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. 2011 Dec 16;6(12):e28976. doi: 10.1371/journal.pone.0028976

Figure 2. Ion trap mass spectra of purified synthetic peptides containing citrulline and chemically modified synthetic peptides.

Figure 2

Peptides (YAGCitLLTK-NH2 [monoisotopic Mr = 920.5], PIECitTKLY-NH2 [monoisotopic Mr = 1018.6], and PIECitTYLK-NH2 [monoisotopic Mr = 1018.6]) were synthesized based on fluorenyl methoxycarbonyl (Fmoc) chemistry, purified using RP-HPLC, chemically modified with antipyrine and 2,3-butanedione and repurified by RP-HPLC. The Mr of the purified synthetic peptides was determined by deconvolution of the multiple charged ions in the raw spectra. As expected the Mr of the chemically modified synthetic peptides differs 238 mass units from the corresponding unmodified peptide. Total ion chromatograms (TIC; black lines) and extracted ion chromatograms for the charged ions of the specific peptides (EIC; gray fill) are shown as inserts in the experimentally determined mass spectra for (A) YAGCitLLTK-NH2 [Mr = 920.6], (B) YAGCit*LLTK-NH2 [Mr = 1158.6], (C) PIECitTKLY-NH2 [Mr = 1018.7], (D) PIECit*TKLY-NH2 [Mr = 1256.8], (E) PIECitTYLK-NH2 [Mr = 1018.7] and (F) PIECit*TYLK- NH2 [Mr = 1256.8]. Citrullines (Cit) marked with an asterisk are chemically modified.