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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 3.

Figure 3

UStags for characterization of unexpected modifications. (A) UStag SSIFDASAGI measured from b ions (Figure 3A) led to the identification of the peptide D.SHSSIFDASAGIQL... predicted from the yeast protein Chr VII. The precursor ion mass (survey MS) was shifted by +28.042 u corresponding to the (C)(H4)(N2)(-O) change in elemental composition, which could readily be explained by a Gln to Arg switch. Measured values are denoted in black; theoretical values derived from the sequence database are given in red, and theoretical values for corrected sequence are given in blue. (B) An example showing a case where both, deamidation on Gln and Val to Tyr substitution were determined to provide correct interpretation of the spectrum. Measured values and theoretical values for corrected sequence are denoted in blue; theoretical values derived for deamidated sequence are given in green.