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. Author manuscript; available in PMC: 2009 Mar 15.
Published in final edited form as: Anal Chem. 2008 Feb 14;80(6):1871–1882. doi: 10.1021/ac702328x

Figure 4.

Figure 4

The UStags identifies peptides that challenge conventional proteomics approaches. (A) UStags allow identification of peptides arising from multiplexed spectra. Two UStags: GFTFSFPA from protein Chr VII and INFLTE from protein Chr III were measured in a single spectrum. The selection of the precursor ion at m/z =1073 u (with selection window 3 m/z units wide) yielded two partially overlapping isotopic envelopes and two UStag-identified proteins. Measured values are denoted in black; theoretical values derived from the two UStag-identified peptides are denoted in red and blue, respectively. (B) UStags allow identification of non-tryptic peptides. An UStag was measured using both b- or y ion series for protein Chr VII and no modification(s) were found that could make the sequence has Arg/Lys terminus and still support the measured UStag, precursor mass and fragment masses. Measured values are denoted in black; theoretical values derived from the UStag-identified peptide are denoted in red.