TABLE 3.
Molecular masses of major species identified by LC-ESI-MS as a result of anaerobic incubation with sodium sulfite of fully reduced CstR
The conditions used were: 10 mm Hepes, pH 7.0, 0.2 m NaCl, at 25.0 °C. The indicated fold-excess is molar excess over Cys residues (20 μm protomer, 40 μm cysteine).
| Reaction condition | Molecular mass observed | Assignment | Molecular mass expected |
|---|---|---|---|
| Da | Da | ||
| No reaction | 9640.7 | CstRa | 9641.2 |
| 9662.8 | CstR + Na+ | 9663.2 | |
| +5X SO32- | 9639.8 | CstR | 9641.2 |
| 19280.0 | CstR2S-S | 19280.4 | |
| 19311.8 (+32)b | CstR2S-S-S | 19312.4 | |
| 19324.7 (+45) | CstR2S-S + 2 Na+ | 19324.4 | |
| 19343.7 (+64) | CstR2(S-S-S)×2 | 19344.4 | |
| +10X SO32- | 9640.4 | CstR | 9641.2 |
| 9661.2 | CstR + Na+ | 9663.2 | |
| 19280.7 | CstR2S-S | 19280.4 | |
| 19295.1 (+14) | CstR2S-S + Oc | 19296.4 | |
| 19312.4 (+32) | CstR2S-S-S | 19312.4 | |
| 19323.4 (+44) | CstR2S-S + 2 Na+ | 19324.4 | |
| 19334.0 (+53) | CstR2S-S-S + Na+ | 19334.4 | |
| 19357.6 (+77) | CstR2S-S-S + 2 Na+ | 19356.4 | |
| 19366.5 (+86) | CstR2(S-S-S)×2 + Na+ | 19366.4 | |
| +100X SO32- | 9640.1 | CstR | 9641.2 |
| 19280.0 | CstR2S-S | 19280.4 | |
| 19311.3 (+31) | CstR2S-S-S | 19312.4 | |
| 19332.7 (+43) | CstR2S-S-S + Na+ | 19334.4 | |
| 19343.0 (+63) | CstR2(S-S-S)×2 | 19344.4 |
a CstR, reduced CstR monomer (starting material).
b Mass increase relative to oxidized dimer (CstR2S-S).
c One disulfide linkage, with one sulfenic acid (–SOH) on the opposite side of the dimer; tentative assignment.