Table 1.
MDI conjugation sites on human albumin identified by MS/MS.
| Position | Peptide sequence | m/z [M+2H] and/or [M+3H] | Monoisotopic mass | Notes |
|---|---|---|---|---|
| 4 | DAHKSEVAHR | 467.2 | 1398.7 | Second NCO group not hydrolyzed |
| 137 | KYLYEIAR | 640.4 | 1278.7 | |
| 162 | YKAAFTECCQAADK | 629.6 | 1885.8 | |
| 199 | LKCASLQK | 586.3 | 1170.6 | |
| 212 | AFKAWAVAR | 622.3 | 1242.6 | Loss of MDI at x8, x7, y8, and y7 |
| 262 | ADLAKYICENQDSISSK | 722.7 | 2165.1 | |
| 351 | LAKTYETTLEK | 760.9 | 1519.8 | |
| 391 | QNCELFEQLGEYK | 926 | 1849.9 | Second NCO group not hydrolyzed, cysteine not acetylated |
| 414 | KVPQVSTPTLVEVSR | 932.5 (954.5) 622.0 |
1863.1 (1890.0) | Doubly and triply charged species observed (masses with second NCO present in different HPLC fractions) |
| 429 | NLGKVGSK | 513.8 | 1025.6 | |
| 432 | NLGKVGSK | 625.5 | 1249.6 | Peptide doubly conjugated with MDI on the asparagine; spectrum shows several losses of MDI masses |
| 436 | VGSKCCK | 531.8 | 1061.5 | Loss of MDI for M+H, y6, y5, and y4 |
| (?) | HPEAKR | 481.3 | 960.5 | Arg6/Lys5 not conjugated, but only very low b1 ions, suggesting possible conjugation at histidine |
| 525 | KQTALVELVK | 679.9 451.6 |
1351.8 | Doubly and triply charged species observed |
| 541 | ATKEQLK | 521.3 (534.3) | 1040.6 (1066.6) | See x6-MDI, x5-MDI, y6-MDI, and y5-MDI, acting like phosphorylated neutral loss (masses with second NCO present in different HPLC fractions) |