Figure 1.

Example Mass Spectrometry Data from the Unmodified Peptide ³⁴⁴SPTGEVIFGGETM³⁵⁷R and the Oxidatively Modified Peptide ³⁴⁴SPTGEVIFGGETM³⁵⁷R+16. A. Top, spectrum of the CID dissociation of the unmodified peptide ³⁴⁴SPTGEVIFGGETM³⁵⁷R. Various identified ions are labeled. Bottom, table of all predicted masses for the y- and b- ions generated from this peptide sequence. Ions identified in the CID spectrum (above) are shown in red. The b’⁺⁺, b’⁺ y’⁺⁺ and y’⁺ ions are generated by the neutral loss of water. B. Top, spectrum of the CID dissociation of the modified peptide³⁴⁴SPTGEVIFGGETM³⁵⁷R+16. Various identified ions are labeled. Bottom, table of all predicted masses for the y- and b- ions generated from this peptide sequence. Ions identified in the CID spectrum are shown in red. The b’⁺⁺, b’⁺ y’⁺⁺ and y’⁺ ions are generated by the neutral loss of water. Note the additional mass of 16 amu (in comparison with Fig. 1A) arising from modification of ³⁵⁷R. This modification is evident in all identified y-ions species but is absent in all identified b-ions. Both of these spectra are from Biological Replicate #1.