In top-down proteomics, intact protein molecular ions generated by ESI or MALDI are introduced into mass analyzer and are subjected to gas-phase fragmentation. Top-down analysis facilitates direct observation of C- and N-termini for identification of truncations and distinguish one isoform from the other by different sequences. Top-Down based Sequencing https://www.creative-proteomics.com/services/top-down-based-sequencing.htm
