TABLE 2.
List of apoB-100-derived tryptic peptides carrying modifications generated only by the MPO-H2O2-Cl− system under soft conditions (molar ratios = 25:1 and 50:1)
| Peptide | Error (ppm) | Peptide Score | % SPI | Z | Sequence with Fragmentation | Modified Residue |
| 74–83 | 2.7 | 15.0 | 75 | 2 | (K)E V|y/G/F/N/P E/G K(A) | Cl-Tyr76 |
| 716–733 | 3.3 | 10.9 | 83 | 3 | (K)D D/K H E Q D\m V|N|G I/m L S V/E/K(L) | O-Met723, 728 |
| 1,074–1,088 | 4.1 | 15.8 | 75 | 2 | (K)I/T/E|V|A/L/m G H/L|S C D|T\K(E) | O-Met1080 |
| 1,189–1,197 | 2.8 | 14.5 | 79 | 2 | (R)V/P|Q/T/D m T F/R(H) | O-Met1194 |
| 1,282–1,290 | 5.0 | 7.9 | 64 | 2 | (R)D/L/K/m/L\E/T V/R(T) | O-Met1285 |
| 1,711–1,723 | 1.6 | 14.9 | 80 | 2 | (K)L/S|N D|m m/G S/Y/A/E/m/K(F) | O-Met1715, 1716, 1722 |
| 2,392–2,396 | 0.8 | 6.8 | 75 | 3 | (K)F/L/D m L I/K/K(L) | O-Met2395 |
| 2,810–2,826 | 1.2 | 11.6 | 81 | 3 | (R)T E H G S E m\L|F|F/G N A I E/G K(S) | O-Met2816 |
| 3,393–3,403 | 2.5 | 10.4 | 89 | 2 | (K)N/m|E|V|S V A/T T T K(A) | O-Met3394 |
| 3,411–3,422 | 2.4 | 11.3 | 78 | 3 | (R)m/N/F/K\Q E\L/N/G N T K(S) | O-Met3411 |
| 3,435–3,447 | 3.3 | 15.0 | 78 | 2 | (K)Y D|F|n|S/S m L Y/S/T/A/K(G) | O-Met3441 |
| 4,151–4,158 | −0.5 | 17.3 | 85 | 2 | (R)V/T|Q/E/F H|m/K(V) | O-Met4157 |
| 4,515–4,526 | −0.8 | 9.5 | 83 | 2 | (K)L/Q|S T/T/V m N/P Y m/K(L) | O-Met4521, 4525 |
LDL was modified by HOCl generated by the MPO-H2O2-Cl− system using 50 or 100 µM of H2O2 (oxidant/LDL molar ratio = 25:1 and 50:1, considering almost equimolar formation of HOCl). ApoB-100 mapping was carried out by RRLC-MS/MS. Peptides carrying a modification observed in Table 1 were omitted, indicating PTMs to be MPO specific. Each modified peptide is characterized by its peptide score, % SPI, mass error, fragmentation, and position(s) of modified residue(s).