Table 2.
Identification of Cys residues modified by NEM or IAN
| Cys residue | Peptide amino acids | Modified thiol | Retention time, min | Mass
|
|
|---|---|---|---|---|---|
| Predicted | Observed | ||||
| Cys-99 | 92-100 | NEM | 21 | 1178.3 | 1178.8 |
| 92-100 | IAN | 23 | 1110.3 | 1110.6 | |
| 91-100 | NEM | 21 | 1306.5 | 1306.4 | |
| 91-100 | IAN | 22 | 1238.4 | 1238.7 | |
| Cys-134 | 101-136 | IAN | 64 | 4265.3 | 4265.3 |
| Cys-139 | 137-154 | IAN | ND | 2289.8 | — |
| Cys-288 | 277-317 | IAN | ND | 4842.7 | — |
| Cys-311 | 277-317 | IAN | ND | 4842.7 | — |
| Cys-323 | 318-326 | IAN | 24 | 1150.4 | 1150.6 |
| Cys-343 | 335-346 | IAN | 21 | 1306.5 | 1306.4 |
| Cys-450 | 446-453 | NEM | 20 | 1066.2 | 1066.4 |
| 446-457 | NEM | 31 | 1517.8 | 1516.6 | |
| Cys-598 | 589-622 | IAN | 47 | 3991.5 | 3990.9 |
| Cys-700 | 695-704 | IAN | 32 | 1227.5 | 1228.0 |
Peptides from a chromatogram (Fig. 2) of tryptic-digested modified carboxylase were detected by LC-ESMS (supplemental Methods). No free thiol-containing peptides were detected. Predicted and observed masses are for the actual peptide masses, derived from their positive ion masses. M+H ions were observed for Cys-99, Cys-323, Cys-343, Cys-450, and Cys-700. M+2H ions were observed for Cys-99, Cys-323, Cys-343, Cys-450, Cys-598, and Cys-700. M+3H ions were observed for Cys-134 and Cys-598. M+4H ions were observed for Cys-134. ND is not detected.