Assigning peaks and modeling ETD in top-down mass spectrometry

Among many techniques of modern mass spectrometry, the top down methods are becoming continuously more popular in the overall strive to describe the proteome. These techniques are based on fragmentation of ions inside mass spectrometers instead of being proteolytically digested. In some of these techniques, the fragmentation is induced by electron transfer. It can trigger several concurring reactions: electron transfer dissociation, electron transfer without dissociation, and proton transfer reaction. The evaluation of the extent of these reactions is important for the proper understanding of the functioning of the instrument and, what is even more important, to know if it can be used to reveal important structural information. We present a workflow for assigning peaks and interpreting the results of electron transfer driven reactions. We also present software written in Python and available under GNU v3 license.