Probing of ECD Charge Reduced Ions Using ECD and CID (2009)

Undergraduate: Daniel Thomas

Faculty Advisor: Gary Glish
Department: Chemistry

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Electron capture by positively charged peptides and proteins produces stable charge reduced radical species, [M+nH](n-1)+•. By applying CID and ECD to these intermediate states, we can survey the characteristics of the charge reduced radical ions to better understand the reaction mechanism of ECD. The charge reduced species of Angiotensin I and shortened forms of this peptide were surveyed. Two types of charge reduced species, [M+3H]2+• and [M+2H]+•, were produced from [M+3H]3+ and [M+2H]2+ by electron capture. ECD of [M+3H]2+• of Angiotensin I suggests that the neutralized hydrogen is localized at the His9 residue. Similar ECD/ECD experiments of Angiotensin II and Angiotensin III did not yield definitive information about neutralized hydrogen location. CID of [M+3H]2+• of each peptide yielded primarily "b" and "y" product ions. In contrast, the most abundant fragment ions from CID of [M+2H]+• of Angiotensin I were a His side chain loss and "c’" and "z•" ions; "a" ions were also observed. CID of [M+2H]+• of all other forms of Angiotensin examined yielded a His side chain loss and "a" product ions as the most abundant fragment ions. These results demonstrate that CID of the charge reduced species does not always produce "c'" and "z•" ions, which indicates that the charge reduced species may not always be a long-lived radical ion. The data also suggests that the charge reduced species [M+3H]2+• has a different structure than [M+2H]+•, causing different fragmentation patterns.