Figure 3.

MS-derived sequence for BSA, SRF and Elk-1. The spectra show the derivative ions from doubly charged ions derived from (A) sample 2 (m/z = 464.24), (B) sample 3 (m/z = 525.76) and (C) sample 4 (m/z = 650.30) (see Fig. 2). Peptide sequences are generated from Y ions whereby Y1 corresponds to the C-terminal amino acid, in each case an arginine, consistent with their origin from tryptic digestion. In the case of SRF, the peptide shown differs from the retrieved sequence by one amino acid (asterisk). This difference is interpreted as a deamidation of N47.