FIG. 1.

Analysis of tryptic peptides from untreated (A) and tBHP-oxidized (B) SspC. SspC and SspC oxidized with tBHP for 3 h were digested with trypsin, and the products were resolved by HPLC as described in Materials and Methods. Because tBHP was removed by dialysis, the actual exposure to oxidant was longer than 3 h. The SspC peptides identified are as follows: 1, A47 to K57; 2 and 2*, L62 to H72; 3, L29 to R46; 4 and 4*, S9 to K28; and 5, S9 to R46. Peptides 2*, 4*, and 5 contain methionine sulfoxide residues. Peptide 5 results from additional oxidation at lysine 28. The identity of this peptide was established by performing amino acid analysis and mass spectrometry and determining resistance to trypsin cleavage. No peptides were eluted prior to 10 min.