospray ionization process. Segments with charge values different from those in solution correspond to protein regions that are the first to unfold on transfer into the gas phase, consistent with an increased gas phase basicity of, and facile proton transfer to, the newly exposed sites. Changes in the charge distribution at elevated temperatures indicate further unfolding, as well as proton transfer as a result of the increased electrostatic interactions in a gas phase environment.