Peptide and protein ion/ion reactions in electrodynamic ion traps: tools and methods

Flame Atmospheric Pressure Chemical Ionization Coupled with Negative Electrospray Ionization Mass Spectrometry for Ion Molecule Reactions

Flame atmospheric pressure chemical ionization (FAPCI) combined with negative electrospray ionization (ESI) mass spectrometry was developed to detect the ion/molecule reactions (IMRs) products between nitric acid (HNO₃) and negatively charged amino acid, angiotensin I (AI) and angiotensin II (AII), and insulin ions. Nitrate and HNO₃-nitrate ions were detected in the oxyacetylene flame, suggesting that a large quantity of nitric acid (HNO₃) was produced in the flame. The HNO₃ and negatively charged analyte ions produced by a negative ESI source were delivered into each arm of a Y-shaped stainless steel tube where they merged and reacted. The products were subsequently characterized with an ion trap mass analyzer attached to the exit of the Y-tube. HNO₃ showed the strongest affinity to histidine and formed (M_histidine-H+HNO₃)^- complex ions, whereas some amino acids did not react with HNO₃ at all. Reactions between HNO₃ and histidine residues in AI and AII resulted in the formation of dominant [M_AI-H+(HNO₃)]^- and [M_AII-H+(HNO₃)]^- ions. Results from analyses of AAs and insulin indicated that HNO₃ could not only react with basic amino acid residues, but also with disulfide bonds to form [M-3H+(HNO₃)_n]^3- complex ions. This approach is useful for obtaining information about the number of basic amino acid residues and disulfide bonds in peptides and proteins. Graphical Abstract ᅟ.

Top-Down Mass Spectrometry: Proteomics to Proteoforms

This chapter highlights many of the fundamental concepts and technologies in the field of top-down mass spectrometry (TDMS), and provides numerous examples of contributions that TD is making in biology, biophysics, and clinical investigations. TD workflows include variegated steps that may include non-specific or targeted preparative strategies, orthogonal liquid chromatography techniques, analyte ionization, mass analysis, tandem mass spectrometry (MS/MS) and informatics procedures. This diversity of experimental designs has evolved to manage the large dynamic range of protein expression and diverse physiochemical properties of proteins in proteome investigations, tackle proteoform microheterogeneity, as well as determine structure and composition of gas-phase proteins and protein assemblies.