TABLE 2.
Molecular masses of reaction products obtained upon anaerobic incubation of reduced S. aureus CstR or CsoR with various sulfur-containing compounds
The conditions used are: 10 mm Hepes, pH 7.0, 0.2 m NaCl, at 25.0 °C. All 10-fold molar excess of Cys residues unless otherwise indicated, 20 μm protomer.
| Protein | Reactant | Molecular mass observed | Assignment | Expected modification | Molecular mass expecteda |
|---|---|---|---|---|---|
| Da | Da | ||||
| CstR | No addition | 9640.7 | 9641.2 | ||
| Na2S2O3 | 9640 | NRb | –SH (×2) | 9673.2 (9705.2) | |
| Na2S | 9640 | NR | –SH (×2) | 9673.2 (9705.2) | |
| Na2SO3 | 19280 | CstR2S-S | CstR2S-S | 19280.4 | |
| 19312 | CstR2S-S-S | CstR2S-S-S | 19312.4 | ||
| 19344 | CstR2(S-S-S)2c | CstR2(S-S-S)2c | 19344.4 | ||
| MMTS | 9732 | –SCH3 ×2 | –SCH3 (×2) | 9733.2 | |
| CsoR | No addition | 11035 | 11036.6 | ||
| Na2S2O3 | 11035 | NR | –SH (×2) | 11068.6 (11100.6) | |
| Na2S | 11035 | NR | –SH (×2) | 11068.6 (11100.6) | |
| Na2SO3d | 11035 | NR | CsoR2S-S | 22073.2 | |
| CsoR2S-S-S | 22105.2 | ||||
| MMTS | 11128 | –SCH3 ×2 | –SCH3 (×2) | 11130.6 |
a Expetced masses were calculated as average masses [M] with no modifictions at EXPASY.
b NR, no reaction.
c Both interprotomer cysteine linkages incorporate a sulfur atom in the dimer.
d 100-fold excess of reagent.